Anaesthesia for orthopaedic surgery

General anaesthesia

General anaesthesia is appropriate for some types of orthopaedic surgery, but regional anaesthesia is the preferred technique for many procedures, for reasons discussed later. Patients undergoing procedures of long duration (e.g. hip revision) often require general anaesthesia because of the discomfort incurred by remaining in the same position for a prolonged time. In many countries, including the UK, patients often expect to receive general anaesthesia and may not have been aware in advance of their surgery that regional anaesthesia represents a viable option. The implementation of preoperative patient education about their anaesthetic options, often undertaken during routine nurse-led assessment clinics, leads to better patient understanding of the benefits of regional anaesthesia in orthopaedic surgery. General anaesthesia causes the greatest loss of control for the patient, and many patients are pleasantly surprised to find that regional anaesthesia is an option for their operation.

Regional anaesthesia

Central neuraxial block (intrathecal or epidural anaesthesia) reduces the stress response to surgery and has been shown to reduce some serious complications after many types of surgery. Benefits may include a reduction in the incidences of deep vein thrombosis, blood loss, myocardial infarction, respiratory and renal complications and possibly pulmonary embolism. There is a high incidence of thromboembolic events in patients undergoing major lower limb arthroplasty, which makes this type of anaesthesia an attractive option.

Lower limb arthroplasty and minor lower limb procedures are often carried out using central neuraxial block alone. For longer procedures, such as hip arthroplasty, the use of sedation may be preferable.

After central neuraxial block, the patient is usually pain free in the immediate postoperative period. Careful thought should be given to administration of analgesia after the block has worn off. There is a higher incidence of urinary retention in patients who have undergone joint arthroplasty under central neuraxial block, particularly when long-acting intrathecal opioids have been coadministered. Patients may be managed by prophylactic urethral catheterisation or increasingly by monitoring of bladder volume postoperatively using ultrasound. If an intrathecal opioid has not been used, routine prophylactic urethral catheterisation is no longer routinely mandated.

Peripheral nerve block is commonly used as a sole technique for many procedures, with the advantages of excellent early pain relief, reduction of surgical stress, avoidance of complications of general anaesthesia and earlier discharge in the day-case setting. Orthopaedic surgery in patients at high risk of complications from general anaesthesia may also be carried out under peripheral nerve block. Patients report a high degree of satisfaction after surgery carried out using this form of anaesthesia. Table 36.1 shows the sites at which surgery may be performed in association with specific nerve blocks. This form of anaesthesia requires a high level of expertise and an understanding of the issues of managing a conscious patient during surgery.

Intravenous regional anaesthesia (IVRA) is suitable for manipulation of fractures and brief operations (less than 30 min) on the forearm and lower leg. It is technically easy to perform, but fatalities have occurred as a result of large doses of local anaesthetic reaching the systemic circulation. Before performing IVRA, it is essential to understand how the risk of complications may be minimised and how they may be treated if they occur. Details of the technique and safety precautions are described in Chapter 25 .

Oral and intravenous agents

Many patients are already taking regular analgesics for pre-existing bone and joint pain. Paracetamol is very useful in reducing the dose requirements of other analgesics and may occasionally be sufficient analgesia alone. It is virtually free from adverse effects in standard doses and is contraindicated only in patients with hepatocellular insufficiency. Caution should be used when dosing paracetamol in elderly and frail patients who weigh less than 50 kg and should therefore receive less than the standard adult dose. The addition of NSAIDs, in the absence of contraindications, is often beneficial and further reduces the requirement for opioid analgesia.

NSAIDs inhibit the formation of prostaglandins and are widely used as analgesics in the treatment of acute bone-related pain. Selective cyclo-oxygenase-2 (COX-2) inhibitors potentially widen the number of patients who could benefit from NSAIDs by reducing the potential for gastroduodenal ulceration, but their use has been severely curtailed because of the increased incidence of myocardial infarction and stroke in patients taking long-term COX-2 inhibitors; this led to the withdrawal of rofecoxib in September 2004. The only COX-2 inhibitors currently licensed in the UK are celecoxib, parecoxib and etoricoxib.

Prostaglandins are known to have an important role in bone repair and homeostasis. Animal studies have demonstrated that NSAIDs impair fracture healing. This has raised concerns regarding their use as anti-inflammatory or analgesic drugs in patients undergoing orthopaedic procedures; however, the clinical implications of this are probably minimal and they remain extremely important analgesic agents for orthopaedic patients.

NSAIDs also affect platelet function and therefore could be expected to increase perioperative blood loss. The clinical evidence for increased blood loss in major arthroplasty surgery patients receiving NSAIDs is minimal.

Opioids are often used after major joint arthroplasty. Orthopaedic procedures, unlike many other forms of surgery, do not usually result in disruption to the enteral route of drug delivery, and therefore oral opioids are commonly used for severe postoperative pain. These can be prescribed on an ‘as required’ basis as immediate-release preparations, dosed regularly as modified-release capsules or a combination of the two. Patient-controlled analgesia systems using i.v. opioids are relatively rarely required in orthopaedic surgery. The doses of opioid required are reduced by the use of other analgesic agents and regional techniques, thus minimising the risk of adverse effects. For operative procedures undertaken using central neuraxial or peripheral regional anaesthesia, adequate systemic analgesia should be prescribed to provide adequate pain relief when the block recedes.

