Cerebral Oximetry

Dr. Chang

Cerebral Oximetry: Monitoring the Brain as the Index Organ

Anesthesiology. January 2011, Volume 114, Issue 1, pages 12-13.

Note: the influence of this article comes from observing increased use of cerebral oximetry at a top-rated U.S. institution with a high volume of on-pump cardiac surgeries. (HC)

A prospective evaluation of 1,178 consecutive adult patients undergoing on-pump cardiac surgery, showed by Heringlake et al., presented compelling evidence that baseline cerebral oxygen saturation (Sco₂) is an independent risk factor for 30-day and one-year mortality.

A general idea behind cerebral oximetry goes as such: cerebral autoregulation reflects the coupling of cerebral oxygen delivery to cerebral metabolic rate and occurs primarily via modulation of cerebral blood flow in the presence of decreased cerebral arterial oxygen content. This is postulated either due to hypoxemia or moderate hemodilution. This study alluded to the failure of oxygen supplementation to increase Sco₂ beyond a cut-off value of about 50% indicated the potential for significantly higher morbidity and mortality.

One challenge of cerebral oximetry is the fact that perturbations in Sco₂, although highly sensitive, are conversely relatively nonspecific. Like any other perioperative parameter, it is for the clinician to determine whether a decrease in Sco₂ reflects a derangement of systemic perfusion, regional cerebral hypoperfusion, relative hypoxemia, increased cerebral metabolic rate, or some other such combination of factors. The numeric value should complement the larger clinical picture.

Now the study by Heringlake et al. looked at on-pump cardiac surgeries. Another study referenced in the article looked at a cohort of pediatric patients. If the observations can further be confirmed in various settings, the idea to employ this device as a sensitive, yet simple addition to the preoperative assessment of the non-cardiac patient may demonstrate similar findings and efficacy in the operating room.