COMPLICATIONS OF ANAESTHESIA
Final Objective: To demonstrate an understanding of the frequency, causes and management of complications that may occur in relation to anaesthesia.
Enabling Objective: To achieve this goal, you should know how to:
Reference Reading:
§ Developing Anaesthesia Chapters 36, 40 and 42-62.
§ Jenkins K, Baker, AB. Consent and anaesthetic risk. Anaesthesia, 2003, 58; 962-84.
Minor complications of anaesthesia are common. Serious, life-threatening complications are rare, but an anaesthetist must have a deep knowledge of such complications in order to best manage them when they occur.
The anaesthetist should prepare and perform anaesthesia so as to minimise the risk of harm to a patient, but accept that even in the best circumstances complications will occur. Thought should always be given to how a particular anaesthetic technique may fail and how the anaesthetist will then insure a patient’s safety and comfort.
CLASSIFICATION.
Complications can be classified by:
COMMON COMPLICATIONS.
While common complications tend to be minor, it is important to have a good understanding of their cause, presentation and management, as they will be experienced by a significant proportion of patients.
Post-Operative Nausea And Vomiting
Post-operative nausea and vomiting (PONV) is the most common complication of anaesthesia, occurring in 20-30% of patients. It is often described by patients as being one of the most distressing complications of anaesthesia. Risk factors for PONV include:
Investigation of intra-operative PONV prophylaxis in 2004, showed that a 5HT-3 antagonist (ondansetron 4 mg), dexamethasone (4 mg), droperidol (1.25 mg) or a total intravenous anaesthesia technique (TIVA – avoiding both nitrous oxide and volatile agents, maintaining anaesthesia with propofol infusion) each decreased PONV by just under one third. The interventions were independent and additive in their effect. Avoiding nitrous oxide only reduced PONV by 12%.
Post-Operative Sore Throat
Sore throat is a common, though relatively minor, complication following anaesthesia occurring in approximately 12% of patients. Sore throat is more common following intubation (45%) than laryngeal mask airway use (18%) or facemask (3%). Use of local anaesthetic gels on airway devices does not reduce the incidence of sore throat.
Post-Operative Headache
Headaches occur in approximately 17% of patients after an anaesthetic. They are more common in patients who normally experience frequent headaches; prolonged fasting times; and patients with a daily caffeine consumption > 400 mg (~ 4 cups of coffee).
Post-Operative Drowsiness And Dizziness
Drowsiness after discharge occurs in approximately 40% of patients and dizziness in 18%. Intravenous fluid 1 L intra-operatively has been reported to reduce post-operative drowsiness and dizziness.
Dental Damage
Oral trauma and dental damage are common complications of general anaesthesia (approximately 7% of all anaesthesia cases) and a common precipitant of medicolegal claims. A 10 year study showed dental injury requiring intervention occurred in 1 in 4500 anaesthetics. Half of these occurred during laryngoscopy and intubation.
UNCOMMON COMPLICATIONS.
Post-Operative Cognitive Dysfunction
Post-operative cognitive dysfunction (POCD) most commonly occurs in elderly patients and is usually of mild severity, effecting memory and concentration. In a multicenter study of patients over 60 years old, POCD was present in 25% after 1 week and 10% at three months. Up to 14% of general surgical patients develop post-operative delirium. There was no difference in long-term cognitive function between general and regional anaesthesia. POCD may persist in 1% of patients.
Note that POCD is as much a complication of surgery or acute illness as it is due to anaesthesia. It is very difficult to separate the relative contribution to POCD of each.
Peri-Operative Cerebrovascular Accident
Peri-operative cerebrovascular accident (CVA) occurs in between 0.1 and 3% of general surgical patients. On average these occur on the 7th post-operative day (range: day 1-10). Risk factors include:
Peri-Operative Myocardial Infarct
Peri-operative myocardial infarct (MI) has a high morbidity and a great risk of mortality. Risk factors include:
Patients having recently suffered an acute myocardial infarct are at particularly high risk of re-infarction peri-operatively. Delaying surgery should be considered if possible so as to reduce this risk. Patients undergoing surgery within 3 months of MI may suffer peri-operative infarct in over 30% of cases; between 3 and 6 months in 15%; after 6 months in 5%. Aggressive peri-operative monitoring (eg. arterial line monitoring, 5-lead ECG) and management has been shown to lower morbidity and mortality.
