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New Real-Time Blood Monitoring May Lessen the Need for Transfusions During Surgery

An advance that tracks a patient's hemoglobin levels without drawing blood could drastically cut down the need for extra blood in the operating room
hemoglobin monitor during surgery to reduce transmissions



MASIMO CORPORATION

A patient on the operating table starts bleeding profusely. Medical staff use sponge after sponge to soak up the blood, unsure of exactly how much has been lost. Should the attending physician order a transfusion? The patient may still have enough red blood cells for the rest of the surgery, but a lab test to confirm the count can take 15 to 45 minutes.

Confronted with this scenario many physicians opt for a transfusion—to the tune of 1.9 million given in the U.S. during surgery annually. It's unclear, however, if all these are necessary. Now, a new technology could clear that up and staunch the flow. Researchers have developed a noninvasive device that takes real-time measurements of a patient's red blood cells (specifically, hemoglobin levels), giving physicians continuous information about when a patient actually needs a transfusion.

In a small clinical trial of elective orthopedic surgery procedures (such as knee and hip replacements), researchers found that standard protocol, which includes lab work and observation, resulted in about 4.5 percent of patients receiving blood transfusions during surgery, whereas for those relying on the new device, only 0.6 percent required extra blood. The device also seemed to reduce the amount of blood used on average. Jesse Ehrenfeld, director of the Center for Evidence Based Anesthesia at Vanderbilt University Medical Center, will present his team's results Monday afternoon at the American Society of Anesthesiologists annual meeting in San Diego.

"It's got the potential to be a technology that will be really helpful in the operating room," Ehrenfeld says. In his hospital alone, he notes, some 33,000 to 38,000 units of blood were given to patients, and chances are good that "some of that blood we probably didn't need to give."

The device does not puncture the skin. Rather, a sticker (which, Ehrenfeld says, "looks like a Band–Aid") is placed on a patient's finger. A clip-on device employs near-infrared light to measure hemoglobin levels—similar to blood oxygen level-monitoring technology. Blood absorbs light differently based on the concentrations of its relative components, including hemoglobin; the device relies on several different wavelengths to assess the relative quantity of red blood cells circulating in the body, explains Dana Banks, a spokesperson for Masimo Corp., the company that makes the sensor.

Elliott Bennett-Guerrero, director of perioperative clinical research at Duke University, welcomed news of the clinical trial. Bennett-Guerrero, who was not involved in the study, notes that transfusion research has long relied on observational studies rather than more robust randomized controlled trials.

"There's no good science to guide us" about the best time to transfuse a patient, he says. "If the patient's actively bleeding in front of you, and you're not sure what the hemoglobin [level] is, it's not surprising that many of those patients are transfused," he notes.

All in the numbers
For the recent trial of orthopedic operations researchers studied the transfusion rates during surgery for 327 patients, about half of whom were assigned to a standard care group whereas the remainder had their hemoglobin levels monitored during surgery using the new device.

The number of patients needing transfusions during surgery was small (seven in the standard-care group and one in the real-time monitoring group), so researchers dug back through the records to find a matched cohort from six months before of patients under standard transmission protocol. They found that about the same percentage of patients (4.6 percent) had required transfusion during surgery. Given the slight difference in the number of transfusions in the trial's standard care population, the retrospective comparison "gave us some confidence" that the difference was a result of the monitoring technique rather than just a fluke, Ehrenfeld says.

Bennett-Guerrero, however, points out that the data do not include the rate of transfusions beyond 12 hours into the post-op period. These details could be crucial to the device's larger success because the findings are "not as clinically relevant if the patient receives the transfusion a day later for anemia." He also noted that the study was not blind: attending physicians knew whether their patient's hemoglobin was being monitored. Such knowledge could have a sizable impact on the results.

"By virtue of patients having this device, clinicians might have been less likely to transfuse them," Bennett-Guerrero suggests.

A consistent monitoring strategy could help create more usable—and adopted—transfusion guidelines. The level that should prompt a transfusion lies between eight and 10 grams of hemoglobin per deciliter of blood for an elderly surgical patient, Bennett-Guerrero says. But in the operating room, there is a large range of transfusion rates.

In a study published in the October 13 issue of JAMA The Journal of the American Medical Association, Bennett-Guerrero and his colleagues found that rates of transfusions during bypass surgery varied widely across 798 different U.S. centers (from 7.8 percent of patients at some hospitals to 92.8 percent at others). These differences "are disconcerting" and "strongly suggest inappropriate transfusions," noted Aryeh Shander of the Department of Anesthesiology at the Englewood Hospital and Medical Center in New Jersey, and Lawrence Goodnough of the Department of Pathology at the Stanford School of Medicine in an editorial in the same issue of JAMA. "Published guidelines have not been effective in reducing this variability in blood transfusion," they wrote.

Cutting down on blood
Red blood cells are not the only key facet of blood—other substances, such as saline- or gelatin-based blood substitutes, can replace lost fluid if a patient's hemoglobin levels remain high enough. And despite high hopes for an oxygen-carrying red blood cell-alternative, synthetic blood products have lagged behind expectations.

Many efforts have been made already to reduce the amount of blood needed during surgery. The notion of "bloodless surgery" has persisted for nearly a century and now comes with a set of guidelines to help cut down on transfusions.

The risks of blood transfusions include infectious disease transmissions, which are increasingly rare with improved screening techniques, and reactions to the blood itself. Scientists still debate the larger drawbacks of transfusions, and some data suggest that they can cause cancer to recur or hamper lung function.

In any case, Bennett-Guerrero says, "transfusion is expensive and involves the use of a scarce resource." In the future, he notes, "a cost analysis would be helpful."

The monitoring device has already found use at Brookdale University Hospital in Brooklyn, which runs a bloodless surgery program. But before it is widely adopted more data on its efficacy will be critical. The next steps, Ehrenfeld explains, will be to expand use of the device in a larger trial to examine its impact on transfusion rates for different patient populations, such as people undergoing cardiac or trauma procedures, where extra blood is needed more frequently.

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