Unmasking the Hypovolemic Shock Continuum: The Compensatory Reserve.

Hypovolemic shock exists as a spectrum, with its early stages characterized by subtle pathophysiologic tissue insults and its late stages defined by multi-system organ dysfunction. The importance of timely detection of shock is well known, as early interventions improve mortality, while delays render these same interventions ineffective. However, detection is limited by the monitors, parameters, and vital signs that are traditionally used in the intensive care unit (ICU). Many parameters change minimally during the early stages, and when they finally become abnormal, hypovolemic shock has already occurred. The compensatory reserve (CR) is a parameter that represents a new paradigm for assessing physiologic status, as it comprises the sum total of compensatory mechanisms that maintain adequate perfusion to vital organs during hypovolemia. When these mechanisms are overwhelmed, hemodynamic instability and circulatory collapse will follow. Previous studies involving CR measurements demonstrated their utility in detecting central blood volume loss before hemodynamic parameters and vital signs changed. Measurements of the CR have also been used in clinical studies involving patients with traumatic injuries or bleeding, and the results from these studies have been promising. Moreover, these measurements can be made at the bedside, and they provide a real-time assessment of hemodynamic stability. Given the need for rapid diagnostics when treating critically ill patients, CR measurements would complement parameters that are currently being used. Consequently, the purpose of this article is to introduce a conceptual framework where the CR represents a new approach to monitoring critically ill patients. Within this framework, we present evidence to support the notion that the use of the CR could potentially improve the outcomes of ICU patients by alerting intensivists to impending hypovolemic shock before its onset.

A Deeper Dive Into Combat Medic Training.

The recent article by Knisely et al. provides a comprehensive review and summary of recent literature describing simulation techniques, training strategies, and technologies to teach medics combat casualty care skills. Some of the results reported by Knisely et al. align with the findings of our team's work, and these findings may be helpful to military leadership with their ongoing efforts to maintain medical readiness. Accordingly, we provide some additional contextual understanding to the results of Knisely et al. in this commentary. Our team recently published two papers describing the results of a large survey that examined Army medic pre-deployment training. Combining the findings of Knisely et al. along with some of the contextual information from our work, we provide some recommendations for improving and optimizing the pre-deployment training paradigm for medics.

Initial treatment strategies in new-onset atrial fibrillation in critically ill burn patients.

INTRODUCTION: Atrial fibrillation is associated with increased morbidity and mortality in critically ill patients. Few studies have specifically examined this arrhythmia in burn patients. Given the significant clinical implications of atrial fibrillation, understanding the optimal management strategy of this arrhythmia in burn patients is important. Consequently, the purpose of this study was to examine rate- and rhythm-control strategies in the management of new onset atrial fibrillation (NOAF) and assess their short term outcomes in critically ill burn patients. METHODS: We identified all patients admitted to our institution's burn intensive care unit between January 2007 and May 2018 who developed NOAF. Demographic information and burn injury characteristics were captured. Patients were grouped into two cohorts based on the initial pharmacologic treatment strategy: rate-(metoprolol or diltiazem) or rhythm-control (amiodarone). The primary outcome was conversion to sinus rhythm. Secondary outcomes included relapse or recurrence of atrial fibrillation, drug-related adverse events, and complications and mortality within 30 days of the NOAF episode. RESULTS: There were 68 patients that experienced NOAF, and the episodes occurred on median days 8 and 9 in the rate- and rhythm-control groups, respectively. The length of the episodes was not significantly different between the groups. Conversion to sinus rhythm occurred more often in the rhythm-control group (P = 0.04). There were no differences in the incidences of relapse and recurrence of atrial fibrillation, and the complications and mortality between the groups. Hypotension was the most common drug-related adverse event and occurred more frequently in the rate-control group, though this difference was not significant. CONCLUSIONS: Conversion to sinus rhythm occurred more often in the rhythm-control group. Outcomes were otherwise similar in terms of mortality, complications, and adverse events. Hypotension occurred less frequently in the rhythm-control group, and although this difference was not significant, episodes of hypotension can have important clinical implications. Given these factors, along with burn patients having unique injury characteristics and a hypermetabolic state that may contribute to the development of NOAF, when choosing between rate- and rhythm control strategies, rhythm-control with amiodarone may be a better choice for managing NOAF in burn patients.

Physiology of Human Hemorrhage and Compensation.

