Individual-Specific, Beat-to-beat Trending of Significant Human Blood Loss

Abstract

Current monitoring technologies are unable to detect early, compensatory changes that are associated with significant blood loss. We previously introduced a novel algorithm to calculate the Compensatory Reserve Index (CRI) based on the analysis of arterial waveform features obtained from photoplethysmogram recordings. In the present study, we hypothesized that the CRI would provide greater sensitivity and specificity to detect blood loss compared with traditional vital signs and other hemodynamic measures. Continuous noninvasive vital sign waveform data, including CRI, photoplethysmogram, heart rate, blood pressures, SpO2, cardiac output, and stroke volume, were analyzed from 20 subjects before, during, and after an average controlled voluntary hemorrhage of ∼1.2 L of blood. Compensatory Reserve Index decreased by 33% in a linear fashion across progressive blood volume loss, with no clinically significant alterations in vital signs. The receiver operating characteristic area under the curve for the CRI was 0.90, with a sensitivity of 0.80 and specificity of 0.76. In comparison, blood pressures, heart rate, SpO2, cardiac output, and stroke volume had significantly lower receiver operating characteristic area under the curve values and specificities for detecting the same volume of blood loss. Consistent with our hypothesis, CRI detected blood loss and restoration with significantly greater specificity than did other traditional physiologic measures. Single measurement of CRI may enable more accurate triage, whereas CRI monitoring may allow for earlier detection of casualty deterioration.

Comparison of compensatory reserve during lower-body negative pressure and hemorrhage in nonhuman primates

“…The algorithm for determining compensatory reserve is unique in that it captures the status of "individuals" by estimating the relative amount of reserve remaining for compensation during blood loss without having to "know" demographics or any other information. Within this construct, it is noteworthy that compensatory reserve responses of baboons during either LBNP or hemorrhage are similar to those previously reported in humans during LBNP (6,21,23) or hemorrhage (7,22,27). This detailed model, which captures individual status, is best demonstrated by the different slopes of regression for baboons with low compared with high tolerance to progressive reductions in central blood volume (Fig.…”

“…Therefore, depending on how each animal presented at baseline relative to its peers (perhaps related to various factors that can compromise compensatory mechanisms such as the level of tolerance, sedation, or hydration), it is possible that the model yielded a lower baseline CRI because that particular Nth baboon was more compromised at baseline. Although this method is valid, it produced an algorithm that exhibited greater variability compared with our previous experience with the CRI algorithm derived from human data (7,27). As a result, the baboon CRI algorithm provided a wide range of baseline CRI values (0.9 to 0.4) that contributed to a low median value (0.74) relative to humans.…”

“…4B). Differences in slopes of the stimulus-response (blood volume-CRI) relationship have been shown to represent the individual reserve required to compensate for the reduction in circulating blood volume (7). Previous experiments using LBNP (6,23) support the notion that individuals with relatively low tolerance to reductions in central blood volume display more rapid depletion of their compensatory reserve.…”

“…More recently, the measurement of compensatory reserve has been shown to be more specific than standard vital signs in the tracking of circulating blood volume in humans during actual mild (ϳ10%) to moderate (ϳ20%) hemorrhage (7,22,27). However, for obvious ethical reasons, human hemorrhage experiments cannot be designed with decompensation endpoints to demonstrate the capability of the CRI algorithm to distinguish individuals with high and low tolerance to actual blood loss.…”

Detection of volume loss using the Nexfin device in blood donors

“…In contrast to our findings, they showed that the receiver AUROC was larger for systolic blood pressure than for cardiac output when detecting the loss of 450 ml of blood [28]. Convertino and colleagues used an algorithm-based analysis of photoplethysmography and showed a ROC AUC of 0.90 for the compensatory reserve index for detecting blood loss [29]. The controlled volume loss in their study was, however, twice as large as in our investigation, ranging from 1 l to 1.3 l [29].…”