Important complications of general anaesthesia

The practice of anaesthesia is fundamental to the practice of medicine. However, anaesthesia is not without its problems. General anaesthesia is thought to be a direct cause of mortality in 1 out of 10,000 operations.^[1] Data from perioperative deaths are difficult to analyse as they probably represent a combination of anaesthetic and surgical factors. Nonetheless, in 1987 a confidential enquiry into perioperative deaths revealed that very few deaths were actually as a direct result of general anaesthesia - 0.0007%.^[1] 

Figures of anaesthetic-related morbidity are more difficult to determine. Estimates suggest that up to 2% of intensive care unit admissions at any one time are related to anaesthetic problems.^[1] Although general anaesthesia is not without risk, it should be remembered that it allows necessary procedures to be performed in a humane way - without which the patient might otherwise die. Along these lines, if a patient is high-risk for a general anaesthetic, eg pre-existing comorbidities, then they should still be referred for surgery like any other patient. The decision to operate and which form of anaesthesia used should then be a decision made by the surgeon and anaesthetist.

Some specific complications of general anaesthesia

Anaphylaxis

• Anaphylaxis can occur to any anaesthetic agent and in all types of anaesthesia.^[1] The severity of the reaction may vary but features may include rash, urticaria, bronchospasm, hypotension, angioedema, and vomiting. It needs to be carefully looked for in thepreoperative assessment and previous general anaesthetic charts may help.
• Patients who are suspected of an allergic reaction should be referred for further investigation to try to determine the exact cause.^[2] If necessary, this may involve provocation testing or skin prick testing and patients should be referred to local immunologists. Anaphylaxis needs to be promptly recognised and managed and patients should be given MedicAlert® bracelets once they recover.

Aspiration pneumonitis

• A reduced level of consciousness can lead to an unprotected airway. If the patient vomits they can aspirate the vomitus contents into their lungs. This can set up lung inflammation with infection. The risk of aspiration pneumonitis and aspiration pneumonia is reduced by fasting for several hours prior to the procedure and cricoid cartilage pressure during induction of anaesthesia.^[1] However, the evidence for the use of cricoid pressure is not clearly documented and further investigation is required.^[3]
• Other methods of reducing aspiration pneumonitis associated with anaesthesia are the use of metoclopramide to enhance gastric emptying and ranitidine or proton pump inhibitors to increase the pH of gastric contents. The evidence for the benefit of these methods appears promising.^[4]
• Aspiration pneumonitis may also occur in spinal anaesthesia if the level of spinal block is too high, leading to paralysis or impairment of the vocal cords and respiratory impairment.

Peripheral nerve damage

• This can occur with all the types of anaesthesia and results from nerve compression. The most common cause is exaggerated positioning for prolonged periods of time. Both the anaesthetist and the surgeons should be aware of this potential complication and patients should be moved on a regular basis if possible. The severity varies and recovery may be prolonged. The most common nerves affected are the ulnar nerve and the common peroneal nerve. More rarely, the brachial plexus may be affected.^[1]
• Injury to nerves can be avoided by prevention of extreme postures for lengthy periods during surgery. If nerve damage occurs then patients should be followed up and further investigations such as electromyography may be required.^[5]

Damage to teeth

It is now common practice to check the teeth in the anaesthetist's preoperative assessment. Damage to teeth is actually the most common cause of claims made against anaesthetists. The tooth most commonly affected is the upper left incisor.^[6]

Embolism

Embolism is rare during an anaesthetic but is potentially fatal. Air embolism occurs more commonly during neurosurgical procedures or pelvic operations. Prophylaxis ofthromboembolism is common and begins preoperatively with thromboembolic deterrents (TEDS) and low molecular weight heparin (LMWH).^[7]

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