Continuous monitoring of jugular bulb oxygen saturation and the effect of drugs acting on cerebral metabolism.

The laser absorption spectrophotometric technique was used to continuously monitor jugular bulb oxygen saturation (SjO2), and thus to calculate arteriovenous oxygen differences (AVDO2), in three subgroups of intensively monitored, severely head injured patients. We have used this data to address two questions: 1. How do cerebral and systemic haemodynamic changes affect SjO2 and AVDO2; and 2. Can ADVO2 measurements be used to detect therapeutic changes in brain metabolism, in response to drugs. The major haemodynamic factor affecting SjO2 and AVDO2 was intracranial pressure (ICP). Increases in ICP were associated with concomitant increases in SjO2, and decreases in AVDO2, suggesting cerebral hyperaemia in response to ICP waves. Systemic changes were less frequent, but potent influences on SjO2. The short acting anaesthetic agent propofol produced a marked increase in SjO2 (decrease in AVDO2 to below the normal range) which became less marked with time. A new high affinity glutamate antagonist produced no change in SjO2. With rigorous attention to technical factors, and exclusion of extra and intracranial haemodynamic effects, SjO2 monitoring may be a useful "surrogate end point" for the effect of drugs acting on brain metabolism.