Regional distribution of blood flow during proximal aortic cross‐clamping: An experimental study using coloured microspheres

Outcomes Associated With Aortic Balloon Occlusion Time in Patients With Zone 1 Resuscitative Endovascular Balloon Occlusion of the Aorta

INTRODUCTION

Resuscitative endovascular balloon occlusion of the aorta (REBOA) has the potential to cause clinically relevant systemic ischemic burden with long durations of aortic occlusion (AO). We aimed to examine the association between balloon occlusion time and clinical complications and mortality outcomes in patients undergoing zone 1 REBOA.

METHODS

A retrospective cohort analysis of American Association for the Surgery of Trauma Aortic Occlusion for Resuscitation in Trauma and Acuteregistry patients with Zone 1 REBOA between 2013 and 2022 was performed. Patients with cardiopulmonary resuscitation on arrival or who did not survive past the emergency department were excluded. Total AO times were categorized as follows: <15 min, 15-30 min, 31-60 min, and >60 min. Clinical and procedural variables and in-hospital outcomes were compared across groups using bivariate and multivariate regression analyses.

RESULTS

There were 327 cases meeting inclusion criteria (n = 51 < 15 min, 83 15-30 min, 98 31-60 min, and 95 > 60 min, respectively). AO >60 min had higher admission lactate (8 ± 6; P = 0.004) compared to all other time groups, but injury severity score, heart rate, and systolic blood pressure were similar. Group average times from admission to definitive hemorrhage control ranged from 82 to 103 min and were similar across groups (85 min in AO >60 group). Longer AO times were associated with greater red blood cell, fresh frozen plasma transfusions (P < 0.001), and vasopressor use (P = 0.001). Mortality was greatest in the >60 min group (73%) versus the <15 min, 15-30 min, and 31-60 min groups (53%, 43%, and 45%, P < 0.001). With adjustment for injury severity score, systolic blood pressure, and lactate, AO >60 min had greater mortality (OR 3.7, 95% CI 1.6-9.4; P < 0.001) than other AO duration groups. Among 153 survivors, AO >60 min had a higher rate of multiple organ failure (15.4%) compared to the other AO durations (0%, 0%, and 4%, P = 0.02). There were no differences in amputation rates (0.7%) or spinal cord ischemia (1.4%). acute kidney injury was seen in 41% of >60 min versus 21%, 27%, and 33%, P = 0.42.

CONCLUSIONS

Though greater preocclusion physiologic injury may have been present, REBOA-induced ischemic insult was correlated with poor patient outcomes, specifically, REBOA inflation time >60 min had higher rates of mortality and multiple organ failure. Minimizing AO duration should be prioritized, and AO should not delay achieving definitive hemostasis. Partial REBOA may be a solution to extend safe AO time and deserves further study.

Effect of cerebrospinal fluid pressure elevation on spinal cord perfusion during aortic cross-clamping with distal aortic perfusion

OBJECTIVES

Distal aortic perfusion (DaP) is a widely accepted protective adjunct facilitating early reinstitution of visceral perfusion during extended thoracic and thoraco-abdominal aortic repair. DaP has also been suggested to secure distal inflow to the paraspinal collateral network via the hypogastric arteries and thereby reduce the risk of spinal cord ischaemia. However, an increase in cerebrospinal fluid (CSF) pressure is frequently observed during thoracoabdominal aortic aneurysm repair. The aim of this study was to evaluate the effects of DaP on regional spinal cord blood flow (SCBF) during descending aortic cross-clamping and iatrogenic elevation of cerebrospinal fluid pressure.

METHODS

Eight juvenile pigs underwent central cannulation for cardiopulmonary bypass according to our established experimental protocol followed by aortic cross-clamping of the descending thoracic and abdominal aorta-mimicking sequential aortic clamping-with the initiation of DaP. Thereafter, CSF pressure elevation was induced by the infusion of blood plasma until baseline CSF pressure was tripled. At each time-point, microspheres of different colours were injected allowing for regional SCBF analysis.

