J Neurosurg 76:1029-1031, 1992 Apnea testing for the determination of brain death: a modified protocol Technical note EDWARD C. BENZEL, M.D., JAY P. MASHBURN, M.D., STEVEN CONRAD, M.D., PH.D., AND DENISE MODLING, R.N. Division of Neurosurgery, University of New Mexico, Albuquerque, New Mexico, and Departments of Pathology and Internal Medicine, Divisions of Neurosurgery and Pulmonary and Critical Care Medicine, Louisiana State University, Shreveport, Louisiana w The absence of spontaneous respirations at a PaCO2 of 60 mm Hg or above has traditionally been accepted as the respiratory criteria for the determination of brain death. The testing of patients for the presence or absence of apnea has been complicated because the rate of PaCO2 elevation may vary substantially from patient to patient, and a nonlinear relationship exists between the rate of PaCO2 increase and the duration of apnea. In an attempt to refine the apnea test and to further elucidate the physiology of hypereapnia in humans, 11 patients who met all but the respiratory criteria for brain death were evaluated using a modification of a previously utilized apnea testing protocol. All patients were brought to a PaCO2 of 40 mm Hg or above prior to the apnea test. Baseline PaCO2 ranged from 40 to 45 mm Hg in six patients (Group I) and from 46 to 51 mm Hg in five patients (Group II). The mean rate of PaCO2 increase was 5.1 _+ 1.4 mm Hg/min in Group I and 6.7 _+ 3.1 mm Hg/min in Group II. No problems with cardiovascular instability or hypoxia were en- countered during testing in this series. This refinement of the apnea test allows for a streamlined and safe ap- proach to brain death detection. KEY WORDS 9 brain death 9 apnea test 9 hypercapnia 9 acidosis 9 oxygenation T HE determination of brain death is of concern to all physicians caring for critically ill patients. It is, of course, crucial to demonstrate that cere- bral function has ceased before a patient can be consid- ered brain dead. This is not demonstrated unless apnea is documented.~'3'5-s The methodology of apnea testing differs from center to center. Controversies persist regarding the safest and most appropriate techniques. An analysis of 11 consec- utive patients undergoing brain death determination studies was therefore undertaken in order to evaluate the effect of an increased baseline PaCO2 on the dura- tion of apnea required for the completion of the test. Clinical Material and Methods Patient Population From July, 1988, to April, 1989, 11 consecutive patients who met the neurological criteria for brain death ~'2 underwent a modified apnea test as the final step of their brain death determination. There were 10 males and one female, with a mean age of 39 years (range 17 to 69 years). Five were black, and six were white. The etiology of the neurological injury was trauma in three patients, hypertensive intracerebral hemorrhage in three, subarachnoid hemorrhage in two, meningitis in two, and metastatic tumor in one. Apnea Test Procedure With the exception of minor modifications, the tech- nique of apnea testing utilized here is as previously reported.~ After a 15-minute preoxygenation period with 100% O2 delivered via mechanical ventilation, the ventilation was adjusted to allow the patient's PaCOz to rise to 40 mm Hg or above. Then, 100% 02 was delivered via a cannula placed through the endotracheal tube to the estimated level of the carina. After a baseline arterial blood gas determination, further samples were J. Neurosurg. / Volume 76/June, 1992 1029