Hemorrhage is a leading cause of death following traumatic injuries in the United States. Much of the previous work in assessing the physiology and pathophysiology underlying blood loss has focused on descriptive measures of hemodynamic responses such as blood pressure, cardiac output, stroke volume, heart rate, and vascular resistance as indicators of changes in organ perfusion. More recent work has shifted the focus toward understanding mechanisms of compensation for reduced systemic delivery and cellular utilization of oxygen as a more comprehensive approach to understanding the complex physiologic changes that occur following and during blood loss. In this article, we begin with applying dimensional analysis for comparison of animal models, and progress to descriptions of various physiological consequences of hemorrhage. We then introduce the complementary side of compensation by detailing the complexity and integration of various compensatory mechanisms that are activated from the initiation of hemorrhage and serve to maintain adequate vital organ perfusion and hemodynamic stability in the scenario of reduced systemic delivery of oxygen until the onset of hemodynamic decompensation. New data are introduced that challenge legacy concepts related to mechanisms that underlie baroreflex functions and provide novel insights into the measurement of the integrated response of compensation to central hypovolemia known as the compensatory reserve. The impact of demographic and environmental factors on tolerance to hemorrhage is also reviewed. Finally, we describe how understanding the physiology of compensation can be translated to applications for early assessment of the clinical status and accurate triage of hypovolemic and hypotensive patients. © 2021 American Physiological Society. Compr Physiol 11:1531-1574, 2021.

Characteristics of burn casualties treated at role 2 in Afghanistan.

BACKGROUND: Role 2 medical treatment facilities (MTFs) are frequently located in austere settings and have limited resources. A dedicated assessment of burn casualties treated at this level of care has not been performed. Therefore, the objective of this study was to characterize burn casualties presenting to role 2 MTFs in Afghanistan, along with the procedures they required, complications, and mortality to begin understanding the resources consumed by their care. METHODS: We identified burn casualties from the Department of Defense Trauma Registry (DODTR). The inclusion criteria were (1) experienced burn injuries in Afghanistan between October 2005 and April 2018 and (2) had documentation of treatment at role 2 in the DODTR. We excluded casualties with only first-degree burns, not otherwise specified burns, or only corneal burns. Casualty demographics, injury characteristics, procedures, and outcomes were reported. RESULTS: We identified 453 burn casualties with a median (interquartile range) Injury Severity Score of 10 (4-22) and percent total body surface area burned of 11 (5-30). There were 123 casualties (27.2%) with inhalation injury, and the casualties experienced 3,343 additional traumatic injuries and needed 2,530 procedures. Casualties with documentation of resuscitation information received a median (interquartile range) of 1.9 (0.7-3.7) L of crystalloid fluids. Complications were documented in 53 casualties (11.7%). Final mortality was reported in 36 casualties (8.0%), and mortality at role 2 MTFs was reported in 7 casualties (1.5%). CONCLUSION: Burn casualties had many injuries and needed many procedures, including those related to airway management, resuscitation, and wound care. Given the urgency of these procedures, ensuring that there is enough equipment and supplies will be important in the future. Although infrequent, some casualties experienced complications. Factors that may influence resuscitation include injury severity, concomitant traumatic injuries, and available supplies. Obtaining more contextual information on the patient care environment will be useful going forward. LEVEL OF EVIDENCE: Epidemiological, level III.

An Assessment of Pre-deployment Training for Army Nurses and Medics.

INTRODUCTION: Although military nurses and medics have important roles in caring for combat casualties, no standardized pre-deployment training curriculum exists for those in the Army. A large-scale, survey-based evaluation of pre-deployment training would help to understand its current state and identify areas for improvement. The purpose of this study was to survey Army nurses and medics to describe their pre-deployment training. MATERIALS AND METHODS: Using the Intelink.gov platform, a web-based survey was sent by e-mail to Army nurses and medics from the active and reserve components who deployed since 2001. The survey consisted of questions asking about pre-deployment training from their most recent deployment experience. Descriptive statistics were used to analyze the results, and free text comments were also captured. RESULTS: There were 682 respondents: 246 (36.1%) nurses and 436 (63.9%) medics. Most of the nurses (n = 132, 53.7%) and medics (n = 298, 68.3%) reported that they were evaluated for clinical competency before deployment. Common courses and topics included Tactical Combat Casualty Care, Advanced Cardiac Life Support, cultural awareness, and trauma care. When asked about the quality of their pre-deployment training, most nurses (n = 186; 75.6%) and medics (n = 359; 82.3%) indicated that their training was adequate or better. Nearly all nurses and medics reported being moderately confident or better (nurses n = 225; 91.5% and medics n = 399; 91.5%) and moderately prepared or better (nurses n = 223; 90.7% and medics n = 404; 92.7%) in their ability to provide combat casualty care. When asked if they participated in a team-based evaluation of clinical competence, many nurses (n = 121, 49.2%) and medics (n = 180, 41.3%) reported not attending a team training program. CONCLUSIONS: Most nurse and medic respondents were evaluated for clinical competency before deployment, and they attended a variety of courses that covered many topics. Importantly, most nurses and medics were satisfied with the quality of their training, and they felt confident and prepared to provide care. Although these are encouraging findings, they must be interpreted within the context of self-report, survey-based assessments, and the low response rate. Although these limitations and weaknesses of our study limit the generalizability of our results, this study attempts to address a critical knowledge gap regarding pre-deployment training of military nurses and medics. Our results may be used as a basis for conducting additional studies to gather more information on the state of pre-deployment training for nurses and medics. These studies will hopefully have a higher response rate and better quantify how many individuals received any form of pre-deployment training. Additionally, our recommendations regarding pre-deployment training that we derived from the study results may be helpful to military leadership.

