Effect of hemorrhage on superior mesenteric artery flow during increased intra-abdominal pressures

BACKGROUND: Elevations in intra-abdominal pressure (IAP) adversely affect organ function. Prior hemorrhage and resuscitation exacerbates the cardiac and pulmonary effects of IAP. We have recently shown that superior mesenteric artery flow (SMAF) is reduced with increasing IAP. This study was designed to determine whether and how hemorrhage and resuscitation affects SMAF with increasing IAP. METHODS: Ten pigs were divided into two groups after placement of a Doppler flow probe around the proximal SMA and insertion of a pulmonary artery (PA) catheter. Group 1 underwent intraperitoneal infusion of fluid to increase IAP to 10, 20, 30, and 40 mm Hg followed by a 20-minute equilibration period at each IAP. Group 2 was hemorrhaged 20% of circulating volume followed by standard resuscitation. After equilibration, this group had IAP increased in the same manner as group 1. Cardiac output (CO), PA pressures, and SMAF were recorded 1 hour after laparotomy and after equilibration at each IAP. Comparisons were made using repeated measures of analysis of variance, Student's t test, and linear regression analysis. RESULTS: In group 2, a reduction in SMAF was noted at 30 and 40 mm Hg of IAP when compared with baseline (p = 0.009). This reduction was not seen in group 1. There was also a significant (p = 0.001) reduction in CO between baseline and all levels of increased IAP in group 2. This decrease was again not seen in group 1. The correlation between CO and SMAF in group 2 was r = 0.74, r2 = 0.55, p = 0.0001. There was no significant correlation between CO and SMAF in group 1. CONCLUSION: SMAF and CO are reduced with increasing IAP to a greater degree when preceded by hemorrhage and resuscitation. Although there is a strong correlation between the reductions in CO and SMAF, the reduction in SMAF is greater than the reduction in CO. This finding suggests that optimizing cardiac function alone during periods of even moderate levels of increased IAP may be inadequate to normalize SMAF. This lends further support for early abdominal decompression in the treatment of trauma patients with increased IAP.