Lightweight noninvasive trauma monitor for early indication of central hypovolemia and tissue acidosis: A review
ABSTRACT Hemorrhage is a major cause of soldier death; it must be quickly identified and appropriately treated. We developed a prototype patient monitor that noninvasively and continuously determines muscle oxygen saturation (SmO₂), muscle pH (pHm), and a regional assessment of blood volume (HbT) using near-infrared spectroscopy. Previous demonstration in a model of progressive, central hypovolemia induced by lower body negative pressure (LBNP) showed that SmO₂ provided an early indication of impending hemodynamic instability in humans. In this review, we expand the number of subjects and provide an overview of the relationship between the muscle and sublingual microcirculation in this model of compensated shock.
Healthy human volunteers (n = 30) underwent progressive LBNP in 5-minute intervals. Standard vital signs, along with stroke volume (SV), total peripheral resistance, functional capillary density, SmO₂, HbT, and pHm were measured continuously throughout the study.
SmO₂ and SV significantly decreased during the first level of central hypovolemia (-15 mm Hg LBNP), whereas vital signs were later indicators of impending cardiovascular collapse. SmO₂ declined with SV and inversely with total peripheral resistance throughout LBNP. HbT was correlated with declining functional capillary density, suggesting vasoconstriction as a cause for decreased SmO₂ and subsequently decreased pHm. CLINICAL TRANSLATION: The monitor has been miniaturized to a 58-g solid-state sensor that is currently being evaluated on patients with dengue hemorrhagic fever. Early results demonstrate significant decreases in SmO₂ similar to those observed with progressive reductions in central blood volume. As such, this technology has the potential to (1) provide a monitoring capability for both nontraumatic and traumatic hemorrhage and (2) help combat medics triage casualties and monitor patients during lengthy transport from combat areas.
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ABSTRACT: Survival after severe traumatic shock can be complicated by a number of pathophysiologic processes that ensue after the initial trauma. One of these is trauma-induced coagulopathy (TIC) whose onset may occur before initial fluid resuscitation. The pathogenesis of TIC has not yet been fully elaborated, but evolving evidence appears to link severe tissue hypoxia and damage to the endothelium as key factors, which evolve into measurable structural and biochemical changes of the endothelium resulting in a coagulopathic state. This paper will provide a general review of these linkages and identify knowledge gaps as well as suggest new approaches and areas of investigation, which may both limit the development of TIC as well as produce insights into its pathophysiology. A better understanding of these issues will be necessary in order to advance the practice of remote damage control resuscitation.Transfusion 01/2013; 53(S1). DOI:10.1111/trf.12034 · 3.57 Impact Factor
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ABSTRACT: New patient monitoring technologies can noninvasively and directly provide an assessment of the adequacy of tissue perfusion through the simultaneous determination of muscle oxygen saturation (SmO2) and muscle pH (pHm). Non-pulsatile near infrared spectroscopy is used to determine these microvascular parameters. Two separate studies were conducted using an isolated perfused swine limb preparation to widely vary venous blood oxygen saturation (SviO2) and pH (pHvi) to assess the accuracy of a noninvasive sensor with the capability to simultaneously measure both parameters. The isolated limb model is necessary to establish equilibrium between the venous output of the perfusion circuit and the venule measurement of the spectroscopic sensor. The average absolute difference between SmO2 and SviO2 determined over 50 conditions of SviO2 between 13% and 83% on 3 pig limbs was 3.8% and the coefficient of determination (R(2)) was 0.95. The average absolute difference between pHm and pHvi determined over 69 conditions of pHvi between pHvi 6.9 and pHvi 7.5 on 3 pig limbs was 0.045 pH units with an R(2) of 0.92. Measured accuracy was acceptable to support clinically relevant decision making for the assessment of impaired tissue perfusion and acidosis. Sensors were also evaluated on human subjects. There was no statistical difference in SmO2 by gender or location when multiple sensors were evaluated on the right and left calf, deltoid, and thigh of resting men and women (N = 33). SmO2 precision for subjects at rest was 5.6% over the six locations with four different sensors.Physiological Measurement 07/2013; 34(8):859-871. DOI:10.1088/0967-3334/34/8/859 · 1.62 Impact Factor
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ABSTRACT: We hypothesize that limited transthoracic echocardiogram (LTTE) is a useful tool to guide therapy during the initial phase of resuscitation in trauma patients. All highest-level alert patients with at least one measurement of systolic blood pressure less than 100 mm Hg, a mean arterial pressure less than 60 mm Hg, and/or a heart rate greater than 120 beats per minute who arrived to the trauma bay (TB) were randomized to have either LTTE performed (LTTEp) or not performed (non-LTTE) as part of their initial evaluation. Images were stored, and results were reported regarding contractility (good vs. poor), fluid status (empty inferior vena cava [hypovolemic] vs. full inferior vena cava [not hypovolemic]), and pericardial effusion (present vs. absent). Time from TB to operating room, intravenous fluid administration, blood product requirement, intensive care unit admission, and mortality were examined in both groups. A total of 240 patients were randomized. Twenty-five patients were excluded since they died upon arrival to the TB, leaving 215 patients in the study. Ninety-two patients were in the LTTEp group with 123 patients in the non-LTTE group. The LTTEp and non-LTTE groups were similar in age (38 years vs. 38.8 years, p = 0.75), Injury Severity Score (ISS) (19.2 vs. 19.0, p = 0.94), Revised Trauma Score (RTS) (5.5 vs. 6.0, p = 0.09), lactate (4.2 vs. 3.6, p = 0.14), and mechanism of injury (p = 0.44). Strikingly, LTTEp had significantly less intravenous fluid than non-LTTE patients (1.5 L vs. 2.5 L, p < 0.0001), less time from TB to operating room (35.6 minutes vs. 79.1 min, p = 0.0006), higher rate of intensive care unit admission (80.4% vs. 67.2%, p = 0.04), and a lower mortality rate (11% vs. 19.5%, p = 0.09). Mortality differences were particularly evident in the traumatic brain injury patients (14.7% in LTTEp vs. 39.5% in non-LTTE, p = 0.03). LTTE is a useful guide for therapy in hypotensive trauma patients during the early phase of resuscitation. Therapeutic study, level II.01/2014; 76(1):31-8. DOI:10.1097/TA.0b013e3182a74ad9