All surgery requires some form of anaesthesia. This is done by “numbing” various parts of the body or creating a state of “deep sleep” with medication. This allows your surgery to proceed comfortably.


Your anaesthetist is a doctor with specialised knowledge of illnesses, drugs and treatment of serious medical problems. This doctor gives you the anaesthesia during surgery and will stay with you and monitor you closely throughout your surgery. Your anaesthetist will help you with pain relief during and after surgery.

The anaesthetist who assesses you before surgery in the Pre- assessment clinic may not be the same one who gives you your anaesthetic on the day of surgery. Our anaesthetists work as a team. All information will be in your hospital record and will be reviewed with you on the day of surgery.

Before the Anaesthetic

During anaesthesia, the systems that keep food and drink safely in your stomach become weak. Food and drink may find its way out of your stomach and into your lungs, by vomiting or regurgitation, and can cause serious problems. This is why it is important to have an empty stomach before surgery. You will be told when you need to stop eating and drinking at your pre-assessment clinic visit.

What are the Risks of Anaesthesia

All operations and all anaesthesia have some risks. The risk depends on the type of surgery, the type of anaesthesia, and your health. Serious risks are extremely rare. Your anaesthetist will discuss your health and your operation and will tailor your anaesthetic to minimise your risk. Rest assured that your anaesthetist has your safety as their priority and is trained to deal with any eventuality.

Types of Anaesthesia

For hip and knee replacement procedures, two kinds of anaesthesia are common: general or spinal. You will have an opportunity to discuss with your anaesthetist which type is best for you. This is influenced by your general health and the type of surgery you are having.

General Anaesthetics

General anaesthesia often involves multiple medications. They can be given through your intravenous line or in the form of a gas you breathe. Your anaesthetist will choose the most suitable method for you.

In general anaesthesia, you are fully asleep during surgery. Once you are asleep, a breathing tube is placed in your mouth and throat and you will be kept asleep during surgery. When your surgery is finished, your anaesthetist will wake you up and the breathing tube is removed.

What are the Risks of General Anaesthesia?


  • A mild sore throat
  • Feeling sick (nausea) or being sick
  • Drowsiness


  • Damage to teeth

Very rare:

  • Regurgitation of stomach contents into your lungs (aspiration)

Extremely rare:

  • Allergic reactions, anaphylaxis

Spinal Anaesthetic

Spinal anaesthesia is given through an injection in your lower back and it is done in a strictly aseptic (clean) fashion. You will be asked to sit up or lie down on your side. After numbing your skin in your back, a very thin needle is used to inject the medication into the spinal fluid surrounding the spinal cord. Once the medication is in, the needle is removed. This freezes the nerves so that you have virtually no feeling or movement in your legs. This numbness is variable but usually lasts about 4-8 hours. Spinal anaesthesia is suitable for surgeries in the lower half of the body. You may be offered some sedation to help you relax before your spinal injection. This sedation may be continued through your surgery, keeping you in a light sleep so that you are not fully aware of the operation. Your level of sedation can be adjusted to your requirements by your anaesthetist. You may also choose to be awake during your surgery. Your anaesthetist will discuss your anaesthetic in details with you and you will have ample opportunity to ask questions. 

What are the benefits of a spinal anaesthetic?

  • You will not need a breathing tube so you will not have a sore throat afterwards
  • You can eat and drink immediately after your operation
  • Reduced post-operative nausea and vomiting
  • You won’t feel as drowsy especially if sedation is not used
  • There may be less bleeding, reducing the chances of needing a blood transfusion after your operation
  • It decreases the chances of blood clots in your leg veins (deep vein thrombosis) and in the lungs (pulmonary embolus)

What are the risks of a spinal anaesthetic?

Common (1 in 10):

  • Inability to pass urine post-operatively, you may need a temporary catheter (tube) passed into your bladder
  • Low blood pressure, your anaesthetist will monitor your blood pressure closely and treat it immediately if needed

Uncommon (less than 1 in 100):

Failure of the anaesthetic – this will be rectified immediately by your anaesthetist with either another spinal injection or another medication through your vein


Extremely rare (less than 1 in 10,000):

  • Nerve damage

​Bleeding around the spinal cord causing pressure on the nerves

Infection around the spinal cord

Sunnybrook’s Holland Orthopaedic & Arthritic Centre has developed part of this material and this has been edited by Mr. Fahad G. Attar & Dr. Archana Senathirajah.  Permission to add this link to our website has been granted by Sunnybrook Health Sciences Centre. Copyright 2012 by Sunnybrook Health Sciences Centre, Toronto, Ontario. All rights reserved.


Dr. Narendran – Anaesthetist

Dr. Naveed Zafar – Anaesthetist

  • Spire Cheshire Hospital - Spire Healthcare
  • Ten Harley Street
  • BMI Beaumont Hospital
  • Spire Manchester Hospital
  • BMI Health Care
  • HEarly Health Village