The evolving role of the laryngeal mask airway in obstetrics.

Abstract

HI Sedition of the Journal contains a repor t that can be considered as astounding in tw o regards: first, that 1067 healthy women fo r elective Cesarean section were given a gene ral anesthetic (GA); and second, a laryngeal mask airwa y (LMA) was used for airway management/ventilation . 1 Both practices go against the mantra that obstetric ane sthesiologists have been teaching for the past 15 years: us e regional anesthesia and protect the obstetric airway . The reasons for this mantra are well-founded . Anesthesia is still a notable cause of maternal mortality . Although the British “Why Mothers Die”, publishe d for the triennium 1994–1996, showed a large improv e ment in anesthesia-related mortality , 2 Joy Hawkins ’ 1997 statistics from the USA showed GA to be 1 6 times more lethal than regional anesthesia in the pa rturient . 3 Some of this large difference in risk is definit e ly attributable to the fact that GA is more likely to b e used in emergency situations. It is also true, however , that regional anesthesia is a very safe and effective ane sthetic for Cesarean section. The majority of anesthesia related maternal deaths worldwide are secondary t o aspiration and/or failed intubation . 2– 4 There is no que stion that endotracheal tubes (ETT) are not the perfec t means to prevent aspiration or failure to ventilate – indeed the ETT and these two complications are ine x tricably intertwined. Maternal enquiries consistentl y find that, in inexperienced hands, the ETT can be fatal . In fact, there is a concern that anesthesiologists are lo sing their skills in providing general ETT anesthesia i n the pregnant woman, and that is contributing to th e wide difference in risk attributable to general anesthesi a v sregional. Of course, we cannot always use regiona l anesthesia, and must therefore have the capability an d means to provide safe general anesthesia . In this issue, Han et al. publish the results of thei r prospective study of 1067 parturients and conclude tha t “the LMA is effective and probably safe for electiv e Cesarean section”. Why so shocking? Ever sinc e Mendelson’s publication in 1946, where gastric aspir a tion syndrome was described in parturients undergoin g GA with an unprotected airway , 5 anesthesiologists hav e been diligent in teaching that protection of the pregnan t airway is vital . The purpose of Han’s study was to show that in th e hands of experienced operators, the LMA could provid e a safe and effective airway in a population classicall y considered to be at increased risk of aspiration. W e know pregnant women have many reasons to have a “full stomach”: hormonal changes that effect lowe r esophageal sphincter tone; gastric acid production ; motility changes; the physical effects of the enlarge d uterus; and effect of labour pain and narcotics on ga stric emptying. Admittedly, the appropriately fasted ele c tive C-section patient with no overt symptoms of reflu x is at the low end of the risk scale. But, rather tha n focussing on absence of reflux/regurgitation/aspir a tion and ease of ventilation, the authors instead co n centrated on minor issues such as ease of insertion , minimal sore throat, and smooth emergence . The study population was carefully selected: slim (average pregnancy weight of 67 kg), fully fasted for si x hours, no clinical history of reflux or hiatus hernia, an d prophylaxed with antacids. They had optimal anesthesi a present upon insertion of the LMA, including the us e of muscle relaxation. Cricoid pressure was used, bu t there is no data on the frequency with which it had t o be relaxed to facilitate LMA insertion or ventilation . The prolonged use of cricoid pressure – in this cas e until delivery – is unlikely to provide any real “prote c tion” against passive reflux . 6 In 98% of patients th e LMA was inserted on the first attempt, which is a n important point to keep in mind. Insertion of a LM A during light anesthesia may predispose to regurgitatio n and aspiration – the situation one is likely to encounte r during a failed intubation/ventilation case . 7 Han’s study shows no clinically apparent aspiration a t discharge from the postanesthesia care unit. But, give n