Effects of remote ischemic preconditioning on early markers of intestinal injury in experimental hemorrhage in rats.

The maintenance of intestinal integrity and barrier function under conditions of restricted oxygen availability is crucial to avoid bacterial translocation and local inflammation. Both lead to secondary diseases after hemorrhagic shock and might increase morbidity and mortality after surviving the initial event. Monitoring of the intestinal integrity especially in the early course of critical illness remains challenging. Since microcirculation and mitochondrial respiration are main components of the terminal stretch of tissue oxygenation, the evaluation of microcirculatory and mitochondrial variables could identify tissues at risk during hypoxic challenges, indicate an increase of intestinal injury, and improve our understanding of regional pathophysiology during acute hemorrhage. Furthermore, improving intestinal microcirculation or mitochondrial respiration, e.g. by remote ischemic preconditioning (RIPC) that was reported to exert a sufficient tissue protection in various tissues and was linked to mediators with vasoactive properties could maintain intestinal integrity. In this study, postcapillary oxygen saturation (µHbO2), microvascular flow index (MFI) and plasmatic D-lactate concentration revealed to be early markers of intestinal injury in a rodent model of experimental hemorrhagic shock. Mitochondrial function was not impaired in this experimental model of acute hemorrhage. Remote ischemic preconditioning (RIPC) failed to improve intestinal microcirculation and intestinal damage during hemorrhagic shock.

A nomogram for predicting hemorrhagic shock in pediatric patients with multiple trauma.

The timely detection and management of hemorrhagic shock hold paramount importance in clinical practice. This study was designed to establish a nomogram that may facilitate early identification of hemorrhagic shock in pediatric patients with multiple-trauma. A retrospective study was conducted utilizing a cohort comprising 325 pediatric patients diagnosed with multiple-trauma, who received treatment at the Children's Hospital, Zhejiang University School of Medicine, Zhejiang, China. For external validation, an additional cohort of 144 patients from a children's hospital in Taizhou was included. The model's predictor selection was optimized through the application of the Least Absolute Shrinkage and Selection Operator (LASSO) regression. Subsequently, a prediction nomogram was constructed using multivariable logistic regression analysis. The performance and clinical utility of the developed model were comprehensively assessed utilizing various statistical metrics, including Harrell's Concordance Index (C-index), receiver operating characteristic (ROC) curve analysis, calibration curve analysis, and decision curve analysis (DCA). Multivariate logistic regression analysis identified systolic blood pressure (ΔSBP), platelet count, activated partial thromboplastin time (APTT), and injury severity score (ISS) as independent predictors for hemorrhagic shock. The nomogram constructed using these predictors demonstrated robust predictive capabilities, as evidenced by an impressive area under the curve (AUC) value of 0.963. The model's goodness-of-fit was assessed using the Hosmer-Lemeshow test (χ2 = 10.023, P = 0.209). Furthermore, decision curve analysis revealed significantly improved net benefits with the model. External validation further confirmed the reliability of the proposed predictive nomogram. This study successfully developed a nomogram for predicting the occurrence of hemorrhagic shock in pediatric patients with multiple trauma. This nomogram may serve as an accurate and effective tool for timely and efficient management of children with multiple trauma.

Resuscitative Endovascular Balloon Occlusion of The Aorta (REBOA) And Mortality in Hemorrhagic Shock Associated with Severe Pelvic Fracture: a National Data Analysis.

