Randomized Comparison of Actual and Ideal Body Weight for Size Selection of the Laryngeal Mask Airway Classic in Overweight Patients

Size selection of the laryngeal mask airway (LMA) Classic based on actual body weight remains a common practice. However, ideal body weight might allow for a better size selection in obese patients. The purpose of our study was to compare the utility of ideal body weight and actual body weight when choosing the appropriate size of the LMA Classic by a randomized clinical trial. One hundred patients with age 20 to 70 yr, body mass index ≥25 kg/m2, and the difference between LMA sizes based on actual weight and ideal weight were allocated to insert the LMA Classic using either actual body weight or ideal body weight in a weight-based formula for size selection. After insertion of the device, several variables including insertion parameters, sealing function, fiberoptic imaging, and complications were investigated. The insertion success rate at the first attempt was lower in the actual weight group (82%) than in the ideal weight group (96%), even it did not show significant difference. The ideal weight group had significantly shorter insertion time and easier placement. However, fiberoptic views were significantly better in the actual weight group. Intraoperative complications, sore throat in the recovery room, and dysphonia at postoperative 24 hr occurred significantly less often in the ideal weight group than in the actual weight group. It is suggested that the ideal body weight may be beneficial to the size selection of the LMA Classic in overweight patients (Clinical Trial Registry, {"type":"clinical-trial","attrs":{"text":"NCT 01843270","term_id":"NCT01843270"}}NCT 01843270). Graphical Abstract Keywords: Airway Management, Laryngeal Masks, Body Weight, Complications INTRODUCTION Adequate size selection is of utmost importance in ensuring the performance and safety of supraglottic airway devices (1). In clinical practice, the manufacturers' guideline based on actual body weight is the most commonly used method for size selection of supraglottic airway devices due to easy identification of the weight range printed on the airway tube (2). However, this weight-related size selection may not be satisfactory in many patients because of the wide range of weights for each device size and individual anatomical variation (2,3,4). To address this issue, various alternative strategies for size selection have been suggested to replace weight-based size selection (3,4,5,6,7,8). Despite these efforts, prediction of the optimal size of devices remains tenuous and size determination for most supraglottic airway devices still depends on guidelines based on actual body weight. Obesity can influence pharyngeal structure and geometry (9). Previous articles have demonstrated that increased peri-pharyngeal fat disposition in obese patients results in a decreased upper airway size (10). As a result, in obsese patients, the supraglottic airway device selected by standard guidelines on actual body weight may be inadequately inserted in the much narrower upper airway. The concept of ideal body weight was first introduced for better estimation of drug clearance in patients with obesity (11). In the field of anesthesia, ideal body weight has frequently been applied to determine drug dose and tidal volume in obese patients (12,13). Therefore, we hypothesized that the ideal body weight might allow for a better size selection of supraglottic airway devices in obese patients. To validate our hypothesis, we compared the utility of ideal body weight and actual body weight in choosing the size of the laryngeal mask airway (LMA) Classic.