低潮气量通气对非紫绀型先心病患儿心内直视术中呼吸力学及血气的影响

Effects of low tidal-volume ventilation on blood gases and respiratory mechanics in childran during open heart surgery

目的 观察低潮气量(V_T)通气对非紫绀型先心病患儿心内直视术中血气和呼吸力学的影响。方法 40例3～6岁左向右分流的先心病患儿,有肺血增多,心功能Ⅰ～Ⅱ级,随机分为两组:小V_T组(A组,V_T为7ml/kg)、对照组(B组,V_T,为9ml/kg),每组20例。选择小儿标准频率,固定吸呼比,全麻插管后至手术结束行间歇正压机械通气,分别于切皮前、转流前、缝皮后即刻记录生命体征、呼吸力学指标并行动脉血气分析。结果 与B组比较,A组在切皮前、转流前和缝皮后即刻气道峰压(Ppeak)、平台压(Pplat)、平均气道压(Pmean)均降低(P<0.05)、肺顺应性(Cdyn)无显著性差异(P>0.05)。与切皮前即刻比较,两组Ppeak、Pplat、Pmean在CPB后均增高(P<0.05);A组Cdyn在CPB后无显著性差异(P>0.05),而B组Cdyn在CPB后下降(P<0.05)。与B组比较,A组在切皮前、转流前和缝皮后即刻呼气末二氧化碳分压和动脉血二氧化碳分压增高(P<0.05)、动脉血氧分压、呼吸指数、肺泡-动脉血氧分压差和动脉血-呼气末二氧化碳分压差无显著性差异(P>0.05)。结论 以小儿标准频率对3～6岁非紫绀型先心病患儿术中在全麻下行机械通气时,小V_T机械通气有利于肺保护。

Objective To evaluate the effects of low tidal-volume ventilation on blood gases and respiratory mechanics during open heart surgery in children with acyanotic congenital heart disease. Methods Forty NYHA class Ⅰ-Ⅱ patients with atrial or ventricular septal defect aged 3-6 yrs weighing 12-18 kg undergoing open heart surgery were randomly divided into 2 groups according to the tidal volume of mechanical ventilation: group A low tidal volume(V_r=7ml·kg^(-1),n=20) and group B conventional tidal volume(V_T=9 ml·kg^(-1), n=20). The respiratory rate(RR) was 21-23 bpm, I: E ratio 1:2 and FiO_2 100% in both groups. The patients were premedicated with intramuscular morphine 0.1 mg·kg^(-1) and scopolamine 0.01 mg·kg^(-1). Anesthesia was induced with midazolam 0.1 mg·kg^(-1), fentanyl 10 μg·kg^(-1) and vecuronium 0.1 mg·kg^(-1) and maintained with infusion of fentanyl 4 μg·kg^(-1)·h^(-1) and vecuronium 80 μg·kg·h^(-1) supplemented with isoflurane inhalation(<0.7 MAC) and intermittent i.v. boluses of midazolam. Left radial artery was cannulated for BP monitoring and blood gas analysis. Respiratory mechanics and blood gases were measured before skin incision(T_1), before CPB(T_2) and immediately after skin suture(T_3). Results Peak airway pressure(Ppeak), plateau and mean airway pressure(Pplateau, Pmean) were significantly lower while PaCO_2 and P_(ET)CO_2 were significantly higher in group A (low V_T)than in group B(traditional V_T)at T_(1.3)(P<0.05), but they were all within normal range. There was no significant difference in the dynamic lung compliance(Cdyn), PaO_2, P_(A-a)O_2, P_(a-ET)CO_2 and respiratory index (P_(A-a)O_2/PaO_2) between the two groups. Ppeak, Pplateau, Pmean and PaCO_2, P_(ET)CO_2, P_(A-a)O_2 and P_(a-ET)CO_2 were significantly increased after operation(T_3)compared to the baseline values before surgery(T_1) in both groups. There was no significant difference in Cdyn during and after operation in group A, while in group B Cdyn decreased significantly after operation. Conclusion The results suggest that low V_T of 7 ml·kg^(-1) is preferred for lung protection against barotraumas during surgery in children undergoing open heart surgery.