Management of peri-operative MI follows the same principals as those for managing MI in other settings. Provide high concentration oxygen (FiO2 100%), control heart rate (beta-blockers) and reduce cardiac afterload (GTN, calcium antagonists) so as to reduce the cardiac work and anti-coagulate (aspirin, heparin, low-molecular weight heparins). Consider thrombolysis or coronary artery stenting if available in your hospital.
Peri-Operative Visual Dysfunction
Up to 4% of patients reported blurred vision lasting at least 3 days, and of these up to 25% will have permanent blurred vision requiring treatment. The majority of these are due to corneal abrasions, and are best avoided with careful taping of the eye closed during general anaesthesia. Visual loss or blindness after non-cardiac surgery is very rare (1:250,000) although more common in cardiac surgery (0.1-2%).
Pulmonary Aspiration
Pulmonary aspiration is a serious complication that is more likely in inadequately fasted patients, those suffering gastro-oesophageal reflux disease, pregnant patients and in emergency surgery. One study reports an incidence as high as ~1:2000 with a mortality of 1:45,000. 17% of patients required ventilation because of the aspiration. The development of pneumonitis due to aspiration of acidic gastric fluid has a high mortality.
Other than CPAP or PEEP, no specific therapy has been shown to be beneficial in treatment of aspiration pneumonitis. Management should be supportive, with ventilation and ICU admission if required. Steroids have not been shown to improve outcomes and antibiotics are only indicated in demonstrated pneumonia.
Children are at higher risk of regurgitation and aspiration, though it is rarely associated with pneumonitis.
Awareness
The incidence of conscious awareness with recall and severe pain is occurs in less than 1 in 3000 general anaesthetics. Conscious awareness without pain is more common, occurring in between 1 in 150 to 1000. Risk factors for awareness include:
Peripheral Neuropathy
Peripheral nerve injury following general anaesthesia is estimated to occur in 1 in 1000 cases, although recent studies suggest the incidence may be higher. Most commonly this involves the ulnar nerve, followed by the brachial plexus and lumbosacral nerves. Careful position of the limbs, avoidance of extremes of extension or flexion and careful documentation of pre-existing neuropathy (especially in diabetics) is essential to avoid development of neuropathy.
RARE COMPLICATIONS.
Rare complications of anaesthesia are frequently life-threatening.
Anaphylaxis
Anaphylaxis is a serious and life-threatening complication that occurs in up to 1 in 10,000 anaesthetics. The most common causes are neuromuscular blocking drugs (70%), latex (12%) and antibiotics (8%). Clinically it is associated with:
Cardiac Arrest
Risk of cardiac arrest due to anaesthesia has fallen dramatically in the past 25 years. Common causes include drug-related events, hypovolaemia, myocardial infarct, arrhythmia or other cardiovascular dysfunction, and inadequate airway management. Cardiac arrest due to general anaesthesia is estimated to occur in 1 in 15,000 cases.
Malignant Hyperthermia
Malignant hyperthermia (MH) is a rare, life-threatening condition due to an autosomal dominant disorder of muscle metabolism. Exposure to certain drugs, such as volatile anaesthetic agents or suxamethonium, leads to a hypermetabolic state associated with increased oxygen consumption, carbon dioxide production and acidosis. Clinically this presents as:
Death
Anaesthetic-related mortality is very rare, although is often difficult to distinguish from other causes of peri-operative mortality. 30 day peri-operative mortality in the UK is ~3% although less than 10% is thought to relate to anaesthesia. Studies have shown that inadequate peri-operative assessment, preparation, resuscitation, monitoring, supervision, post-operative care and inappropriate anaesthetic technique are major contributors to anaesthetic mortality.
