Characterization of the mesenteric circulatory physiology during hemorrhagic shock in a swine model

Introduction: This study aimed to characterize blood flow through the mesenteric circulation during hemorrhage and resuscitation in a large animal model. Methods: Five male swine (50-70 kg) underwent anesthesia and placement of flow probes and pressure catheters around and within the superior mesenteric artery, portal vein, and inferior vena cava. A laser doppler flow probe was placed on the intestine to measure end-organ perfusion. Animals were then exsanguinated to a systolic blood pressure of <50mmHg with 60-minutes of shock followed by resuscitation for 120-minutes. Results: Animals were placed into hemorrhagic shock (lactate peak 5.9 ± 2.1 mmol/L vs baseline: 3.4 ± 0.7 mmol/L) with lower pressures and flows during shock and restoration to baseline following resuscitation: SMA (70 vs 36 vs 75 mmHg, p<0.001; 856 vs 371 vs 762 mL/min, p<0.001), portal vein (9 vs 8 vs 10mmHg, p<0.001; 200 vs 52 vs 141 mL/min, p<0.001), IVC (12 vs 7 vs 10 mmHg, p<0.001; 209 vs 27 vs 163 mL/min, p<0.001), and mean arterial pressure (MAP) (67 vs 36 vs 69 mmHg, p<0.001). LDF fell during hemorrhage (1.38 vs 0.38 blood perfusion units (BPU), p<0.001) and did not return to baseline during resuscitation (0.70 BPU, p<0.001). The intestine achieved only 51% of baseline LDF perfusion after resuscitation despite return of mesenteric hemodynamics. Conclusion: Despite macrovascular physiologic restoration after hemorrhagic shock, end organ perfusion did not adequately recover following resuscitation to baseline MAP. Continuous physiologic insult to the mesentery is likely ongoing after systemic hemodynamic restoration.