Anaesthesia for Head and Neck Surgery
Final Objective: The ability to provide anaesthesia for eye, ear, nose and throat surgery, dentistry and basic head and neck procedures.
Enabling Objective: To achieve this goal, you should know how to:
Many procedures are performed on paediatric patients and many patients will be discharged on the same day of surgery, requiring a smooth emergence and control of nausea and vomiting. It is very important to communicate well with the surgical team and the parents.
The patient’s eyes must be carefully protected.
EYE SURGERY
The success of eye surgery is dependant on the ability to keep the eye still during the procedure. A local or general anaesthetic technique may be chosen for surgery, but if a local or regional anaesthetic is used, it is important that the patient keeps still and is able to lie flat during the procedure. The use of ‘conscious sedation’ may be helpful, but may also be counter productive if communication with the patient is lost.
Intraocular pressure
The Aqueous humour is a transparent fluid (0.3 ml) that circulates in the anterior and posterior chambers of the eye. The pressure within the aqueous humour is the intraocular pressure (IOP). The normal intraocular pressure is 12 - 20 mmHg. The IOP depends on (1) the balance between the production and elimination of aqueous humour. (2) Choroidal blood volume and (3) external pressure. If the intraocular pressure exceeds retinal artery pressure then retinal artery blood flow is reduced resulting in retinal ischaemia.
Factors that increase intraocular pressure are an increase in venous pressure (which can be caused by coughing, straining, the head down position, vomiting, valsalva manoeuvre), increased extraocular muscle activity, hypercarbia, hypertension, topical anticholinergic drugs (which cause mydriasis), suxamethonium (6 – 12 mmHg 4-6 minute, transient increase), ketamine, and laryngoscopy (10 - 20 mmHg increase), and severe hypoxaemia.
Factors that reduce intraocular pressure include hyperventilation and hypocarbia, anaesthetic agents, non-depolarising muscle relaxants, mannitol and acetazolamide.
Oculo-cardiac reflex
The oculocardiac reflex is a trigeminal-vagal reflex that manifests as hypotension and bradycardia (or other arrhythmias) in response to pain, pressure and manipulation of the eyeball. The afferent pathway is along the long and short ciliary nerves to the ciliary ganglion and then to the gasserian ganglion along the ophthalmic division of the trigeminal nerve. The efferent fibres travel along the vagus to cause negative inotropy and conduction effects in the heart.
The reflex can be triggered by pressure on the globe caused by the introduction of local anaesthetic during retrobulbar injection, but more commonly, it occurs during manipulation or traction on the extraocular muscles during strabismus surgery. The management of the oculocardiac reflex is by stopping the stimulus. If arrhythmias persist, atropine administration may be required. It is important to ensure that the depth of anaesthesia is adequate during further manipulation. The reflex tends to fatigue during further manipulation, but local anaesthetic administration may help to block it.
Pharmacology
Eye drops are readily absorbed through the conjunctivae resulting in systemic effects. This can be minimized by the use of lower concentrations of medication or limiting instillation to only one or two drops and occluding the nasolacrimal duct at the time of instillation.
Phenylephrine is used as a mydriatic, particularly before cataract surgery. It can cause severe hypertension, arrhythmias, headaches and myocardial ischaemia.
Cyclopentolate is used as a mydriatic and can cause confusion and seizures.
Beta-adrenergic blocking agents are used to treat glaucoma and can produce bradycardia, hypotension, bronchospasm and congestive cardiac failure.
Anticholinesterases are used to decrease intraocular pressure. They will produce a prolonged response to suxamethonium and ester linked local anaesthetics.
Acetylcholine is used to produce miosis and will cause bradycardia, hypotension, bronchospasm and increased bronchial secretions.
Acetazolamide is a carbonic anhydrase inhibitor administered systemically to control aqueous humour secretion. It can lead to hyponatremia, hypokalemia and metabolic acidosis.
Preoperative evaluation and choice of anaesthetic technique Patients for ophthalmic surgery may present with multiple co-morbidities. The elderly patient for cataract surgery may have co-existing cardiovascular or respiratory disease and may be receiving anticoagulant or anti-platelet medications. If eye surgery under regional anaesthesia is planned, it is important that the patient is able to lie still. Movement disorders, orthopnea and a chronic cough will create difficult conditions for surgery. Paediatric patients will generally require a general anaesthetic. The patient with a penetrating eye injury will be at risk for aspiration of gastric contents and it is also important to control intraocular pressure to prevent the further extrusion of eye contents.
General anaesthesia
As with all head and neck procedures, a major consideration in eye surgery is poor access to the patient’s airway during surgery. Most commonly, an artificial airway device is used such as an endotracheal tube or laryngeal mask. The use of the laryngeal mask will require close co-operation with the surgeon. It is important to remain vigilant about the potential for circuit disconnection or dislodgement of the airway device.
Eye surgery is very stimulating and an adequate depth of anaesthesia is required to keep the patient from coughing, moving and straining and to control blood pressure, as all of these will increase intraocular pressure and may result in injury from surgical instruments.
A smooth emergence is important. It may be useful to administer intravenous lignocaine 1-1.5 mg/kg five minutes before extubation to reduce coughing. Pharyngeal suctioning should be performed whilst the patient is still under deep anaesthesia.
Post operative nausea and vomiting are common. It is important to try to control it with anti-emetic agents. Vomiting will cause large increases in intraocular pressure.
Ketamine causes blepharospasm, nystagmus, eye movement and may increase intraocular pressure. It is usually a poor choice of anaesthesia.
Local anaesthesia
Many ophthalmic procedures can be done under local or regional anaesthesia, including cataract surgery, corneal transplants, lid surgery, trabeculectomy and vitrectomy or repair of a detached retina. Local anaesthetic techniques include peribulbar, retrobulbar, and sub-tenon blocks as well as topical anaesthesia. It is essential that the anaesthetist know where the eyeball is in relationship to the floor, walls, roof and apex of the bony orbit. The orbit is a pyramidal shape, 40 – 50 mm deep, with the base at the orbital opening and the apex at the optic foramen. The volume of the orbit is approximately 30 ml. The volume of the globe and muscle cone is approximately 7 ml. The globe sits at the anterior part of the orbit, nearer the roof than the floor and nearer the lateral wall than the medial wall.
Peribulbar block
There are several different peribulbar blocks but all involve the injection of local anaesthetic outside the muscle cone of the eye. It is effective for producing analgesia and akinesia for surgery. Care should be taken in the patient with an eyeball axial length of greater than 26 mm, as there is an increased risk of globe perforation. Compared with a retrobulbar block, peribulbar anaesthesia requires larger volumes of 6 to 8 ml that may cause an increase in intraocular pressure and the onset time of 5-10 minutes is longer however it should be safer as the needle should be outside of the muscle cone, away from the artery, vein and nerve. However, peribulbar eye blocks do have complications that are life threatening and serious including perforation of the globe, retrobulbar haemorrhage, nerve damage, myotoxicity of the inferior rectus muscle and systemic complications (seizures, bradycardia).
Prior to the injection, local anaesthetic drops are applied topically to the cornea. A 25 to 27-gauge 22 mm needle is used for the injection. One technique is to insert the needle in the lateral aspect of the infratemporal quadrant of the eye through the inferior fornix of the conjunctiva rather than through the skin of the eyelid. With the patient supine, the needle inserted perpendicular to all planes. If the needle tip contacts the bone, the needle is redirected slightly superomedially. The globe must be observed carefully for any sign of rotation during insertion, indicating that the needle is contacting the globe. The needle is not inserted beyond 25 mm because vessels and the optic nerve may be injected. The patient is asked to maintain a neutral gaze and all injections are performed slowly to ensure patient comfort.