SELF-ASSESSMENT QUESTIONS
ASSIGNMENT
During your pre-anaesthetic assessment, how do you decide which potential complications to describe to a patient prior to providing general anaesthesia? How will you communicate the potential degree of risk of these complications to your patient?
COMPLICATIONS of ANAESTHESIA CASE STUDIES
Case No 10.1
Tsahim is a 30 year old male with no significant past medical or surgical history who has acute appendicitis. Five minutes after induction of anaesthesia (thiopentone, suxamethonium, atracurium, fentanyl, oxygen, nitrous oxide and halothane) the patient develops hypotension of 90/60 mmHg.
List common and uncommon causes of hypotension during anaesthesia. What do you suspect may be the cause of the hypotension in this case? What is your initial management?
If the patient does not respond to your initial treatment what do you suspect the cause of the hypotension might be and what is your further management?
When (clinical parameters) would you declare that this patient had a life threatening emergency? What would be your management plan?
Case No 10.2
You are preparing to anaesthetise a patient who has bilateral fracture femurs, a fractured pelvis and a ruptured spleen after crashing his car without wearing a seat belt. His Hb is 60 and you plan to give him a blood transfusion and restore his circulating blood volume before surgery.
What anaesthetic techniques may be used to minimise the need for a blood transfusion?
What are the potential complications of blood transfusion?
After 50mls of blood, the patient develops chest pain, flank pain, headache and a fever. How do you manage a transfusion reaction and how can the risk of a transfusion reaction be minimised?
Case No 10.3
During a relaxant general anaesthetic using halothane, atracurium and morphine your patient develops an arrhythmia.
What are the three basic questions that you must immediately answer?
The ECG shows atrial fibrillation with an atrial rate of 350 beats/minute. How do you manage intraoperative atrial fibrillation?
Despite controlling the atrial fibrillation the patient develops ST elevation with Q waves. What is your management?
What are the potential causes of asystole or pulseless electrical activity?
Case No 10.4
Ganbold requires intubation for surgery for a ruptured appendix. The laryngoscopy and intubation is difficult but you are able to pass the endotracheal tube and can hear breath sounds on both sides of the lungs and the chest appears to be rising. Unfortunately you do not have a carbon dioxide monitor available to confirm endotracheal intubation.
List the potential causes of hypoxia.
Is cyanosis an appropriate indicator of hypoxia?
After 5 minutes the oxygen saturation has fallen from 98% to 89%. Describe your management.
Case No 10.5
Laryngospasm is the reflex closure of the vocal cords. It is caused by irritation of the airway (e.g. secretions, blood, vomit and laryngoscopy) or in response to other stimulation (e.g. peripheral pain) during light anaesthesia.
Mild laryngospasm is incomplete closure of the vocal cords and the patient will have stridor. Severe laryngospasm is the complete closure of the vocal cords and there may be no airway noise because the patient’s airway is completely obstructed.
How can the risk of laryngospasm be reduced?
How is laryngospasm managed?
Final Objective: To demonstrate an understanding of the frequency, causes and management of complications that may occur in relation to anaesthesia.
Enabling Objective: To achieve this goal, you should know how to:
- Identify common minor anaesthetic complications and rare life-threatening complications.
- Understand the degree of risk of different anaesthetic complications.
- Manage anaesthetic complications.
- Discuss with patients and their families the risks and occurrence of complications associated with anaesthesia.
Reference Reading:
§ Developing Anaesthesia Chapters 36, 40 and 42-62.
§ Jenkins K, Baker, AB. Consent and anaesthetic risk. Anaesthesia, 2003, 58; 962-84.
Minor complications of anaesthesia are common. Serious, life-threatening complications are rare, but an anaesthetist must have a deep knowledge of such complications in order to best manage them when they occur.
The anaesthetist should prepare and perform anaesthesia so as to minimise the risk of harm to a patient, but accept that even in the best circumstances complications will occur. Thought should always be given to how a particular anaesthetic technique may fail and how the anaesthetist will then insure a patient’s safety and comfort.
CLASSIFICATION.
