Effect of Laryngeal Mask Cuff Shape on Pharyngeal Stress

Anesthesia, General, Airway Management, Postoperative Sore Throat

laryngeal mask airway, supraglottic airway device, cuff design, haemodynamic response, pharyngeal morbidity, SaCoVLM, LMA Supreme, Ambu AuraGain

Laryngeal masks are widely used supraglottic airway devices, but their cuffs differ considerably in shape and design. The cuff exerts pressure on the pharyngeal structures, which may provoke a physiological stress response and contribute to postoperative pharyngeal complaints. This prospective, randomized, two-centre trial compares three commercially available laryngeal masks with different cuff designs (SaCoVLM, LMA Supreme and Ambu AuraGain) in 162 adult patients undergoing elective surgery under general anaesthesia. Anaesthesia induction is standardized and guided by State Entropy, and cuff pressure is standardized to 40-50 cmH2O in all groups. The primary outcome is the change in mean arterial pressure after laryngeal mask insertion. Secondary outcomes include heart rate, nociception and depth-of-anaesthesia indices (Surgical Pleth Index, Response Entropy - State Entropy difference), insertion characteristics, oropharyngeal leak pressure and postoperative pharyngolaryngeal complaints up to 24 hours. The hypothesis is that cuff shape modifies the stress exerted on the pharynx and thereby influences the patient's stress response.

Design: prospective, randomized, controlled, parallel-group (1:1:1), two-centre trial (Masaryk Hospital Usti nad Labem and Decin Hospital, Krajska zdravotni, a.s., Czech Republic). Allocation is based on a computer-generated randomization sequence. Participants: 162 adult patients (ASA physical status I-II) scheduled for elective surgery under general anaesthesia with a laryngeal mask airway, randomized to SaCoVLM, LMA Supreme or Ambu AuraGain (54 patients per group). Blinding: patients (anaesthetized during device insertion) and outcome assessors in the post-anaesthesia care unit and at the 24-hour follow-up are blinded to group allocation. The anaesthesiologist inserting the device cannot be blinded because the devices are visibly different. Investigators: all devices are inserted by board-certified anaesthesiologists with at least 5 years of practice and more than 4,000 documented general anaesthetics. Anaesthesia protocol: standardized induction with sufentanil 0.3 ug/kg ideal body weight and propofol up to 3 mg/kg titrated to a State Entropy of 40-60. Depth of anaesthesia is maintained at a State Entropy of 40-60. No neuromuscular blocking agents are administered before or during the haemodynamic measurement period; they may be used later during surgery if required. Device size is selected according to the manufacturer's recommendations. After insertion, cuff pressure is measured with a manometer and adjusted to 40-50 cmH2O, below the manufacturers' maximum recommended pressure of 60 cmH2O. Measurements: mean arterial pressure, heart rate, Surgical Pleth Index (SPI), State Entropy (SE) and Response Entropy (RE) are recorded before laryngeal mask insertion (baseline, at SE 40-60), immediately after insertion, and 5 and 10 minutes after insertion. The number of insertion attempts, need for airway manipulation and oropharyngeal leak pressure are recorded. After device removal, sore throat (VAS), hoarseness, blood staining of the device, coughing and postoperative nausea and vomiting are assessed until discharge from the post-anaesthesia care unit and at 24 hours. Sample size: a between-group difference of 10% of baseline mean arterial pressure (MAP; approximately 8.2 mmHg at a baseline of 82 mmHg) was considered clinically relevant. The standard deviation of MAP after laryngeal mask insertion was estimated at 12 mmHg, derived from the systolic and diastolic blood pressures reported 5 minutes after LMA Supreme insertion (Iran Red Crescent Med J, doi:10.5812/ircmj.28615) and consistent with the MAP variability reported by Montazari et al. (Acta Med Iran 2004;42:437-440). With a two-sided alpha of 0.0167 (Bonferroni correction for three pairwise comparisons) and 80% power, 47 patients per group are required; allowing for a 10% drop-out rate, 54 patients per group (162 in total) will be enrolled.

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