If a further ‘top up’ is needed use a medial canthus injection. At a point just medial to the caruncle the needle is passed backward with the bevel facing the globe, at an angle of 10 degrees to the sagittal plane, directed towards the medial wall of the orbit. .
Relative contraindications to peribulbar block include an INR > 2, axial length > 26 mm, perforated or infected eye and inability to lie flat or co-operate.
Topical anaesthesia
Cataract surgery can be performed under topical anaesthetic eye drops. The advantages are the avoidance of the risks associated with regional anaesthesia including globe perforation, haemorrhage, brainstem anaesthesia and optic nerve damage. This technique requires a very cooperative patient and careful surgery with smaller incisions. The choice of local anaesthetic drops includes bupivacaine, lignocaine and tetracaine. Lignocaine and bupivacaine will sting initially.
Traumatic eye injuries
A penetrating eye injury presents as a surgical emergency. There is a need to balance the risk aspiration of gastric contents against the prevention of sudden increases in intraocular pressure that may cause extrusion of ocular contents and loss of vision.
Prevention of aspiration may be aided by the administration of metoclopramide and an H2 receptor antagonist and by the performance of a rapid sequence induction. Although it can cause a transient increase in intraocular pressure, suxamethonium is used to facilitate intubation. The increase in intraocular pressure is of the order of 6-12 mmHg after a dose of suxamethonium that lasts for up to 10 minutes. The increase in pressure is attributed to contraction of the extraocular muscles, fasciculations of the orbicularis oculi and venous congestion within the eye.
Strategies to reduce the increase in intraocular pressure with intubation include the intravenous administration of lignocaine (1.5 mg/kg) and ensuring that the patient is completely paralysed before attempts at intubation. Coughing and straining at intubation will increase intraocular pressure by 30 - 40 mmHg. Most anaesthetic agents (other than ketamine) reduce the intraocular pressure. Mask ventilation may result in direct pressure on the eye. During the operation, normocarbia is maintained to avoid increases in intraocular pressure. It is important to control nausea and vomiting, which can cause large increases in pressure.
EAR SURGERY
Procedures on the ear include myringotomy for middle ear effusion resulting in conductive hearing loss, and procedures on the mastoid process for mastoiditis that may occur as a result of untreated or failed antibiotic response to chronic otitis media.
Important considerations are the fact that many of the patients are paediatric, upper respiratory tract infection is common and that postoperative nausea and vomiting are frequent. Ear surgery may involve dissection and preservation of the facial nerve, which has a long intra-osseous course and may be vulnerable to injury. The middle ear communicates with the oropharynx via the Eustachian tube, which may be blocked by trauma, oedema, inflammation and infection and large adenoids in children. The normal ability to equalize the pressures between the inner ear and outer ear is disturbed if there is a blocked Eustachian tube, which usually allows air to vent into the pharynx. The pressure in the middle ear may become raised leading to conduction deafness in the chronic situation and tympanic membrane rupture if the pressure rises acutely.
Nitrous oxide can diffuse into air filled cavities including the middle ear and cause expansion of the cavity, leading to an increase in middle ear pressure. At the end of the anaesthetic, there is rapid absorption of the nitrous oxide, which can result in profound negative pressure. These changes in middle ear pressure can result in a decline in hearing, tympanic membrane rupture, graft disruption and nausea and vomiting.
Positioning during ear surgery usually involves a slight elevation of the head (to reduce bleeding) and turning the patient’s head to the contralateral side. The patient’s normal range of head movement should be assessed before surgery. Access to the airway may be limited during long procedures. The endotracheal must be carefully secured. In procedures such as stapedectomy and mastoidectomy, facial nerve monitoring may be performed, so it is important that neuromuscular paralysis has worn off. The need for the patient to be immobile in operations on the ossicles requires deep anaesthesia. Emergence from anaesthesia needs to be smooth so that there is no increase in venous pressure. After mastoidectomy, a head bandage will be applied and there can be much movement of the head resulting in coughing and bucking on the endotracheal tube. This is not desirable due to the risk of bleeding, so a deep plane of anaesthesia is maintained until the bandage has been applied. Postoperative nausea and vomiting can disrupt grafts and prostheses and needs to be controlled.
NASAL SURGERY
Nasal and sinus surgery carries the risk of bleeding into the airway and aspiration of blood. It is usually performed under general anaesthesia with an endotracheal tube and a throat pack, but some procedures can be carried out under local anaesthesia. When a throat pack is used the anaesthetist must be certain that it has been removed at the end of surgery. Some anaesthetists like to tie the end of the throat pack to the endotracheal tube so that it cannot be left behind. Local anaesthesia and vasoconstrictors are commonly used to reduce bleeding even with general anaesthetic techniques. Surgeons may infiltrate with adrenaline and apply cocaine. (The maximum cocaine dose should not exceed 1.5 mg/kg). Both these drugs will cause tachycardia, hypertension and dysrhythmias especially when used with halothane. Patients must be monitored with an ECG.
Swallowed blood after emergence will increase the risk of postoperative nausea and vomiting. Care should be taken to limit the dose of adrenaline in the presence of halothane anaesthesia, as arrhythmias will occur.
The nasal operations are not usually very painful. After the procedure, a direct laryngoscopy is performed and the pharynx is suctioned under vision. There may be some blood in the nasopharynx, so the head is lifted and the nasopharynx is suctioned after turning the Yankauer sucker through 180 degrees to suction behind the uvula and soft palate. Some surgeons will pack the nose after surgery, which can be distressing to the patient after emergence. A Guedel airway will encourage the patient to breathe through the mouth at this time. Mask ventilation may be difficult on emergence, as the surgeon will not want pressure on the nose, particularly after rhinoplasty.
Reduction of a nasal fracture is a brief procedure can be performed under brief but deep general anaesthesia. This can be achieved in the slight head up position after adequate pre-oxygenation using fentanyl for analgesia and a bolus dose of propofol and allowing the surgeon to do his reduction. If there is expected to be blood loss, the airway needs to be protected with either a laryngeal mask or endotracheal tube.
Patients with severe epistaxis may present for internal maxillary artery ligation. They may have lost a substantial amount of blood and commonly have other co-existing disease, particularly hypertension. Adequate preoperative hydration is important and it is assumed that they have a full stomach (rapid sequence induction).
The nasal sinuses may require drainage and this sometimes requires a surgical approach. The important considerations are the risks of haemorrhage, eye injury, venous air embolism, cerebrospinal fluid leak and permanent neurologic injury.
THROAT SURGERY
By its very nature, throat surgery involves the sharing of the airway with the surgeon. Good management requires excellent communication with the surgeon. The patients can present with an abnormal airway that is congenital or acquired (such as infection, tumour, radiation and foreign body). Perioperative airway management must be carefully designed. Extubation after airway surgery must be planned. Throat packs must be removed, the pharynx suctioned under direct vision, the patient oxygenated and only extubated after full protective airway reflexes have returned. Excessive bleeding, oedema, or extensive surgery may make extubation unsafe.
Epiglottitis
Epiglottitis is an acute bacterial infection that is usually caused by Haemophilus influenza type B. There is now a vaccine for children so its incidence is less common. The classic presentation is of a sudden onset of high fever, sore throat, stridor, dysphagia and drooling. The patient is commonly in the sitting position and will be pale and anxious.
Adult epiglottitis can occur, and it is usually treated conservatively with antibiotics (cephalosporin) and intubation is rarely required. In the child, total airway obstruction can occur at any time and the patient is intubated in a controlled setting under deep inhalation anaesthesia with an ear nose and throat surgeon on standby. Muscle relaxation is avoided. The endotracheal tube size is 0.5 to 1 size smaller than usual. If there is airway obstruction during inhalation induction, a rigid bronchoscopy or tracheostomy is performed.
