Lipid Emulsion for Reversal of Spinal Anesthesia in Ambulatory Surgery

Overview

Ambulatory surgery places high demands on anesthetic technique. rapid onset and offset of anesthesia, rapid recovery of protective reflexes, mobility and micturition, are required. Since the inception of ambulatory surgery, the favored anesthetic technique has been general anesthesia with short-acting drugs. Concerns about the time to perform spinal anesthesia and the risks of prolonged motor block and urinary retention have limited its use. Alpha-blockers, lavage fluids for epidural space, insulin, and intravenous lipid emulsions, are still being discussed to shorten and reverse adverse effect of different LAs used for spinal anaesthesia, hence we will evaluate the effectiveness of intravenous lipid emulsion for reversing the neural blockade of spinal anaesthesia in patients undergoing ambulatory surgery.

An increasing number of ambulatory surgical patients is challenging the currently used anaesthesia methods, reliable surgical anaesthesia should be quick, with rapid recovery and minimal side effects. Spinal anaesthesia (SA) is an easy and reliable technique that has grown in popularity for inpatient surgery, but its use in ambulatory surgery has been limited due to several factors including the prolonged neurological block with long-acting local anaesthetics (LA), delayed ambulation, risk of urinary retention and pain after block regression therefore delaying patient discharge. On the other hand, general anaesthesia with short-acting drugs grants rapid recovery enabling the early discharge. While recovery after spinal anaesthesia has been recently improved by lowering the dose of the commonly used long-acting local anaesthetics such as bupivacaine, discharge times are still prolonged compared to general anaesthesia. Intravenous lipid emulsions (ILEs) were originally developed as a part of parenteral nutrition for critically ill patients, dating back to the 1960s. Over the last ten years, there has been rising interest in ILEs in clinical toxicology beyond its established role in the treatment of acute intoxication with local anaesthetics (LAST). The use of ILEs for the treatment of lipophilic drug toxicity is increasing nowadays with several studies reported alleviation of intractable cardiovascular collapse induced by toxic doses of these non-local anaesthetic drugs including calcium channel blockers (verapamil), tricyclic antidepressants (amitriptyline) and beta-blockers. In addition, Complications following intrathecal administration of bupivacaine have been reported to be successfully managed with intravenous administration of lipid emulsion. While the precise mechanism by which ILEs exerts its effect remains unknown, the leading theory is that the ILEs intravascular action entails creating a concentration gradient which favours LA redistribution to the extracellular space. Lipid vesicles then encapsulate LA creating lipid sinks and the formation of this "trap" removes the toxins from the various tissues and organs, reducing their bioavailability and the sequestration mechanism where LA is rapidly redistributed by "lipid shuttles" to sites of metabolism (liver), storage (adipose tissue) or elimination (kidney). Alternative theories include reduced binding of local anaesthetics to sodium transport channels, direct promotion of sodium channel function recovery, and replenishing ATP stores from increased uptake of fatty acids by mitochondria. Considering the few published reports supporting the effectiveness of ILEs in reversing the primary nervous system effects of regional anaesthesia such as total or high spinal anaesthesia, prolonged neural blockade, and reverse phrenic nerve palsy secondary to a brachial plexus block with the well-known favourable safety profile of ILEs. We hypothesized that ILEs could be an attractive effective option to reverse the sensory and motor actions of intrathecal bupivacaine thus accelerating the neurological recovery after spinal anaesthesia which could avert the delayed hospital discharge and facilitate the use of SA for ambulatory surgeries.