The availability of circulating blood volume values alters fluid management in critically ill surgical patients.

BACKGROUND: This study evaluated whether commercially available blood volume measurements in critically ill surgical patients altered fluid management. METHODS: Patients admitted to the surgical intensive care unit of a tertiary care teaching hospital were prospectively evaluated. The frequency of changes in fluid management when results of blood volume measurements were available was determined. RESULTS: In a pilot study, the frequency of instances when measurement of blood volume would have altered fluid management was statistically significant (P = .0003). In 40 subsequent patients, treatment change occurred in 36% of instances when blood volume results were obtained (P < .001). In the majority, no immediate qualitative change in clinical status occurred, with a desirable clinical response in 39% and no negative treatment responses (P < .001). CONCLUSIONS: Blood volume measurements may assist in the management of critically ill surgical patients by providing a direct measure of intravascular volume. Further studies are warranted to determine its effect on outcome.

Peripheral blood hematocrit in critically ill surgical patients: an imprecise surrogate of true red blood cell volume.

BACKGROUND: Peripheral blood hematocrit (red blood cell volume/total blood volume) is conventionally used to determine the need for blood transfusions. In critically ill surgical patients, this variable may not accurately approximate true red blood cell volume. We compared peripheral blood hematocrit to (1) plasma volume, (2) estimated circulating blood volume, and (3) a normalized hematocrit to clarify their relationships. METHODS: Consecutive patients admitted to the surgical intensive care unit were evaluated using the BVA-100 Blood Volume Analyzer (Daxor Corporation, New York City, NY). Plasma volume was directly measured by serial tagged albumin concentration. Red blood cell volume was calculated using plasma volume and the peripheral blood hematocrit result. All volumes were presented as percentage deviation from ideal volumes. These ideal volumes were obtained using a patented formula incorporating ideal body weight as determined by Metropolitan Life tables. The peripheral blood hematocrit was compared with a "normalized" hematocrit, defined as the hematocrit value if plasma volume was adjusted to a normal whole blood volume. RESULTS: Eighty-six data points were recorded for 40 patients with average age 61 +/- 20 yr, APACHE II score 20 +/- 6, and a 13% mortality rate. The primary reasons for admission were severe sepsis/septic shock (n = 11), hemorrhagic shock (n = 7), respiratory failure (n = 20), and cardiac failure (n = 2). Bland-Altman analysis showed a mean difference of 3.4 +/- 7.8 hematocrit percentage points between normalized and peripheral blood hematocrit methods, with a 95% confidence interval of 1.7-5.1 and limits of agreement of +/-15.2 hematocrit percentage points. Peripheral blood hematocrit was lower than the normalized hematocrit in 48% of measurements, higher in 17%, and equivalent in 35%. CONCLUSIONS: Peripheral blood hematocrit may not accurately estimate red blood cell volume in a cohort of critically ill surgical patients. This remains to be validated in a larger group of patients, comparing these results with the double isotope technique.

Circulating blood volume measurements correlate poorly with pulmonary artery catheter measurements.

BACKGROUND: Determination of the intravascular volume status of a critically ill surgical patient is paramount for appropriate fluid and cardiovascular management. Many clinical parameters have been utilized to estimate intravascular volume but none are precise indicators of circulating blood volume. The purpose of this observational pilot study was to compare measured blood volume with hemodynamic parameters obtained from the pulmonary artery catheter and to determine if incorporation of these measurements altered treatment decisions in critically ill surgical patients. METHODS: Blood volume measurements were prospectively obtained in twenty surgical intensive care unit patients with a pulmonary artery catheter when intravascular volume status was deemed uncertain by traditional clinical parameters. RESULTS: There was a statistically significant, but weak, correlation between blood volume results and pulmonary artery occlusion pressure, but no correlation with central venous pressure, cardiac index, and stroke volume index. Blood volume information altered treatment in 21% of instances, and 5 of these 6 patients demonstrated a favorable clinical response. CONCLUSIONS: Circulating blood volume measurements may be useful in critically ill surgical patients when clinical appraisal of intravascular volume is uncertain. This remains to be validated in a larger, prospective randomized trial.