Washko George R, O'Donnell Carl R, Loring Stephen H
Department of Anesthesia and Critical Care, Beth Israel Deaconess Medical Center, Boston, MA 02215, USA.
J Appl Physiol (1985). 2006 Mar;100(3):753-8. doi: 10.1152/japplphysiol.00697.2005. Epub 2005 Nov 23.
Ventilator management decisions in acute lung injury could be better informed with knowledge of the patient's transpulmonary pressure, which can be estimated using measurements of esophageal pressure. Esophageal manometry is seldom used for this, however, in part because of a presumed postural artifact in the supine position. Here, we characterize the magnitude and variability of postural effects on esophageal pressure in healthy subjects to better assess its significance in patients with acute lung injury. We measured the posture-related changes in relaxation volume and total lung capacity in 10 healthy subjects in four postures: upright, supine, prone, and left lateral decubitus. Then, in the same subjects, we measured static pressure-volume characteristics of the lung over a wide range of lung volumes in each posture by using an esophageal balloon catheter. Transpulmonary pressure during relaxation (PLrel) averaged 3.7 (SD 2.0) cmH2O upright and -3.3 (SD 3.2) cmH2O supine. Approximately 58% of the decrease in PLrel between the upright and supine postures was due to a corresponding decrease in relaxation volume. The remaining 2.9-cmH2O difference is consistent with reported values of a presumed postural artifact. Relaxation volumes and pressures in prone and lateral postures were intermediate. To correct estimated transpulmonary pressure for the effect of lying supine, we suggest adding 3 cmH2O (95% confidence interval: -1 to +7 cmH2O). We conclude that postural differences in estimated transpulmonary pressure at a given lung volume are small compared with the substantial range of PLrel in patients with acute lung injury.
了解患者的跨肺压有助于更好地做出急性肺损伤中的呼吸机管理决策，跨肺压可通过食管压力测量来估算。然而，食管测压很少用于此目的，部分原因是推测在仰卧位存在体位性伪影。在此，我们描述健康受试者中体位对食管压力影响的大小和变异性，以更好地评估其在急性肺损伤患者中的意义。我们测量了10名健康受试者在四种体位（直立位、仰卧位、俯卧位和左侧卧位）下松弛容积和肺总量的体位相关变化。然后，在同一受试者中，我们使用食管球囊导管在每个体位的广泛肺容积范围内测量肺的静态压力-容积特性。直立位时松弛期跨肺压（PLrel）平均为3.7（标准差2.0）cmH2O，仰卧位时为-3.3（标准差3.2）cmH2O。直立位和仰卧位之间PLrel下降的约58%是由于松弛容积相应减少所致。其余2.9 cmH2O的差异与报道的推测体位性伪影值一致。俯卧位和侧卧位的松弛容积和压力介于两者之间。为校正仰卧位对估算跨肺压的影响，我们建议增加3 cmH2O（95%置信区间：-1至+7 cmH2O）。我们得出结论，与急性肺损伤患者PLrel的较大范围相比，给定肺容积下估算跨肺压的体位差异较小。
