Anaesthesia for general, gynaecological and genitourinary surgery

Patient positioning

Patient positioning is also discussed in detail in Chapter 22 .

Lloyd-Davies and lithotomy

Access to the anus, perineum and genitals can be facilitated by use of the Lloyd-Davies or lithotomy positions (see Fig. 22.3 ). Both have the patient supine with the hips flexed and abducted with bent knees. Lithotomy uses a greater hip flexion (typically close to 90 degrees). Prolonged extreme hip flexion can result in femoral nerve compression, or sciatic/ obturator nerve stretching (see Fig. 22.4 ). Care should be taken to avoid prolonged pressure against the femoral and tibial condyles (common peroneal or saphenous nerve compression). Typically the patient's legs are put into the leg attachments, which are raised to achieve the desired position. If patients’ hands are by their sides, fingers may be trapped in the operating table mechanism ( Fig. 35.1 ). Patients with prosthetic joints should be identified and care taken to avoid accidental dislocation.

Low-pressure calf muscle compartment syndrome is a rare complication of prolonged leg-up positioning – often appearing several hours after surgery. The cause is unknown but may relate to direct calf pressure or femoral vein obstruction as a result of hip flexion. The use of intermittent calf compression devices (e.g. Flowtron therapy) whilst in the leg-up position may increase the risk. Periodic lowering of the legs during prolonged procedures may help.

Absolute or relative hypovolaemia from blood loss or regional anaesthesia may be masked when legs are raised, only becoming apparent only after they are lowered.

Laparoscopic surgery

Laparoscopic surgery is associated with lower intraoperative blood loss and heat loss, reduced postoperative analgesia requirements and faster recovery times.

Most laparoscopic surgery requires a pneumoperitoneum produced by the insufflation of carbon dioxide. Exceptions include renal surgery, in which a retroperitoneal approach is possible, and some radical prostate surgery using an anteroperitoneal approach.

The pneumoperitoneum is typically held at pressures of 10–15 mmHg. This can be achieved by surgically inserting a laparoscopic port or by using a Veress needle. During insertion, inadvertent damage to bowel or major blood vessels can occur. Subcutaneous insufflation can result in surgical emphysema, whilst i.v. insufflation can cause venous gas embolism. Gas insufflation or port insertion can sometimes cause peritoneal stimulation, triggering a vagal bradycardic response requiring rapid deflation; occasionally, anticholinergic treatment is needed.

Peritoneal insufflation increases venous return, cardiac output and systemic vascular resistance. If higher pressures are used, compression of the vena cava may occur. It also decreases functional residual capacity, and when combined with the Trendelenburg position, there is an increased risk of atelectasis and ventilation/perfusion (V̇/Q̇) mismatch ( Table 35.1 ).

Tracheal intubation and ventilation with PEEP may minimise effects of pneumoperitoneum, but patients with marked respiratory disease may not tolerate a prolonged pneumoperitoneum (although this should be balanced against the risk of inadequate breathing after open surgery). On occasion, congenital diaphragmatic fistulae or surgical diaphragmatic breaches can result in a pneumothorax.

Carbon dioxide is absorbed through the peritoneum during laparoscopic surgery, resulting in elevated P a co ₂ , tachycardia and increased myocardial contractility. Pneumoperitoneum will often result in significant pain in the first few postoperative hours, until the carbon dioxide is absorbed. Retro- or anteroperitoneal insufflation often results in a faster onset of hypercapnia, which may persist after surgery, as well as sometimes causing surgical emphysema in the scrotum and/or chest and face. Nitrous oxide diffuses into gas-filled cavities and so is often avoided during laparoscopic surgery.

Conversion from laparoscopic to open surgery is a potential but infrequent risk that should be borne in mind during anaesthetic planning.

Robotic surgery

After inserting laparoscopic ports in the standard manner, robotic surgery involves ‘docking’ a surgical telemanipulator, which manoeuvres the laparoscopic camera and instruments. A three-dimensional image is transmitted to the operator, who remotely controls instruments which have a much wider range of movement than standard laparoscopic equipment. At present, robotic radical prostatectomy is the most common procedure, but major colorectal and gynaecological surgeries are increasingly using robotic equipment.

