Spectral Reflectance Can Differentiate Tracheal and Esophageal Tissue in the Presence of Bodily Fluids and Soot.

Endotracheal intubation is a common life-saving procedure implemented in emergency care to ensure patient oxygenation, but it is difficult and often performed in suboptimal conditions leading to high rates of patient complications. Undetected misplacement in the esophagus is a preventable complication that can lead to fatalities in 5-10% of patients who undergo emergency intubation. End-tidal carbon dioxide monitoring and other proper placement detection methods are useful, yet the problem of misplacement persists. Our previous work demonstrated the utility of spectral reflectance sensors for differentiating esophageal and tracheal tissues, which can be used to confirm proper endotracheal tube placement. In this study, we examine the effectiveness of spectral characterization in the presence of saline, blood, "vomit", and soot in the trachea. Our results show that spectral properties of the trachea that differentiate it from the esophagus persist in the presence of these substances. This work further confirms the potential usefulness of this novel detection technology in field applications.

Testing of novel spectral device sensor in swine model of airway obstruction.

Loss of a patent airway is a significant cause of prehospital death. Endotracheal intubation is the gold standard of care but has a high rate of failure and complications, making development of new devices vital. We previously showed that tracheal tissue has a unique spectral profile which could be utilized to confirm correct airway device placement. Therefore, the goals of this study were twofold: 1- to develop an airway obstruction model and 2- use that model to assess how airway compromise affects tissue reflectance. Female swine were anesthetized, intubated, and instrumented. Pigs were allowed to breathe spontaneously and underwent either slow- or rapid-onset obstruction until a real-time pulse oximeter reading of ≤50%. At baseline, 25%, 50%, 75%, and 100% obstruction, a fiber-optic reflection probe was inserted into the trachea and esophagus to capture reflectance spectra. Both slow- and rapid-onset obstruction significantly decreased arterial oxygen concentration (sO2 ) and increased partial pressure of CO2 (pCO2 ). The presence of the tracheal-defining spectral profile was confirmed and remained consistent despite changes in sO2 and pCO2 . This study validated a model of slow- and rapid-airway obstruction that results in significant hypoxia and hypercapnia. This is valuable for future testing of airway device components that may improve airway management. Additionally, our data support the ability of spectral reflectance to differentiate between tracheal and esophageal tissues in the presence of a clinical condition that decreases oxygen saturation.

Survival of Casualties Undergoing Prehospital Supraglottic Airway Placement Versus Cricothyrotomy.

BACKGROUND: Airway compromise is the second leading cause of preventable death on the battlefield. Unlike a cricothyrotomy, supraglottic airway (SGA) placement does not require an incision and is less technically challenging. We compare survival of causalities undergoing cricothyrotomy versus SGA placement. METHODS: We used a series of emergency department (ED) procedure codes to search within the Department of Defense Trauma Registry (DoDTR) from January 2007 to August 2016. This is a subanalysis of that dataset. RESULTS: During the study period, 194 casualties had a documented cricothyrotomy and 22 had a documented SGA as the sole airway intervention. The two groups had similar proportions of explosive injuries (57.7% versus 63.6%, p = .328), similar composite injury severity scores (25 versus 27.5, p = .168), and similar AIS for the head, face, extremities, and external body regions. The cricothyrotomy group had lower AIS for the thorax (0 versus 3, p = .019) a trend toward lower AIS for the abdomen (0 versus 0, p = .077), more serious injuries to the head (67.5% versus 45.5%, p = .039), and similar rates of serious injuries to the face (4.6% versus 4.6%, p = .984). Glasgow Coma Scale (GCS) scores were similar upon arrival to the ED (3 versus 3, p = .467) as were the proportion of patients surviving to discharge (45.4% versus 40.9%, p = .691). On repeated multivariable analyses, the odds ratios (ORs) for survival were not significantly different between the two groups. CONCLUSION: We found no difference in short-term outcomes between combat casualties who received an SGA vs cricothyrotomy. Military prehospital personnel rarely used either advanced airway intervention during the recent conflicts in Afghanistan and Iraq.

Survival of Casualties Undergoing Prehospital Supraglottic Airway Placement Versus Cricothyrotomy.