Predeployment training of Army medics assigned to prehospital settings.

BACKGROUND: Medics have numerous responsibilities in the combat theater, which include performing lifesaving interventions, providing basic medical and nursing care, and caring for casualties in a variety of scenarios unique to the battlefield. An evaluation of the medic predeployment training paradigm is important and will help to understand its current state and identify areas for improvement. Therefore, the purpose of this study was to perform a focused assessment of Army medic predeployment training to identify patterns that might inform future medic training. METHODS: A web-based survey was created using the Intelink.gov platform and sent by e-mail to Army medics who deployed since 2001. Medics were asked to reflect upon the predeployment training from their most recent deployment experience. There were multiple choice, Likert-type scale, and free-text response questions. Descriptive statistics were used to analyze the results. RESULTS: There were 254 respondents who met the study inclusion criteria. Most of the respondents had their clinical competency evaluated (68.5%, n = 174). Respondents reported several acute trauma, basic nursing, and battlefield medicine skills as being critical but also felt that many of these same skills would have benefited from additional predeployment training. Most of the respondents felt very or fully confident and prepared to provide combat casualty care (74.8%, n = 190 and 74.8%, n = 190). There were 64 respondents (25.2%) who reported feeling not at all, slightly, or moderately confident, and 54 (84.4%) of these respondents described in a free-text question wanting additional training before deployment. CONCLUSION: Respondents reported many skills as being critical to combat casualty care, but several of these skills would have benefited from additional predeployment training. Respondents with more deployment experience or completion of more predeployment training reported feeling more confident and prepared to provide combat casualty care. A common sentiment was the desire for more training of any form before deployment. LEVEL OF EVIDENCE: Epidemiological, level IV.

Tracking DO2 with Compensatory Reserve During Whole Blood Resuscitation in Baboons.

Hemorrhagic shock can be mitigated by timely and accurate resuscitation designed to restore adequate delivery of oxygen (DO2) by increasing cardiac output (CO). However, standard care of using systolic blood pressure (SBP) as a guide for resuscitation may be ineffective and can potentially be associated with increased morbidity. We have developed a novel vital sign called the compensatory reserve measurement (CRM) generated from analysis of arterial pulse waveform feature changes that has been validated in experimental and clinical models of hemorrhage. We tested the hypothesis that thresholds of DO2 could be accurately defined by CRM, a noninvasive clinical tool, while avoiding over-resuscitation during whole blood resuscitation following a 25% hemorrhage in nonhuman primates. To accomplish this, adult male baboons (n = 12) were exposed to a progressive controlled hemorrhage while sedated that resulted in an average (±â€ŠSEM) maximal reduction of 508 ±â€Š18 mL of their estimated circulating blood volume of 2,130 ±â€Š60 mL based on body weight. CRM increased from 6 ±â€Š0.01% at the end of hemorrhage to 70 ±â€Š0.02% at the end of resuscitation. By linear regression, CRM values of 6% (end of hemorrhage), 30%, 60%, and 70% (end of resuscitation) corresponded to calculated DO2 values of 5.9 ±â€Š0.34, 7.5 ±â€Š0.87, 9.3 ±â€Š0.76, and 11.6 ±â€Š1.3 mL O2·kg·min during resuscitation. As such, return of CRM to ∼65% during resuscitation required only ∼400 mL to restore SBP to 128 ±â€Š6 mmHg, whereas total blood volume replacement resulted in over-resuscitation as indicated by a SBP of 140 ±â€Š7 mmHg compared with an average baseline value of 125 ±â€Š5 mmHg. Consistent with our hypothesis, thresholds of calculated DO2 were associated with specific CRM values. A target resuscitation CRM value of ∼65% minimized the requirement for whole blood while avoiding over-resuscitation. Furthermore, 0% CRM provided a noninvasive metric for determining critical DO2 at approximately 5.3 mL O2·kg·min.