Foreign body in the airway Aspiration of a foreign body is common in young children. The child can present with a sudden onset of obstructive breathing (stridor), hoarse voice, barking cough or wheezing. Immediate first aid includes back blows and chest thrusts. Care must be taken to avoid dislodging the foreign body into the upper part of the trachea, where it can cause total obstruction. In the acute situation, it may be possible to perform rigid laryngoscopy in the non-anaesthetised patient. More commonly, removal of the foreign body is performed with the child anaesthetised with a spontaneous ventilation technique. This is performed with gentle mask induction without positive pressure ventilation and a rigid bronchoscope is inserted to remove the foreign body. The surgeon must be prepared to perform an emergency tracheostomy or cricothyroidotomy. Laryngeal and subglottic oedema may persist after removal of the foreign body and the patient should be observed carefully for 24 hours.
Tonsillectomy Tonsillectomy is performed in patients with recurrent tonsillitis or obstructive sleep apnoea secondary to adenotonsillar hypertrophy. The patients with sleep apnoea are at increased risk of postoperative airway obstruction. Preoperative evaluation involves inquiry about snoring and sleep apnoea, respiratory tract infection, checking for loose teeth and ensuring normal coagulation. Respiratory tract infections will increase the risk of a respiratory complication such as laryngospasm or bronchospasm and desaturation. However, there is no association with increased morbidity unless the patient is very unwell or has other respiratory disease (such as asthma).
Anaesthetic considerations include the provision of deep anaesthesia to prevent reflex induced hypertension and tachycardia, adequate airway protection and the avoidance of bucking, coughing and straining. Emergence may present problems with acute bleeding, stridor and laryngeal spasm.
Technique:
Anaesthesia induction for the paediatric patient may be performed with an inhalation or intravenous technique. The patients with obstructive sleep apnoea may benefit from continuous positive airways pressure after the loss of consciousness to maintain airway patency during induction. Intravenous access with an adequate sized cannula is important, as the patient may lose a significant amount blood.
A balanced technique is used for the maintenance of anaesthesia. The use of muscle relaxants may be helpful, but the surgery is only of short duration (15-30 minutes) and care must be taken to avoid long acting agents and to ensure adequate reversal of paralysis at the end of the procedure. Some anaesthetists may choose to ventilate the patient via the endotracheal tube under deep volatile anaesthesia with no neuromuscular paralysis. Care should be taken with halothane, as it has the potential to cause bradycardia and depress the myocardium in high concentrations. After the trachea is intubated, the surgeon will place a gag to expose the tonsils. The endotracheal tube may become occluded, and it is important to ensure that the tube dose not become dislodged or disconnected from the circuit under the surgical drapes. Monitoring the end tidal carbon dioxide with capnography is useful.
At the conclusion of the operation, there are the considerations of reducing venous pressure (avoidance of coughing and straining), avoidance of laryngospasm and adequate airway protection. The patient needs to be breathing spontaneously and ideally, should be able to maintain his or her airway. Intravenous lignocaine has been used to suppress laryngospasm. Suction the oropharynx under direct vision. Avoid blind pharyngeal suctioning as it may cause bleeding. The patient is placed in the lateral position with the head down to direct blood and secretions away from the vocal cords. After emergence, the trachea is extubated.
Paracetamol and opioid is usually used for postoperative analgesia and tramadol may be useful. Care should be taken with the non-steroidal anti-inflammatory agents, as they will inhibit platelet function and may lead to an increase in bleeding. It is preferable to limit the use of morphine in the patients with obstructive sleep apnoea. Local anaesthetic infiltration of the tonsil bed has only a minimal effect on pain.
Postoperative bleeding is the most serious concern but persistent vomiting and poor oral intake are more common. Strategies to reduce nausea and vomiting and adequate hydration are important during this time. Intraoperative dexamethasone (0.5 mg/kg maximum of 8 mg) decreases vomiting, increases postoperative oral intake and reduces pain.
Patients should be observed in recovery and checked for no bleeding before discharge.
Post tonsillectomy haemorrhage A routine patient will lose approximately 4 ml/kg of blood during a tonsillectomy. In 5% of cases, there will be a post tonsillectomy haemorrhage. It may occur within 24 hours or a few days later (secondary haemorrhage, usually due to infection). Beware of continual swallowing in the recovery unit, as it may be a sign of bleeding.
The degree of blood loss is often underestimated as the blood is usually swallowed. The patient is usually hypovolemic and has a stomach full of blood. This is a surgical emergency. Careful assessment of the patient is required and intravenous fluid resuscitation must be carried out prior to induction of anaesthesia. Transfusion of packed red blood cells may be required. Induction of anaesthesia in a hypovolaemic bleeding child can cause severe hypotension and cardiac arrest. Check haematocrit and coagulation.
Induction of anaesthesia is with a rapid sequence induction using cricoid pressure. Two suckers are desirable, as the bleeding may be brisk and quickly obscure the airway. The endotracheal tube size may need to be one size smaller than anticipated. Intubation may be difficult. The surgeon should be present.
Abscess A peritonsillar abscess can present with trismus, dysphagia and a distorted airway with obstruction. There may be a need to perform drainage of the abscess with awake needle aspiration prior to induction of anaesthesia to minimize the risk of rupture during induction of anaesthesia or intubation. The other risks of anaesthesia include the potential for airway obstruction and difficult intubation.
A difficult intubation can be expected due to distortion of the airway, oedema and ongoing trismus after induction. Laryngoscopy may also rupture the abscess causing aspiration. There are three options for management if obstruction is expected. They include:
1. Awake intubation under vision.
2. Mask induction with the patient breathing spontaneously. Intubation is then performed slowly and gently to avoid airway contamination with pus.
3. Elective tracheostomy.
In cases of cellulitis of the submandibular and sublingual spaces, there may be involvement of the anterior compartments of the neck. Visualization of the glottis is not usually possible and general anaesthesia is contraindicated if there is stridor at rest. There may be no alternative but to perform a tracheostomy under local anaesthesia through the cellulitis.
DENTAL SURGERY
Most dental surgery is performed under local anaesthesia in the outpatient setting. Some patients having multiple extractions or extensive dental work may require general anaesthesia. Many of the patients requiring general anaesthesia are very young children or have behavioural problems.
The main anaesthetic considerations are the possible requirement for nasal intubation, a shared airway with the dentist, blood in the airway requiring a throat pack that must be removed at the end of the procedure and the management of an anxious or uncooperative patient.
Patients should be positioned supine with head up. They should not be in a ‘dental chair’ sitting position. Arrhythmias are common, due to hypoxia, hypercarbia and volatile anaesthetic agents. Halothane has a high rate of arrhythmias.
Nasal intubation is performed in the following way. The endotracheal tube is softened in warmed water. It may need to be smaller than an oral tube and will need to be flexible enough to direct towards the forehead so as to be away from the surgical field. The patient should sniff to see if one nostril is blocked. The larger patent nostril is chosen and is prepared with a vasoconstrictor and lubricant. After anaesthesia is induced, the endotracheal tube is introduced into the prepared nostril and advanced parallel to the palate (not in a superior direction) until it enters the pharynx. There will be a resistance in the nasal passage until the tube passes over the inferior turbinate. Laryngoscopy is performed and any blood is suctioned. The tip of the endotracheal tube is seen on the posterior pharyngeal wall. Advancement of the tube to the larynx may require the use of MacGill forceps. The tube is secured to the nose, taking care not to cause pressure on the nose.
MAXILLOFACIAL SURGERY
Maxillofacial surgery is required to repair facial trauma and to correct facial deformity.
Mid-face fractures are classified according to the Le Fort classification:
Class I involves the lower third of the nasal septum and maxilla passing above the nasal floor. The maxillary alveolar process, palate, part of the palatine bone and lower third of the pterygoid plates are mobile. In this situation, oral or nasal intubation can be performed and the airway is usually intact.
