EXPLORE PAST ISSUES
In Theatre
Vol. 21 No 3 | Spring 2019
Feature
Providing anaesthesia in gynaecological surgery
Dr Alexandra Hill
FANZCA trainee
Dr Nam Le
MBBS, FANZCA, GCertHealthProfEd

Much like for the aviation industry, the community expectation in a developed country such as Australia is for perioperative anaesthetic to be low risk. It is fortunate that, due to the high quality of anaesthetic and gynaecological training and practice in Australia, that modern-day perioperative risk is indeed low. To achieve these positive outcomes, anaesthetists must consider a multitude of specific issues pertaining to the patient and the planned surgical procedure. This is particularly so for gynaecological surgery as it encompasses a broad range of procedure types, operative duration, complexity and associated risk. There are often anaesthesia-gynaecological compromises that need to be reached through good communication and discussion in order to achieve safe and effective surgical outcomes (such as the opposing desires for the degree of Trendelenburg during laparoscopic surgery).

In this article, we will summarise some of the major anaesthesia-related gynaecological issues facing the perioperative team for routine elective gynaecological surgery.

Airway management

At the induction of anaesthesia, mask ventilation of the patient by hand prior to endotracheal intubation or laryngeal mask insertion is routine. During this mask ventilation, inadvertent insufflation of the stomach with gas may occur. This can result in increased risk of gastric perforation during laparoscopic entry, particularly with the Palmer’s point. Communication between the anaesthetist and the gynaecologist is essential, with recognition of difficult mask ventilation and pre-emptive emptying of the stomach with an orogastric tube.

Pneumoperitoneum

Pressurised insufflation of gas into the peritoneal cavity causes visceral stretch that may result in vagal effects, such as bradycardia, which may be so profound as to be interpretable as asystole. Management is via anticholinergic agents, such as atropine, releasing the pneumoperitoneum and CPR (if only to circulate the anticholinergic agents). These effects are usually transient and may be prevented with judicious use of pre-emptive anticholinergics, particularly when vagal effects are noted on ECG, even with innocuous stimuli (such as when cleaning the umbilicus prior to access).

Venous air embolism, a potentially fatal complication, may result from inadvertent pressurised gas insufflation of a vascular structure during creation of pneumoperitoneum. An anaesthetist’s first recognition of this event may be only moments after commencement of insufflation, through a sudden and progressive reduction in end-tidal CO2 observable on the anaesthetic monitor. This abnormal decrease in expired CO2 is produced via occlusion of pulmonary vessels with insufflation gas preventing normal CO2 transfer to the patient’s expired gases. Venous air embolism may also present as arrhythmia, hypotension and hypoxia. In the worst cases, a large volume of gas reaching the heart may produce an ‘air-lock’ which prevents forward flow of blood from the right ventricle to pulmonary circulation and will result in cardiac arrest. Management of this event includes immediate cessation of gas insufflation, support of the circulation with fluids and vasopressors, repositioning to the left lateral position to keep gas in the right atrium, and CPR to maintain cardiac output, which may also potentially break up the ‘air-lock’.

Prolonged laparoscopic surgery, especially with significant operative intervention (such as high-grade endometriosis) results in progressive circulatory uptake of the CO2 that has been instilled into the peritoneum, which is highly soluble in the blood. Greater than physiological minute ventilation is often required, which may be challenging to achieve in obese patients in the Trendelenburg position as the abdominal contents encroach upon the thoracic structures, reducing lung compliance and pulmonary functional residual capacity. Resultant relative hypoventilation may produce hypercarbia, respiratory alkalosis, cardiac arrhythmia, decreased cardiac contractility, cerebral oedema and narcosis. In patients with significant cardiorespiratory disease, laparoscopy may not be appropriate, necessitating laparotomy.

Positioning

Trendelenburg positioning may result in gastric juice regurgitation which, due to gravity, may flow from the oral cavity towards the eyes that may result in conjunctival and corneal damage. Hence the use of occlusive eye tapes (such as Tegaderm) is often used.

Increased hydrostatic pressure in the body areas below the heart (such as the head and neck when in Trendelenburg) may result in laryngeal oedema, which can present as stridor and acute airway obstruction post extubation. Anaesthetists often exercise caution after prolonged Trendelenburg positioning and perform a ‘cuff-leak test’ where the endotracheal cuff is deflated and a leak of inspiratory gas around the endotracheal tube is sought prior to extubation. If a leak is not present, the anaesthetist may reposition the patient sitting up for a period of time, or potentially delay extubation by transferring the patient to an intensive care setting to allow airway swelling to subside slowly.

Laparoscopy in lithotomy (especially when combined with Trendelenburg) increases the risk of lower limb ischaemia secondary to increased lower limb venous pressures combined with reduced lower limb arterial pressures due to hydrostatic forces. Lower limb compartment syndrome may occur rarely, particularly in the presence of poorly positioned stirrups causing excessive pressure on the calves.

Extreme Trendelenburg positioning may also carry risk of the patient slipping and associated neurological injury, particularly if the legs are in lithotomy. It is often useful for anaesthetists to use an electronic inclinometer (most modern smartphones have this functionality built-in) in order to monitor and negotiate degree of Trendelenburg.

Indicator dyes

Where ureteric injury is suspected, anaesthetists are occasionally requested to administer intravenous indicator dyes such as indigo carmine. All such agents are associated with anaphylaxis, hypotension and a transient false decrease in oxygen saturation when measured with pulse oximetry.

Reversal agents

Most laparoscopic procedures require the anaesthetist to provide muscle relaxant medications in order to provide a near-motionless operative field. These medications require reversal prior to emergence. Sugammadex is one such reversal agent and is unique in that it may bind certain drugs, including hormonal contraceptives. Accordingly, women using oral contraceptive medications who have received intraoperative sugammadex require counselling and must use an additional non-hormonal contraceptive method for seven days postoperatively to maintain contraception. It is important to note that this effect is unique to sugammadex and does not occur with other more commonly used reversal agents, such as neostigmine.

Hysteroscopic surgery

Operative hysteroscopic procedures, especially in the setting of prolonged surgery with high distention pressures, may be associated with inadvertent circulatory uptake of distention fluids such as glycine. Excessive uptake may result in fluid overload and hyponatremia. In worst cases, potentially fatal pulmonary and cerebral oedema may occur. Prevention is via close monitoring of fluid balance for distension fluids instilled, minimisation of distension pressures and monitoring of arterial blood sodium levels.

Recovery

Many patients presenting for gynaecological surgery suffer from chronic pain and may be tolerant of opioids due to chronic use. Frequently, acute-on-chronic post-surgical pain is difficult to manage and unexpected admissions for day surgery patients due to this complication are common. Opioid-tolerant patients should be managed with multimodal analgesia while taking into account their baseline opioid requirement. Regional analgesia is a useful adjunct in severe cases. Where chronic pain is an issue, anaesthetists will often discuss the analgesic management with the patient’s pain specialist.

Postoperative nausea and vomiting (PONV) is also frequent and is another cause of unexpected admission after day surgery. Of the commonly recognised risk factors for PONV (female, past history of PONV or motion sickness, non-smoker, emetogenic surgery such as gynaecological surgery and postoperative opioid use) gynaecological patients will often have many, if not all, risk factors. Management of PONV is via risk stratification and pre-emptive management where PONV is likely (such as pre-emptive intraoperative antiemetics, choosing anaesthesia techniques associated with less PONV, such as propofol infusion based anaesthesia, as well as avoidance of emetogenic agents such as nitrous oxide).


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