Page 27 - Journal of Special Operations Medicine - Spring 2016

combat casualty care and military operational medicine. during child delivery in case 5 demonstrates the efficacy
Measurement of the reserve to compensate for relative of this technology to provide rapid assessment of phar-
blood volume deficit has proven to provide a medical macologic impacts that could compromise compensa-
capability to the military with the most sensitivity and tory response(s). This capability could prove critical to
specificity for blood loss compared with all standard the use of analgesics and anesthetics during pain man-
vital signs and hemodynamic measurements. For this agement on the battlefield and during surgery at higher
12
report, we intentionally chose nine distinct case studies echelons of battlefield care. In this case, a prolonged
in an effort to demonstrate the versatility provided by uterine contraction was used as a clinical indicator for
measurement of compensatory reserve in different clini- dosing a β -agonist, based on the controversial premise
2
cal and operational conditions of central hypovolemia that the use of such tocolytics might prevent perinatal
when standard vital signs were generally dismissed as morbidity and mortality. Although the agonist was ef-
15
a result of clinical assessments that did not account for fective in inhibiting the uterine contraction, the resulting
compensatory changes. Cases presented here reinforce prolonged reduction in peripheral vascular resistance
that the measurement of compensatory reserve can over- due to vasodilation caused significant blunting of the
come numerous limitations associated with standard autonomically mediated vasoconstrictor response, a
vital signs and other clinical assessment techniques, be- critical mechanism for compensation. This was reflected
cause CRI provides a continuous, real-time, beat-to-beat in the patient’s reflex tachycardia and rapid decrease in
indicator of patient status and is specific to each patient. compensatory reserve to less than 40% (CRI, <0.4) of
the remaining reserve to compensate. Taken together,
The development and use of technology for real-time it is important to recognize that many therapeutic in-
arterial-waveform-feature analysis, presented as a green, terventions could compromise a patient’s ability to ad-
yellow, and red fuel gauge, was specifically developed equately respond to a severe hemorrhagic insult. Given
for use by Combat Medic who may not have the ex- that postpartum hemorrhage is a life-threatening event,
perience required to accurately and rapidly assess de- it was fortunate that this patient experienced very little
cline in the stability of a bleeding or dehydrated Soldier blood loss (approximately 250mL). As such, this exam-
displaying “normal” mentation because of effective ple serves to reinforce the importance of implementing
compensation for hypovolemia. Given the challenges of clinical decisions and interventions based on the inte-
nonspecificity of traditional vital signs and laboratory grated capacity of the body to maintain an adequate
values, our case studies corroborate that the measure- compensatory reserve.
ment of compensatory reserve provides the capability
needed for the simple, rapid, and accurate assessment In case 6, the CRI algorithm was able to interrogate
of central volume status in acutely ill or traumatically CPR-generated waveforms and quantify peripheral per-
injured patients. fusion. There was a measureable drop in compensatory
reserve when CPR stopped, which returned to approxi-
In the cases of hemorrhage presented here, measurement mately 75% (CRI, 0.75) when compressions resumed.
of the compensatory reserve demonstrated a continuous The ability of the CRI to interpret the waveforms gener-
quantitative assessment of the individual patient’s re- ated by chest compressions suggests that measurement
serve remaining to compensate for blood loss. It is criti- of compensatory reserve may serve as a useful adjunct
cal for military caregivers to appreciate that the patient’s for rescuers during resuscitation efforts, since real-time
status is not dictated by the magnitude of hypovolemia CPR-sensing and feedback technology has been shown
alone but by the capacity of the individual patient to to modestly improve the quality of CPR during in-
compensate for the volume loss. 12,13 In this regard, casu- hospital cardiac arrest. As a result of findings from
16
alties with sensitive compensatory mechanisms may not case 6, collection of CRI measurements during CPR are
require the immediate treatment needed by those who continuing in an effort to test the hypothesis that mea-
are “poor” compensators with lower tolerance for hypo- surement of the compensatory reserve can be associated
volemia. The cases we present corroborate earlier find- with gains in CPR quality and translate into improve-
8,9
ings that measurement of the integrated compensatory ments in patient survival.
reserve based on feature changes of arterial waveforms
represents the only known technology that can provide In addition to clinical orthostatic intolerance affect-
military as well as civilian medical caregivers with a sim- ing one-half million civilians, more than 10,000 active
ple, noninvasive capability with superior specificity 8,12,14 component Servicemembers experience approximately
for early and accurate triage decision support. 9 21,500 cases of syncope in military operational envi-
ronments annually, with women displaying nearly three
In addition to a clinically continuous, sensitive, and spe- times the rate of fainting events as men. Situations as-
cific evaluation of circulating blood volume loss and its sociated with syncope in US Armed Forces personnel in-
restoration during resuscitation, the monitoring of CRI clude invasive medical procedures (e.g., blood donations,

Machine Learning and Hemodynamic Instability 11