Department of Anesthesia, University of Manitoba, Winnipeg, MB, Canada.
Can J Anaesth. 2011 Aug;58(8):740-50. doi: 10.1007/s12630-011-9517-3. Epub 2011 Jun 4.
Resolution of the acute respiratory distress syndrome (ARDS) requires clearance of pulmonary edema. Biologically variable ventilation (BVV) strategies that improve gas exchange, lung mechanics, and inflammatory mediators in ARDS may be beneficial in this regard. We used quantitative computed tomography (CT), a single indicator thermodilution system (PiCCO®) to determine extravascular lung water (EVLW), and the change in edema protein concentration over time to compare edema clearance with BVV vs conventional mechanical ventilation (CMV) in a porcine ARDS model.
Sixteen pigs with oleic acid lung injury were randomized to four hours of ventilation with either CMV (n = 8) or BVV (n = 8) at identical low tidal volume and minute ventilation over time. Hemodynamic variables, gas exchange, lung mechanics, and PiCCO derived EVLW were determined hourly. Computed tomography images and edema fluid samples were obtained at baseline lung injury and after four hours of ventilation. Wet and dry lung weights were determined postmortem.
At four hours with BVV, peak airway pressure was decreased significantly and lung compliance improved compared with CMV (P = 0.003; P < 0.001, respectively). Hemodynamic variables and gas exchange were not different between groups. Also at four hours, computed tomography revealed an increase in total gas volume (P = 0.001) and a decrease in total lung weight and global lung density (P = 0.005; P = 0.04 respectively) with BVV. These findings were associated with a significant increase in the gas volume of normally aerated lung regions (P < 0.001) and a decrease in the poorly and non-aerated lung regions (P = 0.001). No change in any CT parameter occurred with CMV. The lung weights derived from computed tomography correlated well with postmortem wet weights (R(2) = 0.79; P < 0.01). The decrease in PiCCO derived EVLW from injury to four hours did not differ significantly between BVV and CMV. Extravascular lung water showed no correlation with postmortem wet weights and significantly underestimated lung water. Average alveolar fluid clearance rates were positive (1.4%·hr(-1) (3%)) with BVV and negative with CMV (-2.0%·hr(-1) (4%)).
In a comparison between BVV and CMV, computed tomography evidence suggests that BVV facilitates enhanced clearance and/or redistribution of edema fluid with improved recruitment of atelectatic and poorly aerated lung regions; no such evidence was seen with either single thermodilution measurement of EVLW or edema clearance rates. The results of computed tomography provide further evidence of the benefit of BVV over conventional ventilation in ARDS.
急性呼吸窘迫综合征（ARDS）的解决需要清除肺水肿。在 ARDS 中改善气体交换、肺力学和炎症介质的生物可变通气（BVV）策略可能对此有益。我们使用定量计算机断层扫描（CT）、单指示剂热稀释系统（PiCCO®）来确定血管外肺水（EVLW），并随时间变化测量水肿蛋白浓度的变化，以比较 BVV 与常规机械通气（CMV）在猪 ARDS 模型中的肺水肿清除情况。
16 头油酸肺损伤猪随机分为 CMV 通气 4 小时（n=8）或 BVV 通气 4 小时（n=8），两组均采用相同的小潮气量和分钟通气量。每小时测定血流动力学变量、气体交换、肺力学和 PiCCO 衍生的 EVLW。在基线肺损伤和通气 4 小时后获取 CT 图像和水肿液样本。死后测定肺的湿重和干重。
与 CMV 相比，BVV 通气 4 小时时气道峰压显著降低，肺顺应性改善（P=0.003；P<0.001）。两组的血流动力学变量和气体交换无差异。同样在通气 4 小时时，CT 显示总气量增加（P=0.001），全肺重量和全肺密度降低（P=0.005；P=0.04），而 BVV 通气后正常充气肺区的气量增加（P<0.001），充气不良和不充气肺区的气量减少（P=0.001）。CMV 组 CT 各参数无变化。CT 计算的肺重量与死后湿重相关性良好（R²=0.79；P<0.01）。从损伤到 4 小时，BVV 和 CMV 之间 PiCCO 衍生 EVLW 的降低无显著差异。血管外肺水与死后湿重无相关性，且明显低估了肺水。BVV 的平均肺泡液清除率为正（1.4%·hr（-1）（3%）），CMV 为负（-2.0%·hr（-1）（4%））。
在 BVV 与 CMV 的比较中，CT 证据表明，BVV 促进了水肿液的增强清除和/或再分布，改善了不张和充气不良肺区的再充气；EVLW 或水肿清除率的单次热稀释测量均未发现这种情况。CT 结果进一步证明了 BVV 在 ARDS 中的常规通气相比具有优势。