BACKGROUND: The purpose of the study was to evaluate the mortality of patients who received Resuscitative Endovascular Balloon Occlusion of The Aorta (REBOA) in severe pelvic fracture with hemorrhagic shock. METHODS: The American College of Surgeon Trauma Quality Improvement Program (ACS-TQIP) database for the calendar years 2017-2019 was accessed for the study. The study included all patients aged 15 years and older who sustained severe pelvic fractures, defined as an injury with an abbreviated injury scale (AIS) score of ≥ 3, and who presented with the lowest systolic blood pressure (SBP) of < 90 mmHg. Patients with severe brain injury were excluded from the study. Propensity score matching was used to compare the patients who received REBOA with similar characteristics to patients who did not receive REBOA. RESULTS: Out of 3,186 patients who qualified for the study, 35(1.1%) patients received REBOA for an ongoing hemorrhagic shock with severe pelvic fracture. The propensity matching created 35 pairs of patients. The pair-matched analysis showed no significant differences between the group who received REBOA and the group that did not receive REBOA regarding patients' demography, injury severity, severity of pelvic fractures, lowest blood pressure at initial assessment and laparotomies. There was no significant difference found between REBOA versus no REBOA group in overall in-hospital mortality (34.3% vs. 28.6, P = 0.789). CONCLUSION: Our study did not identify any mortality advantage in patients who received REBOA in hemorrhagic shock associated with severe pelvic fracture compared to a similar cohort of patients who did not receive REBOA. A larger sample size prospective study is needed to validate our results. CASE-CONTROL RETROSPECTIVE STUDY: Level of Evidence IV.

The Role of Whole Blood Hemostatic Resuscitation in Bleeding Geriatric Trauma Patients.

INTRODUCTION: Whole blood (WB) has recently gained increased popularity as an adjunct to the resuscitation of hemorrhaging civilian trauma patients. We aimed to assess the nationwide outcomes of using WB as an adjunct to component therapy (CT) versus CT alone in resuscitating geriatric trauma patients. METHODS: We performed a 5-y (2017-2021) retrospective analysis of the Trauma Quality Improvement Program. We included geriatric (age, ≥65 y) trauma patients presenting with hemorrhagic shock (shock index >1) and requiring at least 4 units of packed red blood cells in 4 h. Patients with severe head injuries (head Abbreviated Injury Scale ≥3) and transferred patients were excluded. Patients were stratified into WB-CT versus CT only. Primary outcomes were 6-h, 24-h, and in-hospital mortality. Secondary outcomes were major complications. Multivariable regression analysis was performed, adjusting for potential confounding factors. RESULTS: A total of 1194 patients were identified, of which 141 (12%) received WB. The mean ± standard deviation age was 74 ± 7 y, 67.5% were male, and 83.4% had penetrating injuries. The median [interquartile range] Injury Severity Score was 19 [13-29], with no difference among study groups (P = 0.059). Overall, 6-h, 24-h, and in-hospital mortality were 16%, 23.1%, and 43.6%, respectively. On multivariable regression analysis, WB was independently associated with reduced 24-h (odds ratio, 0.62 [0.41-0.94]; P = 0.024), and in-hospital mortality (odds ratio, 0.60 [0.40-0.90]; P = 0.013), but not with major complications (odds ratio, 0.78 [0.53-1.15]; P = 0.207). CONCLUSIONS: Transfusion of WB as an adjunct to CT is associated with improved early and overall mortality in geriatric trauma patients presenting with severe hemorrhage. The findings from this study are clinically important, as this is an essential first step in prioritizing the selection of WB resuscitation for geriatric trauma patients presenting with hemorrhagic shock.

Has the balloon really burst? Analysis of "the UK-REBOA randomized clinical trial".

BACKGROUND: Uncontrolled hemorrhagic shock is a leading cause of early death after injury. Resuscitative endovascular balloon occlusion of the aorta (REBOA) represents a paradigm shift in achieving hemodynamic stability and its implementation still remain controversial in different settings. The recently published UK-REBOA Randomized Clinical Trial aimed to determine the effectiveness of REBOA in patients with hemorrhagic shock, concluding its increased mortality compared with standard care alone. METHODS: An adjustment of the statistical analysis was performed and a comprehensive analysis was proposed to address the study's limitations and demonstrate that these conclusions cannot be considered as benchmarks. RESULTS: Primary and secondary outcomes were analyzed using Bayesian logistic regression and generalized linear models suitable for the outcome distribution. No statistically significant differences were observed between the two groups for the primary outcome (p-value 0.3341) nor in most of the secondary outcomes. The results of the principal stratum analyses (to account for intercurrent events) also did not show significant differences after the statistical analysis tests. CONCLUSION: It cannot be stated that REBOA increases mortality compared with standard care alone in trauma patients with exsanguinating hemorrhage. Further studies and adequate simulation training programs in REBOA are critical to its successful implementation within a trauma system and to identify the optimum settings and patients.