Central neuraxial drugs

Single-dose intrathecal or epidural anaesthesia using local anaesthetic alone usually provides analgesia for relatively short periods after operation. An adjuvant, such as an opioid agent, administered into the intrathecal or epidural space with the local anaesthetic improves the quality of the block and extends the duration of analgesia. These benefits must be weighed against the increased incidence of intrathecal opioid-related adverse effects such as pruritus, nausea and urinary retention.

Epidural infusions may be used for up to 5 days after major orthopaedic surgery. Careful observation for signs of inadequate analgesia (often a result of catheter migration) and infection is required. The involvement of an acute pain team is very useful in this regard. Many units manage these patients in an extended recovery or high-dependency setting to increase the level of nursing care and to facilitate early detection and prompt management of complications.

Peripheral nerve blocks

Peripheral nerve block, with or without a central neuraxial block or general anaesthesia, provides excellent pain relief for several hours postoperatively, allowing transition to oral or intravenous analgesia. Analgesic regimes should be commenced before peripheral nerve blocks wear off after painful procedures to avoid onset of severe rebound pain.

More recently, early rehabilitation after orthopaedic surgery has led to the development of motor-sparing blocks such as adductor canal blockade for knee surgery. Periarticular infiltration of high-volume, low-concentration local anaesthetic agents and an emphasis on early mobilisation after surgery as part of orthopaedic enhanced recovery programmes have reduced the use of more traditional peripheral nerve blocks to reduce prolonged motor blockade after lower limb arthroplasty.

Single-dose peripheral nerve blocks using a long-acting local anaesthetic such as levobupivacaine may last for more than 16 h. Additives such as dexamethasone may be used to prolong the duration of single-dose blocks, although the magnitude of this effect seems similar regardless of whether the dexamethasone is given perineurally or intravenously. Alternatively, a perineural catheter may be inserted, allowing an infusion of a low-concentration local anaesthetic drug (e.g. ropivacaine 0.2%) for several days postoperatively.

Nerve injury as a result of peripheral nerve block is rare (see Chapter 26 ), and patients with concurrent comorbidity such as diabetes or vascular disease may have an increased risk. However, the incidence of nerve injury secondary to orthopaedic surgery (direct trauma, tourniquet or positioning) is more common and often occurs in the sensory distribution of the nerve block.

Positioning

A patient's ability to assume the position required for operation must be assessed carefully; it is often useful to ask the patient to adopt that position before induction of anaesthesia if there is concern that mobility of joints may be an issue. Patients with arthritis often have restricted mobility of joints, and positioning at the extremes of the range of movement may cause severe postoperative pain in addition to the pain resulting from the operation. Orthopaedic surgery often requires the use of unusual positions, some of which carry risks of nerve damage, soft tissue ischaemia, electrical and thermal injury and joint pain. Care must be taken in protecting areas at risk of injury. These include bony promontories, sites of poor tissue viability and locations where nerves run close to the skin or close to the surface of a bone.

Forceful movement of the patient by the surgeon is often inevitable during orthopaedic surgery. When such movement occurs, it is advisable to recheck the patient's position, ensuring that soft tissues, nerves, eyes and venous access sites are protected.

Some positions adopted during orthopaedic surgery are associated with venous air embolism. These postures include the lateral position for hip surgery, the sitting position for shoulder surgery and the prone position for spinal surgery. Monitoring for and treatment of air embolism are discussed in detail in Chapter 27 .

Prophylaxis against infection

Prophylactic i.v. antibiotics are often used during orthopaedic surgery. Infection of bone is particularly threatening to the patient and is very difficult to eradicate; consequently, prevention is a high priority. Allergic reactions to antibiotics may occur, and facilities must be available to treat such a reaction when antibiotics are used.

Laminar flow is used commonly in orthopaedic theatres to provide a constant flow of microscopically filtered air over the surgical field and to minimise the risk of wound infection by environmental pathogens. The evidence for laminar flow in the antibiotic era is controversial. This high flow of air over the patient's body surface greatly speeds convective heat loss, and precautions should be taken to avoid hypothermia.

Various in-theatre rituals exist for the prevention of cross-infection. These include the wearing of face masks and hats; however the evidence supporting their use is scant.

Prophylaxis against hypothermia

After induction of general or regional anaesthesia, heat is redistributed from the core to the peripheries. After induction of general anaesthesia, there is typically a reduction in core temperature of 1°C in the first 30 min of anaesthesia. Core temperature reduces more slowly after this initial redistribution phase, typically by approximately 0.5°C per hour, although the rate of fall is heavily dependent on ambient temperature, exposure and insulation, and the use of warming devices (see Chapter 13 ).

Hypothermia is known to be associated with increased blood loss because of the narrow temperature range in which enzyme-dependent systems work and perhaps because of platelet sequestration in the spleen. Hypothermia is also associated with poor postoperative wound healing and postoperative hypoxaemia.

The most effective method of reducing heat loss is forced air warming. However, warmed intravenous and surgical irrigation fluids and impermeable surgical drapes to reduce heat loss by evaporation are also useful.