What are the risks of anaesthesia?

While Australia and New Zealand are among the safest nations in the world in which to have anaesthesia, receiving multiple medications and altering normal human body function carries risks, some of which may be potentially life threatening. Risks and side effects include nausea and vomiting, physical injuries, reactions to drugs, awareness and even death. If you are concerned about these side effects please discuss them with your anaesthetist.

Physical injuries

Damage to teeth occurs in fewer than 1 in 100 general anaesthetic cases (Jenkins K, Baker AB. Consent and anaesthesia risk. Anaesthesia 2003: 58: 962-84). This usually occurs during a process known as laryngoscopy (inserting an instrument into the mouth), when a breathing tube is inserted through the vocal cords in your airway while you are asleep or if a plastic sucker has to be used to clear fluid in your mouth. The anaesthetist will take care during the anaesthesia and will examine your mouth prior to the operation and document the status of your teeth, including presence of caps, crowns, loose teeth or dentures. 

Sore throat

Sore throat may occur in up to 45 per cent of patients having anaesthesia requiring a breathing tube known as an endotracheal tube, and in 20 per cent of patients when a laryngeal mask, which is a mask and tube that is inserted into the back of the throat, is used. The sore throat usually gets better by itself and may take a few days. Persistent sore throat may need to be referred back to the anaesthetist or reviewed by your doctor.

Nerve injuries

Nerve injury (damage to nerve fibres) following nerve blocks (regional anaesthesia) occurs in approximately 0.02 per cent or 1 in 500 cases (Jenkins K, Baker AB. Consent and anaesthesia risk. Anaesthesia 2003: 58: 962-84). Risks associated with epidurals are discussed under regional anaesthesia

Blindness

All complications are unfortunate and this complication is extremely rare, occurring in approximately one in 1,250,000 anaesthetics (Taylor TH. Avoiding iatrogenic injuries in theatre. BMJ 1992: 305: 595-6). Patients who are at a higher risk of blindness include smokers and those with high blood pressure or diabetes. Patients undergoing spinal and cardiac surgery involving cardiopulmonary bypass are at a higher risk than patients undergoing other types of surgery. If you have any of these conditions, discuss any concerns with your anaesthetist before your procedure. If you develop visual disturbance after your operation you should seek urgent medical attention.

Death

Death related to anaesthesia is extremely rare. Type of surgery (in particular if the surgery is an emergency such as for major trauma), underlying medical condition, physical status, and age all impact on the rate of death.

According to the American Society of Anaesthetists (ASA) classification system, which is based upon the overall health of the patient, for a healthy patient (known as ASA 1) undergoing surgery the incidence of death is about one in 100,000. If combined, the incidence of death of patients with all different physical conditions, including those that are not expected to survive with or without the operation (ASA 4), is one in 50,000 (Contractor S, Hardman JG, Injury during anaesthesia, CEACCP, Volume 6, Number 2 2006).

Could I react to an anaesthetic drug? 

It is possible to have an allergic reaction to medications given as part of anaesthesia. 
The reaction varies from a mild allergic reaction, such as a rash, to a life-threatening reaction called anaphylaxis, which is a severe life-threatening allergic reaction. The incidence of anaphylaxis reactions to anaesthetic agents in Australia is 1 in 10,000 to 1 in 20,000.

Neuromuscular (nerve and muscle blocking medications are responsible for 70 per cent of the life-threatening allergic reactions during anaesthesia. In 80 per cent of reactions to these medications, there had been no previous history of use.

Antibiotic medications and latex (rubber) are the other common causes of allergic reaction. Penicillin is the most common antibiotic to cause an allergic reaction. It is important that you tell your anaesthetist if you have experienced an allergic reaction to any medications in the past.

 Will I experience nausea or vomiting?

In the past, nausea or vomiting were relatively common after general anaesthesia however with new and improved anaesthesia medication and delivery systems, and appropriate use of anti-nausea medication, there has been a reduction in the number of patients experiencing these symptoms.

Postoperative nausea and vomiting (PONV) occurs in 20 to 30 per cent of the general surgical population and in up to 70 to 80 per cent of high-risk surgical patients. 
Risk factors for PONV can be divided into three categories:

• Patient-specific risk factors
• Female gender, non-smoking status, history of PONV/motion sickness.
• Anaesthesia risk factors
• Use of vapour anaesthesia.
• Use of nitrous oxide (gas).
• Use of intraoperative and postoperative opioid medications such as morphine.
• Surgical risk factors
• Duration of surgery (each 30 minute increase in duration increases PONV risk by 60 per cent).
• Type of surgery, for example laparoscopy (key hole), gynaecological (reproductive), ophthalmologic (eye surgery) and breast.
• Some studies report migraine, youth, anxiety and patients with a low ASA (American Society of Anaesthetists) risk classification as independent predictors for PONV, although the strength of these factors varies from study to study.
• Longer procedures under general vapour anaesthesia accompanied by longer exposure to the vapour anaesthesia and increased postoperative opioid consumption are associated with an increased incidence of PONV.
• Use of regional anaesthesia is associated with a lower incidence of PONV than general anaesthesia in both children and adults.

It is important that you notify your anaesthetist if you have experienced nausea and vomiting after a previous anaesthesia. There are measures that can be taken to minimise the chance of

I am frightened that I may be aware during an operation. Is that possible?

This experience, known as “awareness”, is one of the biggest concerns for patients about to undergo surgery. Though it may worry patients, this condition can be almost entirely eliminated by the anaesthetist, with fewer than 1 in a 1000 patients remembering any part of their operation and most of these not recalling any pain.

Conscious awareness without recall of pain is more common; it has been estimated at 0.1 to 0.7 per cent of cases (1 in 142 to 1 in 1000).

Some operations are associated with a higher risk of awareness than others. They include cardiac surgery, emergency surgery, surgery associated with significant blood loss and caesarean section. 

Specialised monitoring equipment is available to assist anaesthetists to assess the depth of anaesthesia. Such equipment includes processed electro-encephalography such as Bispectral Index Scale (BIS) and Entropy, which record electrical wave patterns in the brain and assign a score which reflects the depth of unconsciousness. These monitors have been shown to reduce the incidence of awareness, particularly in high-risk cases. 

What is regurgitation and aspiration?

Regurgitation is a passive process whereby the stomach contents are brought up into the oesophagus (food tube). It may occur at any point during anaesthesia. Aspiration is the inhaling of those contents into the lungs, where the acidic contents may damage the lung tissue.
Several factors work towards regurgitation and aspiration happening, including emergency surgery, light anaesthesia, upper and lower gastrointestinal (gut) disease, obesity, gastroesophageal reflux (heartburn), impaired consciousness level and hiatus hernia of the stomach. 
Trauma, labour and opioid medications slow down stomach emptying. The anaesthetist will account for these factors and may perform a “rapid sequence induction”. In this procedure, 100 per cent oxygen is administered for several minutes before administering the drugs that put you to sleep. This fills your lungs with 100 per cent oxygen. The assistant to the anaesthetist will lightly press on your throat before any loss of consciousness to prevent any substances coming up from the stomach (regurgitation) and into the throat from where they can then be inhaled into the lungs (aspiration).

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