CHICAGO – Switching from conventional to small-volume phlebotomy tubes is an easy step toward reducing iatrogenic blood loss in critically ill adults, a new study suggests.
“We were looking at the amount of blood we were drawing off these patients and when we asked the nurses, the numbers were crazy. It could be as high as 20 mL per time that they drew off the patient and we felt we had to do better. The common sense dictum is the more blood you draw off, the more harm you are causing the patient,” principal investigator Dr. Heather Dolman from Detroit Receiving Hospital, Wayne State University, said in an interview.
Dr. Heather Dolman
For patients staying only a day or 2 at the hospital, the type of blood tube used may not make a difference. But for the critically ill, who studies suggest can have an average of 5 to more than 24 samples drawn a day, the cumulative blood loss over an extended stay can be sizable.
Clinicians are also inclined to order more diagnostic tests as the severity of illness increases, thus putting their sickest patients at the greatest risk of iatrogenic anemia and transfusion. Anemia secondary to phlebotomy accounts for up to 40% of packed red blood cells transfused, Dr. Dolman noted at the annual meeting of the Central Surgical Association.
The process of blood sampling itself also involves a fair amount of waste. Conventional arterial line systems require that an initial blood sample be removed to “clear the line.” This typically results in 2-10 mL of blood being discarded before a second sample of undiluted blood can be obtained.
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Some hospitals have turned to closed blood sampling devices that avoid the need for a second sample. The impact of blood-conserving devices on transfusion rates has been underwhelming, with only one study showing a positive impact leading to reduced blood product use.
As part of their blood-conserving strategy, Dr. Dolman and her colleagues asked the hospital to invest in small-volume phlebotomy tubes (SVTs), which are sized somewhere between a conventional-volume tube (CVT) and a pediatric blood tube.
SVTs reduce the amount of blood needed from 8.5 mL with a conventional tube to 5.0 mL for a basic metabolic panel, from 6.0 mL to 2.0 mL for a complete blood count (CBC) or cross-matching, and from 2.7 mL to 1.8 mL for a prothrombin time /internationalized ratio/partial thromboplastin time, Dr. Dolman said. The cost of an SVT is the same as a CVT, as is the cost of the machinery needed to analyze the samples.
“Everyone is worried about missing out on data, but if you look at the research on the amount of blood the machine really needs, it is only 0.1 mL, that’s less than a cc,” she said. “The technology has been there for a while, I just think the common sense aspect of all this, no one has ever thought of.”
The investigators then retrospectively compared 248 critically ill patients in the ICU, of whom 116 had blood drawn with an SVT and 132 with a CVT. The two groups were well matched with respect to age (55 years vs. 57 years), admission to the emergency surgery/trauma service (63% vs. 64%), and mean APACHE II scores (14.1 vs. 12.7).
Transfusion was at the discretion of the primary team using a restrictive hemoglobin threshold of < 7.0 gm/dL, unless hemodynamic instability or active bleeding were present.
Utilizing an SVT significantly reduced daily blood loss from phlebotomy from 31.7 mL with a CVT to 22.5 mL (P < .0001) and overall phlebotomy blood loss from 299 mL to 174 mL (P < .001), Dr. Dolman reported.
This translated into a nonsignificant trend for fewer units of packed red blood cells transfused in the SVT group (mean 4.4 vs. 6.0; P = .16).
The same pattern was observed in the 158 patients admitted to the emergency surgery/trauma service, with SVT also leading to significantly fewer episodes of severe anemia (6 vs. 20; P = .01) and a trend toward shorter ICU stays (9.2 days vs. 10.6 days; P = .46), she said.
Patients with an APACHE score of at least 20, a group one would anticipate to derive greater advantage from a blood-conserving strategy, did not benefit from use of an SVT vs. a CVT, but the number of patients was very low at just 27 and 19, respectively, Dr. Dolman noted.
Anemia, however, had a profound impact on the critically ill cohort. Patients with severe anemia were significantly more likely than those with a hemoglobin level of at least 7 gm/dL to have longer ICU stays (16 days vs. 7.7 days; P < .001), longer hospital stays (23.3 days vs. 13.6 days; P < .001), and to die in the hospital (29% vs. 13%; P = .01).