In critical care, perioperative and interventional settings across the country, nurses are becoming increasingly aware of the value of cerebral and somatic oximetry for measuring the "color of life."

Using the same near-infrared technology familiar to nurses from finger pulse oximetry devices, cerebral oximetry measures regional saturation of oxygen (rSO2) in a specific area of the brain, while somatic oximetry can be used on virtually any area of the body.

When clinicians strategically place cerebral/somatic sensors on body surfaces, the devices emit near-infrared wavelengths that pass easily through bone tissues. Inside the body, the near-infrared light is readily absorbed by red-colored oxygenated hemoglobin molecules within red blood cells, while molecules of deoxy-hemoglobin absorb less of the light.

After subtracting out surface data from the skull or skin, cerebral and somatic oximetry provides an rSO2 value unique to the body region under the sensor.

Early Warning

Traditional vital signs reflect systemic status, and lab results are time-delayed, which means they sometimes fail to detect regional changes in oxygenation in a timely manner.

Regional saturation of oxygen fills this void by instantaneously recording changes in rSO2 within the brain or other body area directly under the sensor. This timely measurement provides the care team with valuable information about oxygenation imbalances linked to both positive and negative outcomes. Once the team evaluates the problem and intervenes, changes in the rSO2 readings provide immediate feedback about the effectiveness of interventions.

Used in adult, pediatric and neonatal patients, cerebral/somatic oximetry provides a noninvasive, continuous and immediate guide to changes in rSO2 within the brain (cerebral oximetry) or other body parts (somatic oximetry). The technology is invaluable in cardiac, vascular and general surgery, interventional cardiac catheterization labs, critical care units and other settings where reduction of blood flow to the brain or other regions of the body is a potential risk.

Watching for Stroke

At Duke University Medical Center in Durham, NC, Joseph A. Rybicki, MSN, CRNA, staff nurse anesthetist in the department of electrophysiology, uses cerebral oximetry on all patients under general anesthesia or being intubated for lengthy procedures such as atrial fibrillation ablation or ventricular tachycardia ablation.

"One of the potential complications of these procedures is a stroke, so we use the regional oximeter to look at frontal lobe perfusion," he said. "Used in conjunction with an ongoing EEG, cerebral oximetry provides valuable clues to the perfusion within the frontal lobe of the brain when sensors are placed on either side of the forehead."

Rybicki also uses cerebral oximetry to indirectly track high levels of carbon dioxide, or hypercarbia.

"When the surgeon uses a transeptal needle to access the left side of the heart through the atrioventricular wall during an ablation procedure, we hold respirations, sometimes for as long as 4-6 minutes," he explained. "The patient naturally becomes hypercarbic, and the cerebral oximetry readings go up in both sides of the brain simultaneously.

"When I evaluate perfusion readings, I am looking for trends rather than absolute saturations," Rybicki concluded. "We have had no events at all, no strokes or deaths in the electrophysiology lab since we started using cerebral oximetry 1 years ago."

Peripheral Perfusion

Jamie Ridout, MSN, RN, ACNP, the director of cardiac surgery at St. Joseph's Hospital in Atlanta, oversees more than 1,200 cardiovascular procedures each year. She described how cardiothoracic surgeon Douglas Murphy, MD, utilizes somatic oximetry to prevent postoperative complications from venous thrombosis following robotic mitral valve procedures.

"When this approach is used, there's no sternal incision," Ridout explained. "The procedure is done endoscopically É and the patient is placed on cardiopulmonary bypass with cannulae placed in the femoral artery and femoral vein. The decannulation process and repair of the femoral artery poses a potential risk of compromising the distal perfusion to the leg."

After the patient is decannulated in the OR and ready for transfer to the cardiac ICU, the OR nurses place sensor pads on the calves of both legs for somatic oximetry.

"The patient begins monitoring in the CVICU, where a baseline is established, and is monitored for 12 hours until he or she is alert. This monitoring gives us important information the patient can't convey when intubated and sedated in the immediate postop period," Ridout said.

"If the patient has a poor perfusion due to low cardiac output, both legs would demonstrate a drop in perfusion. If only the affected leg is showing perfusion changes, then there would be concern about a possible thrombosis," she continued. "We would usually see a gradual decline in perfusion before the foot turns blue or cold, which clues us in to the possibility of a thrombosis in the femoral artery."