Mondoñedo Jarred R, Herrmann Jacob, McNeil John S, Kaczka David W
Department of Biomedical Engineering and School of Medicine, Boston University, 44 Cummington Mall, Boston, MA, 02215, USA.
Departments of Biomedical Engineering and Anesthesia, University of Iowa, Iowa City, IA, 52242, USA.
J Clin Monit Comput. 2017 Dec;31(6):1263-1271. doi: 10.1007/s10877-016-9956-z. Epub 2016 Nov 14.
Volatile anesthetics alter the physical properties of inhaled gases, such as density and viscosity. We hypothesized that the use of these agents during mechanical ventilation would yield systematic biases in estimates of flow ([Formula: see text]) and tidal volume (V ) for two commonly used flowmeters: the pneumotachograph (PNT), which measures a differential pressure across a calibrated resistive element, and the hot-wire anemometer (HWA), which operates based on convective heat transfer from a current-carrying wire to a flowing gas. We measured [Formula: see text] during ventilation of a spring-loaded mechanical test lung, using both the PNT and HWA placed in series at the airway opening. Delivered V was estimated from the numerically-integrated [Formula: see text]. Measurements were acquired under baseline conditions with room air, and during ventilation with increasing concentrations of isoflurane, sevoflurane, and desflurane. We also evaluated a simple compensation technique for HWA flow, which accounted for changes in gas mixture density. We found that discrepancies in estimated V between the PNT and HWA occurred during ventilation with isoflurane (6.3 ± 3.0%), sevoflurane (10.0 ± 7.3%), and desflurane (25.8 ± 17.2%) compared to baseline conditions. The magnitude of these discrepancies increased with anesthetic concentration. A simple compensation factor based on density reduced observed differences between the flowmeters, regardless of the anesthetic or concentration. These data indicate that the choice and concentration of anesthetic agents are primary factors for differences in estimated V between the PNT and HWA. Such discrepancies may be compensated by accounting for alterations in gas density.
挥发性麻醉剂会改变吸入气体的物理性质，如密度和粘度。我们假设，在机械通气期间使用这些药物会导致两种常用流量计对流量（[公式：见正文]）和潮气量（V）的估计产生系统性偏差：一种是气动流速仪（PNT），它通过测量经过校准的电阻元件两端的压差来工作；另一种是热线风速仪（HWA），它基于从载流导线到流动气体的对流热传递来工作。我们在一个弹簧加载的机械测试肺通气期间测量了[公式：见正文]，将PNT和HWA串联放置在气道开口处。通过对[公式：见正文]进行数值积分来估计输送的V。在使用室内空气的基线条件下以及使用异氟烷、七氟烷和地氟烷浓度不断增加的气体进行通气期间进行测量。我们还评估了一种针对HWA流量的简单补偿技术，该技术考虑了气体混合物密度的变化。我们发现，与基线条件相比，在使用异氟烷（6.3±3.0%）、七氟烷（10.0±7.3%）和地氟烷（25.8±17.2%）通气期间，PNT和HWA对V的估计存在差异。这些差异的大小随着麻醉剂浓度的增加而增大。基于密度的简单补偿因子减少了流量计之间观察到的差异，无论使用何种麻醉剂或浓度如何。这些数据表明，麻醉剂的选择和浓度是导致PNT和HWA对V估计存在差异的主要因素。通过考虑气体密度的变化，这种差异可能得到补偿。