OMX: A NOVEL OXYGEN DELIVERY BIOTHERAPEUTIC IMPROVES OUTCOMES IN AN OVINE MODEL OF CONTROLLED HEMORRHAGIC SHOCK.

ABSTRACT: Hemorrhagic shock is a major source of morbidity and mortality worldwide. While whole blood or blood product transfusion is a first-line treatment, maintaining robust supplies presents significant logistical challenges, particularly in austere environments. OMX is a novel nonhemoglobin (Hb)-based oxygen carrier derived from the H-NOX (heme-nitric oxide/oxygen binding) protein family. Because of their engineered oxygen (O 2 ) affinities, OMX proteins only deliver O 2 to severely hypoxic tissues. Additionally, unlike Hb-based oxygen carriers, OMX proteins do not scavenge nitric oxide in the vasculature. To determine the safety and efficacy of OMX in supporting tissue oxygen delivery and cardiovascular function in a large animal model of controlled hemorrhage, 2-3-week-old lambs were anesthetized, intubated, and mechanically ventilated. Hypovolemic shock was induced by acute hemorrhage to obtain a 50% reduction over 30 min. Vehicle (n = 16) or 400 mg/kg OMX (n = 13) treatment was administered over 15 min. Hemodynamics, arterial blood gases, and laboratory values were monitored throughout the 6-h study. Comparisons between groups were made using t tests, Wilcoxon rank sum test, and Fisher's exact test. Survival was assessed using Kaplan-Meier curves and the log-rank test. We found that OMX was well-tolerated and significantly improved lactate and base deficit trends, and hemodynamic indices ( P < 0.05). Median survival time was greater in the OMX-treated group (4.7 vs. 6.0 h, P < 0.003), and overall survival was significantly increased in the OMX-treated group (25% vs. 85%, P = 0.004). We conclude that OMX is well-tolerated and improves metabolic, hemodynamic, and survival outcomes in an ovine model of controlled hemorrhagic shock.

The employment of resuscitative endovascular balloon occlusion of the aorta in deployed settings.

BACKGROUND: Resuscitative endovascular balloon occlusion of the aorta (REBOA) has been often used in place of open aortic occlusion for management of hemorrhagic shock in trauma. There is a paucity of data evaluating REBOA usage in military settings. STUDY DESIGN AND METHODS: We queried the Department of Defense Trauma Registry (DODTR) for all cases with at least one intervention or assessment available within the first 72 h after injury between 2007 and 2023. We used relevant procedural codes to identify the use of REBOA within the DODTR, and we used descriptive statistics to characterize its use. RESULTS: We identified 17 cases of REBOA placed in combat settings from 2017 to 2019. The majority of these were placed in the operating room (76%) and in civilian patients (70%). A penetrating mechanism caused the injury in 94% of cases with predominantly the abdomen and extremities having serious injuries. All patients subsequently underwent an exploratory laparotomy after REBOA placement, with moderate numbers of patients having spleen, liver, and small bowel injuries. The majority (82%) of included patients survived to hospital discharge. DISCUSSION: We describe 17 cases of REBOA within the DODTR from 2007 to 2023, adding to the limited documentation of patients undergoing REBOA in military settings. We identified patterns of injury in line with previous studies of patients undergoing REBOA in military settings. In this small sample of military casualties, we observed a high survival rate.

Percutaneous ultrasound-guided versus open cut-down access to femoral vessels for the placement of a REBOA catheter.

