Bhalla Anoopindar K, Rubin Sarah, Newth Christopher J L, Ross Patrick, Morzov Rica, Soto-Campos Gerardo, Khemani Robinder
Department of Anesthesiology and Critical Care Medicine, Children's Hospital Los Angeles, Los Angeles, California. Keck School of Medicine, University of Southern California, Los Angeles, California.
Department of Anesthesiology and Critical Care Medicine, Children's Hospital Los Angeles, Los Angeles, California.
Respir Care. 2015 Nov;60(11):1548-55. doi: 10.4187/respcare.03892. Epub 2015 Jul 21.
Volumetric capnography dead-space measurements (physiologic dead-space-to-tidal-volume ratio [VD/VT] and alveolar VD/VT) are considered more accurate than the more readily available time-based capnography dead-space measurement (end-tidal alveolar dead-space fraction [AVDSF]). We sought to investigate the correlation between volumetric capnography and time-based capnography dead-space measurements.
This was a single-center prospective cohort study of 65 mechanically ventilated children with arterial lines. Physiologic VD/VT, alveolar VD/VT, and AVDSF were calculated with each arterial blood gas using capnography data.
We analyzed 534 arterial blood gases from 65 children (median age 4.9 y, interquartile range 1.7-12.8). The correlation between physiologic VD/VT and AVDSF (r = 0.66, 95% CI 0.59-0.72) was weaker than the correlation between alveolar VD/VT and AVDSF (r = 0.8, 95% CI 0.76-0.85). The correlation between physiologic VD/VT and AVDSF was weaker in children with low PaO2 /FIO2 (< 200 mm Hg), low exhaled VT (< 100 mL), a pulmonary reason for mechanical ventilation, or large airway VD (> 3 mL/kg). All 3 dead-space measurements were highly correlated (r > 0.7) in children without hypoxemia (PaO2 /FIO2 > 300 mm Hg), mechanically ventilated for a neurologic or cardiac reason, or on significant inotropes or vasopressors.
In mechanically ventilated children without significant hypoxemia or with cardiac output-related dead-space changes, physiologic VD/VT was highly correlated with AVDSF and alveolar VD/VT. In children with significant hypoxemia, physiologic VD/VT was poorly correlated with AVDSF. Alveolar VD/VT and AVDSF correlated well in most tested circumstances. Therefore, AVDSF may be useful in most children for alveolar dead-space monitoring.
容积式二氧化碳描记法的死腔测量值（生理死腔与潮气量之比[VD/VT]和肺泡VD/VT）被认为比更容易获得的基于时间的二氧化碳描记法死腔测量值（呼气末肺泡死腔分数[AVDSF]）更准确。我们试图研究容积式二氧化碳描记法与基于时间的二氧化碳描记法死腔测量值之间的相关性。
这是一项对65例有动脉置管的机械通气儿童进行的单中心前瞻性队列研究。使用二氧化碳描记法数据，通过每次动脉血气分析计算生理VD/VT、肺泡VD/VT和AVDSF。
我们分析了65例儿童（中位年龄4.9岁，四分位间距1.7 - 12.8岁）的534次动脉血气分析结果。生理VD/VT与AVDSF之间的相关性（r = 0.66，95%可信区间0.59 - 0.72）弱于肺泡VD/VT与AVDSF之间的相关性（r = 0.8，95%可信区间0.76 - 0.85）。在动脉血氧分压/吸入氧浓度（PaO2/FIO2）低（< 200 mmHg）、呼出潮气量（VT）低（< 100 mL）、因肺部原因进行机械通气或大气道死腔大（> 3 mL/kg）的儿童中，生理VD/VT与AVDSF之间的相关性较弱。在无低氧血症（PaO2/FIO2 > 300 mmHg）、因神经或心脏原因进行机械通气、或使用显著的正性肌力药物或血管升压药的儿童中，所有3种死腔测量值高度相关（r > 0.7）。
在无明显低氧血症或死腔变化与心输出量相关的机械通气儿童中，生理VD/VT与AVDSF和肺泡VD/VT高度相关。在有明显低氧血症的儿童中，生理VD/VT与AVDSF相关性较差。在大多数测试情况下，肺泡VD/VT与AVDSF相关性良好。因此，AVDSF可能对大多数儿童的肺泡死腔监测有用。
