Department of Anesthesiology, Hospital Privado de Comunidad, Mar del Plata, Argentina.
J Clin Monit Comput. 2012 Jun;26(3):183-90. doi: 10.1007/s10877-012-9358-9. Epub 2012 Apr 7.
We tested whether the ratio of alveolar dead space to alveolar tidal volume (VD(alv)/VT(alv)) can detect states of low pulmonary blood flow (PBF) in a non-invasive way. Fifteen patients undergoing cardiovascular surgeries with cardiopulmonary bypass (CPB) were studied. CPB is a technique that excludes the lungs from the general circulation. The weaning of CPB is a model that manipulates PBF in vivo because each time blood flow through the CPB decreases, expected PBF (ePBF) increases. Patients were liberated from CPB in steps of 20 % every 2' starting from 100 % CPB (very low ePBF) to 0 % CPB (100 % ePBF). During constant ventilation, volumetric capnograms were recorded and Bohr's dead space ratio (VD(Bohr)/VT), VD(alv)/VT(alv) and the ratio of airway dead space to tidal volume (VD(aw)/VT) were calculated. Before CPB, VD(Bohr)/VT was 0.36 ± 0.05, VD(aw)/VT 0.21 ± 0.04 and VD(alv)/VT(alv) 0.18 ± 0.06 (mean ± SD). During weaning from CPB, VD(aw)/VT remained unchanged while VD(Bohr)/VT and VD(alv)/VT(alv) decreased with increasing ePBF. At CPB of 80, 60, 40 and 20 % VD(Bohr)/VT was 0.64 ± 0.06, 0.55 ± 0.06, 0.47 ± 0.05 and 0.40 ± 0.04, respectively; p < 0.001 and VD(alv)/VT(alv) 0.53 ± 0.07, 0.40 ± 0.07, 0.29 ± 0.06 and 0.25 ± 0.04, respectively; p < 0.001). After CPB, VD(Bohr)/VT and VD(alv)/VT(alv) reached values similar to baseline (0.37 ± 0.04 and 0.19 ± 0.06, respectively). At constant ventilation the alveolar component of VD(Bohr)/VT increased in proportion to the deficit in lung perfusion.
我们测试了肺泡死腔与潮气量的比值（VD(alv)/VT(alv)）是否可以无创地检测低肺血流（PBF）状态。研究了 15 名接受心肺旁路（CPB）心血管手术的患者。CPB 是一种将肺部排除在体循环之外的技术。CPB 的脱机是一种操纵体内 PBF 的模型，因为每次通过 CPB 的血流量减少，预期的 PBF（ePBF）就会增加。患者从 100%CPB（极低的 ePBF）到 0%CPB（100%ePBF）以 20%的步长逐步脱离 CPB。在持续通气期间，记录容量二氧化碳图，并计算 Bohr 的死腔比（VD(Bohr)/VT）、VD(alv)/VT(alv)和气道死腔与潮气量的比值（VD(aw)/VT）。CPB 前，VD(Bohr)/VT 为 0.36 ± 0.05，VD(aw)/VT 为 0.21 ± 0.04，VD(alv)/VT(alv)为 0.18 ± 0.06（平均值 ± SD）。在 CPB 脱机期间，VD(aw)/VT 保持不变，而 VD(Bohr)/VT 和 VD(alv)/VT(alv)随 ePBF 的增加而降低。在 CPB 为 80%、60%、40%和 20%时，VD(Bohr)/VT 分别为 0.64 ± 0.06、0.55 ± 0.06、0.47 ± 0.05 和 0.40 ± 0.04，p < 0.001，VD(alv)/VT(alv)分别为 0.53 ± 0.07、0.40 ± 0.07、0.29 ± 0.06 和 0.25 ± 0.04，p < 0.001）。CPB 后，VD(Bohr)/VT 和 VD(alv)/VT(alv)恢复到与基线相似的值（分别为 0.37 ± 0.04 和 0.19 ± 0.06）。在持续通气下，VD(Bohr)/VT 的肺泡成分与肺灌注不足成比例增加。