Class II fractures involve the upper nasal bone, under the zygomaticomaxillary suture and through the pterygoid plate. Nasal intubation is contraindicated.
Le Fort Class III fracture separates the base of the skull from the midface and nasal intubation is contraindicated.
In all facial fractures, a careful airway assessment needs to be carried out. There may be other injuries and airway compromise. Intubation may be difficult and may need to be secured via an alternative technique such as awake fiberoptic intubation or retrograde intubation. An armoured reinforced endotracheal tube may be necessary to prevent kinking.
Nasal intubation is only an option for a class I fracture and in patients who have no cerebrospinal fluid (CSF)) leak. Nasal intubation can be complicated by bleeding, damage to nasal turbinates and increased risk of sinusitis and otitis. It should not be performed blindly if there is disruption to the nasopharynx. The tube can enter a sinus, the orbit, hypopharynx and intracranially. Where there is doubt about the presence of a base of skull fracture or in severe facial trauma, a tracheostomy needs to be considered.
In the patient for maxillofacial reconstruction or orthognathic surgery, there is the potential for severe blood loss and contamination of the airway with blood. The surgeons will request a nasal intubation to allow better surgical access and a throat pack will be placed. Hypotensive anaesthesia may reduce the amount of blood loss. This technique is only safe in the young and fit patient. Blood entering the stomach will cause postoperative nausea and may be aspirated into the lungs. The patient is extubated when he is fully awake and airway reflexes have returned
HEAD AND NECK SURGERY
Head and neck surgery includes parotid surgery, thyroid and parathyroid surgery and the management of head and neck cancers. Airway management is a major consideration, as well as the potential for endocrine problems and injury to adjacent structures (nerves, blood vessels). Many of these procedures may be prolonged.
Unilateral vocal cord paralysis will cause hoarseness. Bilateral vocal cord paralysis will cause increasing upper airway obstruction and stridor.
Parotidectomy Parotid salivary gland may be inflamed or may require resection for masses. The duration of surgery is often prolonged and the anaesthetist’s access to the head is restricted. For these reasons, endotracheal intubation is preferred. The patient is positioned with the operative side up and the back slightly elevated. The major surgical complication is facial nerve injury. If nerve stimulation is to be used to identify the facial nerve, neuromuscular paralysis should be absent.
Thyroidectomy Thyroid surgery is performed for goitre that causes compression, tumour or for hyperthyroidism that cannot be controlled with medication. Preoperative examination should include a careful assessment of obstructive symptoms (a large goitre may cause tracheal compression, decreased venous return or tracheal deviation and tracheomalacia) and the airway as well as an assessment of thyroid function. The patient must be treated so that they are euthyroid before surgery. The potential complications of thyroid surgery include life threatening thyroid storm (severe thyrotoxicosis), injury to the recurrent laryngeal nerve causing postoperative airway obstruction due to vocal cord paralysis, tracheomalacia and the need for reintubation, difficult intubation (more likely with a cancer than a benign goitre), and postoperative bleeding. Postoperative bleeding can lead to severe airway compromise due to tracheal compression and airway oedema due to venous engorgement. Intubation may be very difficult. The neck haematoma should be evacuated urgently to improve airway obstruction. Unintentional parathyroidectomy may result in hypocalcaemia that may become apparent only several hours after the operation. The treatment involves the administration of intravenous calcium chloride.
Pain after thyroidectomy is moderate but not usually severe. Postoperative nausea and vomiting is a significant issue, as it is important to try and avoid straining and a rise in venous pressure postoperatively as this may cause bleeding.
Parathyroidectomy The parathyroid glands regulate calcium metabolism by producing parathyroid hormone (PTH). PTH elevates serum calcium via its actions on the gastrointestinal tract, bone and kidneys. It also leads to a reduced serum phosphate by increasing its excretion. Adenomas of the parathyroid gland will produce PTH and cause an increase in serum calcium, low phosphate, hyperchloremic acidosis, polyuria and polydipsia.
Parathyroidectomy surgery can be prolonged due to difficulty identifying the glands. The main anaesthetic concerns are ensuring adequate hydration, monitoring for cardiac arrhythmias, correcting acidosis (avoid hypoventilation), and ensuring adequate reversal of paralysis (the patient may be weak due to hypercalcemia). As with thyroid surgery, there may be recurrent laryngeal nerve injury or postoperative bleeding that may lead to airway obstruction.
SELF-ASSESSMENT QUESTIONS
1. What factors increase the risk of laryngeal spasm after nose and throat surgery? Describe the management of laryngeal spasm after extubation.
2. Describe the technique of nasal intubation. What are the indications and contraindications to nasal intubation?
3. What is the oculocardiac reflex? Discuss the afferent and efferent nerves involved. How is it treated?
A twelve-year-old child has been brought in to your hospital from the countryside one week after first complaining of a sore throat. He is febrile 39 C and flushed. His mother says he has not been able to swallow well and has not eaten for two days. He has very bad breath and cannot open his mouth to allow you to examine his throat well. You suspect he has a peritonsillar abscess. Outline your initial assessment and discuss the management of this problem. In particular outline the options for airway management and discuss the advantages and disadvantages of each option.
EYE, ENT, DENTAL, MAXILLOFACIAL AND HEAD AND NECK SURGERY CASE STUDIES
Case 13.1
Aruina was brought in to your hospital with an open eye injury following a fall from a horse. She has just eaten lunch and she is feeling nauseated. The surgeon wants to fix her eye as soon as possible.
What factors will influence your choice of anaesthetic?
Describe the anaesthetic technique you will use.
What can you do to reduce intraocular pressure during induction, during the operation and on emergence?
Case 13.2
Ganbat is a four-year-old boy who has presented for an adenotonsillectomy. He has had recurrent tonsillitis and his mother says he has a runny nose at the present time. He is not cooperative and does not allow you to examine him.
What are the indications for tonsillectomy?
What features on the history will influence your choice of anaesthetic?
Describe your anaesthetic technique in detail and discuss the reasons behind your choice of anaesthetic.
How will you manage emergence from anaesthesia and his extubation?
You are called to the ward by the surgeon three hours later because Ganbat has just vomited a large amount of blood. How will you assess the degree of blood loss?
The surgeon says that he needs to take Ganbat back to theatre. Outline your management and describe your anaesthetic technique.
Case 13.3
Tsahim is a 55-year-old herder and needs a thyroidectomy for a large goitre. You meet him on the ward the night before surgery where he has been admitted. He is a smoker but otherwise well.
Outline your preoperative assessment.
What further preoperative testing would you like to perform?
Describe your major concerns for management of the anaesthetic.
How will you manage his extubation?
He has been in recovery for half an hour and the nurse calls you in urgently because she is concerned about his airway. She says he has stridor and is starting to desaturate. What could be causing the stridor?
The surgeon says he needs to take him back to theatre for an immediate evacuation of a haematoma. Describe your management of this situation.
Twelve hours later, the nurse says that Tsahim is tachycardic and febrile. What could be causing the problem? How should he be managed?
Case 13.4
Tsungaa is twenty and had been hit in the face with a railway sleeper. There has been no loss of consciousness but she has black eyes and there is clear fluid and blood from the nose. She has an obvious maxillary depression. The surgeon would like to take her to theatre to fix her facial fractures.
How will you assess Tsungaa’s airway?
Tsungaa is unable to open her mouth. What are the options for airway management? Outline the advantages and disadvantages of each.
Final Objective: The ability to provide anaesthesia for eye, ear, nose and throat surgery, dentistry and basic head and neck procedures.
