不同通气策略对瓣膜置换术病人肺内分流和氧合的影响

Effects of different mechanical ventilation methods on oxygenation and shunt fraction in patients undergoing valve replacement

目的 :比较不同潮气量及呼吸频率对瓣膜置换手术体外循环前后肺内分流和氧合的影响。方法 :30例ASAⅡ～Ⅲ级择期行瓣膜置换术的病人 ,随机分为A组 [潮气量 (TV) =7ml/kg ,呼吸频率 (f) =12次 /分 ) ],B组(TV =5ml/kg ,f=15次 /分 ) ,C组 (TV =7ml/kg ,f=15次 /分 ) ,分别于全麻诱导通气 30min后、转流前 10min、术毕测定动脉及混合静脉血血气 ,计算肺内分流率及呼吸指数 (RI)。结果 :术毕与全麻诱导通气 30min时相比 ,A组患者PaO2 显著下降 (P <0 .0 5 ) ,P(A a)DO2 ,RI,分流率显著增高 (P <0 .0 1) ,B ,C组患者PaO2 ,P(A a)DO2 ,RI,分流率差异均无统计学意义 (P >0 .0 5 )。术毕B ,C组与A组相比较PaO2 ,P(A a)DO2 ,RI ,分流率差异均有统计学意义(P <0 .0 1)。术毕C组PaCO2 低于正常值 (<35mmHg) ,A ,B组在正常值范围内。结论 :呼吸频率 15次 /min ,潮气量 5ml/kg的机械通气方式可改善瓣膜置换手术后肺内分流及氧合 。

Objective To determine the effects of different mechanical ventilation on oxygenation and shunt fraction in patient undergoing valve replacement.Methods Thirty ASA Ⅱ～Ⅲ patients(12 males,18 females),aged 25～56 years, undergoing valve replacement were randomly divided into 3 groups according to the mechanical ventilation method. Anesthesia was induced with midazolam 0.1 mg/kg, fentanl 10 μg/kg,vecuronium 0.1mg/kg,and etomidate 0.3mg/kg.Valve replacement was performed with moderate hypothermic cardiopulmonary bypass(CPB). The patients were mechanically ventilated with pure oxygen and I∶E ratio 1∶2.Group A (TV=7 ml/kg, f=12 bpm),Group B (TV=5 ml/kg, f=15 bpm), and Group C (TV=7 ml/kg, f=15 bpm). ECG, BP, SPO 2, and CVP were routinely monitored . Blood samples were taken from the radial artery and pulmonary artery at 30 min after the induction of anesthesia,10 min before CPB,and the end of operation for blood gas analysis. Respiratory index (P(A-a)DO 2/ PaO 2) ,and Qs/Qt were calculated.Results There was no significant difference in age, weight,duration of operation of CPB time and aortic cross-clamping time among the 3 groups. At the end of operation, PaO 2 decreased significantly,P (A-a)DO 2,RI, and Qs/Qt increased significantly in group A, while there was no significant change in group B and group C. At the end of the operation, PaCO 2 was lower than the baseline value (<35mmHg )in Group A, but it was normal in Group B and group C.Conclusion The mechanical ventilation method of lower tidal volume and higher respiratory rate might increase the oxygenation and decrease shunt fraction and might be more suitable in patients undergoing valve replacement.