Assessing your risk before surgery
Safety starts well before the day of your procedure. Before surgery you will usually complete a health questionnaire, and I will review your overall health. That includes your heart and lungs, any neurological conditions, your medications and allergies, previous operations, and how you have found anaesthesia in the past. If you have ever been told your airway was difficult, reacted strongly to a medication, or were slow to wake up, please tell me.
Anaesthetists often describe overall fitness for surgery using the ASA physical status scale, developed by the American Society of Anesthesiologists. In plain terms, it ranges from a healthy person with no significant medical problems, through people with mild or more serious long-term conditions, to people who are critically unwell. It is a simple summary that helps the whole team plan, and it is only one part of the picture.
For major surgery, or when there are significant medical issues, I may also use the NSQIP risk calculator from the American College of Surgeons National Surgical Quality Improvement Program. It estimates the chance of particular complications for someone with your health profile having your type of operation. These estimates help us discuss your individual risk honestly and tailor your care, for example by planning extra monitoring or a period in intensive care afterwards.
An example of an individual risk estimate
The table below is a made-up example, not a real patient. It shows the kind of estimate the calculator gives for a 58-year-old woman who needs an urgent revision of a hip replacement and who also has advanced cancer, diabetes, a low body weight and serious medical illness. Her estimated risks are shown beside the average risk for people having the same operation.
| Outcome after surgery | Estimated risk for this example patient | Average risk |
|---|---|---|
| Any complication | 19.2% | 10.0% |
| Serious complication | 17.7% | 9.1% |
| Pneumonia | 2.0% | 0.7% |
| Heart complication | 1.6% | 0.6% |
| Blood clot in the legs or lungs | 2.0% | 1.1% |
| Kidney failure | 0.8% | 0.4% |
| Return to the operating theatre | 7.7% | 5.2% |
| Readmission to hospital | 13.4% | 7.7% |
| Discharge to a rehabilitation or nursing facility | 46.4% | 23.3% |
| Death | 4.3% | 0.3% |
Example calculated with the American College of Surgeons NSQIP Surgical Risk Calculator. Estimates come from large numbers of patients, mostly in North American hospitals, and cannot predict what will happen to any one person. They are one part of our discussion, together with your own health, your priorities and the alternatives available.
Common side effects
Most side effects of anaesthesia are mild and short-lived. They usually settle within hours to a day or so, and many can be prevented or treated. They include:
- Feeling sick or vomiting. Medications to reduce nausea are given routinely when the risk is higher, and more can be given in recovery.
- Sore throat. This can follow the use of a breathing tube or laryngeal mask, and usually settles within a day or two.
- Shivering and feeling cold. Your temperature is monitored, and warming blankets and warmed fluids are used.
- Thirst and a dry mouth, partly from fasting beforehand.
- Bruising or discomfort where the drip was placed.
- Drowsiness, temporary confusion or memory problems, which are more likely in older people and usually improve over hours to days.
- Pain from the surgery itself, which is planned for in advance.
Uncommon complications
Some complications are less frequent but still worth knowing about:
- Minor injury to the lips, tongue or mouth when an airway device is placed.
- Minor nerve injury, causing numbness or tingling, which is usually temporary. It can relate to positioning during surgery or to a nerve block.
- Breathing difficulties or a chest infection after surgery, which are more likely in people with lung disease or who smoke.
- Headache after a spinal or epidural, which is treatable if it occurs.
Rare but serious complications
Serious complications are rare, and very rare for healthy people having routine procedures. The figures below come from the Royal College of Anaesthetists (UK) 2024 patient information. They are averages from research studies of people who mostly had routine surgery and no significant health conditions. Your own risk may be higher or lower, and we will talk about the risks that matter most for you.
Common side effects of general anaesthesia
| What happened | For how long | How often |
|---|---|---|
| Shivering | For 20–30 minutes in the recovery room | 15 in 100 |
| Feeling sick (nausea) | For 1–24 hours | About 15 in 100 |
| Sore throat | For 24–48 hours; depends on the type of breathing tube | 20–40 in 100 |
| Bruising or pain from injections | Goes away in a few days | 10 in 100 |
| Minor lip or tongue injury | Heals in a few days | 1–5 in 100 |
| Chest infection | Days or weeks; more likely in smokers, people with existing medical conditions and some types of surgery | 2–20 in 100 |
| Becoming confused (delirium) | Days, weeks or months; more likely in older people with existing conditions having complex or emergency surgery | 10–50 in 100 |
Rare and very rare risks
| What happened | For how long | How often |
|---|---|---|
| Damage to teeth | Needs to be seen by a dentist | 5 in 10,000 |
| Blurred vision, eye irritation or pain from a small scratch or dry eyes | A few days | About 5 in 10,000 |
| Tingling, numbness, pain or weakness from nerve damage | Temporary (weeks to months) | 1–5 in 10,000 |
| Nerve damage | Permanent | 1 in 10,000 |
| Severe allergic reaction (anaphylaxis) | Happens quickly; treated immediately | 1 in 10,000 |
| Cardiac arrest (the heart stopping) during surgery | Treated immediately | 3 in 10,000 |
| Waking briefly during a general anaesthetic (accidental awareness) | Most often less than five minutes, before surgery starts or after it finishes; about 1 in 100,000 people felt some pain | 5 in 100,000 |
| Loss of sight from pressure on, or blood clots affecting, the optic nerve | Permanent | 1 in 100,000 |
| Death due to the anaesthetic | Varies greatly: higher for some operations and for people who are frail, older or have certain health conditions | 1 in 100,000 |
Source: Royal College of Anaesthetists (UK), General anaesthetics: risks and side effects, 2024, reproduced in adapted form with acknowledgement. Download the RCoA infographic (PDF) or see rcoa.ac.uk. Figures are general guides and are not specific to any individual or practitioner.
