Detection of Low-volume Blood Loss: Compensatory Reserve Versus Traditional Vital Signs
ARMY INST OF SURGICAL RESEARCH FORT SAM HOUSTON TX
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BACKGROUND Humans are able to compensate for low-volume blood loss with minimal change in traditional vital signs. We hypothesized that a novel algorithm, which analyzes photoplethysmogram PPG wave forms to continuously estimate compensatory reserve would provide greater sensitivity and specificity to detect low-volume blood loss compared with traditional vital signs. The compensatory reserve index CRI is a measure of the reserve remaining to compensate for reduced central blood volume, where a CRI of 1 represents supine normovolemia and 0 represents the circulating blood volume at which hemodynamic decompensation occurs values between 1 and 0 indicate the proportion of reserve remaining. METHODS Subjects underwent voluntary donation of 1 U approximately 450 mL of blood. Demographic and continuous noninvasive vital sign wave form data were collected, including PPG, heart rate, systolic blood pressure, cardiac output, and stroke volume. PPG wave forms were later processed by the algorithm to estimate CRI values. RESULTS Data were collected from 244 healthy subjects 79 males and 165 females, with a mean SD age of 40.1 14.2 years and mean SD body mass index of 25.6 4.7. After blood donation, CRI significantly decreased in 92 0.05 95 confidence interval CI, 88 95 of the subjects. With the use of a threshold decrease in CRI of 0.05 or greater for the detection of 1 U of blood loss, the receiver operating characteristic area under the curve was 0.90, with a sensitivity of 0.84 and specificity of 0.86. In comparison, systolic blood pressure 52 95 CI, 45 59, heart rate 65 95 CI, 58 72, cardiac output 47 95 CI, 40 54, and stroke volume 74 95 CI, 67 80 changed in fewer subjects, had significantly lower receiver operating characteristic area under the curve values, and significantly lower specificities for detecting the same volume of blood loss.
- Anatomy and Physiology
- Medicine and Medical Research