Complications can be classified by:
- System: cardiovascular, respiratory, neurological, immunological, gastrointestinal.
- Cause & technique: airway, drugs, equipment, regional anaesthesia, general anaesthesia.
- Time of occurrence: induction, maintenance, emergence, post-operative.
- Severity: minor, mild, severe.
- Frequency: common, uncommon, rare.
COMMON COMPLICATIONS.
While common complications tend to be minor, it is important to have a good understanding of their cause, presentation and management, as they will be experienced by a significant proportion of patients.
Post-Operative Nausea And Vomiting
Post-operative nausea and vomiting (PONV) is the most common complication of anaesthesia, occurring in 20-30% of patients. It is often described by patients as being one of the most distressing complications of anaesthesia. Risk factors for PONV include:
- Children – bimodal distribution peaking in 4-5 year olds and adolescents.
- Women – three times the risk than for men.
- Non-smokers
- Past history of motion sickness
- Post-operative opioid requirement
- Overweight patients
- Surgical procedures: laparoscopy; strabismus surgery; ear, nose & throat surgery; dental; tonsillectomy; plastics and orthopaedic surgery.
Investigation of intra-operative PONV prophylaxis in 2004, showed that a 5HT-3 antagonist (ondansetron 4 mg), dexamethasone (4 mg), droperidol (1.25 mg) or a total intravenous anaesthesia technique (TIVA – avoiding both nitrous oxide and volatile agents, maintaining anaesthesia with propofol infusion) each decreased PONV by just under one third. The interventions were independent and additive in their effect. Avoiding nitrous oxide only reduced PONV by 12%.
Post-Operative Sore Throat
Sore throat is a common, though relatively minor, complication following anaesthesia occurring in approximately 12% of patients. Sore throat is more common following intubation (45%) than laryngeal mask airway use (18%) or facemask (3%). Use of local anaesthetic gels on airway devices does not reduce the incidence of sore throat.
Post-Operative Headache
Headaches occur in approximately 17% of patients after an anaesthetic. They are more common in patients who normally experience frequent headaches; prolonged fasting times; and patients with a daily caffeine consumption > 400 mg (~ 4 cups of coffee).
Post-Operative Drowsiness And Dizziness
Drowsiness after discharge occurs in approximately 40% of patients and dizziness in 18%. Intravenous fluid 1 L intra-operatively has been reported to reduce post-operative drowsiness and dizziness.
Dental Damage
Oral trauma and dental damage are common complications of general anaesthesia (approximately 7% of all anaesthesia cases) and a common precipitant of medicolegal claims. A 10 year study showed dental injury requiring intervention occurred in 1 in 4500 anaesthetics. Half of these occurred during laryngoscopy and intubation.
UNCOMMON COMPLICATIONS.
Post-Operative Cognitive Dysfunction
Post-operative cognitive dysfunction (POCD) most commonly occurs in elderly patients and is usually of mild severity, effecting memory and concentration. In a multicenter study of patients over 60 years old, POCD was present in 25% after 1 week and 10% at three months. Up to 14% of general surgical patients develop post-operative delirium. There was no difference in long-term cognitive function between general and regional anaesthesia. POCD may persist in 1% of patients.
Note that POCD is as much a complication of surgery or acute illness as it is due to anaesthesia. It is very difficult to separate the relative contribution to POCD of each.
Peri-Operative Cerebrovascular Accident
Peri-operative cerebrovascular accident (CVA) occurs in between 0.1 and 3% of general surgical patients. On average these occur on the 7th post-operative day (range: day 1-10). Risk factors include:
- Advanced age
- Previous CVA – 10x increased risk: 2%; mortality 60%.
- Hypertension – 4x increased risk.
