Combined continuous monitoring of systemic and cerebral oxygenation in acute brain injury: preliminary observations.

OBJECTIVE: To continuously evaluate the relationship between global systemic and cerebral oxygenation during temporary profound hypocapnia, which was attempted for prompt management of posttraumatic intracranial hypertension.

DESIGN: Prospective, intervention study.

SETTING: Neuroscience intensive care unit of a university hospital.

PATIENTS: Young adults (n = 21) with acute brain trauma, undergoing routine monitoring of jugular bulb and pulmonary artery oxyhemoglobin saturations, along with other monitoring.

MEASUREMENTS AND MAIN RESULTS: In 102 multivariate observations carried out on days 2 and 3 post-trauma, two new physiologic variables were assessed. These variables, systemic-cerebral oxygenation index and the systemic-cerebral ventilatory index, were evaluated in terms of baseline and post-hyperventilation changes. Overall, when intracranial pressure was largely increased, this increase was associated with decreased cerebral oxygen extraction ("luxury perfusion"), and high values of systemic-cerebral oxygenation index. In response to transient profound hypocapnia, the cerebral oxygen extraction normalized (increased), as did the systemic-cerebral oxygenation index (decreased), under most circumstances. The systemic-cerebral ventilatory index showed adequate systemic-cerebral response to hypocapnia in 92 (90.2%) observations. In the remaining ten (9.8%) observations, this response was considered inadequate, but it did not result in abnormal systemic or cerebral oxygenation parameters.

CONCLUSIONS: In young adults with severe acute brain trauma who require prompt management of intracranial hypertension, transient profound hypocapnia is effective in lowering the intracranial pressure, as well as in offsetting the cerebral luxury perfusion, while improving or maintaining adequate systemic oxygenation. The systemic-cerebral oxygenation index and the systemic-cerebral ventilatory index are potentially useful, physiologically monitorable variables for the combined assessment of global systemic and cerebral oxygenation in a variety of areas involving physiologic and/or therapeutic approaches.