Hoftman Nir, Eikermann Eric, Shin John, Buckley Jack, Navab Kaveh, Abtin Fereidoun, Grogan Tristan, Cannesson Maxime, Mahajan Aman
From the Departments of Anesthesiology and Perioperative Medicine.
Radiology.
Anesth Analg. 2017 Dec;125(6):1922-1930. doi: 10.1213/ANE.0000000000001885.
Tidal volume selection during mechanical ventilation utilizes dogmatic formulas that only consider a patient's predicted body weight (PBW). In this study, we investigate whether forced vital capacity (FVC) (1) correlates better to total lung capacity (TLC) than PBW, (2) predicts low pulmonary compliance, and (3) provides an alternative method for tidal volume selection.
One hundred thirty thoracic surgery patients had their preoperative TLC calculated via 2 methods: (1) pulmonary function test (PFT; TLCPFT) and (2) computed tomography 3D reconstruction (TLCCT). We compared the correlation between TLC and PBW with the correlation between TLC and FVC to determine which was stronger. Dynamic pulmonary compliance was then calculated from intraoperative ventilator data and logistic regression models constructed to determine which clinical measure best predicted low compliance. Ratios of tidal volume/FVC plotted against peak inspiratory pressure were utilized to construct a new model for tidal volume selection. Calculated tidal volumes generated by this model were then compared with those generated by the standard lung-protective formula Vt = 7 cc/kg.
The correlation between FVC and TLC (0.82 for TLCPFT and 0.76 for TLCCT) was stronger than the correlation between PBW and TLC (0.65 for TLCPFT and 0.58 for TLCCT). Patients with very low compliance had significantly smaller lung volumes (forced expiratory volume at 1 second, FVC, TLC) and lower diffusion capacity of the lungs for carbon monoxide when compared with patients with normal compliance. An FVC cutoff of 3470 cc was 100% sensitive and 51% specific for predicting low compliance. The proposed equation Vt = FVC/8 significantly reduced calculated tidal volume by a mean of 22.5% in patients with low pulmonary compliance without affecting the mean tidal volume in patients with normal compliance (mean difference 0.9%).
FVC is more strongly correlated to TLC than PBW and a cutoff of about 3.5 L can be utilized to predict low pulmonary compliance. The equation Vt = FVC/8 reduced mean calculated tidal volume in patients with low pulmonary compliance and/or small lungs.
机械通气期间潮气量的选择采用的是仅考虑患者预测体重（PBW）的教条式公式。在本研究中，我们调查用力肺活量（FVC）是否（1）与肺总量（TLC）的相关性比PBW更好，（2）能预测低肺顺应性，以及（3）为潮气量选择提供一种替代方法。
130例胸外科手术患者术前的TLC通过两种方法计算：（1）肺功能测试（PFT；TLCPFT）和（2）计算机断层扫描三维重建（TLCCT）。我们比较了TLC与PBW之间的相关性以及TLC与FVC之间的相关性，以确定哪一个更强。然后根据术中呼吸机数据计算动态肺顺应性，并构建逻辑回归模型以确定哪种临床指标能最好地预测低顺应性。利用潮气量/FVC与吸气峰压的比值构建一个新的潮气量选择模型。然后将该模型计算出的潮气量与标准肺保护性公式Vt = 7 cc/kg计算出的潮气量进行比较。
FVC与TLC之间的相关性（TLCPFT为0.82，TLCCT为0.76）强于PBW与TLC之间的相关性（TLCPFT为0.65，TLCCT为0.58）。与顺应性正常的患者相比，顺应性极低的患者肺容积（1秒用力呼气量、FVC、TLC）明显更小，肺一氧化碳弥散量更低。FVC临界值为3470 cc时，预测低顺应性的敏感度为100%，特异度为51%。所提出的公式Vt = FVC/8在低肺顺应性患者中使计算出的潮气量平均显著降低22.5%，而不影响顺应性正常患者的平均潮气量（平均差异0.9%）。
FVC与TLC的相关性比PBW更强，约3.5 L的临界值可用于预测低肺顺应性。公式Vt = FVC/8降低了低肺顺应性和/或肺容积小的患者计算出的平均潮气量。
