A large French study has shown that monitoring both hemoglobin (SpHb) and plethysmography variability index (PVI) as part of a vascular filling algorithm allows for optimal transfusion among surgical patients, thereby reducing mortality. The researchers noted that inclusion of such noninvasive devices may significantly affect patient outcomes in the future, particularly among patients undergoing serious, more invasive surgeries.
“We know that anemia and inadequate volume filling are two important factors in morbidity and mortality after anesthesia,” said Nathalie Nathan, MD, the head of the Department of Anesthesiology at Centre Hospitalier Universitaire de Limoges, in Limoges, France.
“Although meta-analyses have demonstrated the utility of adapting filling volume and blood transfusions to correct anemia on a case-by-case basis, most of these trials lacked external validity. Therefore, we wanted to see if continuous monitoring of hemoglobin and PVI, when integrated into an algorithm, could improve mortality and transfusion needs in a single hospital center.”
Dr. Nathan and her colleagues set out to compare the percentage of patients receiving transfusion during the first 48 hours after surgery, as well as 30- and 90-day mortality between two identical 11-month periods in 2013 and 2014. The difference between the two periods was that during 2014, all operating rooms, recovery rooms and ICUs were equipped with and personnel were trained on the Masimo Radical-7 to monitor hemoglobin and PVI. Each patient received vascular filling with either crystalloids or blood, according to an institutional algorithm.
Demographic, anesthesia, surgical and transfusion data were obtained from an electronic database. Data from the hemoglobin and PVI monitors were collected from a secure, proprietary third-party system.
Surgical Severity Differences
As Dr. Nathan reported at the 2016 annual meeting of the American Society of Anesthesiologists (abstract A1103), 18,867 patients were eligible for analysis. A total of 3,540 patients in 2014 underwent goal-directed therapy guided by hemoglobin and PVI data provided by the noninvasive device. “However, these patients were older, had longer duration of surgery and a greater severity of surgery than those from 2013,” Dr. Nathan explained.
The study found that the percentage of transfused patients at 48 hours did not change between the two periods (7.9% in 2013 vs. 8.5% in 2014; P=0.1323). The same was true for the number of units of blood transfused at 48 hours (3.4±2.7 vs. 3.4±2.9; P>0.05). Nevertheless, patients who underwent goal-directed therapy were more often transfused in the operating room than their counterparts who did not when SpHb was used in noncardiac surgery (72.9% vs. 56.1%; P=0.0002).
“These results seem to say that there is no effect when using the Radical-7 because mortality was the same between the groups when no goal-directed therapy was used,” Dr. Nathan explained. “To confirm these results, we did a Cox regression analysis to evaluate the risk of death between the two periods, and we found that intermediate- and high-severity procedures were associated with a higher incidence of death, with odds ratios of 2.42 and 8.98, respectively.”
The analysis also revealed that patients who received goal-directed therapy in the second year had a significantly lower risk for 30-day mortality (odds ratio, 0.69; 95% CI, 0.50-0.99; P=0.0426).
“To conclude,” Dr. Nathan said, “continuously monitoring SpHb and PVI in a single institution seems to reduce mortality by 30% at 30 days after surgery. This is likely the result of being able to exactly adjust to patients’ needs and give blood products at exactly the right time based on the proper monitoring.”
“You stated that you used SpHb as an indicator for transfusion,” said session co-moderator Uday Jain, MD, PhD, a staff anesthesiologist at Alameda Health System, in Oakland, Calif. “However, there’s insufficient validation of this technique for transfusion. You may have transfused some patients who didn’t need it and may not have sufficiently transfused others who did need it. Did you also get hemoglobin values through a more conventional technique?”
“Of course,” Dr. Nathan replied. “We did two things: At the beginning of surgery, we adjusted the value of hemoglobin given by this device with the value obtained from an invasive method before surgery; we also continued to measure hemoglobin in the laboratory.
“I can say that the number of invasive measurements that we used at the hospital diminished as a result of the SpHb monitoring,” she added.
“What I get out of this study,” Dr. Jain said, “is that the plethysmographic variability index is an easy-to-measure number that alerts you when the patient is getting hypovolemic because of blood loss. A simultaneous reduction in SpHb value is confirmatory. This prompts you to measure hemoglobin by a more conventional technique; you do not base the transfusion decision entirely on the SpHb value. The reduction in mortality you observed suggests that critical hypovolemia and anemia may be missed in the absence of monitoring.”