Froessler B, Brommundt J, Anton J, Khanduja R, Kuhlen R, Rossaint R, Coburn M
Department of Anaesthesia, Lyell McEwin Hospital, Haydown Road, 5112 Elizabeth Vale, South Australia.
Anaesthesist. 2010 Nov;59(11):1003-4, 1006-7. doi: 10.1007/s00101-010-1764-0. Epub 2010 Sep 11.
Spontaneous ventilation is a popular mode of ventilation for patients with the laryngeal mask airway (LMA). Studies have shown, however, that spontaneous ventilation impairs gas exchange and that assisting or controlling ventilation results in higher oxygen saturation. Atelectasis during general anesthesia is a well described mechanism which impacts on gas exchange. Positive end-expiratory pressure (PEEP) increases the lung volume available for gas exchange. This study investigated whether the application of PEEP leads to an improvement of oxygen saturation in unassisted spontaneously breathing patients with a LMA. A total of 80 adult patients under general anesthesia were prospectively randomized into two groups. Both groups were left to breathe spontaneously. In group 1 the adjustable pressure limiting (APL) valve was opened resulting in zero end-expiratory pressure. In group 2 the valve was set to a PEEP of +7 cm H₂O. Oxygen saturation was measured by pulse oxymetry at four different phases: pre-induction, after induction and insertion of the LMA, during maintenance and in recovery. The application of PEEP did not improve oxygen saturation. In both groups the mean oxygen saturation was similar (97.2±1.8% in group 1 versus 97.2±1.9% in group 2, p=0.941) during maintenance. No effect on oxygen saturation in recovery could be found either (96.0±1.8% in group 1 versus 96.1±2.0% in group 2, p=0.952) and hemodynamics were unaffected by the application of PEEP. The application of a PEEP of +7 cm H₂O with a LMA under spontaneous ventilation cannot be recommended. Limitations of our study were the selection of healthy patients and omitting pre-oxygenation before induction which might have limited the development of atelectasis. In addition arterial partial pressure of oxygen (p(a)O₂) measurements could have revealed subtle changes in oxygenation.
自主通气是喉罩气道（LMA）患者常用的通气模式。然而，研究表明，自主通气会损害气体交换，而辅助通气或控制通气可使氧饱和度更高。全身麻醉期间的肺不张是一种已被充分描述的影响气体交换的机制。呼气末正压（PEEP）可增加可用于气体交换的肺容积。本研究调查了在使用LMA的自主呼吸患者中应用PEEP是否能提高氧饱和度。总共80例全身麻醉下的成年患者被前瞻性随机分为两组。两组均让患者自主呼吸。第1组打开可调压力限制（APL）阀，使呼气末压力为零。第2组将阀设置为+7 cm H₂O的PEEP。通过脉搏血氧饱和度仪在四个不同阶段测量氧饱和度：诱导前、诱导并插入LMA后、维持期间和恢复期间。应用PEEP并未提高氧饱和度。在维持期间，两组的平均氧饱和度相似（第1组为97.2±1.8%，第2组为97.2±1.9%，p = 0.941）。在恢复过程中也未发现对氧饱和度有影响（第1组为96.0±1.8%，第2组为96.1±2.0%，p = 0.952），并且血流动力学不受PEEP应用的影响。不建议在自主通气下使用LMA时应用+7 cm H₂O的PEEP。我们研究的局限性在于选择了健康患者，且诱导前未进行预给氧，这可能限制了肺不张的发生。此外，动脉血氧分压（p(a)O₂）测量可能会揭示氧合的细微变化。
