BehindTheMedspeak: Measuring Brain Oxygenation Noninvasively

One of the greatest ongoing controversies in 21st–century anesthesiology revolves around the use of cerebral function/brain activity monitors during surgery.

The companies that make them have, for decades, been trumpeting these costly machines as the solution to intraoperative awareness.

Some of the manufacturers have gone as far as to claim that using such a device represents the "standard of care."

Such a claim renders anyone who doesn't adhere to it liable for negligence in a court of law.

Anesthesiologists are not nearly as impressed: most of us find claims of efficacy overstated and also recognize that they can pose a danger to patients.

If you trust the readout that says your patient is too light, it's quite reasonable to increase the depth of anesthesia in response.

Do this one time too many and you'll find yourself pumping on the patient's chest doing CPR during a Code Blue as a result of having taken the blood pressure down to the basement while trying to deepen the patient.

The various brain monitors on the market work by taking raw EEG signals and then using a proprietary algorithm to process them into a signal that purports to measure the depth of anesthesia.

Hamamatsu, a long–established Japanese company working in optics and related fields, has created an alternative approach which appears to this observer potentially more useful than the various cerebral function monitors currently on the market.

What Hamamatsu has done is invent a device which measures brain oxygenation using light.

This seems to me a much better approach than fiddling around trying to calculate the depth of consciousness and anesthesia.

I recall back in the early days of brain monitoring: one day I asked one of our residents who was quite knowledgeable about the monitors what he did when the machine showed that the patient was light.

He smiled, then said, "Unplug it."

That's how useful they were back then.

Things haven't gotten a whole lot better since.

If brain oxygenation is optimal, damage due to hypoxia won't occur.

Q.E.D.

We use finger monitors to detect arterial oxygenation in the peripheral circulation; such devices work by measuring differential light absorption by oxygenated and nonoxygenated blood.

They are enormously useful and represent the single greatest advance in clinical anesthesia over the past quarter century.

The reason: they offer advance notice of impending hypoxia far enough ahead of catastrophe that they can help avert a disaster.

True, they are prone to false alarms but that's OK: one errs on the side of caution.

Similarly with the Hamamatsu NIRO (Noninvasive Infra–Red Oxygenation) monitor: if it tells me the patient's brain is getting less oxygen, I can turn up the oxygen concentration and increase ventilation.

No harm done even if it was a false alarm.

That's a heckuva lot different than the scenario I noted above involving CPR as the final common pathway.