Smaller Blood Draws Reduce Transfusions in ICU, Trial Suggests

SAN FRANCISCO — Switching to routine use of small-volume blood draws in adult intensive care units (ICUs) for most laboratory testing appeared to cut blood transfusions without compromising those tests, a cluster randomized trial showed.

The number of red blood cell (RBC) units transfused dropped by 9.84 per 100 patients admitted for 48 hours or more among ICUs using so-called soft draws compared with standard volume collection (least squares mean 0.71 vs 0.80, P=0.04), reported Deborah Siegal, MD, of the University of Ottawa in Ontario.

After excluding the pandemic period during which ICUs paused on switching tube types, that difference lost statistical significance although maintaining a similar magnitude of effect (7.24 fewer RBC units per 100 patients in low-volume draw ICUs, least squares mean 0.72 vs 0.79, P=0.19), according to findings presented at the Society of Critical Care Medicine Critical Care Congress.

“There’s a small effect, really, at the individual level but potential for impact at the health system level,” Siegal told attendees at a session here. “We believe that the totality of the findings, particularly the consistency in the magnitude and direction of the effect that we saw with small-volume tubes, in addition to the mitigation of the hemoglobin reduction in ICU, suggests there is an effect.”

As a secondary endpoint, the decrease in hemoglobin was numerically but not significantly smaller after ICUs transitioned to smaller blood collection tubes.

The rate of specimens with insufficient quantity in the tube for testing was less than 0.03% in both groups overall, and actually numerically highest at 0.031% among standard volume tube ICUs during the pandemic.

Across the course of the trial, that totaled only one excess case in which there was insufficient quantity out of around half a million tests and in exchange it saved some 15,000 RBC units, with all the cost and impact on the blood supply that those transfusions would have taken, Siegal noted at the session.

“Hopefully it is easily translatable and may help save blood product and help decrease the number of transfusions,” commented session co-chair Sheila Alexander, BSN, PhD, RN, of the University of Pittsburgh. “The fewer we can give and still save lives, the better.”

After a week in the ICU, almost all patients have some degree of anemia, with some 40% of patients getting RBC transfusion because of it, Siegal noted.

While there are many mechanisms, iatrogenic blood loss represents a potentially modifiable contributor, she pointed out. One ICU study of over 7,000 patients showed greater than 200 mL blood loss per ICU stay; another study found a loss of up to 41 mL per day in the ICU — the equivalent of 1 unit of blood approximately every 8 days.

Because only about 10% of the volume of a typical 4-6 mL standard blood draw tube is used for testing (the rest discarded as waste), pediatric care has largely switched to small-volume (1.8-3 mL) collection tubes, Siegal noted.

These tubes are available for the same cost and with the same dimensions to the larger-volume tubes such that they can be used on the same analyzers in the laboratory, simply with a lower pressure vacuum draw that pulls less blood into the container.

The even lower-volume “microtainer” style of blood collection tubes don’t work on standard analyzers and thus were not used in the trial.

In the trial’s stepped-wedge cluster design, 25 participating medical-surgical ICUs were randomized as to when to switch to small tubes for all adult patients admitted (with the exception of blood gas testing or blood culture tubes). Two units switched over every 6 weeks until all had done so.

Excluding patients admitted in the week after the transition as a washout period, that left 27,411 total patients and 21,201 not admitted during the pandemic-related delay in switching over the final seven ICUs, from March 2 through Aug. 17, 2020. The prespecified protocol change in trial endpoint to exclude those patients was done without breaking the data lock, Siegal noted. Mean age of the patients was 63, and around 40% of the patients were female.

Clinical staff received only a brief targeted educational intervention at the time of switching, when large-volume tubes were removed and replaced with small-volume ones.

Limitations included pragmatic data collection without quality-of-life data, and the use of a single brand of small-volume tubes, although others are available worldwide.

Alexander noted in an interview with MedPage Today that the cost savings from a relatively simple change may be motivating in the C-suite.