RESULTS

DaP led to a pronounced hyperperfusion of the distal spinal cord [SCBF up to 480%, standard deviation (SD): 313%, compared to baseline]. However, DaP provided no or only limited additional flow to the upper and middle segments of the spinal cord (C1-Th7: 5% of baseline, SD: 5%; Th8-L2: 24%, SD: 39%), which was compensated by proximal flow only at C1-Th7 level. Furthermore, DaP could not counteract an experimental CSF pressure elevation, which led to a further decrease in regional SCBF most pronounced in the mid-thoracic spinal cord segment.

CONCLUSIONS

Protective DaP during thoraco-abdominal aortic repair may be associated with inadequate spinal protection particularly at the mid-thoracic spinal cord level ('watershed area') and result in the adverse effect of a potentially dangerous hyperperfusion of the distal spinal cord segments.

Large Animal Models of Proximal Aortic Balloon Occlusion in Traumatic Hemorrhage: Review and Identification of Knowledge Gaps Relevant to Expanded Use

BACKGROUND

The aim of this study was to review and summarize the large animal data on resuscitative endovascular balloon occlusion of the aorta (REBOA) for traumatic hemorrhage and identify knowledge gaps pertinent to the proposed broader use of the technique in prehospital situations.

METHODS

A review of published large animal models of traumatic hemorrhage incorporating REBOA with a primary outcome of the effect of aortic occlusion was performed. Data were collected on experimental protocols, hemodynamic effects, resuscitation requirements, mortality, metabolic and tissue consequences of induced ischemia-reperfusion, and effects on hemorrhage volume and other injuries.

RESULTS

A limited number of REBOA studies exist, and there is variability in the species and size of animals used. Various controlled and uncontrolled hemorrhage protocols have been studied, and a number of balloon devices used. Hemodynamic effects of occlusion were consistent as were basic systemic physiological effects. Minimal study of the effects of partial aortic occlusion and hemodynamic and metabolic physiology distal to the balloon has been performed, and partial or complete occlusion times >90 min have not been studied.

CONCLUSIONS

Significant knowledge gaps exist, which are potentially relevant to the expanded use of REBOA. Investigation into the physiology of partial occlusion and the metabolic effects and potential mitigation strategies for large-scale ischemia and reperfusion are particularly needed.

Assessment of Blood Flow Patterns Distal to Aortic Occlusion Using CT in Patients with Resuscitative Endovascular Balloon Occlusion of the Aorta

BACKGROUND

Resuscitative endovascular balloon occlusion of the aorta (REBOA) is used to decrease hemorrhage below the level of aortic occlusion (AO); however, the amount of collateral blood flow below the level of occlusion is unknown. Our aim was to investigate blood flow patterns during complete AO in patients who underwent CT scan after REBOA.

STUDY DESIGN

Between February 2013 and January 2017, patients who received REBOA and underwent CT scan with intravenous contrast during full AO were included. Patients were excluded if they had a CT scan performed with the balloon partially or fully deflated.

RESULTS

Nine patients (8 men) were included; all had blunt trauma. Mean Injury Severity Score (±SD) was 48 ± 8 and mean age was 45 ± 19 years. Four had supra-celiac AO, and 5 had infra-renal AO. Arterial contrast enhancement was noted below the level of AO in all patients, and distal to REBOA sheath placement in 5. Collateralization from arteries above and below the AO was identified in all patients. Contrast extravasation distal to AO was identified in 4 patients, and hematomas in 8. Distal vascular enhancement patterns varied by level of AO and contrast administration site.

CONCLUSIONS

Aortic occlusion appears to dramatically decrease, but does not completely impede, distal perfusion during REBOA due to multiple pathways of collateralization. Active extravasation and hematomas can still be detected in the setting of full AO, with purposefully timed contrast and image acquisition. Blood flow persists below the level of both the AO and in-dwelling sheath. Dynamic flow studies are needed to determine the contribution of AO and sheath placement to distal tissue ischemia.