When any patient undergoes surgery on their knee or hip there is always more than one possible anaesthetic. These include

  • General anaesthetic
  • Spinal anaesthetic
  • Nerve block (to decrease post-operative pain)
  • Combination of anaesthetics

Prior to any surgery a full explanation of which anaesthetic would be the most appropriate for each individual is given in some detail and of course every patient’s wishes are taken into consideration. Before surgery every patient attends a pre-op assessment clinic and there will an opportunity to meet the anaesthetist especially if there are complex medical issues. Patients will be asked about their general health, any serious illnesses (e.g. diabetes, heart disease, emphysema etc.), any previous anaesthetic problems, current medication, allergies and whether they smoke or drink alcohol.

On rare occasions it may be necessary to postpone the date of surgery in order to obtain some further tests or even start some new medication in order to improve a patient’s overall health (e.g. to bring down high blood pressure or to control an irregular heart rate). If it is felt that the risks of any anaesthetic are unduly high based on a patient’s poor health then after further consultation it may be advised that surgery should not be carried out. Clearly these are important decisions that are made only with the full input and understanding from the patient from the very beginning.

General Anaesthetic

When a patient receives a general anaesthetic (GA), both the feeling of pain and the reaction to it are totally abolished by inducing a controlled state of reversible unconsciousness. There is also a complete blockade of all motor (muscle) function. General anaesthetic agents can be administered into a vein (intravenously) or inhaled. It will be necessary to place a breathing tube (endotracheal tube) in the patient’s throat to protect the airway and allow direct control of the breathing or ventilation. This tube also allows oxygen to be delivered easily to the lungs. If a muscle relaxant has been given then a breathing machine (ventilator) will also be used.

During the administration of anaesthetics, regular and careful assessments of the patient’s vital signs are carried out by the anaesthetist. This will include monitoring the pulse, respiratory rate, blood pressure and the amount of oxygen in the blood. Changes in these vital signs can also occur due to blood loss, the insertion of orthopaedic cement and the application of a tight tourniquet around the thigh. The choice of anaesthetic agent and its rate of administration can be adjusted at any time to provide the best conditions for the particular surgery in progress. Once the operation is over the anaesthetic is stopped and on average it takes about 5 to 20 minutes before full consciousness is regained.

Despite the fact that the vast majority of patients receiving general anaesthesia have no serious ill effects, there are some risks and these include

  • The need for strong pain killers after the operation – such as morphine
  • Sickness – treated with anti-sickness drugs
  • Sore throat
  • Drowsiness, headache and blurred vision
  • Temporary confusion and memory loss
  • Possible damage to teeth, lips and gums
  • Rarely a serious allergic reaction to drugs or a chest infection, both of which can treated promptly

Spinal Anaesthetic

A spinal anaesthetic is a local anaesthetic agent injected into the lower back to numb the nerves from the waist down to the toes for a period of up to 4-6 hours (this more than adequately covers the duration of most knee and hip operations). To receive the ‘spinal’ the patient either sits on the side of the bed or curled up on his or her side with the legs tucked up towards the chest. The patient remains conscious but feels no pain and cannot move their legs – it is however possible to administer drugs that make the patient sleepy and relaxed (sedation) during the surgery. At times the patient may feel sensations of movement or pressure as the surgery progresses.

There are some advantages to having a spinal anaesthetic and these are as follows

  • It helps to reduce incidence of blood clots in the legs
  • There may be less bleeding during surgery
  • The patient remains in full control of his/her breathing during the surgery
  • Less strong pain killing medication is required in first few hours following surgery
  • There is generally less sickness and drowsiness after surgery
  • The patient is able to eat and drink sooner after surgery

With a spinal anaesthetic the patient is able to communicate with the anaesthetist and surgeon before and during surgery. Usually a screen is put up across the patient’s upper chest so that the actual surgery can not be seen. However if arthroscopic surgery is being carried out the patient may even be able to view the operation on a monitor if desired! The patient will be aware of the ‘busy goings on’ in the theatre but once surgery commences the patient can relax, sleep or listen to some music through personal headphones. The patient can at any point talk to the anaesthetist if there are any concerns and adjustments to care can be made throughout the operation.

It must be stressed however that the patient may still require general anaesthesia if

  • There are difficulties performing the spinal satisfactorily
  • The spinal does not work satisfactorily
  • The surgery turns out to be more complicated or prolonged than initially anticipated

As with all anaesthetic techniques there can be unwanted side effects. These include

  • Headache once the spinal has worn off
  • Low blood pressure with associated faintness and sickness
  • Itching due to morphine-like drugs used in combination with the local anaesthetic
  • Problems passing water (urinary retention) – bladder function returns to normal only when the spinal anaesthetic has completely worn off and during this time it may be necessary for the patient to have a catheter placed into the bladder temporarily (this can be done either in theatre or on the ward afterwards)
  • Pain during the injection – if the patient feels pain in his or her legs or bottom the anaesthetist must be immediately told as this can be due to damage to a nerve and the needle will have to be repositioned

Following spinal anaesthesia the nurses looking after the patient will ensure the numb areas (bottom and legs) are protected from injury and any excess pressure until normal sensation returns. As the spinal wears off the patient may experience tingling in the skin and some pain and discomfort from the operative site and at this point the patient should ask for more pain relief which can easily be given. It is usual for most patients to be able to drink fluids and possibly eat something light within one hour of the surgery finishing. The patient must not attempt to get out of bed for the first time following spinal anaesthesia without the close supervision and assistance of a physiotherapist or a nurse.

Nerve block

A nerve block is a carefully placed injection of local anaesthetic near to the main nerves supplying the leg. This enables the hip or knee joint to be completely numb during the surgery. The most commonly ‘blocked’ nerve in knee surgery is the femoral nerve which supplies the front of the thigh and the knee. To ensure that the nerve block is given swiftly and effectively a small ultrasound machine is often used to locate and visualise the femoral nerve in the groin so that a needle can be introduced very accurately into the correct area.

The operative site should be numb and pain-free for many hours after the surgery. It will not be possible to move the leg properly during this time. A nerve block is given in conjunction with a general anaesthetic and is often given when the patient is already unconscious.

The main advantage with a nerve block is that the patient usually requires a lighter general anaesthetic with subsequently less sickness and grogginess afterwards. The requirement for strong analgesic medication should also be less after the anaesthetic due to the strong pain killing properties of the nerve block which works for several hours.

Combination of anaesthetics

It is possible to have a spinal and general anaesthetic together. The patient has the benefits of a spinal anaesthetic but is also unconscious during the surgery. As a result the general anaesthetic will be a little ‘lighter’ and the unwanted side-effects of a general anaesthesia may be reduced. In addition it is possible to have a nerve block with a general anaesthetic as mentioned above.


Ultimately the patient does have a choice of anaesthesia. The anaesthetist will assess the patient’s overall preferences and requirements for the specific type of surgery planned and fully discuss these with the patient. The patient will never be forced to have any anaesthetic procedure that they do not want. However it is the case that certain types of anaesthesia will suit certain types of patients and clearly these will be recommended.