Enabling Objective: To achieve this goal, you should know how to:
- Outline the factors affecting intra-ocular pressure
- Discuss the anaesthetic techniques for open eye injuries
- Describe the anaesthetic techniques for basic ear, nose and throat procedures
- Describe the problems of the shared airway and their management
- Discuss the peri operative management of the bleeding tonsil, quinsy, thyroidectomy and facial trauma
- Developing Anaesthesia (Chapter on airway assessment)
- Oxford Handbook of Anaesthesia Chapters 25, 26 & 27.
- Anaesthesia and co-existing disease seminar notes (thyroid disease)
Many procedures are performed on paediatric patients and many patients will be discharged on the same day of surgery, requiring a smooth emergence and control of nausea and vomiting. It is very important to communicate well with the surgical team and the parents.
The patient’s eyes must be carefully protected.
EYE SURGERY
The success of eye surgery is dependant on the ability to keep the eye still during the procedure. A local or general anaesthetic technique may be chosen for surgery, but if a local or regional anaesthetic is used, it is important that the patient keeps still and is able to lie flat during the procedure. The use of ‘conscious sedation’ may be helpful, but may also be counter productive if communication with the patient is lost.
Intraocular pressure
The Aqueous humour is a transparent fluid (0.3 ml) that circulates in the anterior and posterior chambers of the eye. The pressure within the aqueous humour is the intraocular pressure (IOP). The normal intraocular pressure is 12 - 20 mmHg. The IOP depends on (1) the balance between the production and elimination of aqueous humour. (2) Choroidal blood volume and (3) external pressure. If the intraocular pressure exceeds retinal artery pressure then retinal artery blood flow is reduced resulting in retinal ischaemia.
Factors that increase intraocular pressure are an increase in venous pressure (which can be caused by coughing, straining, the head down position, vomiting, valsalva manoeuvre), increased extraocular muscle activity, hypercarbia, hypertension, topical anticholinergic drugs (which cause mydriasis), suxamethonium (6 – 12 mmHg 4-6 minute, transient increase), ketamine, and laryngoscopy (10 - 20 mmHg increase), and severe hypoxaemia.
Factors that reduce intraocular pressure include hyperventilation and hypocarbia, anaesthetic agents, non-depolarising muscle relaxants, mannitol and acetazolamide.
Oculo-cardiac reflex
The oculocardiac reflex is a trigeminal-vagal reflex that manifests as hypotension and bradycardia (or other arrhythmias) in response to pain, pressure and manipulation of the eyeball. The afferent pathway is along the long and short ciliary nerves to the ciliary ganglion and then to the gasserian ganglion along the ophthalmic division of the trigeminal nerve. The efferent fibres travel along the vagus to cause negative inotropy and conduction effects in the heart.
The reflex can be triggered by pressure on the globe caused by the introduction of local anaesthetic during retrobulbar injection, but more commonly, it occurs during manipulation or traction on the extraocular muscles during strabismus surgery. The management of the oculocardiac reflex is by stopping the stimulus. If arrhythmias persist, atropine administration may be required. It is important to ensure that the depth of anaesthesia is adequate during further manipulation. The reflex tends to fatigue during further manipulation, but local anaesthetic administration may help to block it.
Pharmacology
Eye drops are readily absorbed through the conjunctivae resulting in systemic effects. This can be minimized by the use of lower concentrations of medication or limiting instillation to only one or two drops and occluding the nasolacrimal duct at the time of instillation.
Phenylephrine is used as a mydriatic, particularly before cataract surgery. It can cause severe hypertension, arrhythmias, headaches and myocardial ischaemia.
Cyclopentolate is used as a mydriatic and can cause confusion and seizures.
Beta-adrenergic blocking agents are used to treat glaucoma and can produce bradycardia, hypotension, bronchospasm and congestive cardiac failure.
Anticholinesterases are used to decrease intraocular pressure. They will produce a prolonged response to suxamethonium and ester linked local anaesthetics.
Acetylcholine is used to produce miosis and will cause bradycardia, hypotension, bronchospasm and increased bronchial secretions.
Acetazolamide is a carbonic anhydrase inhibitor administered systemically to control aqueous humour secretion. It can lead to hyponatremia, hypokalemia and metabolic acidosis.
Preoperative evaluation and choice of anaesthetic technique Patients for ophthalmic surgery may present with multiple co-morbidities. The elderly patient for cataract surgery may have co-existing cardiovascular or respiratory disease and may be receiving anticoagulant or anti-platelet medications. If eye surgery under regional anaesthesia is planned, it is important that the patient is able to lie still. Movement disorders, orthopnea and a chronic cough will create difficult conditions for surgery. Paediatric patients will generally require a general anaesthetic. The patient with a penetrating eye injury will be at risk for aspiration of gastric contents and it is also important to control intraocular pressure to prevent the further extrusion of eye contents.
General anaesthesia
As with all head and neck procedures, a major consideration in eye surgery is poor access to the patient’s airway during surgery. Most commonly, an artificial airway device is used such as an endotracheal tube or laryngeal mask. The use of the laryngeal mask will require close co-operation with the surgeon. It is important to remain vigilant about the potential for circuit disconnection or dislodgement of the airway device.
Eye surgery is very stimulating and an adequate depth of anaesthesia is required to keep the patient from coughing, moving and straining and to control blood pressure, as all of these will increase intraocular pressure and may result in injury from surgical instruments.
A smooth emergence is important. It may be useful to administer intravenous lignocaine 1-1.5 mg/kg five minutes before extubation to reduce coughing. Pharyngeal suctioning should be performed whilst the patient is still under deep anaesthesia.
Post operative nausea and vomiting are common. It is important to try to control it with anti-emetic agents. Vomiting will cause large increases in intraocular pressure.
Ketamine causes blepharospasm, nystagmus, eye movement and may increase intraocular pressure. It is usually a poor choice of anaesthesia.
Local anaesthesia
Many ophthalmic procedures can be done under local or regional anaesthesia, including cataract surgery, corneal transplants, lid surgery, trabeculectomy and vitrectomy or repair of a detached retina. Local anaesthetic techniques include peribulbar, retrobulbar, and sub-tenon blocks as well as topical anaesthesia. It is essential that the anaesthetist know where the eyeball is in relationship to the floor, walls, roof and apex of the bony orbit. The orbit is a pyramidal shape, 40 – 50 mm deep, with the base at the orbital opening and the apex at the optic foramen. The volume of the orbit is approximately 30 ml. The volume of the globe and muscle cone is approximately 7 ml. The globe sits at the anterior part of the orbit, nearer the roof than the floor and nearer the lateral wall than the medial wall.
Peribulbar block
There are several different peribulbar blocks but all involve the injection of local anaesthetic outside the muscle cone of the eye. It is effective for producing analgesia and akinesia for surgery. Care should be taken in the patient with an eyeball axial length of greater than 26 mm, as there is an increased risk of globe perforation. Compared with a retrobulbar block, peribulbar anaesthesia requires larger volumes of 6 to 8 ml that may cause an increase in intraocular pressure and the onset time of 5-10 minutes is longer however it should be safer as the needle should be outside of the muscle cone, away from the artery, vein and nerve. However, peribulbar eye blocks do have complications that are life threatening and serious including perforation of the globe, retrobulbar haemorrhage, nerve damage, myotoxicity of the inferior rectus muscle and systemic complications (seizures, bradycardia).
Prior to the injection, local anaesthetic drops are applied topically to the cornea. A 25 to 27-gauge 22 mm needle is used for the injection. One technique is to insert the needle in the lateral aspect of the infratemporal quadrant of the eye through the inferior fornix of the conjunctiva rather than through the skin of the eyelid. With the patient supine, the needle inserted perpendicular to all planes. If the needle tip contacts the bone, the needle is redirected slightly superomedially. The globe must be observed carefully for any sign of rotation during insertion, indicating that the needle is contacting the globe. The needle is not inserted beyond 25 mm because vessels and the optic nerve may be injected. The patient is asked to maintain a neutral gaze and all injections are performed slowly to ensure patient comfort.
