Kuo C Y, Gerhardt T, Bolivar J, Claure N, Bancalari E
University of Miami School of Medicine, Department of Pediatrics, FL 33101, USA.
Pediatr Pulmonol. 1996 Jul;22(1):35-43. doi: 10.1002/(SICI)1099-0496(199607)22:1<35::AID-PPUL6>3.0.CO;2-J.
We studied the effect of leaks around the endotracheal tube (ETT) on the measurement of pulmonary mechanics during mechanical ventilation. We also evaluated the influence of different ventilator settings on the magnitude of leak. An adjustable leak was created at the end of the ETT in a lung model with constant compliance. Flow, tidal volume, and pressure changes were measured above and below the leak. Compliance (Ci) and resistance (Ri) during inspiration were determined by linear regression analysis (LRA) using the equation of motion and the Mead and Wittenberger method (MWM). The ventilatory change that influenced the degree of leak most was prolongation of inspiratory time (Ti). The presence of a leak around the ETT resulted in an overestimation of the Ci and Ri values, which was proportional to the size of the leak. This overestimation was also influenced by the method used to determine Ci and Ri. Because the contribution of the leak to the fidal volume progressively increases as inspiration continued, methods of analysis that depended mainly on measurement points at the end of inspiration showed a larger deviation from the true Ci and Ri values than methods mainly influenced by measurement points at the beginning of inspiration. Because of this, shortening of inspiration, or analysis of points at the beginning of inspiration reduces the error in the measurements of Ci and Ri when a leak is present. Breaths with a large leak should be excluded from any analysis of pulmonary mechanics.
我们研究了气管内导管（ETT）周围漏气对机械通气期间肺力学测量的影响。我们还评估了不同呼吸机设置对漏气程度的影响。在具有恒定顺应性的肺模型中，在ETT末端制造了一个可调节的漏气。测量漏气上方和下方的流量、潮气量和压力变化。吸气期间的顺应性（Ci）和阻力（Ri）通过使用运动方程以及米德和维滕贝格尔方法（MWM）的线性回归分析（LRA）来确定。对漏气程度影响最大的通气变化是吸气时间（Ti）的延长。ETT周围存在漏气会导致Ci和Ri值被高估，且与漏气大小成正比。这种高估也受到用于确定Ci和Ri的方法的影响。由于随着吸气持续，漏气对潮气量的贡献逐渐增加，主要依赖吸气末期测量点的分析方法与真实的Ci和Ri值相比，偏差大于主要受吸气初期测量点影响的方法。因此，当存在漏气时，缩短吸气时间或分析吸气初期的点可减少Ci和Ri测量中的误差。任何肺力学分析都应排除漏气量大的呼吸。
