• Anesthesia and analgesia · Jan 2020

    Comparative Study

    Performance of Air Seal of Flexible Reinforced Laryngeal Mask Airway in Thyroid Surgery Compared With Endotracheal Tube: A Randomized Controlled Trial.

    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.

    Concluding

    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.

    Hang on...

    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.

    Be smart

    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'.

    summary
    • Yahong Gong, Jin Wang, Xiaohan Xu, Jianjin Li, Ruiyue Song, and Jie Yi.
    • From the Department of Anesthesiology, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing, China.
    • Anesth. Analg. 2020 Jan 1; 130 (1): 217-223.

    BackgroundFlexible reinforced laryngeal mask airway (FLMA®) has gained popularity in thyroid surgery, but air leak and displacement are still concerns.MethodsIn this randomized, single-blinded, noninferiority, controlled trial, we randomized patients scheduled for elective radical thyroidectomy to an endotracheal tube (ETT) group or a FLMA group. The primary outcomes were ventilation leak volume, peak airway pressure, and partial pressure of end-tidal carbon dioxide (PetCO2). Data for primary outcomes were collected after insertion of ETT/FLMA, at incision, and at 10-minute intervals during surgery. Ten milliliters, 5 cm H2O, and 10 mm Hg were used as the noninferiority deltas for ventilation leak volume, peak airway pressure, and PetCO2, respectively. We assessed noninferiority of FLMA to ETT on the primary outcomes over time using the results of a linear mixed-effects model. The position of FLMA mask was evaluated before and after surgery, and the airway complications were recorded.ResultsA total of 132 patients were included: 65 in ETT group and 67 in FLMA group. Differences (FLMA group minus ETT group) of ventilation leak volume, peak airway pressure, and PetCO2 from the mixed-effects models were 2.09 mL (98.3% confidence interval [CI], -6.46 to 10.64), -0.60 cm H2O (98.3% CI, -2.15 to 0.96), and 1.02 mm Hg (98.3% CI, 0.04-1.99), respectively. Score of fiber-optic position of FLMA was significantly higher after surgery than before. There was no severe shift, loss of the mask seal, regurgitation, or aspiration in the FLMA group. One patient in the FLMA group experienced brief and easily controlled laryngospasm.ConclusionsIn thyroid surgery, FLMA is noninferior to ETT in the peak airway pressure and PetCO2 although mild to moderate mask shift could occur during surgical manipulation. There is no evidence for a higher complication rate when FLMA is used.

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    Notes

    summary
    1

    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.

    Concluding

    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.

    Hang on...

    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.

    Be smart

    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'.

    Daniel Jolley  Daniel Jolley
    pearl
    1

    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.

    Daniel Jolley  Daniel Jolley
     
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