If a further ‘top up’ is needed use a medial canthus injection. At a point just medial to the caruncle the needle is passed backward with the bevel facing the globe, at an angle of 10 degrees to the sagittal plane, directed towards the medial wall of the orbit. .
Relative contraindications to peribulbar block include an INR > 2, axial length > 26 mm, perforated or infected eye and inability to lie flat or co-operate.
Topical anaesthesia
Cataract surgery can be performed under topical anaesthetic eye drops. The advantages are the avoidance of the risks associated with regional anaesthesia including globe perforation, haemorrhage, brainstem anaesthesia and optic nerve damage. This technique requires a very cooperative patient and careful surgery with smaller incisions. The choice of local anaesthetic drops includes bupivacaine, lignocaine and tetracaine. Lignocaine and bupivacaine will sting initially.
Traumatic eye injuries
A penetrating eye injury presents as a surgical emergency. There is a need to balance the risk aspiration of gastric contents against the prevention of sudden increases in intraocular pressure that may cause extrusion of ocular contents and loss of vision.
Prevention of aspiration may be aided by the administration of metoclopramide and an H2 receptor antagonist and by the performance of a rapid sequence induction. Although it can cause a transient increase in intraocular pressure, suxamethonium is used to facilitate intubation. The increase in intraocular pressure is of the order of 6-12 mmHg after a dose of suxamethonium that lasts for up to 10 minutes. The increase in pressure is attributed to contraction of the extraocular muscles, fasciculations of the orbicularis oculi and venous congestion within the eye.
Strategies to reduce the increase in intraocular pressure with intubation include the intravenous administration of lignocaine (1.5 mg/kg) and ensuring that the patient is completely paralysed before attempts at intubation. Coughing and straining at intubation will increase intraocular pressure by 30 - 40 mmHg. Most anaesthetic agents (other than ketamine) reduce the intraocular pressure. Mask ventilation may result in direct pressure on the eye. During the operation, normocarbia is maintained to avoid increases in intraocular pressure. It is important to control nausea and vomiting, which can cause large increases in pressure.
EAR SURGERY
Procedures on the ear include myringotomy for middle ear effusion resulting in conductive hearing loss, and procedures on the mastoid process for mastoiditis that may occur as a result of untreated or failed antibiotic response to chronic otitis media.
Important considerations are the fact that many of the patients are paediatric, upper respiratory tract infection is common and that postoperative nausea and vomiting are frequent. Ear surgery may involve dissection and preservation of the facial nerve, which has a long intra-osseous course and may be vulnerable to injury. The middle ear communicates with the oropharynx via the Eustachian tube, which may be blocked by trauma, oedema, inflammation and infection and large adenoids in children. The normal ability to equalize the pressures between the inner ear and outer ear is disturbed if there is a blocked Eustachian tube, which usually allows air to vent into the pharynx. The pressure in the middle ear may become raised leading to conduction deafness in the chronic situation and tympanic membrane rupture if the pressure rises acutely.
Nitrous oxide can diffuse into air filled cavities including the middle ear and cause expansion of the cavity, leading to an increase in middle ear pressure. At the end of the anaesthetic, there is rapid absorption of the nitrous oxide, which can result in profound negative pressure. These changes in middle ear pressure can result in a decline in hearing, tympanic membrane rupture, graft disruption and nausea and vomiting.
Positioning during ear surgery usually involves a slight elevation of the head (to reduce bleeding) and turning the patient’s head to the contralateral side. The patient’s normal range of head movement should be assessed before surgery. Access to the airway may be limited during long procedures. The endotracheal must be carefully secured. In procedures such as stapedectomy and mastoidectomy, facial nerve monitoring may be performed, so it is important that neuromuscular paralysis has worn off. The need for the patient to be immobile in operations on the ossicles requires deep anaesthesia. Emergence from anaesthesia needs to be smooth so that there is no increase in venous pressure. After mastoidectomy, a head bandage will be applied and there can be much movement of the head resulting in coughing and bucking on the endotracheal tube. This is not desirable due to the risk of bleeding, so a deep plane of anaesthesia is maintained until the bandage has been applied. Postoperative nausea and vomiting can disrupt grafts and prostheses and needs to be controlled.
NASAL SURGERY
Nasal and sinus surgery carries the risk of bleeding into the airway and aspiration of blood. It is usually performed under general anaesthesia with an endotracheal tube and a throat pack, but some procedures can be carried out under local anaesthesia. When a throat pack is used the anaesthetist must be certain that it has been removed at the end of surgery. Some anaesthetists like to tie the end of the throat pack to the endotracheal tube so that it cannot be left behind. Local anaesthesia and vasoconstrictors are commonly used to reduce bleeding even with general anaesthetic techniques. Surgeons may infiltrate with adrenaline and apply cocaine. (The maximum cocaine dose should not exceed 1.5 mg/kg). Both these drugs will cause tachycardia, hypertension and dysrhythmias especially when used with halothane. Patients must be monitored with an ECG.
Swallowed blood after emergence will increase the risk of postoperative nausea and vomiting. Care should be taken to limit the dose of adrenaline in the presence of halothane anaesthesia, as arrhythmias will occur.
The nasal operations are not usually very painful. After the procedure, a direct laryngoscopy is performed and the pharynx is suctioned under vision. There may be some blood in the nasopharynx, so the head is lifted and the nasopharynx is suctioned after turning the Yankauer sucker through 180 degrees to suction behind the uvula and soft palate. Some surgeons will pack the nose after surgery, which can be distressing to the patient after emergence. A Guedel airway will encourage the patient to breathe through the mouth at this time. Mask ventilation may be difficult on emergence, as the surgeon will not want pressure on the nose, particularly after rhinoplasty.
Reduction of a nasal fracture is a brief procedure can be performed under brief but deep general anaesthesia. This can be achieved in the slight head up position after adequate pre-oxygenation using fentanyl for analgesia and a bolus dose of propofol and allowing the surgeon to do his reduction. If there is expected to be blood loss, the airway needs to be protected with either a laryngeal mask or endotracheal tube.
Patients with severe epistaxis may present for internal maxillary artery ligation. They may have lost a substantial amount of blood and commonly have other co-existing disease, particularly hypertension. Adequate preoperative hydration is important and it is assumed that they have a full stomach (rapid sequence induction).
The nasal sinuses may require drainage and this sometimes requires a surgical approach. The important considerations are the risks of haemorrhage, eye injury, venous air embolism, cerebrospinal fluid leak and permanent neurologic injury.
THROAT SURGERY
By its very nature, throat surgery involves the sharing of the airway with the surgeon. Good management requires excellent communication with the surgeon. The patients can present with an abnormal airway that is congenital or acquired (such as infection, tumour, radiation and foreign body). Perioperative airway management must be carefully designed. Extubation after airway surgery must be planned. Throat packs must be removed, the pharynx suctioned under direct vision, the patient oxygenated and only extubated after full protective airway reflexes have returned. Excessive bleeding, oedema, or extensive surgery may make extubation unsafe.
Epiglottitis
Epiglottitis is an acute bacterial infection that is usually caused by Haemophilus influenza type B. There is now a vaccine for children so its incidence is less common. The classic presentation is of a sudden onset of high fever, sore throat, stridor, dysphagia and drooling. The patient is commonly in the sitting position and will be pale and anxious.
Adult epiglottitis can occur, and it is usually treated conservatively with antibiotics (cephalosporin) and intubation is rarely required. In the child, total airway obstruction can occur at any time and the patient is intubated in a controlled setting under deep inhalation anaesthesia with an ear nose and throat surgeon on standby. Muscle relaxation is avoided. The endotracheal tube size is 0.5 to 1 size smaller than usual. If there is airway obstruction during inhalation induction, a rigid bronchoscopy or tracheostomy is performed.
