Anaesthesia for Gynaecological and Genitourinary Surgery


Anaesthesia for Gynaecological and Genitourinary Surgery


There are many techniques and considerations which are common to both urological and gynaecological anaesthetic practice. As in other areas of surgery, increasing numbers of older, and often more frail, patients require surgery. In both specialities, the need for pelvic or perineal surgical access requires positioning of the patient which is associated with specific complications. In both specialities, there is widespread adoption of endoscopic surgical techniques and there is increased emphasis on the need for anaesthetic techniques which allow for day-case surgery, or surgery involving fast-track recovery programmes.



GENERAL CONSIDERATIONS



Positioning


Perineal, per urethra and per vaginal surgery mostly require the patient to be supine with the hips flexed and abducted and the knees bent. Lloyd Davies and lithotomy are the two common positions in which this is achieved. The main difference between them is the greater degree of flexion of the hips and knees in the lithotomy position. Because of the risk of nerve damage as a result of either direct compression or excessive stretching, care should be taken to avoid extreme hip flexion (femoral nerve compression, sciatic or obturator nerve stretching) and to avoid any prolonged pressure against the femoral and tibial condyles (common peroneal or saphenous nerve compression). When the patient is first put into either position, care should also be taken to avoid trapping the hands in the operating table mechanism. Calf compression leading to compartment syndrome has been associated with both positions and if the position needs to be adopted for many hours it is advisable to lower the legs intermittently to allow reperfusion to occur.


Hypotension from blood loss or regional anaesthesia may be masked by the legs being raised and may become apparent only after they are lowered at the end of surgery.


The Trendelenburg (head-down) position is often required during pelvic surgery and is associated with decreased functional residual capacity (FRC), increased risk of passive regurgitation and raised intracranial and intraocular pressures. Transperitoneal laparoscopic surgery (for example, laparoscopic prostate surgery or hysterectomy) may require steep Trendelenburg positioning (30–45°) for prolonged periods of time and careful attention to preoperative conditions such as glaucoma is necessary. There have been concerns that prolonged steep Trendelenburg position combined with the hypercapnia which often occurs during laparoscopy might cause a raised intracranial pressure (as much as a 150% rise in animal models) and anecdotal evidence suggests that patients are at risk of developing acute confusional states on emergence from anaesthesia. In order to reduce this risk, some anaesthetists have advocated the routine use of parenteral dexamethasone or mannitol intraoperatively. Studies measuring the degree of intraoperative cerebral oxygenation in urological patients positioned in this way suggest that it is well preserved.


Tracheal intubation is required in most patients who require prolonged head-down positioning in order to maintain adequate ventilation, and in patients who are at high risk of passive regurgitation it should be considered even for short procedures. If passive regurgitation occurs in the head-down position, gastric acid can pool around the eyes leading to corneal burns unless it is washed out rapidly, and the patient should be positioned such that the anaesthetist is able to see the face in case this occurs.


Renal surgery most often requires the patient to be in a lateral position with the table ‘broken’ in the middle in order to extend the flank. Cardiorespiratory stability is maintained in most patients despite one lung being dependent, although temporary hypotension sometimes occurs as a result of decreased venous return. Padding of the legs and arms is required to avoid peroneal, saphenous and ulnar nerve damage and care should be taken to avoid lateral neck flexion which may result in brachial plexus injuries. Corneal abrasions are surprisingly common in the lateral position, mostly as a result of inadvertent contact with apparatus near the head (for example HME filters).


Prone positioning is required only for percutaneous nephrolithotomy. For this procedure, patients require general anaesthesia with tracheal intubation and mechanical ventilation. In this position, it is essential that the tracheal tube is well secured. Careful attention should be paid to the position of the head, eye-padding, avoidance of abdominal compression and pressure-point protection (nose, chin, genitals, knees).



Laparoscopic Procedures


As in other areas of surgery, there has been an increase in the number of urological and gynaecological procedures which are performed laparoscopically, including surgery for hysterectomy, oophorectomy, cystectomy, nephrectomy and prostatectomy. Laparoscopic surgery is associated with lower intraoperative blood loss, lower postoperative analgesia requirements and faster postoperative recovery times. There is also less potential for heat loss than during open surgery.


Most laparoscopic surgery involves a transperitoneal approach and requires a pneumoperitoneum. The exceptions to this include renal surgery, in which a retroperitoneal approach is also possible, and radical prostate surgery, in which anteroperitoneal gas insufflation may be used. It has been suggested that anteroperitoneal and retroperitoneal approaches allow for faster postoperative recovery.


The pneumoperitoneum required for laparoscopic surgery is accomplished by the insufflation of carbon dioxide to a pressure of 10–15 mmHg. This can be performed after the insertion of a laparoscopic port or a Veress insufflation needle. In both cases, there is the potential for inadvertent damage to major blood vessels, or for subcutaneous insufflation resulting in surgical emphysema. Very rarely, venous gas embolism occurs as a result of insufflation directly into a blood vessel.


The cardiovascular effects of peritoneal insufflation include increases in venous return and cardiac output, accompanied by an increase in systemic vascular resistance. If higher pressures are required, compression of the vena cava may occur, resulting in a decrease in venous filling. Occasionally, the peritoneal stimulation which occurs during gas insufflation can cause a vagal bradycardic response requiring rapid deflation and the administration of an anticholinergic.


