POSITIVE PRESSURE VENTILATION WITH THE SIZE-5 LARYNGEAL MASK

Study Objective: To obtain data about the safety and efficacy of the s ize 5 laryngeal mask airway (LMA), which is a scaled-up version of the size 4 and is generally recommended for patients over 90 kg, for posi tive pressure ventilation (PPV), ease of insertion, oropharyngeal and gastric insufflation pressures, fiberoptic positioning, and complicati on rates. Design: Prospective survey. Setting: Teaching hospital. Pati ents: 179 patients undergoing PPV with the size 5 LMA. Interventions: The clinical criteria for using the size 5 LMA and the PPV technique w ere weight above 90 kg or an inadequate seal with a size 4 LMA and sur gery estimated to last longer than 45 minutes. Anesthesia was standard ized and included fentanyl/propofol for induction, N2O/O-2/isoflurane 0.5% to 2% for maintenance, and atracurium for muscle relaxation. Two 20-second attempts were allowed with the standard recommended techniqu e, followed by a single attempt with the Guedel technique. The LMA cuf f was then inflated and the airway pressure at which either oropharyng eal leak or gastric insufflation occurred was determined by closure of the expiratory valve and anterior neck followed by epigastric auscult ation. Measurements and Main Results: The age and weight range were 15 to 82 years and 46 to 153 hg respectively. 29% of patients had a body mass index (BMI) above 30 kg/m(2). On 31 occasions the size 5 was use d following an inadequate seal with the size 4. The weight range of th is subgroup was 46 to 87 kg. The device was placed within 20 seconds i n 94% and there were no failed placements within three attempts. Gastr ic insufflation was detected before oropharyngeal leak in 17% and orop haryngeal leak was detected first in 73%. In 10% of patients there was no leak at an inspiratory pressure of 45 cm H2O. Mean (range) for gas tric insufflation pressure was 31 (range 23-45) cm H2O. Mean (range) f or oropharyngeal leak was 33 (range 8-44) cm H2O. The mean (range) air way pressure was 17 (range 13-26) at tidal volumes of 10 ml/kg. At thi s tidal volume, 97.2% of patients could be ventilated without gastric insufflation and 98.3% without an oropharyngeal bak. At tidal volumes of 8 ml/kg no patient had gastric insufflation and 0.7% had an orophar yngeal leak. Oropharyngeal leak pressure of less than 15 cm H2O occurr ed in 11 patients. There was no correlation between fiberoptic score o r Mallampati score and either gastric insufflation or oropharyngeal le ak. The incidence of problems was 3% and the oxygen saturation remaine d above 94%. There was no correlation between problems, leak pressures , and BMI. Conclusions: Positive pressure ventilation with the size 5 LMA is safe and effective with a low failure/problem rate using tidal volumes of 8 to 10 ml/kg; even in those patients who are moderately ob ese. The device is suitable for patients weighing under 90 kg in whom the seal with the size 4 is inadequate. (C) 1997 by Elsevier Science I nc.