Foreign body in the airway Aspiration of a foreign body is common in young children. The child can present with a sudden onset of obstructive breathing (stridor), hoarse voice, barking cough or wheezing. Immediate first aid includes back blows and chest thrusts. Care must be taken to avoid dislodging the foreign body into the upper part of the trachea, where it can cause total obstruction. In the acute situation, it may be possible to perform rigid laryngoscopy in the non-anaesthetised patient. More commonly, removal of the foreign body is performed with the child anaesthetised with a spontaneous ventilation technique. This is performed with gentle mask induction without positive pressure ventilation and a rigid bronchoscope is inserted to remove the foreign body. The surgeon must be prepared to perform an emergency tracheostomy or cricothyroidotomy. Laryngeal and subglottic oedema may persist after removal of the foreign body and the patient should be observed carefully for 24 hours.
Tonsillectomy Tonsillectomy is performed in patients with recurrent tonsillitis or obstructive sleep apnoea secondary to adenotonsillar hypertrophy. The patients with sleep apnoea are at increased risk of postoperative airway obstruction. Preoperative evaluation involves inquiry about snoring and sleep apnoea, respiratory tract infection, checking for loose teeth and ensuring normal coagulation. Respiratory tract infections will increase the risk of a respiratory complication such as laryngospasm or bronchospasm and desaturation. However, there is no association with increased morbidity unless the patient is very unwell or has other respiratory disease (such as asthma).
Anaesthetic considerations include the provision of deep anaesthesia to prevent reflex induced hypertension and tachycardia, adequate airway protection and the avoidance of bucking, coughing and straining. Emergence may present problems with acute bleeding, stridor and laryngeal spasm.
Technique:
Anaesthesia induction for the paediatric patient may be performed with an inhalation or intravenous technique. The patients with obstructive sleep apnoea may benefit from continuous positive airways pressure after the loss of consciousness to maintain airway patency during induction. Intravenous access with an adequate sized cannula is important, as the patient may lose a significant amount blood.
A balanced technique is used for the maintenance of anaesthesia. The use of muscle relaxants may be helpful, but the surgery is only of short duration (15-30 minutes) and care must be taken to avoid long acting agents and to ensure adequate reversal of paralysis at the end of the procedure. Some anaesthetists may choose to ventilate the patient via the endotracheal tube under deep volatile anaesthesia with no neuromuscular paralysis. Care should be taken with halothane, as it has the potential to cause bradycardia and depress the myocardium in high concentrations. After the trachea is intubated, the surgeon will place a gag to expose the tonsils. The endotracheal tube may become occluded, and it is important to ensure that the tube dose not become dislodged or disconnected from the circuit under the surgical drapes. Monitoring the end tidal carbon dioxide with capnography is useful.
At the conclusion of the operation, there are the considerations of reducing venous pressure (avoidance of coughing and straining), avoidance of laryngospasm and adequate airway protection. The patient needs to be breathing spontaneously and ideally, should be able to maintain his or her airway. Intravenous lignocaine has been used to suppress laryngospasm. Suction the oropharynx under direct vision. Avoid blind pharyngeal suctioning as it may cause bleeding. The patient is placed in the lateral position with the head down to direct blood and secretions away from the vocal cords. After emergence, the trachea is extubated.
Paracetamol and opioid is usually used for postoperative analgesia and tramadol may be useful. Care should be taken with the non-steroidal anti-inflammatory agents, as they will inhibit platelet function and may lead to an increase in bleeding. It is preferable to limit the use of morphine in the patients with obstructive sleep apnoea. Local anaesthetic infiltration of the tonsil bed has only a minimal effect on pain.
Postoperative bleeding is the most serious concern but persistent vomiting and poor oral intake are more common. Strategies to reduce nausea and vomiting and adequate hydration are important during this time. Intraoperative dexamethasone (0.5 mg/kg maximum of 8 mg) decreases vomiting, increases postoperative oral intake and reduces pain.
Patients should be observed in recovery and checked for no bleeding before discharge.
Post tonsillectomy haemorrhage A routine patient will lose approximately 4 ml/kg of blood during a tonsillectomy. In 5% of cases, there will be a post tonsillectomy haemorrhage. It may occur within 24 hours or a few days later (secondary haemorrhage, usually due to infection). Beware of continual swallowing in the recovery unit, as it may be a sign of bleeding.
The degree of blood loss is often underestimated as the blood is usually swallowed. The patient is usually hypovolemic and has a stomach full of blood. This is a surgical emergency. Careful assessment of the patient is required and intravenous fluid resuscitation must be carried out prior to induction of anaesthesia. Transfusion of packed red blood cells may be required. Induction of anaesthesia in a hypovolaemic bleeding child can cause severe hypotension and cardiac arrest. Check haematocrit and coagulation.
Induction of anaesthesia is with a rapid sequence induction using cricoid pressure. Two suckers are desirable, as the bleeding may be brisk and quickly obscure the airway. The endotracheal tube size may need to be one size smaller than anticipated. Intubation may be difficult. The surgeon should be present.
Abscess A peritonsillar abscess can present with trismus, dysphagia and a distorted airway with obstruction. There may be a need to perform drainage of the abscess with awake needle aspiration prior to induction of anaesthesia to minimize the risk of rupture during induction of anaesthesia or intubation. The other risks of anaesthesia include the potential for airway obstruction and difficult intubation.
A difficult intubation can be expected due to distortion of the airway, oedema and ongoing trismus after induction. Laryngoscopy may also rupture the abscess causing aspiration. There are three options for management if obstruction is expected. They include:
1. Awake intubation under vision.
2. Mask induction with the patient breathing spontaneously. Intubation is then performed slowly and gently to avoid airway contamination with pus.
3. Elective tracheostomy.
In cases of cellulitis of the submandibular and sublingual spaces, there may be involvement of the anterior compartments of the neck. Visualization of the glottis is not usually possible and general anaesthesia is contraindicated if there is stridor at rest. There may be no alternative but to perform a tracheostomy under local anaesthesia through the cellulitis.
DENTAL SURGERY
Most dental surgery is performed under local anaesthesia in the outpatient setting. Some patients having multiple extractions or extensive dental work may require general anaesthesia. Many of the patients requiring general anaesthesia are very young children or have behavioural problems.
The main anaesthetic considerations are the possible requirement for nasal intubation, a shared airway with the dentist, blood in the airway requiring a throat pack that must be removed at the end of the procedure and the management of an anxious or uncooperative patient.
Patients should be positioned supine with head up. They should not be in a ‘dental chair’ sitting position. Arrhythmias are common, due to hypoxia, hypercarbia and volatile anaesthetic agents. Halothane has a high rate of arrhythmias.
Nasal intubation is performed in the following way. The endotracheal tube is softened in warmed water. It may need to be smaller than an oral tube and will need to be flexible enough to direct towards the forehead so as to be away from the surgical field. The patient should sniff to see if one nostril is blocked. The larger patent nostril is chosen and is prepared with a vasoconstrictor and lubricant. After anaesthesia is induced, the endotracheal tube is introduced into the prepared nostril and advanced parallel to the palate (not in a superior direction) until it enters the pharynx. There will be a resistance in the nasal passage until the tube passes over the inferior turbinate. Laryngoscopy is performed and any blood is suctioned. The tip of the endotracheal tube is seen on the posterior pharyngeal wall. Advancement of the tube to the larynx may require the use of MacGill forceps. The tube is secured to the nose, taking care not to cause pressure on the nose.
MAXILLOFACIAL SURGERY
Maxillofacial surgery is required to repair facial trauma and to correct facial deformity.