Predictors of hemodynamic decompensation in progressive hypovolemia: Compensatory reserve versus heart rate variability.

BACKGROUND: Hemorrhage remains the leading cause of death following traumatic injury in both civilian and military settings. Heart rate variability (HRV) and heart rate complexity (HRC) have been proposed as potential "new vital signs" for monitoring trauma patients; however, the added benefit of HRV or HRC for decision support remains unclear. Another new paradigm, the compensatory reserve measurement (CRM), represents the integration of all cardiopulmonary mechanisms responsible for compensation during relative blood loss and was developed to identify current physiologic status by estimating the progression toward hemodynamic decompensation. In the present study, we hypothesized that CRM would provide greater sensitivity and specificity to detect progressive reductions in central circulating blood volume and onset of decompensation as compared with measurements of HRV and HRC. METHODS: Continuous, noninvasive measurements of compensatory reserve and electrocardiogram signals were made on 101 healthy volunteers during lower-body negative pressure (LBNP) to the point of decompensation. Measures of HRV and HRC were taken from electrocardiogram signal data. RESULTS: Compensatory reserve measurement demonstrated a superior sensitivity and specificity (receiver operator characteristic area under the curve [ROC AUC] = 0.93) compared with all HRV measures (ROC AUC ≤ 0.84) and all HRC measures (ROC AUC ≤ 0.86). Sensitivity and specificity values at the ROC optimal thresholds were greater for CRM (sensitivity = 0.84; specificity = 0.84) than HRV (sensitivity, ≤0.78; specificity, ≤0.77), and HRC (sensitivity, ≤0.79; specificity, ≤0.77). With standardized values across all levels of LBNP, CRM had a steeper decline, less variability, and explained a greater proportion of the variation in the data than both HRV and HRC during progressive hypovolemia. CONCLUSION: These findings add to the growing body of literature describing the advantages of CRM for detecting reductions in central blood volume. Most importantly, these results provide further support for the potential use of CRM in the triage and monitoring of patients at highest risk for the onset of shock following blood loss.

Anatomic injury patterns in combat casualties treated by forward surgical teams.

BACKGROUND: Role 2 forward surgical teams provide damage-control resuscitation and surgery for life- and limb-threatening injuries. These teams have limited resources and personnel, so understanding the anatomic injury patterns seen by these teams is vital for providing adequate training and preparation prior to deployment. The objective of this study was to describe the spectrum of injuries treated at Role 2 facilities in Afghanistan. METHODS: Using Department of Defense Trauma Registry data, a retrospective, secondary data analysis was conducted. Eligible patients were all battle or non-battle-injured casualties treated by Role 2 forward surgical teams in Afghanistan from October 2005 to June 2018. Abbreviated Injury Scale (AIS) 2005 codes were used to classify each injury and Injury Severity Score (ISS) was calculated for each patient. Patients with multiple trauma were defined as patients with an AIS severity code >2 in at least two ISS body regions. RESULTS: The data set included 10,383 eligible patients with 45,225 diagnosis entries (range, 1-27 diagnoses per patient). The largest number of injuries occurred in the lower extremity/pelvis/buttocks (23.9%). Most injuries were categorized as minor (39.4%) or moderate (38.8%) in AIS severity, while the largest number of injuries categorized as severe or worse occurred in the head (13.5%). Among head injuries, 1,872 injuries were associated with a cerebral concussion or diffuse axonal injury, including 50.6% of those injuries being associated with a loss of consciousness. There were 1,224 patients with multiple trauma, and the majority had an injury to the extremities/pelvic girdle (58.2%). Additionally, 3.7% of all eligible patients and 10.5% of all patients with multiple trauma did not survive to Role 2 discharge. CONCLUSION: The injury patterns seen in recent conflicts and demonstrated by this study may assist military medical leaders and planners to optimize forward surgical care in future environments, on a larger scale, and utilizing less resources. LEVEL OF EVIDENCE: Epidemiological, Level III.

Assessing the NephroCheck® Test System in Predicting the Risk of Death or Dialysis in Burn Patients.