Resuscitative Endovascular Balloon Occlusion of the Aorta (REBOA) may be useful in treating exsanguinating trauma patients. This study seeks to compare rates of success, complications and time required for vascular access between ultrasound-guidance and surgical cut-down for femoral sheath insertion as a prospective observational case control study. Participating clinicians from either trauma surgery or anesthesiology were allocated to surgical cut-down or percutaneous ultrasound-guided puncture on a 1:1 ratio. Time spans to vessel identification, successful puncture, and balloon inflation were recorded. 80 study participants were recruited and allocated to 40 open cut-down approaches and 40 percutaneous ultrasound-guided approaches. REBOA catheter placement was successful in 18/40 cases (45%) using a percutaneous ultrasound guided technique and 33/40 times (83%) using the open cut-down approach (p < 0.001). Median times [in seconds] compared between percutaneous ultrasound-guided puncture and surgical cut-down were 36 (18-73) versus 117(56-213) for vessel visualization (p < 0.001), 136 (97-175) versus 183 (156-219) for vessel puncture (p < 0.001), and 375 (240-600) versus 288 (244-379) for balloon inflation (p = 0.08) overall. Access to femoral vessels for REBOA catheter placement is safer when performed by cut-down and direct visualization but can be performed faster by an ultrasound-guided technique when vessels can be identified clearly and rapidly.

Management of Respiratory Failure in Hemorrhagic Shock.

Hemorrhagic shock results in acute respiratory failure due to respiratory muscle fatigue and inadequate pulmonary blood flow. Because positive pressure ventilation can reduce venous return and cardiac output, clinicians should use the minimum possible mean airway pressure during assisted or mechanical ventilation, particularly during episodes of severe hypovolemia. Hypoperfusion also worsens dead space fraction. Therefore, clinicians should monitor capnography during mechanical ventilation and recognize that hypercapnia may be treated with fluid resuscitation rather than increasing minute ventilation.

Tissue oxygen saturation is positively correlated with oxygen delivery and cardiac output in a canine hemorrhagic shock and resuscitation model.

OBJECTIVE: To determine if tissue oxygen saturation (StO2) correlates with oxygen delivery (DO2) and/or cardiac output (CO) in a canine hemorrhagic shock model. ANIMALS: 8 healthy purpose-bred dogs. METHODS: Dogs were anesthetized, and hemorrhagic shock was induced by withdrawing up to 60% of total blood volume, targeting a mean arterial pressure (MAP) of 40 mm Hg. The withdrawn blood was returned to the patient in 2 equal aliquots. Data was collected at 4 time points: 10 minutes after MAP was stabilized under anesthesia (time point [TP]-1), 10 minutes after up to 60% of blood volume was removed to target a MAP of 40 mm Hg (TP2), 10 minutes after the return of 50% of shed blood (TP3), and 10 minutes after the return of the remaining 50% of shed blood (TP4). Total blood volume withdrawn, StO2, CO, heart rate, and MAP were recorded, and DO2 was calculated at each TP. RESULTS: Mean StO2 significantly decreased between TP1 (77.8% [± 9.54]) and TP2 (44.8% [± 19.5]; P < .001 vs TP1). Mean StO2 increased to 63.1% (± 9.85) at TP3, but remained significantly lower compared to TP1 (P = .002). There was no difference between mean StO2 at TP4 (82.5% [± 12.6]) versus TP1 (P = .466). StO2 has a strong, positive correlation to both CO (r = 0.80; P < .001) and DO2 (r = 0.75; P < .001). CLINICAL RELEVANCE: A decrease in StO2 may be used in conjunction with physical examination findings and diagnostic parameters to support a diagnosis of shock. The return of shed blood was correlated with increases in StO2, DO2, and CO, suggesting that StO2 may be used as a marker of adequate resuscitation.

The degree of aortic occlusion in the setting of trauma alters the extent of acute kidney injury associated with mitochondrial preservation.