Mid-face fractures are classified according to the Le Fort classification:
Class I involves the lower third of the nasal septum and maxilla passing above the nasal floor. The maxillary alveolar process, palate, part of the palatine bone and lower third of the pterygoid plates are mobile. In this situation, oral or nasal intubation can be performed and the airway is usually intact.
Class II fractures involve the upper nasal bone, under the zygomaticomaxillary suture and through the pterygoid plate. Nasal intubation is contraindicated.
Le Fort Class III fracture separates the base of the skull from the midface and nasal intubation is contraindicated.
In all facial fractures, a careful airway assessment needs to be carried out. There may be other injuries and airway compromise. Intubation may be difficult and may need to be secured via an alternative technique such as awake fiberoptic intubation or retrograde intubation. An armoured reinforced endotracheal tube may be necessary to prevent kinking.
Nasal intubation is only an option for a class I fracture and in patients who have no cerebrospinal fluid (CSF)) leak. Nasal intubation can be complicated by bleeding, damage to nasal turbinates and increased risk of sinusitis and otitis. It should not be performed blindly if there is disruption to the nasopharynx. The tube can enter a sinus, the orbit, hypopharynx and intracranially. Where there is doubt about the presence of a base of skull fracture or in severe facial trauma, a tracheostomy needs to be considered.
In the patient for maxillofacial reconstruction or orthognathic surgery, there is the potential for severe blood loss and contamination of the airway with blood. The surgeons will request a nasal intubation to allow better surgical access and a throat pack will be placed. Hypotensive anaesthesia may reduce the amount of blood loss. This technique is only safe in the young and fit patient. Blood entering the stomach will cause postoperative nausea and may be aspirated into the lungs. The patient is extubated when he is fully awake and airway reflexes have returned
HEAD AND NECK SURGERY
Head and neck surgery includes parotid surgery, thyroid and parathyroid surgery and the management of head and neck cancers. Airway management is a major consideration, as well as the potential for endocrine problems and injury to adjacent structures (nerves, blood vessels). Many of these procedures may be prolonged.
Unilateral vocal cord paralysis will cause hoarseness. Bilateral vocal cord paralysis will cause increasing upper airway obstruction and stridor.
Parotidectomy Parotid salivary gland may be inflamed or may require resection for masses. The duration of surgery is often prolonged and the anaesthetist’s access to the head is restricted. For these reasons, endotracheal intubation is preferred. The patient is positioned with the operative side up and the back slightly elevated. The major surgical complication is facial nerve injury. If nerve stimulation is to be used to identify the facial nerve, neuromuscular paralysis should be absent.
Thyroidectomy Thyroid surgery is performed for goitre that causes compression, tumour or for hyperthyroidism that cannot be controlled with medication. Preoperative examination should include a careful assessment of obstructive symptoms (a large goitre may cause tracheal compression, decreased venous return or tracheal deviation and tracheomalacia) and the airway as well as an assessment of thyroid function. The patient must be treated so that they are euthyroid before surgery. The potential complications of thyroid surgery include life threatening thyroid storm (severe thyrotoxicosis), injury to the recurrent laryngeal nerve causing postoperative airway obstruction due to vocal cord paralysis, tracheomalacia and the need for reintubation, difficult intubation (more likely with a cancer than a benign goitre), and postoperative bleeding. Postoperative bleeding can lead to severe airway compromise due to tracheal compression and airway oedema due to venous engorgement. Intubation may be very difficult. The neck haematoma should be evacuated urgently to improve airway obstruction. Unintentional parathyroidectomy may result in hypocalcaemia that may become apparent only several hours after the operation. The treatment involves the administration of intravenous calcium chloride.
Pain after thyroidectomy is moderate but not usually severe. Postoperative nausea and vomiting is a significant issue, as it is important to try and avoid straining and a rise in venous pressure postoperatively as this may cause bleeding.
Parathyroidectomy The parathyroid glands regulate calcium metabolism by producing parathyroid hormone (PTH). PTH elevates serum calcium via its actions on the gastrointestinal tract, bone and kidneys. It also leads to a reduced serum phosphate by increasing its excretion. Adenomas of the parathyroid gland will produce PTH and cause an increase in serum calcium, low phosphate, hyperchloremic acidosis, polyuria and polydipsia.
Parathyroidectomy surgery can be prolonged due to difficulty identifying the glands. The main anaesthetic concerns are ensuring adequate hydration, monitoring for cardiac arrhythmias, correcting acidosis (avoid hypoventilation), and ensuring adequate reversal of paralysis (the patient may be weak due to hypercalcemia). As with thyroid surgery, there may be recurrent laryngeal nerve injury or postoperative bleeding that may lead to airway obstruction.
SELF-ASSESSMENT QUESTIONS
1. What factors increase the risk of laryngeal spasm after nose and throat surgery? Describe the management of laryngeal spasm after extubation.
2. Describe the technique of nasal intubation. What are the indications and contraindications to nasal intubation?
3. What is the oculocardiac reflex? Discuss the afferent and efferent nerves involved. How is it treated?
- What are the problems of a shared airway?
- When is a throat pack useful? What are the potential problems with the use of a throat pack and how can they be avoided?
A twelve-year-old child has been brought in to your hospital from the countryside one week after first complaining of a sore throat. He is febrile 39 C and flushed. His mother says he has not been able to swallow well and has not eaten for two days. He has very bad breath and cannot open his mouth to allow you to examine his throat well. You suspect he has a peritonsillar abscess. Outline your initial assessment and discuss the management of this problem. In particular outline the options for airway management and discuss the advantages and disadvantages of each option.
EYE, ENT, DENTAL, MAXILLOFACIAL AND HEAD AND NECK SURGERY CASE STUDIES
Case 13.1
Aruina was brought in to your hospital with an open eye injury following a fall from a horse. She has just eaten lunch and she is feeling nauseated. The surgeon wants to fix her eye as soon as possible.
What factors will influence your choice of anaesthetic?
Describe the anaesthetic technique you will use.
What can you do to reduce intraocular pressure during induction, during the operation and on emergence?
Case 13.2
Ganbat is a four-year-old boy who has presented for an adenotonsillectomy. He has had recurrent tonsillitis and his mother says he has a runny nose at the present time. He is not cooperative and does not allow you to examine him.
What are the indications for tonsillectomy?
What features on the history will influence your choice of anaesthetic?
Describe your anaesthetic technique in detail and discuss the reasons behind your choice of anaesthetic.
How will you manage emergence from anaesthesia and his extubation?
You are called to the ward by the surgeon three hours later because Ganbat has just vomited a large amount of blood. How will you assess the degree of blood loss?
The surgeon says that he needs to take Ganbat back to theatre. Outline your management and describe your anaesthetic technique.
Case 13.3
Tsahim is a 55-year-old herder and needs a thyroidectomy for a large goitre. You meet him on the ward the night before surgery where he has been admitted. He is a smoker but otherwise well.
Outline your preoperative assessment.
What further preoperative testing would you like to perform?
Describe your major concerns for management of the anaesthetic.
How will you manage his extubation?
He has been in recovery for half an hour and the nurse calls you in urgently because she is concerned about his airway. She says he has stridor and is starting to desaturate. What could be causing the stridor?
The surgeon says he needs to take him back to theatre for an immediate evacuation of a haematoma. Describe your management of this situation.
Twelve hours later, the nurse says that Tsahim is tachycardic and febrile. What could be causing the problem? How should he be managed?
Case 13.4
Tsungaa is twenty and had been hit in the face with a railway sleeper. There has been no loss of consciousness but she has black eyes and there is clear fluid and blood from the nose. She has an obvious maxillary depression. The surgeon would like to take her to theatre to fix her facial fractures.
How will you assess Tsungaa’s airway?
Tsungaa is unable to open her mouth. What are the options for airway management? Outline the advantages and disadvantages of each.