Why is this important?
Indications for the use of laryngeal mask airways (LMAs) increasingly challenge our airway choice for surgical procedures where endotracheal intubation has been the norm. Thyroid surgery, with its limited anaesthetic access to the airway and potential for airway obstruction, has not typically been a first choice for LMA use.
Proponents point to avoiding muscle relaxants and reducing throat pain and laryngeal trauma as the main benefits.
What did they do?
Gong and team randomised 138 ASA 1 & 2 adults to either flexible (reinforced) LMA or intubation with an ETT (7.0 or 7.5 mm). Notably any patients with surgical complexity or BMI > 30 kg/m2 were excluded. The study was single-blinded.
The researchers reported the upper 95%-CI for estimated mean difference in peak airway pressure as +0.96 cmH2O, and for endtidal-CO2 +1.99 mmHg – neither of which are clinically significant.
They concluded that flexible-LMA was non-inferior to ETT in terms of PAP and ET-CO2.
The relevance of this study to most thyroid surgical patients is however limited at best. Not only were common groups of patients excluded (ie. BMI > 30) but one of the major arguments for LMA use (avoiding muscle relaxants) was irrelevant: all patients were paralysed with rocuronium.
Further, in 7% of the LMA cases severe air-leak occured and the surgical team were asked to cease or reduce tracheal traction.
Although the journal editors conclude in their Key Points that "FLMA is a safe alternative for experienced anesthesiologists in thyroid surgery" this seems quite a stretch given that this small study was neither powered for safety and only investigated airway ventilation performance as a narrow surrogate for acceptability.
Additionally the authors themselves highlight very real surgical concerns that LMA use can distort pharyngeal anatomy with serious consequences.
Not dissimilar to arguments for LMA use in GA caesarean section, the use of an LMA for thyroid surgery edges toward 'just because we can, does not mean we should'.
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Using a flexible reinforced laryngeal mask is non-inferior to endotracheal intubation for thyroid surgery when considering only peak airway pressure and end-tidal CO2.
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