Acute kidney injury (AKI) is associated with high mortality in burn patients. Urinary biomarkers can aid in the prediction of AKI and its consequences, such as death and the need for renal replacement therapy (RRT). The purpose of this study was to investigate a novel methodology for detecting urinary biomarkers, the NephroCheck® Test System, and assess its ability to predict death or the need for RRT in burn patients. Burn patients admitted to the United States Army Institute of Surgical Research (USAISR) burn intensive care unit were prospectively enrolled between March 2016 and April 2018. A urine sample was obtained from all study participants using the NephroCheck® system. Patient and injury characteristics were gathered, and descriptive statistics were calculated and multivariable logistic regression analyses were performed using these data. Of the 69 patients in this study, 15 patients (21.7%) attained the composite outcome of death or needing RRT within 30 days of urine collection. NephroCheck® scores were higher for patients with the composite outcome, with P = 0.06 for centrifuged scores and P = 0.04 for noncentrifuged scores. Centrifuged and noncentrifuged scores were in high agreement and correlation (R2 = 0.97, P < 0.0001). Noncentrifuged scores were significant in the unadjusted analysis, but they were not significant in the adjusted analysis. Although these scores had a lower sensitivity and negative predictive value compared with other parameters, they had the second highest specificity and positive predictive value. NephroCheck® scores were higher in burn patients with the composite outcome of death or needing RRT, and they demonstrated comparable sensitivity and specificity to creatinine and TBSA.

Forward Surgical Team Procedural Burden and Non-operative Interventions by the U.S. Military Trauma System in Afghanistan, 2008-2014.

INTRODUCTION: No published study has reported non-surgical interventions performed by forward surgical teams, and there are no current surgical benchmarks for forward surgical teams. The objective of the study was to describe operative procedures and non-operative interventions received by battlefield casualties and determine the operative procedural burden on the trauma system. METHODS: This was a retrospective analysis of data from the Joint Trauma System Forward Surgical Team Database using battle and non-battle injured casualties treated in Afghanistan from 2008-2014. Overall procedure frequency, mortality outcome, and survivor morbidity outcome were calculated using operating room procedure codes grouped by the Healthcare Cost and Utilization Project classification. Cumulative attributable burden of procedures was calculated by frequency, mortality, and morbidity. Morbidity and mortality burden were used to rank procedures. RESULTS: The study population was comprised of 10,992 casualties, primarily male (97.8%), with a median age interquartile range of 25.0 (22.0-30.0). Affiliations were non-U.S. military (40.0%), U.S. military (35.1%), and others (25.0%). Injuries were penetrating (65.2%), blunt (32.8), and burns (2.0%). Casualties included 4.4% who died and 14.9% who lived but had notable morbidity findings. After ranking by contribution to trauma system morbidity and mortality burden, the top 10 of 32 procedure groups accounted for 74.4% of operative care, 77.9% of mortality, and 73.1% of unexpected morbidity findings. These procedure groups included laparotomy, vascular procedures, thoracotomy, debridement, lower and upper gastrointestinal procedures, amputation, and therapeutic procedures on muscles and upper and lower extremity bones. Most common non-operative interventions included X-ray, ultrasound, wound care, catheterization, and intubation. CONCLUSIONS: Forward surgical team training and performance improvement metrics should focus on optimizing commonly performed operative procedures and non-operative interventions. Operative procedures that were commonly performed, and those associated with higher rates of morbidity and mortality, can set surgical benchmarks and outline training and skillsets needed by forward surgical teams.

Interrelationship Between Sex, Age, Blood Volume, and Vo2max.

BACKGROUND: Circulating blood volume (BV) and maximal oxygen uptake (Vo2max) are physiological characteristics important for optimal human performance in aerospace and military operational environments. We tested the hypothesis that BV and Vo2max are lower in older people independent of sex.METHODS: To accomplish this, a "data mining" effort of an historic database generated from NASA and U.S. Air Force experiments was conducted. BV, red cell volume, plasma volume, hematocrit, and Vo2max were measured in 84 healthy individuals (24 women, 60 men) across an age range of 23 to 65 yr to assess the interrelationship between sex, age, BV, and Vo2max. Subjects were classified in age groups by < 40 yr and ≥ 40 yr; these groups identified women as pre- vs. postmenopausal.RESULTS: Consistent with our hypothesis, comparisons revealed that men had higher BV, red cell volume, hematocrit, and Vo2max than women when standardized for body mass. Against expectations, BV was not different in older compared with younger men and women. Vo2max was not different in older compared with younger women, while Vo2max was lower in older men.CONCLUSION: We conclude that physiological mechanisms other than BV associated with aging appear to be responsible for a decline in Vo2max of our older men. Furthermore, factors other than menopause may also influence the control of BV in the women. Our results provide evidence that aging may not compromise men or women in scenarios where BV can affect performance in aerospace and military environments.Koons NJ, Suresh MR, Schlotman TE, Convertino VA. Interrelationship between sex, age, blood volume, and Vo2max. Aerosp Med Hum Perform. 2019; 90(4):362-368.