吸入CO2法实施呼吸暂停试验的安全性研究

目的 探讨改良吸入CO2法实施呼吸暂停试验的安全性.方法 共收集可疑脑死亡病例14例.采用传统方法(试验A)及改良吸入CO2法(试验B)实施呼吸暂停试验.改良吸入CO2法:在气管插管末端连接"T"型管,并分别与呼吸机管路及CO2气体管路连接.与传统方法不同,纯氧机械通气10min后不断离呼吸机,打开CO2阀门,向吸入气中混入1.5L/min CO2,1min后断开呼吸机,继续观察呼吸动作1min.于试验前、吸入纯氧后、脱机后每间隔2min(试验A)、脱机前及脱机1min后(试验B)、重新上机后5min行动脉血气分析,记录血流动力学参数,试验前及试验结束后测定血乳酸浓度.结果 14例呼吸暂停试验结果均为阳性.试验A,脱机后8min内PaCO2显著上升(＞60mmHg,P＜0.01),pH值下降(P＜0.05),但PaO2保持在200mmHg以上;MAP轻度下降,但无统计学意义;与基础值比较,PAP显著升高(P＜0.05).试验B,吸入CO2 1min后,PaCO2能有效上升至60mmHg以上或较基础值升高20mmHg,仅1例超过80mmHg;试验过程中,血流动力学参数均保持相对稳定,PAP无显著变化.两种呼吸暂停试验前后血乳酸浓度无明显变化.结论 吸入CO2法及传统方法实施呼吸暂停试验均能有效保持足够组织氧代谢.传统呼吸暂停试验过程中,由于高PaCO2时间长,存在肺动脉高压以及循环不稳定风险.吸入CO2法能有效避免该并发症,连续PaCO2监测的应用是试验安全的有效保证.

Clinical evaluation of safety of apnea test by modified CO2 inhalation

Objective To evaluate the safety of apnea test by modified CO2 inhalation.Methods Conventional(protocol A)and the modified artificial CO2(protocol B)apnea test were performed in 14 suspected brain death patients.Protocol B was performed as follows:A T-type connector was fixed between the end of endotracheal tube and ventilator pipe line.CO2 infusion tube was connected to the side outlet of the T-type connector.Differed from the conventional way,mechanical ventilation was still maintained after 10 minutes pre-oxygenation with FiO2 100%.Instead,CO2 was insufflated by 1.5L/min.Ventilator was disconnected from the patients 1 minute after.Blood gas was respectively analyzed before apnea test,10 minutes after 100% FiO2 ventilation,at each 2-minute interval after ventilator disconnection for protocol A,before and 1 minute after disconnection for protocol B,and 5 minutes after re-ventilation.Hemodynamic parameters were recorded at the same time points.Plasma concentration of lactate was measured before and at the end of apnea test.Results Spontaneous breathing did not occur in any of 14 suspected brain death patients.PaCO2 higher than 60mmHg was observed within 8 minutes.Blood pH significantly lowered(P<0.05),but PaO2 was maintained higher than 200mmHg during the test with protocol A.Conventional apnea test resulted in slight decrease in MAP(P>0.05),but a significant PAP increase(P<0.05)at the end of the test in comparison with their base lines.Target PaCO2 was obtained after 1 minute CO2 inhalation.On the other hand,PAP increase was not found in protocol B.Plasma lactate level was not altered significantly at the end of the test compared with base line in both protocols A and B.Conclusion Adequate oxygenation could be maintained in both apnea test methods.Risk of hypotension and pulmonary arterial hypertension should be considered during apnea test by conventional way.There was less risk in the modified artificial CO2(protocol B)apnea test.However,it is important to monitor the blood gas closely for patients' safety.