The Use of Apneic-Diffusion Respiration in the Diagnosis of Brain Death

Irreversible cessation of brain function may be sufficient grounds for pronouncement of death. Because the response of the ventilatory center to carbon dioxide is an important component of brain-stem function, apnea testing is often employed in comatose patients in whom the question of death is being considered. Methods: We devised a simple procedure, using readily available apparatus, to standardize and improve the safety and sensitivity of apnea testing. Using the CPAP mode of the Bear 1 ventilator, we employed the principle of apneic-diffusion respiration to maintain acceptable PaO 2 while allowing PaCO 2 to rise steadily, in order to learn whether CO 2 would stimulate respiration. We studied 23 patients in profound coma from a variety of causes. Results: In five patients, PaO 2 fell below 100 torr. Three patients had cardiac instability. In 16 patients (17 tests), oxygen levels remained acceptable as PaCO 2 rose to or above 60 torr. Two patients exhibited spontaneous respiration; the rest remained apneic. There was a wide range of rates at which PaCO 2 increased. Conclusion: Our experience demonstrates that apnea testing may be hazardous if done without adequate cardiac monitoring and oxygenation . (Respir Care 1985;30:328-333.)