[Study on safety of apnea test in clinical determination of brain death].

Objective: To determine the occurrence of severe complications such as hypotension, pulmonary artery hypertension as well as hypercapnia during apnea test in the affirmation of brain death and to investigate the possible effective prophylactic interventions.

Methods: Conventional apnea test was performed in 15 clinically suspected brain death patients. Stable circulation was achieved by adjusting preload only (n=4) or combined with titrating norepinephrine (NE, n=11). Blood gas was respectively analyzed before apnea test, 10 minutes after 100% fraction of oxygen (FiO(2)) ventilation, at each 2-minute interval after disconnecting ventilator and 5 minutes after reventilation. Hemodynamic parameters and dosage of NE were recorded at the same time points. Plasma concentration of lactate was measured before and at the end of apnea test.

Results: Spontaneous breath occurred in 1 case among 15 suspected brain death patients. Partial pressure of carbon dioxide (PaCO(2)) reached higher than 60 mm Hg (1 mm Hg=0.133 kPa) within 8 minutes in positive apnea test patients (P<0.01). pH significantly decreased (P<0.05), but partial pressure of oxygen (PaO(2)) maintained higher than 100 mm Hg during the test. Heart rate (HR) and mean artery pressure (MAP) slightly lowered (P>0.05), but pulmonary artery pressure (PAP) markedly elevated (P<0.05) at the end of the test in comparison with their base lines. On the other hand, HR and MAP increased in the negative apnea test case after ventilator disconnection. Severe arrhythmia events did not occur in all the cases. There was no change in the dosage of NE infusion, the range of which was 0.10-0.60 microg.kg(-1).min(-1) with the mean level of (0.23+/-0.17) microg.kg(-1).min(-1). The trend of HR, MAP, PAP and pulmonary arterial wedge pressure (PAWP) alterations was the same in patients no matter whether or not NE was used. HR, MAP and PAWP lowered, while PAP enhanced. Plasma lactate level was not significantly altered at the end of the test compared with the base line (from (1.41+/-0.05) mmol/L to (1.47+/-0.07) mmol/L).

Conclusion: Adequate oxygenation could be maintained during conventional apnea test. The risk of inducing severe hypotension is low in non brain death patients. Based on adequate preload, low dose of NE infusion could prevent patients with high risk circulation instability from severe hypotension.