Resuscitative endovascular balloon occlusion of the aorta (REBOA) is used to control noncompressible hemorrhage not addressed with traditional tourniquets. However, REBOA is associated with acute kidney injury (AKI) and subsequent mortality in severely injured trauma patients. Here, we investigated how the degree of aortic occlusion altered the extent of AKI in a porcine model. Female Yorkshire-cross swine (n = 16, 68.1 ± 0.7 kg) were anesthetized and had carotid and bilateral femoral arteries accessed for REBOA insertion and distal and proximal blood pressure monitoring. Through a laparotomy, a 6-cm liver laceration was performed and balloon inflation was performed in zone 1 of the aorta for 90 min, during which animals were randomized to target distal mean arterial pressures of 25 or 45 mmHg via balloon volume adjustment. Blood draws were taken at baseline, end of occlusion, and time of death, at which point renal tissues were harvested 6 h after balloon deflation for histological and molecular analyses. Renal blood flow was lower in the 25-mmHg group (48.5 ± 18.3 mL/min) than in the 45-mmHg group (177.9 ± 27.2 mL/min) during the occlusion phase, which recovered and was not different after balloon deflation. AKI was more severe in the 25-mmHg group, as evidenced by circulating creatinine, blood urea nitrogen, and urinary neutrophil gelatinase-associated lipocalin. The 25-mmHg group had increased tubular necrosis, lower renal citrate synthase activity, increased tissue and circulating syndecan-1, and elevated systemic inflammatory cytokines. The extent of renal ischemia-induced AKI is associated with the magnitude of mitochondrial biomass and systemic inflammation, highlighting potential mechanistic targets to combine with partial REBOA strategies to prevent AKI.NEW & NOTEWORTHY Large animal models of ischemia-reperfusion acute kidney injury (IR-AKI) are lacking. This report establishes a titratable IR-AKI model in swine in which a balloon catheter can be used to alter distal pressures experienced by the kidney, thus controlling renal blood flow. Lower blood flow results in greater renal dysfunction and structural damage, as well as lower mitochondrial biomass, elevated systemic inflammation, and vascular dysfunction.

Vascular complications secondary to resuscitative endovascular balloon occlusion of the aorta placement at a Level 1 Trauma Center.

OBJECTIVE: Resuscitative endovascular balloon occlusion of the aorta (REBOA) is designed to manage severe hemorrhagic shock. Popularized in medical care during military conflicts, the concept has emerged as a lifesaving technique that is utilized around the United States. Literature on risks of REBOA placement, especially vascular injuries, are not well-reported. Our goal was to assess the incidence of vascular injury from REBOA placement and the risk factors associated with injury and death among these patients at our institution. METHODS: We performed a retrospective cohort study of all patients who underwent REBOA placement between September 2017 and June 2022 at our Level 1 Trauma Center. The primary outcome variable was the presence of an injury related to REBOA insertion or use. Secondary outcomes studied were limb loss, the need for dialysis, and mortality. Data were analyzed using descriptive statistics, χ2, and t-tests as appropriate for the variable type. RESULTS: We identified 99 patients who underwent REBOA placement during the study period. The mean age of patients was 43.1 ± 17.2 years, and 67.7% (67/99) were males. The majority of injuries were from blunt trauma (79.8%; 79/99). Twelve of the patients (12.1%; 12/99) had a vascular injury related to REBOA placement. All but one required intervention. The complications included local vessel injury (58.3%; 7/12), distal embolization (16.7%; 2/12), excessive bleeding requiring vascular consult (8.3%; 1/12), pseudoaneurysm requiring intervention (8.3%; 1/12), and one incident of inability to remove the REBOA device (8.3%; 1/12). The repairs were performed by vascular surgery (75%; 9/12), interventional radiology (16.7%; 2/12), and trauma surgery (8.3%; 1/12). There was no association of age, gender, race, and blunt vs penetrating injury to REBOA-related complications. Mortality in this patient population was high (40.4%), but there was no association with REBOA-related complications. Ipsilateral limb loss occurred in two patients with REBOA-related injuries, but both were due to their injuries and not to REBOA-related ischemia. CONCLUSIONS: Although vascular complications are not unusual in REBOA placement, there does not appear to be an association with limb loss, dialysis, or mortality if they are addressed promptly. Close coordination between vascular surgeons and trauma surgeons is essential in patients undergoing REBOA placement.

