Cellular edema regulates tissue capillary perfusion after hemorrhage resuscitation

Abstract

Background: Hemorrhage-induced activation of endothelial cell Na+/H+ -exchanger results in cellular swelling, which physically impedes capillary filling and compromises gut perfusion. We hypothesized that correction of the vascular volume deficit by conventional resuscitation does not improve capillary filling unless cellular swelling is prevented. Also, we hypothesized that adjunctive direct peritoneal resuscitation (DPR) with topical peritoneal dialysis solution (Delflex; Fresenius USA, Inc., Ogden, Ut) enhances capillary filling and gut perfusion by mechanisms that are independent of the Na+/H+ function.

Methods: In vivo intravital videomicroscopy and Doppler velocimeter were used by us to measure microvascular diameter and flow, capillary filling (index of functional capillary density, FCD), and endothelial cell function in the terminal ileum of anesthetized rats. Rats were bled to 50% mean arterial pressure for 60 min and resuscitated with the shed blood plus 2 volumes of saline (conventional resuscitation). Prevention of endothelial cell swelling was achieved with topical amiloride (specific Na+/H+ inhibitor) in the tissue bath before hemorrhage or simultaneously with conventional resuscitation. DPR was simulated by instillation of Delflex in the tissue bath as adjunctive to conventional resuscitation. Sham no hemorrhage group and a simulated DPR group that received topical amiloride treatment served as controls.

Results: Conventional resuscitation from hemorrhagic shock restored and maintained central hemodynamics but caused progressive and persistent intestinal vasoconstriction and hypoperfusion associated with low FCD and endothelial cell dysfunction. Prevention of endothelial cell swelling when combined with conventional resuscitation, preserved endothelial cell function, and restored local intestinal microvascular variables to near-prehemorrhage levels. Simulated adjunctive DPR produced rapid, sustained, and generalized vasodilation associated with restoration of endothelial cell function, and maximum recruitment of FCD independent of the Na+/H+ -exchanger function.

Conclusions: Paradoxical endothelial cell swelling occurs early during hemorrhagic shock because of activation of the Na+/H+ exchanger. This cellular edema, which is not resolved by correction of the vascular volume deficit, explains the persistent postresuscitation endothelial cell dysfunction and gut hypoperfusion. Simulated adjunctive DPR in this study reversed endothelial cell swelling and enhanced gut perfusion by mechanisms that are independent of the Na+/H+ exchanger activity.

Fig 1

Timeline protocol. Ach, acetylcholine; Amiloride preemptively, drug administration preemptively at the beginning of hemorrhagic shock; Amiloride simultaneously, drug administration simultaneously with resuscitation; BL, baseline; NP, sodium nitroprusside.

Fig 2

Intestinal microvascular response expressed as percentage change from corresponding baseline (BL). Vessel diameter of inflow distributing arteriole (A1), and the smaller premucosa's proximal precapillary (pA3) and distal (dA3) precapillary arterioles after hemorrhagic shock + conventional resuscitation (solid circles); hemorrhagic shock + conventional resuscitation + Amiloride simultaneously with resuscitation (open diamonds); hemorrhagic shock + conventional resuscitation + Amiloride preemptively at the beginning of hemorrhagic shock (solid diamonds); hemorrhagic shock + conventional resuscitation + DPR (solid squares); hemorrhagic shock + conventional resuscitation + DPR + Amiloride simultaneously with resuscitation (open squares); and after instrumentation, time-matched and Amiloride administration but no hemorrhage controls (open triangles). *P < .01 versus corresponding baseline by repeated-measures 1-way ANOVA followed by Dunnett's multiple-range test, §P < .01 for the simulated DPR group versus the conventional resuscitation group by 2-way ANOVA followed by Bonferroni multiple comparison post-tests, ¥P <.05 for the simulated DPR group versus the sham no hemorrhage group by 2-way ANOVA followed by Bonferroni multiple comparison post-tests.

Fig 3

Intestinal A1 blood flow (upper panel) and functional capillary density (lower panel), each expressed as a percentage change from corresponding baseline after hemorrhagic shock + conventional resuscitation (solid circles); hemorrhagic shock + conventional resuscitation + Amiloride simultaneously with resuscitation (open diamonds); hemorrhagic shock + conventional resuscitation + Amiloride preemptively at the beginning of hemorrhagic shock (solid diamonds); hemorrhagic shock + conventional resuscitation + DPR (solid squares); hemorrhagic shock + conventional resuscitation + DPR + Amiloride simultaneously with resuscitation (open squares); and after instrumentation, time-matched and Amiloride administration but no hemorrhage controls (open triangles). *P < .01 versus corresponding baseline by repeated-measures 1-way ANOVA followed by Dunnett's multiple-range test, §P < .01 for the simulated DPR group versus the conventional resuscitation group by 2-way ANOVA followed by Bonferroni multiple comparison post-tests, ¥P < .05 for the simulated DPR group versus the sham no hemorrhage group by 2-way ANOVA followed by Bonferroni multiple comparison post-tests.

Fig 4

Endothelial cell function in the distal dA3 arteriole assessed from the response to acetylcholine and expressed as a percentage change from maximum dilation capacity (response to sodium nitroprusside). Bar from left to right are the dA3 response after hemorrhagic shock + conventional resuscitation; hemorrhagic shock + conventional resuscitation + Amiloride simultaneously with resuscitation; hemorrhagic shock + conventional resuscitation + Amiloride preemptively at the beginning of hemorrhagic shock; hemorrhagic shock + conventional resuscitation + DPR; hemorrhagic shock + conventional resuscitation + DPR + Amiloride simultaneously with resuscitation; and after instrumentation, time-matched and Amiloride administration but no hemorrhage controls. dA3 response to acetylcholine was impaired significantly in the hemorrhagic shock + conventional resuscitation group. *P < .01 by 2-way ANOVA followed by Bonferroni multiple comparison post-tests.