Fewer sore throats and a better seal: why routine manometry for laryngeal mask airways must become the standard of care

We have three decades of experience with the laryngeal mask airway (LMA) [1], yet most of us do not use it optimally. This is despite accumulating evidence of detrimental effects from cuff overinflation, i.e. postoperative sore throats from mucosal tissue injury and impairment of its primary function, the airway seal. In 1983, Brain described ventilating the lungs of 23 patients for gynaecological procedures with a new airway device [2]. By gently titrating the cuff volume (as little as 7 ml), he found a good seal with little morbidity; only three (13%) patients suffered a mild sore throat. Today, the LMA has become the airway of choice for the majority of anaesthetics and is perceived as easy to insert and with minimal potential for harm. In our experience, insertion and inflation technique are often imparted without recourse to evidence, or even to the instruction leaflet. Here, we concentrate on one aspect of its use: what volume of air should we inject into the LMA’s cuff? Usually, this will be the ‘recommended’ volume or, frequently, whatever our assistant decides. Thirty years later, the rate of sore throat is not 13% but nearer 50% [3]. What are we doing, or rather not doing, that the inventor did? Since 1988, the instructions have advised that cuff pressures should never exceed 60 cmH2O [4–6]. Despite this, clinical practice has tended to follow the ‘recommended’ (in fact maximum) volumes. These are laminated on anaesthetic room walls and recited for the examinations. Videos on YouTube explain that a size-4 LMA needs 30 ml air – no more, no less, no debate [7]. The message is that the LMA is simple and requires little attention to detail. It seems our aim is simply to restore the cuff back to its fully distended shape, since that’s what we believe it should be in vivo. However, mounting evidence over the last 20 years tells a different story. The painful truth is that we clinicians are needlessly overinflating LMA cuffs, impairing their function and giving half of our patients sore throats. We know this is the case: LMA cuff pressures frequently form the subject of trainee audits and consistently show that the vast majority of LMAs are overinflated (> 60 cmH2O). In some reports, 70% of LMAs were overinflated and, in one, a staggering 97% [8, 9]. We recently conducted a national questionnaire that revealed that anaesthetists in the UK are not routinely checking LMA cuff pressures. Furthermore, clinicians were generally unaware of correct inflation pressures (unlike maximum recommended volumes) and half of the respondents were unaware of any evidence for potential harm. It is clear that misconceptions persist surrounding the use of the LMA. Below we aim to debunk some of these myths.