Knotts Derek, Arthur Annette O, Holder Peyton, Herrington Tim, Thomas Stephen H
Department of Emergency Medicine, University of Oklahoma School of Community Medicine and Hillcrest Medical Center, Tulsa, OK 74104, USA.
Air Med J. 2013 May-Jun;32(3):138-43. doi: 10.1016/j.amj.2012.10.014.
In accordance with Boyle's law (as barometric pressure decreases, gas volume increases), thoracostomy is often recommended for patients with pneumothoraces before helicopter EMS (HEMS) transport. We sought to characterize altitude-related volume changes in a pneumothorax model, aiming to improve clinical decisions for preflight thoracostomy in HEMS patients.
This prospective study used 3 devices to measure air expansion at HEMS altitudes. The main device was an artificial pneumothorax model that mimicked a human pulmonary system with a 40 mL pneumothorax. In addition, volume changes were calculated in 2 spherical balloons (6 L and 25 L) by measuring equatorial circumferences. Measurements were recorded at 500-foot altitude increments from 1000 to 5000 feet above ground level.
The 3 models exhibited volume increases of 12.7%-16.2% at 5000 feet compared to ground level. Univariate linear regression yielded similar increases, 1.27%-1.52%, in volume per 500-foot altitude increase for all 3 models. Bivariate indexed linear regression identified no association between volume increase and assessment model (P values .19 and .29). Locally weighted scatterplot smoothing (lowess) plots indicated linearity of the altitude-volume relationship.
This study demonstrated predictable pneumothorax volume changes at typical HEMS altitudes. Increased understanding of altitude-related volume changes will aid decision making before transport.
根据玻意耳定律（气压降低时，气体体积增大），对于气胸患者，通常建议在直升机紧急医疗服务（HEMS）转运前进行胸腔造口术。我们试图描述气胸模型中与海拔相关的体积变化，旨在改善HEMS患者飞行前胸腔造口术的临床决策。
这项前瞻性研究使用3种装置测量HEMS海拔高度下的空气膨胀情况。主要装置是一个人工气胸模型，其模拟了一个有40 mL气胸的人体肺部系统。此外，通过测量赤道周长计算了2个球形气球（6 L和25 L）的体积变化。测量在海拔从地面1000英尺到5000英尺，以500英尺的增量进行记录。
与地面水平相比，这3个模型在5000英尺处的体积增加了12.7%-16.2%。单变量线性回归得出所有3个模型每升高500英尺体积增加相似，为1.27%-1.52%。双变量指数线性回归确定体积增加与评估模型之间无关联（P值分别为0.19和0.29）。局部加权散点图平滑（lowess）图表明海拔-体积关系呈线性。
本研究证明了在典型的HEMS海拔高度下气胸体积变化是可预测的。对与海拔相关的体积变化的进一步了解将有助于转运前的决策制定。