To put these numbers in context, many of the very rare events are less likely than the risks we accept in everyday life, such as travelling by car. That does not make them unimportant. It means they are kept in proportion, and the steps described below are designed to make them even less likely.
How risk is reduced
Anaesthetic safety comes from preparation, careful technique and constant attention. The main strategies include:
- Thorough assessment and planning, so that your anaesthetic is chosen for your health and your procedure.
- Fasting before surgery. Under anaesthesia the reflexes that protect your lungs are reduced. An empty stomach lowers the risk of stomach contents entering the lungs (aspiration), which can cause pneumonia and, rarely, severe illness.
- Reviewing your medications with your surgeon, GP and prescribing doctors, so that any changes are made safely and individually. See Medications Before Anaesthesia.
- Team checks before anaesthesia and surgery start, confirming your identity, the procedure, allergies and the plan.
- Careful positioning and padding to protect your nerves, skin and eyes while you are asleep.
- Preventing nausea, blood clots and infection with medications and measures matched to your risk.
- A specialist anaesthetist with you throughout, from the start of your anaesthetic until your care is handed over in recovery.
Monitoring and equipment
Throughout your anaesthetic, your body's vital functions are watched continuously, in line with the professional standards of the Australian and New Zealand College of Anaesthetists (ANZCA). Standard monitoring includes:
- Pulse oximetry, a small clip on your finger measuring the oxygen level in your blood.
- Capnography, which measures the carbon dioxide you breathe out and confirms that breathing and the airway are working well.
- ECG, showing your heart rhythm.
- Blood pressure, measured regularly with a cuff, or continuously through a fine tube in an artery for some major procedures.
- Temperature, so that you can be kept warm.
- Depth of anaesthesia monitoring where appropriate, using sensors on the forehead that help guide the amount of anaesthetic given.
Anaesthetic machines and equipment are checked before use, and alarms alert the team to any change. For complex surgery, additional monitoring of the heart, circulation or brain may be used.
Individual factors that affect risk
Your risk depends on you and on the procedure you are having. Factors that can increase it include:
- Age and frailty. Older and frailer people may take longer to recover and are more prone to confusion after surgery.
- Heart and lung disease, including heart failure, angina, previous heart attack, asthma and chronic lung disease.
- Obstructive sleep apnoea, which can affect breathing after anaesthesia and with some pain medicines.
- Obesity, which can make the airway, breathing and positioning more challenging.
- Smoking, which increases the risk of breathing problems, wound complications and infection. Stopping, even for a short time before surgery, helps.
- Diabetes, particularly if blood glucose levels have been difficult to control.
- The type and urgency of surgery. Major, long or emergency operations carry more risk than short, planned procedures.
Knowing about these factors allows the plan to be adjusted. Many can be improved before planned surgery, and your GP and surgeon can help with that.
Emergency preparedness
Anaesthetists train to recognise and manage uncommon emergencies quickly and calmly. This includes:
- Difficult airway management. Equipment such as video laryngoscopes and flexible scopes is available, along with agreed plans for an unexpectedly difficult airway.
- Crisis simulation and team training, practising rare events so that the whole team responds in a coordinated way.
- Severe allergic reactions (anaphylaxis), with treatment protocols and medications immediately available.
- Malignant hyperthermia, a rare inherited reaction to some anaesthetic drugs. Hospitals keep the specific treatment, dantrolene, on hand. If you or a blood relative have had this reaction, please tell me.
Patient safety and airway management have been a long-standing focus of my professional work, including contributions to ANZCA airway management guidelines and to guidance on fire safety in the operating room. You can read more on Patient Safety & Leadership.
Communication and informed consent
The figures on this page are general. What matters most is what they mean for you. Before your procedure we will talk about your health, the anaesthetic I recommend and why, the risks that are relevant to you, and the reasonable alternatives. You are welcome to ask questions, including about anything you have read online or asked an AI tool.