Calibrated Drapes May Aid Blood-Loss Estimates : Estimate error was reduced from more than 30% to less than 10% in one study.


SAN FRANCISCO — There's a product niche waiting to be filled, one that might save a life during postpartum hemorrhage.

Health care providers consistently underestimate the amount of postpartum blood loss, and adding calibrations to vaginal delivery drapes could improve blood loss estimates, results of a randomized crossover study suggest.

Participants who viewed calibrated delivery drapes and then were asked to estimate the amount of blood in uncalibrated drapes reduced the error in their estimates from more than 30% to less than 10% for the highest volumes of blood, Robert J. McCarthy, Pharm.D., said in a poster presentation at the annual meeting of the American Society of Anesthesiologists.

There are no vaginal delivery drapes on the market calibrated to indicate the amount of blood loss, added Dr. McCarthy of Northwestern University, Chicago. “It's time consuming to go through and set these up [individually],” he said. If such a product became available, it “could prevent delay in diagnosis and treatment of postpartum hemorrhage.”

The investigators asked 42 obstetricians, 21 nurses, and 43 anesthesiologists to estimate blood loss at eight mock vaginal delivery stations, four with uncalibrated delivery drapes and four with drapes that were marked at 500-mL increments up to 2,500 mL.

Each set of delivery drapes contained expired packed red blood cells diluted to a hematocrit of 33%, in volumes of 300, 500, 1,000, or 2,000 mL, plus 100 mL of urine and 5, 10, or 15 surgical sponges.

Subjects were randomized to view the calibrated or uncalibrated drapes first, then crossed over to the other group of stations.

Viewing the uncalibrated drapes first produced greater underestimates of blood loss that worsened with larger volumes of blood loss, reported Dr. McCarthy, lead investigator Dr. Paloma Toledo, and their associates. All the authors are from Northwestern University.

Errors by those who first viewed uncalibrated drapes ranged from a 16% underestimate of the 300-mL blood volume to a 41% underestimate of the 2000-mL volume.

Subjects who first viewed the calibrated drapes underestimated volumes in the uncalibrated drapes by less than 15%.

The results did not differ by the type of health care provider, the level of training, or number of years of experience.

A previous study reported that estimates of postpartum blood loss based on visual assessment underestimated blood loss by 33%–50% compared with photospectrometry, “which is the gold standard for this,” Dr. McCarthy said (Int. J. Gynecol. Obstet. 2006;93:220–4).

“They used smaller amounts of blood loss—300 mL as their top volume—while we used volumes that were more likely to be clinically important and need some kind of intervention.”

Another previous study reported that estimates of blood loss worsen with increasing volumes of blood loss (Int. J. Gynecol. Obstet. 2000;71:69–70).

Blood loss greater than 500 mL after vaginal delivery (postpartum hemorrhage) is a major cause of maternal morbidity and mortality.

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