‘Normal’ Hemoglobin Decline in ICU Patients
Normal’ Hemoglobin Decline in ICU Patients
Abstract & Commentary
Synopsis: In a cohort of 91 ICU patients without known causes for hemoglobin decline other than blood draws and critical illness, serum hemoglobin levels declined by an average of 0.52 g/dL/d. The decline was more rapid during the first 3 days in the ICU and among patients who were septic.
Source: Ba VN, et al. Time course of hemoglobin concentrations in nonbleeding intensive care unit patients. Crit Care Med. 2003;31(2):406-410.
In this prospective observational study from a combined medical-surgical ICU in Brussels, Ba and colleagues enrolled every patient admitted to the unit who did not have a known reason for bleeding, and followed both the quantity of blood drawn for diagnostic purposes and daily hemoglobin levels. They excluded patients with trauma or recent surgery, as well as those with gastrointestinal bleeding, hematologic or renal disease, and those who left the ICU within 24 hours. Also excluded were patients who developed sepsis after ICU admission. The slope of the linear regression of hemoglobin concentration over time was calculated for each patient.
Of 251 patients admitted to Ba et al’s ICU during the study period, 160 were excluded. This left 91 patients, of whom 33 remained in the ICU longer than 3 days. None of the patients had a clinically apparent reason for acute blood loss other than diagnostic blood draws and other ICU procedures. Admission hemoglobin concentrations were 12.2 ± 2.0 g/dL (mean ± SD).
Overall, the blood hemoglobin levels of the 91 patients declined at a mean rate of 0.52 ± 0.69 g/dL/d. Among the patients who were in the ICU for more than 3 days, this rate was 0.66 ± 0.84 g/dL/d during the first 3 days and 0.12 ± 0.24 g/dL/d thereafter. The decline in hemoglobin levels did not correlate significantly with net fluid balance. The rate of decline was greater in patients with higher APACHE II scores, but only after 3 days in the ICU. The average number of blood samples taken per day was 11.7 ± 4.7, and the total volume of blood drawn per day was 40.3 ± 15.4 mL.
Comment by David J. Pierson, MD
Many ICU patients are anemic, and the questions of when to transfuse and whether to use erythropoietin are much on clinicians’ minds these days. This paper answers neither of them, but provides a potentially important piece of the overall puzzle: How much should patients’ hemoglobin levels be expected to decline simply as a result of being sick enough to be in the ICU? The answer is about half a gram per dL (or roughly 1.5 hematocrit percentage points) per day in the unit, somewhat more if the patient is septic, and less after the first 3 days except in the presence of continued sepsis.
This finding is conceptually useful to think about, but several qualifying issues need to be taken into consideration. By design, the study excluded nearly two-thirds of all patients admitted to the ICU. Thus, the "expected" figure of 0.52 g/dL/d (or 1.21 g/dL/d for patients 1 standard deviation away from the mean value) derives from patients without a recent potential bleeding source who do not have renal or hematologic disease. It also derives from patients with an average admission APACHE II score of 14, whose ICU mortality rate was 13%. One would expect sicker patients to have a more rapid rate of "normal" hemoglobin decline, but this was the case for only one small segment of the patients in this study.
When today’s hemoglobin level is lower than yesterday’s, but there has been no overt bleeding and the patient is not markedly "fluid positive" during that interval, what should the clinician do? How much of a drop should trigger a workup for occult hemorrhage or hemolysis? From a practical perspective, these are difficult questions to answer. The regression plots provided by Ba et al as Figure 2 in their paper suggest a great deal of variability in the slopes of individual patients’ hemoglobin levels over time. And not only do individual patients vary, but also the hemoglobin values reported by the laboratory may vary substantially day-to-day in a given patient. A single hemoglobin level reported to be more than 1.5-2.0 g/dL less than the previous day’s value (or a hematocrit drop of more than 4 or 5%) should prompt consideration of the likelihood of potential causes for blood loss in that patient but should perhaps be repeated before transfusion or further diagnostic testing is undertaken.
An interesting point raised in the discussion of this paper is that the average volume of blood drawn from an ICU patient has apparently declined over the last decade or two. The 40 mL/d found by Ba et al compares with 65 mL/d in a 1986 study1 and 62 mL/d in a study from 1996.2 The current trend toward smaller sample volumes and reduced discard volumes should help to further reduce this component of the "normal" hemoglobin decline during a patient’s stay in the ICU.
References
1. Smoller BR, Kruskall MS. Phlebotomy for diagnostic laboratory tests in adults: Pattern of use and effect on transfusion requirements. N Engl J Med. 1986;314: 1233-1235.
2. Alazia M, et al. Blood loss from blood sample removals in intensive care: A preliminary study. Ann Fr Anesth Reanim. 1996;15:1004-1007.
Dr. Pierson is Professor of Medicine University of Washington Medical Director Respiratory Care Harborview Medical Center Seattle.
In a cohort of 91 ICU patients without known causes for hemoglobin decline other than blood draws and critical illness, serum hemoglobin levels declined by an average of 0.52 g/dL/d. The decline was more rapid during the first 3 days in the ICU and among patients who were septic.Subscribe Now for Access
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