BACKGROUND: Airway compromise is the second leading cause of preventable death on the battlefield. Unlike a cricothyrotomy, supraglottic airway (SGA) placement does not require an incision and is less technically challenging. We compare the survival of causalities undergoing cricothyrotomy versus SGA placement. METHODS: We used a series of emergency department (ED) procedure codes to search within the Department of Defense Trauma Registry (DODTR) from January 2007 to August 2016. This is a subanalysis of that data set. RESULTS: During the study period, 194 casualties had a documented cricothyrotomy and 22 had a documented SGA as the sole airway intervention. The two groups had similar proportions of explosive injuries (57.7% versus 63.6%, p = .328), similar composite injury severity scores (25 versus 27.5, p = .168), and similar AIS for the head, face, extremities, and external body regions. The cricothyrotomy group had lower AIS for the thorax (0 versus 3, p = .019), a trend toward lower AIS for the abdomen (0 versus 0, p = .077), more serious injuries to the head (67.5% versus 45.5%, p = .039), and similar rates of serious injuries to the face (4.6% versus 4.6%, p = .984). Glasgow Coma Scale (GCS) scores were similar on arrival to the ED (3 versus 3, p = .467) as were the proportion of patients surviving to discharge (45.4% versus 40.9%, p = .691). On repeated multivariable analyses, the odds ratios for survival were not significantly different between the two groups. CONCLUSIONS: We found no difference in short-term outcomes between combat casualties who received an SGA vs those who received a cricothyrotomy. Military prehospital personnel rarely used either advanced airway intervention during the recent conflicts in Afghanistan and Iraq.

Measurement of compensatory reserve predicts racial differences in tolerance to simulated hemorrhage in women.

BACKGROUND: The compensatory reserve measurement (CRM) has been established to accurately measure the body's total integrated capacity to compensate for physiologic states of reduced central blood volume and predict hemodynamic decompensation associated with inadequate tissue oxygenation. We previously demonstrated that African American (AA) women have a higher tolerance to reductions in central blood volume. Therefore, we tested the hypothesis that the CRM would identify racial differences during simulated hemorrhage, before the onset of traditional signs/symptoms. METHODS: We performed a retrospective analysis during simulated hemorrhage using lower-body negative pressure (LBNP) in 23 AA (22 ± 1 years; 24 ± 1 kg/m) and 31 white women (WW) (20 ± 1 years; 23 ± 1 kg/m). Beat-by-beat blood pressure (BP) and heart rate (HR) were recorded during progressive lower body negative pressure to presyncope. The BP waveforms were analyzed using a machine-learning algorithm to derive the CRM at each lower body negative pressure stage. RESULTS: Resting mean arterial BP (AA, 78 ± 3 mm Hg vs. WW, 74 ± 2 mm Hg) and HR (AA, 68 ± 2 bpm vs. WW, 65 ± 2 bpm) were similar between groups. The CRM progressively decreased during LBNP in both groups; however, the rate of decline in the CRM was less (p < 0.05) in AA. The CRM was 4% higher in AA at -15 mm Hg LBNP and progressively increased to 21% higher at -50 mm Hg LBNP (p < 0.05). However, changes in BP and HR were not different between groups. CONCLUSION: These data support the notion that the greater tolerance to simulated hemorrhage induced by LBNP in AA women can be explained by their greater capacity to protect the reserve to compensate for progressive central hypovolemia compared with WW, independent of standard vital signs. LEVEL OF EVIDENCE: Diagnostic test, level II.

Effect of pain and analgesia on compensatory reserve.

BACKGROUND: The measurement of the body's capacity to compensate for reduced blood volume can be assessed with a compensatory reserve measurement (CRM). The CRM, which is calculated from changes in features of the arterial waveform, represents the integration of compensatory mechanisms during states of low tissue perfusion and oxygenation, such as hemorrhage. This study was designed to test the hypothesis that pain which activates compensatory mechanisms and analgesia that result in reduced blood pressure are associated with lower compensatory reserve. This study evaluated CRM in obstetric patients during labor as pain intensity increased from no pain to severe pain and compared CRM before and after epidural anesthesia. METHODS: CRM was calculated from a finger pulse oximeter placed on the patient's index finger and connected to the DataOx monitor in healthy pregnant women (n = 20) before and during the active labor phase of childbirth. RESULTS: As pain intensity, based on an 11-point scale (0, no pain; 10, worst pain), increased from 0 to 8.4 ± 0.9 (mean ± SD), CRM was not affected (81 ± 10% to 82 ± 13%). Before analgesia, CRM was 84 ± 10%. CRM at 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, and 60 minutes after analgesia was 82 ± 11%, 83 ± 14%, 83 ± 15%, 86 ± 12%, 89 ± 9%, and 87 ± 10%, respectively. There was a transient 2% reduction followed by a 5% increase in CRM from before to after epidural anesthesia (p = 0.048). Pain scores before and after analgesia were 7 ± 2 and 1 ± 1, respectively (p < 0.001). CONCLUSION: These results indicate that pain and analgesia contribute minimally, but independently to the reduction in compensatory reserve associated with trauma and hemorrhage. As such, our findings suggest that analgesia can be safely administered on the battlefield while maintaining the maximal capacity of mechanisms to compensate for blood loss. LEVEL OF EVIDENCE: Diagnostic study, level II.

