Apnea testing in the diagnosis of brain death

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Abstract
The absence of spontaneous respiration is a crucial determinant in the diagnosis of brain death, standardized criteria for apnea testing have not been established. Guidelines are proposed based on the results of 51 apnea tests and associated physiological measurements. In patients who fulfilled all other conventional criteria for brain death, 3 exhibited non-repetitive back arching and shoulder shrugging when CO2 pressures [pCO2] reached 41-51 mm Hg during apnea testing. These respiratory-like movements were ineffective for ventilation and were not reproducible on the following day at the same or higher pCO2. The nature of these movements, evoked potential testing, and autopsy results suggest thay they were not triggered by normal medually centers, and that these patients were, in fact, brain-dead. In 4 other patients with severe brain damage sparing only the medulla, normal spontaneous ventilation resumed at pCO2 of 30-39 mm Hg (mean 34 mm Hg). High arterial oxygen tension raised this apnea point slightly, but spontaneous breathing always began at pCO2 < 40 mm Hg. This level is therefore adequate to stimulate medullary respiration in patients with severe brain damage who are not brain-dead. In brain-dead patients. pCO2 rises slowly during apnea (2.58 .+-. 0.85 mm Hg/min), in part because CO2 production is diminished (1.8 .+-. 0.23 ml/min per kg). These data allow estimation of a desired length of an apnea test and standardized interpretation of results.