Management of Pelvic Trauma.

Pelvic fractures are common after blunt trauma with patients' presentation ranging from stable with insignificant fractures to life-threatening exsanguination from unstable fractures. Often, hemorrhagic shock from a pelvic fracture may go unrecognized and high clinical suspicion for a pelvic source lies with the clinician. A multidisciplinary coordinated effort is required for management of these complex patients. In the exsanguinating patient, hemorrhage control remains the top priority and may be achieved with external stabilization, resuscitative endovascular balloon occlusion of the aorta, preperitoneal pelvic packing, angiographic intervention, or a combination of therapies. These modalities have been shown to reduce mortality in this challenging population.

The Role of Resuscitative Endovascular Balloon Occlusion of the Aorta.

Resuscitative endovascular balloon occlusion of the aorta (REBOA) has been utilized by trauma surgeons at the bedside for over a decade in both civilian and military settings. Both translational and clinical research suggest it is superior to resuscitative thoracotomy for specific patient populations. Technological advancements in recent years have significantly enhanced the safety profile of REBOA. Resuscitative balloon occlusion of the aorta has also swiftly found implementation in patients in shock from non-traumatic hemorrhage.

What's new in whole blood resuscitation? In the trauma bay and beyond.

PURPOSE OF REVIEW: Transfusion therapy commonly supports patient care during life-threatening injury and critical illness. Herein we examine the recent resurgence of whole blood (WB) resuscitation for patients in hemorrhagic shock following trauma and other causes of severe bleeding. RECENT FINDINGS: A growing body of literature supports the use of various forms of WB for hemostatic resuscitation in military and civilian trauma practice. Different types of WB include warm fresh whole blood (FWB) principally used in the military and low titer O cold stored whole blood (LTOWB) used in a variety of military and civilian settings. Incorporating WB initial resuscitation alongside subsequent component therapy reduces aggregate blood product utilization and improves early mortality without adversely impacting intensive care unit length of stay or infection rate. Applications outside the trauma bay include prehospital WB and use in patients with nontraumatic hemorrhagic shock. SUMMARY: Whole blood may be transfused as FWB or LTOWB to support a hemostatic approach to hemorrhagic shock management. Although the bulk of WB resuscitation literature has appropriately focused on hemorrhagic shock following injury, extension to other etiologies of severe hemorrhage will benefit from focused inquiry to address cost, efficacy, approach, and patient-centered outcomes.

Whole blood storage duration alters fibrinogen levels and thrombin formation.

INTRODUCTION: Whole blood resuscitation for hemorrhagic shock in trauma represents an opportunity to correct coagulopathy in trauma while also supplying red blood cells. The production of microvesicles in stored whole blood and their effect on its hemostatic parameters have not been described in previous literature. We hypothesized that microvesicles in aged stored whole blood are procoagulant and increase thrombin production via phosphatidylserine. METHODS: Whole blood was obtained from male C57BL/6 male mice and stored in anticoagulant solution for up to 10 days. At intervals, stored whole blood underwent examination with rotational thromboelastography, and platelet-poor plasma was prepared for analysis of thrombin generation. Microvesicles were prepared from 10-day-old whole blood aliquots and added to fresh whole blood or platelet-poor plasma to assess changes in coagulation and thrombin generation. Microvesicles were treated with recombinant mouse lactadherin prior to addition to plasma to inhibit phosphatidylserine's role in thrombin generation. RESULTS: Aged murine whole blood had decreased fibrin clot formation compared with fresh samples with decreased plasma fibrinogen levels. Thrombin generation in plasma from aged blood increased over time of storage. The addition of microvesicles to fresh plasma resulted in increased thrombin generation compared with controls. When phosphatidylserine on microvesicles was blocked with lactadherin, there was no difference in the endogenous thrombin potential, but the generation of thrombin was blunted with lower peak thrombin levels. CONCLUSION: Cold storage of murine whole blood results in decreased fibrinogen levels and fibrin clot formation. Aged whole blood demonstrates increased thrombin generation, and this is due in part to microvesicle production in stored whole blood. One mechanism by which microvesicles are procoagulant is by phosphatidylserine expression on their membranes.