The neurovascular complexity index as a potential indicator of traumatic brain injury severity: A case-series study.

BACKGROUND: Multimodal monitoring of brain physiology following a traumatic brain injury (TBI) shows promise as a strategy to improve management and outcomes of TBI patients within civilian and military trauma. Valid and reliable measures of different aspects of brain physiology following a TBI could prove critical to accurately capturing these changes. METHODS: Using a case-series design with a control subject group comparison, we evaluated a new proprietary algorithm called the Neurovascular Complexity Index (NCI) using transcranial Doppler to noninvasively obtain measures of cerebral blood flow variability. Baseline NCI data from 169 control subjects were compared with 12 patients with moderate to severe TBI. RESULTS: Patients with TBI exhibited significantly greater mean and variability in NCI scores compared with control subjects (F = 195.48; p < 0.001). The mean absolute deviation (MAD) of NCI scores increased significantly and in a monotonic fashion with severity of injury, where control subjects exhibited a small MAD of 0.44, patients with moderate TBI had a higher MAD of 4.20, and patients with severe TBI had an MAD of 6.51 (p < 0.001). CONCLUSIONS: Advancement in multimodal monitoring of TBI patients is important in reducing the potential risk of secondary injury. This study reports results indicating that a new noninvasive quantifiable assessment of TBI based on a noninvasive measure of cerebral blood flow variability shows potential for continuous monitoring and early identification of brain-injured patients, deployable in far-forward military environments, to better inform individualized management. LEVEL OF EVIDENCE: Case series, level IV.

Distinguishing tracheal and esophageal tissues with hyperspectral imaging and fiber-optic sensing.

During emergency medical situations, where the patient has an obstructed airway or necessitates respiratory support, endotracheal intubation (ETI) is the medical technique of placing a tube into the trachea in order to facilitate adequate ventilation of the lungs. Complications during ETI, such as repeated attempts, failed intubation, or accidental intubation of the esophagus, can lead to severe consequences or ultimately death. Consequently, a need exists for a feedback mechanism to aid providers in performing successful ETI. Our study examined the spectral reflectance properties of the tracheal and esophageal tissue to determine whether a unique spectral profile exists for either tissue for the purpose of detection. The study began by using a hyperspectral camera to image excised pig tissue samples exposed to white and UV light in order to capture the spectral reflectance properties with high fidelity. After identifying a unique spectral characteristic of the trachea that significantly differed from esophageal tissue, a follow-up investigation used a fiber optic probe to confirm the detectability and consistency of the different reflectance characteristics in a pig model. Our results characterize the unique and consistent spectral reflectance characteristic of tracheal tissue, thereby providing foundational support for exploiting spectral properties to detect the trachea during medical procedures.

Compensatory Reserve for Early and Accurate Prediction of Hemodynamic Compromise: Case Studies for Clinical Utility in Acute Care and Physical Performance.

BACKGROUND: Humans are able to compensate for significant loss of their circulating blood volume, allowing vital signs to remain relatively stable until compensatory mechanisms are overwhelmed. The authors present several clinical and performance case studies in an effort to demonstrate real-time measurements of an individual's reserve to compensate for acute changes in circulating blood volume. This measurement is referred to as the Compensatory Reserve Index (CRI). METHODS: We identified seven clinical and two physical performance conditions relevant to military casualty and operational medicine as models of intravascular volume compromise. Retrospective analysis of photoplethysmogram (PPG) waveform features was used to calculate CRI, where 1 represents supine normovolemia and 0 represents hemodynamic decompensation. RESULTS: All cases had CRI values suggestive of volume compromise (<0.6) not otherwise evident by heart rate and systolic blood pressure. CRI decreased with reduced central blood volume and increased with restored volume (e.g., fluid resuscitation). CONCLUSION: The results from these case studies demonstrate that machine-learning techniques can be used to (1) identify a clinical or physiologic status of individuals through real-time measures of changes in PPG waveform features that result from compromise to circulating blood volume and (2) signal progression toward hemodynamic instability, with opportunity for early and effective intervention, well in advance of changes in traditional vital signs.