Cerebral arterio-venous oxygen difference: a bedside test for cerebral death.

A bedside test is described which compares the patients cerebral arterio-venous oxygen difference with a predicted norm at various levels of arterial CO2 tension. In patients in coma depasse this difference is reduced and is unresponsive to variations in arterial carbon dioxide tension. The test also confirms lack of respiratory efforts in the presence of adequate carbon dioxide tension.