- Peripheral vascular disease
- Chronic Obstructive Airway Disease
- Atrial fibrillation
- Carotid artery stenosis
- Obstructive sleep apnoea
Peri-Operative Myocardial Infarct
Peri-operative myocardial infarct (MI) has a high morbidity and a great risk of mortality. Risk factors include:
- Ischaemic heart disease, particularly if recent MI
- Congestive cardiac failure
- Cerebrovascular disease
- Diabetes mellitus, particularly insulin requiring
- Chronic renal failure
- High-risk surgery
Patients having recently suffered an acute myocardial infarct are at particularly high risk of re-infarction peri-operatively. Delaying surgery should be considered if possible so as to reduce this risk. Patients undergoing surgery within 3 months of MI may suffer peri-operative infarct in over 30% of cases; between 3 and 6 months in 15%; after 6 months in 5%. Aggressive peri-operative monitoring (eg. arterial line monitoring, 5-lead ECG) and management has been shown to lower morbidity and mortality.
Management of peri-operative MI follows the same principals as those for managing MI in other settings. Provide high concentration oxygen (FiO2 100%), control heart rate (beta-blockers) and reduce cardiac afterload (GTN, calcium antagonists) so as to reduce the cardiac work and anti-coagulate (aspirin, heparin, low-molecular weight heparins). Consider thrombolysis or coronary artery stenting if available in your hospital.
Peri-Operative Visual Dysfunction
Up to 4% of patients reported blurred vision lasting at least 3 days, and of these up to 25% will have permanent blurred vision requiring treatment. The majority of these are due to corneal abrasions, and are best avoided with careful taping of the eye closed during general anaesthesia. Visual loss or blindness after non-cardiac surgery is very rare (1:250,000) although more common in cardiac surgery (0.1-2%).
Pulmonary Aspiration
Pulmonary aspiration is a serious complication that is more likely in inadequately fasted patients, those suffering gastro-oesophageal reflux disease, pregnant patients and in emergency surgery. One study reports an incidence as high as ~1:2000 with a mortality of 1:45,000. 17% of patients required ventilation because of the aspiration. The development of pneumonitis due to aspiration of acidic gastric fluid has a high mortality.
Other than CPAP or PEEP, no specific therapy has been shown to be beneficial in treatment of aspiration pneumonitis. Management should be supportive, with ventilation and ICU admission if required. Steroids have not been shown to improve outcomes and antibiotics are only indicated in demonstrated pneumonia.
Children are at higher risk of regurgitation and aspiration, though it is rarely associated with pneumonitis.
Awareness
The incidence of conscious awareness with recall and severe pain is occurs in less than 1 in 3000 general anaesthetics. Conscious awareness without pain is more common, occurring in between 1 in 150 to 1000. Risk factors for awareness include:
- Nitrous oxide-only anaesthesia, without volatile agent – 1 in 14.
- Opioid-only anaesthesia.
- Total intravenous anaesthesia – 1 in 500.
- Trauma, cardiac and obstetric anaesthesia.
Peripheral Neuropathy
Peripheral nerve injury following general anaesthesia is estimated to occur in 1 in 1000 cases, although recent studies suggest the incidence may be higher. Most commonly this involves the ulnar nerve, followed by the brachial plexus and lumbosacral nerves. Careful position of the limbs, avoidance of extremes of extension or flexion and careful documentation of pre-existing neuropathy (especially in diabetics) is essential to avoid development of neuropathy.
RARE COMPLICATIONS.
Rare complications of anaesthesia are frequently life-threatening.
Anaphylaxis
Anaphylaxis is a serious and life-threatening complication that occurs in up to 1 in 10,000 anaesthetics. The most common causes are neuromuscular blocking drugs (70%), latex (12%) and antibiotics (8%). Clinically it is associated with:
- Cardiovascular collapse (55%) and cardiac arrest (4%)
- Rash (70%)
- Bronchospasm (45%)
- Angioedema (10%)
Cardiac Arrest
Risk of cardiac arrest due to anaesthesia has fallen dramatically in the past 25 years. Common causes include drug-related events, hypovolaemia, myocardial infarct, arrhythmia or other cardiovascular dysfunction, and inadequate airway management. Cardiac arrest due to general anaesthesia is estimated to occur in 1 in 15,000 cases.
