SpHb sensor can monitor blood hemoglobin levels during spine surgery

A spectrophotometric hemoglobin (SpHb) sensor may become a useful new approach to noninvasive monitoring of blood hemoglobin levels during surgery, reports a study in the April issue of Anesthesia & Analgesia, official journal of the International Anesthesia Research Society (IARS).

The SpHb technology could reduce the need for invasive monitoring or the need for blood transfusion during surgery. But further development will be needed to make SpHb sufficiently accurate for clinical use, according to the study by Dr. Ronald D. Miller of University of California, San Francisco.

The researchers evaluated SpHb for continuous monitoring of blood hemoglobin levels in 20 patients undergoing spine surgery with general anesthesia. Similar to the familiar "finger clip" pulse oximeter, SpHb works by shining different light wavelengths through blood-perfused tissues. However, the SpHb monitor provides more detailed information on a number of different blood variables, including hemoglobin. During major surgery, regular measurements of hemoglobin—the oxygen-carrying compound in the blood—are made to assess the need for blood transfusion.

Hemoglobin was also measured in blood samples, using both a standard invasive laboratory test and a newer "point of care" device called HemoCue, which provides rapid results in the operating room. The accuracy of the SpHb was compared with these standard approaches, based on different cutoff points for transfusion decisions. (Transfusions may be needed when hemoglobin is less than 10 grams per deciliter [g/dL] and are almost always needed at less than 7 g/dL.) The study included a total of 78 comparisons.

The SpHb monitor was fairly accurate, compared to the standard laboratory test. The difference in hemoglobin levels was less than 1.5 g/dL for 61 percent of comparisons, but more than 2.0 g/dL in 22 percent. The SpHb technique tended to be more accurate in longer surgical procedures and at higher levels of tissue blood perfusion. In contrast, the HemoCue measurements were almost always within 1.0 g/dL of the standard laboratory test.

The ability to measure hemoglobin without the need for a blood sample would help to simplify patient monitoring during surgery. The new results show that SpHb is a fairly good indicator of hemoglobin levels, compared to standard tests. "Yet our study indicates that SpHb may not be as accurate as clinically necessary in some patients," Dr. Miller and coauthors write.

"Improved refinement of continuous, noninvasive technology, such as SpHb, could address important clinical requirements," they add. In the meantime, the researchers suggest that SpHb might be used to guide the timing of direct measurement of hemoglobin in blood samples.