Using hemoglobin vesicles to treat operative hemorrhagic shock after pneu- monectomy in dog models: an experimental study.

Hemoglobin vesicles (HbVs), considered as red blood cell substitutes, are liposomes encapsulating purified hemoglobin, with a phospholipid bilayer membrane (diameter: 250 nm; P50, 28 Torr). In this study, we aimed to investigate HbV function during hemorrhagic shock in lung resection and analyze the details of oxygen delivery. Left pneumonectomy was performed in dogs under mechanical ventilation, followed by rapid exsanguination of approximately 30% of the total circulating blood volume, which led to shock, reducing the mean arterial pressure (MAP) by approximately 60% of baseline. Subsequently, either 5% human serum albumin (HSA) or HbVs suspended in 5% HSA were infused for resuscitation. The MAP only recovered to 75% of baseline after HSA administration, but fully recovered (100%) after HbV administration, with significant differences between the groups (P < 0.005). Oxygen delivery was restored in the HbV group and was significantly higher than that in the HSA group (P < 0.0001). The infusion of HbVs dispersed in a 5% HSA solution compensated for the rapid loss of approximately 30% of the total circulating blood volume in a dog pneumonectomy model, even with impaired lung function. Thus, HbVs can be used for resuscitation from hemorrhagic shock during thoracic surgery.

Near-infrared spectroscopy for kidney oxygen monitoring in a porcine model of hemorrhagic shock, hemodilution, and REBOA.

Acute kidney injury is a common complication of trauma and hemorrhagic shock. In a porcine model of hemorrhagic shock, resuscitative endovascular balloon aortic occlusion (REBOA) and hemodilution, we hypothesized that invasive kidney oxygen concentration measurements would correlate more strongly with noninvasive near infra-red spectroscopy (NIRS) oxygen saturation measurements when cutaneous sensors were placed over the kidney under ultrasound guidance compared to placement over the thigh muscle and subcutaneous tissue. Eight anesthetized swine underwent hemorrhagic shock 4 of which were resuscitated with intravenous fluids prior to the return of shed blood (Hemodilution protocol) and 4 of which underwent REBOA prior to resuscitation and return of shed blood (REBOA protocol). There was a moderate correlation between the NIRS and kidney tissue oxygen measurements (r = 0.61 p < 0.001; r = 0.67 p < 0.001; r = 0.66 p < 0.001for left kidney, right kidney, and thigh NIRS respectively). When the animals were separated by protocol, the Hemodilution group showed a weak or nonsignificant correlation between NIRS and kidney tissue oxygen measurements (r = 0.10 p < 0.001; r = 0.01 p = 0.1007; r = 0.28 p < 0.001 for left kidney, right kidney, and thigh NIRS respectively). This contrasts with the REBOA group, where left and right kidney as well as thigh NIRS were moderately correlated with kidney tissue oxygen (r = 0.71 p < 0.001; r = 0.74 p < 0.001; r = 0.70 p < 0.001; for left kidney, right kidney, and thigh NIRS respectively). There was a strong correlation between both kidney NIRS signals and thigh NIRS measurements (r = 0.85 p < 0.001; r = 0.88 p < 0.001;for left kidney vs thigh and right kidney vs thigh respectively). There was also a strong correlation between left and right kidney NIRS (r = 0.90 p < 0.001). These relationships were maintained regardless of the resuscitation protocol. These results suggest that kidney NIRS measurements were more closely related to thigh NIRS measurements than invasive kidney tissue oxygen concentration.