Heterogeneous Microcirculation in the Rat Small Intestine during Hemorrhagic Shock: Quantification of the Effects of Hypertonic-Hyperoncotic Resuscitation

Abstract

Purpose: In the event of a spatial or temporal microvascular perfusion heterogeneity conventional methods are often inadequate to describe the microcirculatory changes. Our aim was to use a new formula to characterize and compare the microcirculatory reactions in the mucosa and longitudinal muscle of the rat small intestine in response to hypertonic/hyperoncotic and normotonic resuscitation strategies. Methods: Intravital videomicroscopy with an orthogonal polarization spectral (OPS) imaging technique was utilized. Microcirculatory variables were recorded during hemorrhagic shock (HS; 50 mm Hg mean arterial pressure for 60 min) and fluid replacement with 0.9% saline or with 7.2% saline containing 10% hydroxyethylstarch 200/0.5 (Osmohes; 4 ml/kg). Due to the temporal perfusion variability, microcirculatory changes were described using the calculation of the average red blood cell velocity (A-RBCV), while the spatial changes were calculated as a function of the size of the perfused capillary network. Results: During HS and the late phase of resuscitation, perfusion was characterized by capillary flow motion (i.e. variability in time) in the villi, and by spatial flow heterogeneity in the longitudinal muscle layer. The approximately 40% decrease in the calculated villus A-RBCV during HS was only partially affected by 0.9% saline, whereas Osmohes completely restored A-RBCV by increasing both the red blood cell velocity and the duration of high-flow periods at the onset of resuscitation in the villi. The approximately 60% reduction in A-RBCV in the muscle layer during HS was not followed by an appreciable recovery in either group, but Osmohes significantly increased A-RBCV in the late resuscitation phase. Conclusions: The hypertonic/hyperoncotic solution induces a considerable microcirculatory improvement in two distinct layers of the small intestine after HS. This positive effect is related to the amelioration of the intestinal microcirculatory heterogeneity.