低潮气量机械通气对瓣膜置换病人肺换气功能影响的临床研究

目的以心输出量和肺换气功能为指标研究低潮气量通气对瓣膜置换病人心肺功能的影响。方法30例择期行二尖辩置换手术病人随机分成3组：常规（传统）潮气量组（组Ⅰ），潮气量9mL／kg，呼吸频率12次／min；低潮气量常规频率组（组Ⅱ），潮气量7mL／kg，呼吸频率12次／min；低潮气量高频率组（组Ⅲ），潮气量7mL／kg，呼吸频率15次／min。监测平均动脉压（MAP），放置飘浮导管监测心输出量（CO）和心指数（CI），平均肺动脉压（MPAP），肺毛细血管嵌压（PCWP），中心静脉压（CVP），体循环阻力指数（SVRI），肺循环阻力指数（PVRI）。测定动脉氧分压（PaO2）、动脉二氧化碳分压（PaCO2），以及氧合指数（PaO2／FiO2），肺泡动脉氧分压差（PA-aO2），肺内分流量（QS／QT）。结果组Ⅱ，体外循环后60min时与比麻醉后体外循环前比，氧和指数（PaO2／FiO2）显著降低（P〈0．05），肺泡-动脉氧分压差（PA-aO2）和肺内分流量（QS/QT）显著增加（P〈0.05）。组Ⅱ与组Ⅰ和组Ⅲ相比，在体外循环后60min（T4），氧和指数显著降低（P〈0．05），肺泡-动脉氧分压差和肺内分流量显著增加（P＜0．05）。结论低潮气量机械通气对循环功能无明显影响，并能保持起好通气。低潮气量常规频率通气不能减轻体外循环引起的肺换气功能损害。低潮气量高频率通气和常规潮气量通气能减轻或消除体外循环引起的早期肺换气功能损害。

Effects of low tidal volume ventilation on pulmonary gas exchange before and after mitral valve replacement with cardiopulmonary bypass

Objective] To investigate the effect of low tidal volume ventilation on pulmonary gas exchange in patients undergoing mitral valve replacement with cardiopulmonary bypass (CPB). Methods] A prospective randomized study was done in university hospital. Thirty patients undergoing mitral valve replacement with CPB were randomized to receive traditional tidal volume ventilation (TV; tidal volume, 9 mL/kg; respiratory rate, 12 times/min),or low tidal volume ventilation with conventional respiratory rate (LV; tidal volume, 7 mL/kg; respiratory rate, 12times/min), or low tidal volume ventilation with high respiratory rate (HR; tidal volume 7 mL/kg, 15 times/min)throughout surgery. During CPB, patients' lungs were kept inflated with 100% oxygen. Results] Pulmonary gas exchange parameters were determined twice before CPB and after CPB. When final values after CPB were compared with the values before CPB, the arterial oxygen tension-inspired oxygen concentration ratio (PaO2/FiO2) was significantly decreased, and alveolar-artetal (A-a) oxygen gradient P(A-a)O2] and intrapulmonary shunt (Qs/QT) were significantly increased in group LV. No significant differences were found in either group TV or group HR. Conclusions] Low tidal volume ventilation with conventional respiratory rate in patients undergoing mitral valve replacement impaired pulmonary gas exchange early after CPB, while low tidal volume ventilation with high respiratory rate did not. These results suggest that low tidal volume ventilation with high respiratory rate may be useful for reducing lung injury caused by CPB and mechanical ventilation in patients undergoing mitral valve replacement.