Running on empty? The compensatory reserve index

Abstract

Machine modeling can quickly and accurately detect and trend central blood volume reduction in real time during the compensatory phase of hemorrhage as well as estimate when an individual is "running on empty" and will decompensate (CRI, 0), well in advance of meaningful changes in traditional vital signs.

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

“…Since stroke volume is associated with features of the arterial pulse waveform (5,20,24), it is not surprising that stroke volume showed a high correlation with blood loss similar to that of CRI. However, the rate of change in stroke volume during blood loss is similar in individuals regardless of their tolerance to hypovolemia (8,21). This is demonstrated in the present study by the similar rate of stroke volume decrease (slope) in Fig.…”

“…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.…”

“…4A. At decompensation, humans with a high tolerance to blood loss have relatively lower stroke volume than individuals with low tolerance (8,21), which was also observed in the baboons (Fig. 4A).…”

“…Arterial waveforms obtained during hemorrhage and LBNP experiments were analyzed with an algorithm developed to estimate the compensatory reserve called the CRI. The algorithm was originally developed on the basis of extensive analysis of a large body of waveform data obtained from human subjects during progressive central hypovolemia induced with LBNP (6,21). Figure 1 (11) illustrates the different characteristics of an arterial pressure waveform during normovolemia (Fig.…”

“…We call this physiological measurement the compensatory reserve; the algorithm calculates a compensatory reserve index (CRI), which reflects the proportion of intravascular volume remaining before the onset of decompensation (21) and can distinguish those individuals with low tolerance to central hypovolemia (6). CRI ranges from 1 to 0, where CRI ϭ 1 represents normovolemia and CRI ϭ 0 represents hypovolemia at the point of decompensation (6,21).…”