Proquitté Hans, Kusztrich Ariane, Auwärter Volker, Pragst Fritz, Wauer Roland R, Schmalisch Gerd
Clinic of Neonatology, Charité Campus Mitte, and Institute of Legal Medicine, Charité Universitätsmedizin, Berlin, Germany.
Crit Care Med. 2006 Jun;34(6):1789-95. doi: 10.1097/01.CCM.0000220065.93507.AB.
Heptafluoropropane is an inert gas commercially used as propellant for inhalers. Since heptafluoropropane can be detected in low concentrations, it could also be used as a tracer gas to measure functional residual capacity and ventilation homogeneity. The aim of the present study was to validate functional residual capacity measurements by heptafluoropropane wash-in/wash-out (0.8%) during mechanical ventilation in small, surfactant-depleted lungs using a newborn piglet model.
Prospective laboratory and animal trial.
Animal laboratory in a university setting.
Sixteen newborn piglets (age<12 hrs, median weight 1390 g [705-4200 g]) before and after surfactant depletion (Pao2<100 torr in Fio2=1.0) by lung lavage.
Heptafluoropropane was measured with a new infrared mainstream sensor connected with the flow sensor of the Dräger Babylog 8000. Accuracy and precision of the measurement technique were tested in a mechanical lung model with a volume range from 11 to 35 mL. Reproducibility of the method and its sensitivity to detect changes of functional residual capacity were assessed in vivo by variation of ventilatory variables.
In vitro the absolute error of functional residual capacity was <1 mL (relative errors<3%) with a coefficient of variation<4%. The coefficient of variation of consecutive in vivo measurements was only slightly higher (<5.1%). Measurement of heptafluoropropane concentrations in blood showed no significant accumulation for repeated functional residual capacity measurements within short time periods. After lung lavage, the functional residual capacity decreased from 20.9 mL/kg to 14.5 mL/kg (p<.05) despite increased ventilatory pressures, and lung clearance index (p<.001) and moment ratios (p<.01) increased significantly due to uneven alveolar ventilation. In healthy lungs, the increase in peak inflation pressure and positive end-expiratory pressure by 3-4 cm H2O had only a moderate effect on functional residual capacity (20.9+/-8.6 vs. 26.0+/-11.9 mL/kg, p=.17) and no effect on ventilatory homogeneity, whereas in surfactant-depleted lungs the functional residual capacity increased from 14.5+/-6.7 mL/kg to 29.9+/-12.6 mL/kg (p<.001) and lung clearance index and moment ratios decreased significantly (p < .01).
Heptafluoropropane is a suitable tracer gas for precise functional residual capacity measurements tested in vitro and allows for reproducible measurements in ventilated small lungs without any adverse effects on mechanical ventilation. The sensitivity of the method is sufficiently high to demonstrate the effect of changes in ventilatory settings on the functional residual capacity and ventilation homogeneity.
七氟丙烷是一种惰性气体，在商业上用作吸入器的推进剂。由于七氟丙烷能够在低浓度下被检测到，它也可被用作一种示踪气体来测量功能残气量和通气均匀性。本研究的目的是在新生仔猪模型中，验证在机械通气期间使用七氟丙烷冲洗/洗脱（0.8%）来测量功能残气量的方法，该模型的肺小且缺乏表面活性物质。
前瞻性实验室和动物试验。
大学环境中的动物实验室。
16只新生仔猪（年龄<12小时，中位体重1390克[705 - 4200克]），在通过肺灌洗使表面活性物质耗竭（在Fio2 = 1.0时Pao2<100托）前后。
使用与德尔格Babylog 8000的流量传感器相连的新型红外主流传感器测量七氟丙烷。在体积范围为11至35毫升的机械肺模型中测试测量技术的准确性和精密度。通过改变通气变量在体内评估该方法的可重复性及其检测功能残气量变化的敏感性。
在体外，功能残气量的绝对误差<1毫升（相对误差<3%），变异系数<4%。连续体内测量的变异系数仅略高（<5.1%）。在短时间内重复测量功能残气量时，血液中七氟丙烷浓度的测量显示无明显蓄积。肺灌洗后，尽管通气压力增加，但功能残气量从20.9毫升/千克降至14.5毫升/千克（p<.05），并且由于肺泡通气不均匀，肺清除指数（p<.001）和矩比（p<.01）显著增加。在健康肺中，将峰值充气压力和呼气末正压增加3 - 4厘米水柱对功能残气量仅有中等影响（20.9±8.6与26.0±11.9毫升/千克，p = 0.17），对通气均匀性无影响，而在表面活性物质耗竭的肺中，功能残气量从14.5±6.7毫升/千克增加至29.9±12.6毫升/千克（p<.001），肺清除指数和矩比显著降低（p<.01）。
七氟丙烷是一种适用于体外精确测量功能残气量的示踪气体，并且能够在通气的小肺中进行可重复测量，对机械通气无任何不良影响。该方法的敏感性足够高，能够证明通气设置变化对功能残气量和通气均匀性的影响。
