脑死亡判定中呼吸暂停试验临床实施的可行性及对血压和心率的影响

Clinical study on the application of apnea test to the determination of brain death and its impact on the blood pressure and heart rate

目的探讨脑死亡判定标准中呼吸暂停试验临床实施的可行性及对平均动脉压(MAP)、心率(HR)的影响。方法对22例临床可疑的脑死亡患者进行呼吸暂停试验,先经呼吸机吸入纯氧10min,再停机并经插至气管隆突水平的导管以6L/min纯氧供氧10min,观察患者有无自主呼吸,并分别测定其充氧前、充氧后、停机后的动脉血pH值、PaO2、PaCO2的变化,及停机后MAP、HR的动态变化。结果试验过程中,22例患者无一例出现自主呼吸,其中16例试验结束时PaCO2≥60mmHg。停机后所有患者pH值明显下降、PaCO2明显升高(P<0.01),充氧后PaO2明显升高(P<0.05),而停机后PaO2无明显下降趋势(P>0.05)。停机后患者MAP、HR均逐渐下降,且各组停机后与停机前比较均有显著差异(P<0.05),至停机8min时下降尤为显著,再通气后HR回升迅速,而MAP则缓慢。结论呼吸暂停试验为判定脑死亡的关键步骤之一,停机后MAP、HR尽管逐渐下降,但不发生低氧血症,若纠正停机前的过度通气,并控制停机时间在8min内,临床上是可行和安全的。

Objective To investigate the clinical feasibility of apnea test as one of parameters of diagnosis criteria in the determination of brain death and its impact on the mean arterial pressure (MAP) and heart rate(HR). Methods Apnea test was conducted on 22 patients who were suspected of brain death. Patients were given pure oxygen for 10 minutes before the ventilator disconnected. Then the patients were given pure oxygen at a flow of 6 L/min for 10 min via pipe inserted to the carina of trachea after the ventilator disconnected. Whether the patients can breathe spontaneously was observed and the pH, PaO2 and PaCO2 in arterial blood of patients and the dynamic change of their MAP and HR were monitored respectively at pre-oxygenation, post-oxygenation and after the ventilator disconnected. Results No patient can breathe spontaneously during the study period. The PaCO2 in 16 cases was≥60 mmHg at the end of the study. The patients' pH decreased whereas their PaCO2 increased significantly at after ventilator disconnected (P<0.01); Their PaO2 increased significantly at post-oxygenation (P<0.05); but there was no decreasing tendency in PaO2 after ventilator disconnected(P>0.05). The MAP and HR of patients decreased gradually after ventilator disconnected, which were significantly lower than those before ventilator disconnected, especially after 8 min. The HR of patients increased sharply whereas the MAP recovered relatively slowly after the ventilator connected.Conclusions Apnea test is a key step in determining brain death. Although there was a decreasing tendency in MAP and HR of patients during the test, there was no hypoxemia in all cases. If the over-ventilation was corrected before ventilator disconnected and the time of out of ventilator is controlled within 8 min, the apnea test is practicable and safe.