Pneumoperitoneum also results in decreased functional residual capacity, and when combined with the Trendelenburg position, there is an increased risk of atelectasis and V/Q mismatch. Tracheal intubation and mechanical ventilation can help to minimize the effects, particularly if positive end-expiratory pressure is applied, but in patients with marked respiratory disease, a prolonged pneumoperitoneum may not be tolerated well. On rare occasions, a congenital diaphragmatic fistula or a surgical breach of the diaphragm may result in a pneumothorax or pneumomediastinum which can interfere with ventilation.


Carbon dioxide is absorbed through the peritoneum during laparoscopic surgery, resulting in a raised PaCO2, tachycardia and increased myocardial contractility. Retroperitoneal insufflation often results in a greater degree of gas absorption which may persist after surgery. Anteroperitoneal radical prostate surgery is worth a special mention because it can result in severe surgical emphysema in the scrotal area and/or chest and face. The surgical emphysema is caused by carbon dioxide spreading throughout the subcutaneous tissues where it is readily absorbed, resulting sometimes in severe hypercapnia. Methods to decrease the degree of surgical emphysema and hypercapnia include ensuring adequate muscle relaxation (for example by using an infusion of muscle relaxant) and by increasing the minute volume achieved by mechanical ventilation both intraoperatively and sometimes for a short period after surgery has ended. The use of nitrous oxide is not recommended during anteroperitoneal surgery because it exacerbates the degree of surgical emphysema.


The frequency with which laparoscopic procedures are converted to open operation depends on the operation and the experience of the operator. It may be appropriate to ask the surgeon beforehand whether conversion to an open procedure is likely.



Other Endoscopic Surgery


Urethral or transcervical endoscopic approaches can be used to perform bladder, prostate, ureteric and intrauterine surgery. Flexible endoscopes may be used for some procedures, such as surveillance cystoscopy, in which case topical anaesthesia may be sufficient. If surgical resection is necessary, it is probable that a rigid endoscope will be required, facilitated by general or spinal anaesthesia. The rigid endoscope allows the use of rigid instruments, such as a resection diathermy loop, and fluid irrigation which allows visualization of the surgical field and washes away blood and resected tissue.


The choice of irrigation fluid is determined by the surgical technique. If monopolar diathermy equipment is used, a relatively non-conducting irrigating fluid is required so that current is not dissipated away from the point at which the diathermy equipment comes into contact with the body. In contrast, bipolar equipment works better with an irrigating fluid which conducts charge from the active part of the instrument to the nearby return electrode. Until recently, most diathermy equipment used by urologists was monopolar and the irrigation fluid of choice was glycine, which combined good optical properties with poor electrical conduction. Saline irrigation is used with the more recently developed bipolar resectoscopes.


Endoscopic resection with continuous irrigation requires the fluid to be under pressure, achieved usually by hanging the fluid reservoir from a drip-stand. Fluid can be forced under pressure into tissue planes as well as veins or sinuses opened by the diathermy process. In this manner, a large amount of fluid can be absorbed, which can result in fluid overload in susceptible patients. If the irrigating fluid is glycine, TUR (transurethral resection) syndrome may also develop (see below).


Lasers can also be used for transurethral resection and are used commonly for prostatic resection. There are various techniques available using different lasers, including holmium and Greenlight lasers. Smaller instrumentation of the urethra may be possible, including the use of flexible endoscopes, and there is minimal blood loss with faster postoperative recovery times.



TRANSURETHRAL RESECTION (TUR) SYNDROME


Despite the name, TUR syndrome is not exclusive to transurethral surgery. It is sometimes known as TURP (trans-urethral resection of the prostate) syndrome, and, as the name implies, it is most commonly associated with endoscopic prostatic surgery in which prostatic sinuses and veins are cut during resection, allowing irrigating fluid to be absorbed. Less commonly, TUR syndrome has been reported after other procedures, including bladder tumour resection, cystoscopy, various forms of lithotripsy and transcervical endometrial resection.


TUR syndrome occurs if a large volume of hypotonic irrigating solution is absorbed rapidly, resulting in rapid changes in serum osmolality and electrolyte concentrations. Glycine solution is the most commonly used hypotonic irrigating fluid in the UK, and commercial solutions have an osmolality of approximately 200 mosmol L− 1. In high concentrations, glycine can exhibit toxic effects on the cardiovascular and central nervous systems (including retinal neurotransmission) in addition to the effects of altered blood chemistry. The clinical findings associated with TUR syndrome are shown in Table 27.1.



TUR syndrome usually occurs only after more than 2 L of irrigating fluid have been absorbed into the circulation, but because this may occur as a result of fluid redistribution from perivesicular tissue planes into the vasculature, the onset of TUR syndrome may be delayed until some hours after surgery. In addition to the potential effects of fluid overload, the clinical features of TUR syndrome are those of decreased or altered consciousness and cardiovascular compromise. The most obvious biochemical abnormality is acute hyponatraemia. Acute haemolysis has also been associated with TUR syndrome, but is unlikely to occur with modern glycine solutions.


TUR syndrome is more likely to occur when higher irrigation pressures are used or if surgical resection is prolonged or extensive (e.g. if the prostate is very large or if perforation of the prostatic capsule occurs during surgery). Various attempts have been made to monitor the degree of fluid absorption, including adding ethanol to the irrigation fluid (in order to monitor exhaled ethanol concentrations), strict fluid input/output measurement, and semi-continuous weighing of the patient. None of these techniques has gained widespread acceptance because of the inherent difficulties associated with their use.

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May 31, 2016 | Posted by in ANESTHESIA | Comments Off on Anaesthesia for Gynaecological and Genitourinary Surgery

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