The aims of anaesthesia for major knee surgery (including joint replacement) include:
1. Anaesthesia – a state of controlled unconsciousness throughout the operation
2. Analgesia – pain relief for the patient throughout the operation, aiming to reduce the stress response to surgical stimulation
3. Prevention of deep vein thrombosis
4. Prevention of pressure areas / nerve damage from prolonged positioning
5. Post-operative analgesia – appropriate pain relief extending after the operation
The anaesthetic options for major knee surgery are:
a. General Anaesthesia
b. Regional Anaesthesia (usually with sedation)
General anaesthesia refers to being totally unconscious, with no awareness of the surgery in process. Supplemental local or regional blockade is frequently administered while you are asleep, to assist with pain relief post-operatively. Regional anaesthesia for knee surgery most commonly involves an injection of local anaesthetic in your lower back that blocks the nerves supplying the lower limbs, rendering both legs anaesthetized. This is known as a spinal (or occasionally an epidural) anaesthetic, and will usually last 3-4 hours during which the operation will ensue. Anaesthetists will commonly add additional analgesia in the form of peripheral nerve blockade, either by the femoral and/or sciatic nerves (the two major nerves that supply the knee joint)
Most patients perceive that they will receive a general anaesthetic for their operation, and many are surprised to discover that regional anaesthesia (with moderate sedation) is frequently used by their anaesthetist for major joint replacement surgery.
Sedation during regional anaesthesia is entirely optional, however, orthopaedic surgery is noisy (by its nature), and most patients prefer to be sedated even if there is no pain. The degree of sedation will depend upon an understanding between anaesthetist and patient, and can be altered as the operation progresses. It is the anaesthetist’s role to monitor you continuously throughout the operation, and adjust the sedation to keep you comfortable. Most patients will recall some aspects of the operation, particularly early positioning. Anaesthetists do not allow the surgeons to start unless we are certain there will be no pain, and the experience is usually relaxing and peaceful. Many patients recall nothing, and often assume that they have had a general anaesthetic.
The type of anaesthetic that you will receive is influenced by the magnitude / nature of your operation, your past anaesthetic experiences, your past medical history and any medications that you are taking.
Personal preference also plays a part. It is very uncommon for an anaesthetist to declare that you “must” have one particular anaesthetic type. We are usually happy to negotiate a plan with you or to be challenged as to our reasons behind recommending a certain anaesthetic course.
Additional procedures may be required to help keep you safe. An arterial line (a small cannula placed in your radial artery at the level of your wrist) may be placed during your knee surgery. This allows beat-to-beat assessment of your blood pressure, rather than 3-5 minutely readings from a cuff on your upper arm. A central line (usually inserted in your internal jugular vein, on the right side of your neck) is less commonly placed, but may be required if you are having a larger operation or have difficult peripheral intravenous access.
Occasionally patients require a blood transfusion in theatre during their operation, or afterwards in the post-operative period. This is one of the risks associated with major knee surgery, and anaesthetists would pursue this only when the benefits outweigh the risks. Should you warrant a blood transfusion in the days following your operation, this can be discussed at this time.
Your anaesthetist will ask questions about your general health, tablets / medications, and past anaesthetic experiences. It is important to let us know of any allergies or drug sensitivities. Please ensure that you write down your questions, as this will ensure that nothing is missed.
Knee surgery is commonly painful, and most patients require reasonably strong pain relief for the first few days after their operation. You may be given a P.C.A. (Patient Controlled Analgesia) pump, which administers a fixed dose of medication intravenously when you press a button. This is usually morphine, fentanyl, or oxycodone. The advantage of these pumps is that you are in control of your own pain relief, which is an individual preference. Your anaesthetist will place a time-based lockout on your machine, which prevents accidental overdose by multiple presses in the space of a few seconds.
Other pain relief which can be considered includes epidural anaesthesia, however, this is less commonly used than P.C.A. or tablet medications. Your anaesthetist will ensure that you have enough intravenous fluids to prevent dehydration. Application of ice, and elevation of the operative side can both be useful in the days following your operation.
Preparing for Surgery:
There are some things you can do to make your anaesthetic easier and safer.
Fasting is necessary to ensure that your stomach is empty. Food or fluid in the stomach may be regurgitated during anaesthesia. If inhaled this could result in serious lung damage. The same risk applies for regional anaesthesia and local anaesthesia with sedation.
You may have normal food intake with a light meal up to six hours prior to surgery. After this you may have small amounts of clear fluids (water, clear fruit juices such as apple juice, black tea, or coffee without milk) until two hours prior to admission to hospital. Sometimes the order of the list changes, and you may be rapidly promoted. Please do not eat or drink while in hospital unless you have confirmed with your anaesthetist, surgeon, or nursing staff that this is acceptable.
Continue to take all regular medications up to (and including) the day of surgery EXCEPT diuretics (fluid tablets) and drugs which cause indigestion if taken without food. If you are diabetic, your medication management can be discussed with your anaesthetist prior to your admission. The type of medications and the estimated time of your operation will need to be considered.
Please bring all your current medications to hospital with you. You should also cease any drugs that the surgeon has told you to stop taking. Warfarin may need to be stopped some time before surgery and should be sorted out well prior to your operation.
Smoking: DO NOT SMOKE. The longer you can stop, the greater the benefit.
Risks and Complications:
Anaesthesia performed in Australian hospitals is amongst the safest in the world.
The risk of complications and side-effects is still present. Common side effects with general anaesthesia include nausea and vomiting, drowsiness, cough, sore throat, hoarse voice, and headache. There can be bruising at intravenous or arterial access sites, with local pain. Damage to teeth or dental appliances is possible, in spite of every effort made to protect them.
Anaesthetic emergencies are, fortunately, very uncommon. Anaesthetists have specific training in the handling of emergency situations and any such situation will be promptly and expertly handled.
Infection resulting from anaesthesia is extremely rare. All drugs, needles, syringes and intravenous lines are used for one patient only and then discarded. If a regional technique is pursued, it will be performed in a sterile manner, with gown, gloves, mask, and alcoholic cleaning solution applied to the site of injection. Antibiotics are commonly given with major knee surgery to reduce the risk of surgical site infection, and are continued into the post-operative period.
These risks should be balanced against the benefits of the proposed procedure and taken into consideration when making your decision to undergo surgery. If you have any specific concerns, or would like a more comprehensive discussion regarding serious but uncommon complications of anaesthesia as they relate to your situation, please let your anaesthetist know prior to your operation.
Patients undergoing major knee surgery will need to stay in hospital after their operation. It is sensible to limit the amount of visitors to one or two close friends or relatives for the first 24-48 hours, until you are comfortable. You may eat and drink as you wish unless instructed otherwise by your surgeon. It is usually best to commence with clear fluids and progress to light foods as tolerated before returning to a normal diet.