Brimacombe J R
Department of Anaesthesia and Intensive Care, Cairns Base Hospital, Australia.
J Clin Anesth. 1997 Mar;9(2):113-7. doi: 10.1016/S0952-8180(97)00233-X.
To obtain data about the safety and efficacy of the size 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 positive pressure ventilation (PPV), ease of insertion, oropharyngeal and gastric insufflation pressures, fiberoptic positioning, and complication rates.
Prospective survey.
Teaching hospital.
179 patients undergoing PPV with the size 5 LMA.
The clinical criteria for using the size 5 LMA and the PPV technique were weight above 90 kg or an inadequate seal with a size 4 LMA and surgery estimated to last longer than 45 minutes. Anesthesia was standardized and included fentanyl/propofol for induction, N2O/O2/isoflurane 0.5% to 2% for maintenance, and atracurium for muscle relaxation. Two 20-second attempts were allowed with the standard recommended technique, followed by a single attempt with the Guedel technique. The LMA cuff was then inflated and the airway pressure at which either oropharyngeal leak or gastric insufflation occurred was determined by closure of the expiratory valve and anterior neck followed by epigastric auscultation.
The age and weight range were 15 to 82 years and 46 to 153 kg, respectively. 29% of patients had a body mass index (BMI) above 30 kg/m2. On 31 occasions the size 5 was used following an inadequate seal with the size 4. The weight range of this subgroup was 46 to 87 kg. The device was placed within 20 seconds in 94% and there were no failed placements within three attempts. Gastric insufflation was detected before oropharyngeal leak in 17% and oropharyngeal 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 gastric insufflation pressure was 31 (range 23-45) cm H2O. Mean (range) for oropharyngeal leak was 33 (range 8-44) cm H2O. The mean (range) airway pressure was 17 (range 13-26) at tidal volumes of 10 ml/kg. At this tidal volume, 97.2% of patients could be ventilated without gastric insufflation and 98.3% without an oropharyngeal leak. At tidal volumes of 8 ml/kg no patient had gastric insufflation and 0.7% had an oropharyngeal leak. Oropharyngeal leak pressure of less than 15 cm H2O occurred in 11 patients. There was no correlation between fiberoptic score or Mallampati score and either gastric insufflation or oropharyngeal leak. The incidence of problems was 3% and the oxygen saturation remained above 94%. There was no correlation between problems, leak pressures, and BMI.
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 obese. The device is suitable for patients weighing under 90 kg in whom the seal with the size 4 is inadequate.
获取有关5号喉罩气道（LMA）安全性和有效性的数据，5号喉罩是4号喉罩的放大版本，一般推荐用于体重超过90千克的患者，用于正压通气（PPV）、插入的难易程度、口咽和胃内充气压力、纤维支气管镜定位及并发症发生率。
前瞻性调查。
教学医院。
179例使用5号喉罩进行正压通气的患者。
使用5号喉罩的临床标准及正压通气技术为体重超过90千克或使用4号喉罩密封不佳且预计手术持续时间超过45分钟。麻醉标准化，诱导使用芬太尼/丙泊酚，维持使用N₂O/O₂/0.5%至2%异氟烷，使用阿曲库铵进行肌肉松弛。允许按照标准推荐技术进行两次20秒的尝试，然后使用格德尔技术进行一次尝试。然后给喉罩气囊充气，通过关闭呼气阀并按压前颈部随后进行上腹部听诊来确定出现口咽漏气或胃内充气时的气道压力。
年龄范围为15至82岁，体重范围为46至153千克。29%的患者体重指数（BMI）高于30kg/m²。31例患者在使用4号喉罩密封不佳后使用了5号喉罩。该亚组的体重范围为46至87千克。94%的患者在20秒内放置好喉罩，三次尝试内无放置失败情况。17%的患者在口咽漏气前检测到胃内充气，73%的患者首先检测到口咽漏气。10%的患者在吸气压力为45cmH₂O时无漏气。胃内充气压力的平均值（范围）为31（23至45）cmH₂O。口咽漏气压力的平均值（范围）为33（8至44）cmH₂O。潮气量为10ml/kg时气道压力的平均值（范围）为17（13至26）。在此潮气量下，97.2%的患者通气时无胃内充气，98.3%的患者通气时无口咽漏气。潮气量为8ml/kg时，无患者出现胃内充气，0.7%的患者出现口咽漏气。11例患者口咽漏气压力小于15cmH₂O。纤维支气管镜评分或马兰帕蒂评分与胃内充气或口咽漏气之间无相关性。问题发生率为3%，氧饱和度保持在94%以上。问题、漏气压力与BMI之间无相关性。
使用8至10ml/kg潮气量时，5号喉罩进行正压通气安全有效，失败/问题发生率低，即使在中度肥胖患者中也是如此。该装置适用于体重不足90千克且使用4号喉罩密封不佳的患者。