Radical prostatectomy requires the patient to be placed in steep Trendelenburg position (see Fig. 22.8 ), with its attendant risks (see table 35.1 ). Furthermore, robots do not tolerate operating table or patient movement, and neuromuscular blockade is advised until the robot is undocked. Whilst the robot is docked, patient access is limited, so tracheal tube and i.v. line positions should be checked before surgery. In the event of an emergency, access for treatment would require the robot to be rapidly undocked; it is recommended that rapid undocking is practised as a safety drill.

Communication between surgeon and anaesthetist is significantly altered during robot surgery. The surgeon sits in a booth, distant to the surgery, unable to directly view the anaesthetist or operating table. The surgeon's voice is projected by speakers, and allowances must be made for the inherent decrease in non-verbal communication, which will alter the whole dynamic of crisis resource management in an emergency situation.

Other endoscopic surgery

Flexible endoscopes are used for many diagnostic procedures, including oesophagogastroduodenoscopy (OGD), colonoscopy/sigmoidoscopy and surveillance cystoscopy. Flexible biopsy forceps, snares or injection needles may be inserted down the endoscope for certain treatments. Endoscopy can often be performed using topical anaesthesia with or without sedation, but a GA may be required in situations where there is significant risk to the airway (e.g. OGD for major haemorrhage).

Rigid endoscopes allow the use of rigid instruments (e.g. resection diathermy loops) and fluid irrigation. Irrigation allows surgical field visualisation in enclosed spaces (e.g. bladder or uterus) and washes away blood and resected tissue. Rigid scopes mostly require GA or regional anaesthesia.

The choice of irrigation fluid depends on the surgical technique. Monopolar diathermy equipment requires a relatively non-conducting irrigating fluid so that current is not dissipated away from the diathermy loop when it touches the body. Until recently, most diathermy equipment used by urologists was monopolar using glycine, which combines good optical properties with poor conduction. In contrast, newer bipolar resectoscopes require saline irrigation, which conducts a charge from the active part of the instrument to the nearby return electrode.

Endoscopic resection with continuous irrigation requires the fluid to be under pressure, achieved by hanging the fluid reservoir from a drip stand. Fluid can be forced under pressure into tissue planes as well as veins opened by diathermy. Large amounts of fluid can be absorbed, causing fluid overload in susceptible patients. If the irrigating fluid is glycine, transurethral resection (TUR) syndrome may also develop ( see later and Box 35.1 ).

Obese and bariatric patients

Increasing numbers of obese and bariatric patients are being operated on in all fields of surgery. The anaesthetic implications of obesity are described in Chapter 32 , but in the context of general, urological and gynaecological surgery obese patients present specific problems in relation to airway, positioning and recovery.

Because of the attendant risks of lung atelectasis and hypoventilation, there is a preference for regional anaesthesia in obese patients. If a GA is required, there is a lower threshold for tracheal intubation and mechanical ventilation, even though airway manoeuvres will be more difficult, and hypoxic desaturation more rapid.

Elderly and frail patients

Many patients requiring surgery are elderly or frail, especially where any pathological condition is associated with advancing age, such as prostatic disease or cancer of the bowel or bladder. Although the anaesthetic considerations for age and frailty are described in Chapter 31 , it should be noted that coexisting chronic diseases can contribute to frailty. Urology operations are strongly associated with prior renal dysfunction, whilst patients having bowel and gynaecological surgery often have poor nutrition or advanced cancer. These factors, and any associated polypharmacy, increase the risk of biochemical or haematological abnormalities. For example, hyponatraemia and anaemia will affect the ability to tolerate TUR syndrome and haemorrhage, respectively. As a rule, regional techniques are often better tolerated than GA in frail patients.

Cancer and chemotherapy

Anaesthetic assessment for cancer surgery should take into account the possibility of metastatic spread, particularly to the lungs.

Neoadjuvant chemotherapy (chemotherapy given before surgery) is increasingly being used to improve the likelihood of cure, or to reduce tumour burden and facilitate surgery; where patients require surgery for tumour recurrence, it is likely that they will have had intervening chemotherapy. Some chemotherapy regimens can produce systemic effects which may be identifiable preoperatively (e.g. anthracyclines and taxols, used in ovarian, breast and gastric cancers, can reduce cardiac reserve).

Bleomycin, used for germ cell tumours, is implicated in severe pulmonary toxicity, especially in the presence of high inspired oxygen fractions. Reducing delivered oxygen concentrations, targeting saturations of 88%–92%, is recommended.