Malignant Hyperthermia
Malignant hyperthermia (MH) is a rare, life-threatening condition due to an autosomal dominant disorder of muscle metabolism. Exposure to certain drugs, such as volatile anaesthetic agents or suxamethonium, leads to a hypermetabolic state associated with increased oxygen consumption, carbon dioxide production and acidosis. Clinically this presents as:
- Hyperthermia – rapidly increasing temperature, usually >38.8oC
- Hypercapnoea – ETCO2 > 55 mmHg
- Tachycardia – sinus, VT or VF
- Generalised muscle rigidity, often with severe masseter muscle rigidity
Death
Anaesthetic-related mortality is very rare, although is often difficult to distinguish from other causes of peri-operative mortality. 30 day peri-operative mortality in the UK is ~3% although less than 10% is thought to relate to anaesthesia. Studies have shown that inadequate peri-operative assessment, preparation, resuscitation, monitoring, supervision, post-operative care and inappropriate anaesthetic technique are major contributors to anaesthetic mortality.
SELF-ASSESSMENT QUESTIONS
- List common and life threatening complications associated with anaesthesia.
- What are the principles of managing life threatening complications?
- Discuss the risk factors and management of PONV.
- Discuss the risk factors and management of anaphylaxis.
ASSIGNMENT
During your pre-anaesthetic assessment, how do you decide which potential complications to describe to a patient prior to providing general anaesthesia? How will you communicate the potential degree of risk of these complications to your patient?
COMPLICATIONS of ANAESTHESIA CASE STUDIES
Case No 10.1
Tsahim is a 30 year old male with no significant past medical or surgical history who has acute appendicitis. Five minutes after induction of anaesthesia (thiopentone, suxamethonium, atracurium, fentanyl, oxygen, nitrous oxide and halothane) the patient develops hypotension of 90/60 mmHg.
List common and uncommon causes of hypotension during anaesthesia. What do you suspect may be the cause of the hypotension in this case? What is your initial management?
If the patient does not respond to your initial treatment what do you suspect the cause of the hypotension might be and what is your further management?
When (clinical parameters) would you declare that this patient had a life threatening emergency? What would be your management plan?
Case No 10.2
You are preparing to anaesthetise a patient who has bilateral fracture femurs, a fractured pelvis and a ruptured spleen after crashing his car without wearing a seat belt. His Hb is 60 and you plan to give him a blood transfusion and restore his circulating blood volume before surgery.
What anaesthetic techniques may be used to minimise the need for a blood transfusion?
What are the potential complications of blood transfusion?
After 50mls of blood, the patient develops chest pain, flank pain, headache and a fever. How do you manage a transfusion reaction and how can the risk of a transfusion reaction be minimised?
Case No 10.3
During a relaxant general anaesthetic using halothane, atracurium and morphine your patient develops an arrhythmia.
What are the three basic questions that you must immediately answer?
The ECG shows atrial fibrillation with an atrial rate of 350 beats/minute. How do you manage intraoperative atrial fibrillation?
Despite controlling the atrial fibrillation the patient develops ST elevation with Q waves. What is your management?
What are the potential causes of asystole or pulseless electrical activity?
Case No 10.4
Ganbold requires intubation for surgery for a ruptured appendix. The laryngoscopy and intubation is difficult but you are able to pass the endotracheal tube and can hear breath sounds on both sides of the lungs and the chest appears to be rising. Unfortunately you do not have a carbon dioxide monitor available to confirm endotracheal intubation.
List the potential causes of hypoxia.
Is cyanosis an appropriate indicator of hypoxia?
After 5 minutes the oxygen saturation has fallen from 98% to 89%. Describe your management.
Case No 10.5
Laryngospasm is the reflex closure of the vocal cords. It is caused by irritation of the airway (e.g. secretions, blood, vomit and laryngoscopy) or in response to other stimulation (e.g. peripheral pain) during light anaesthesia.
Mild laryngospasm is incomplete closure of the vocal cords and the patient will have stridor. Severe laryngospasm is the complete closure of the vocal cords and there may be no airway noise because the patient’s airway is completely obstructed.
How can the risk of laryngospasm be reduced?
How is laryngospasm managed?
