Prolonged hypervolemic hemodilution decreases functional capillary density of ileal mucosa in pigs revealed by sidestream dark-field imaging

Objective:Hemodilution changes the physical properties of blood by reducing its hematocrit and blood viscosity.We tested whether prolonged hypervolemic hemodilution (HHD) impairs functional capillary density (FCD) of ileal mucosa in healthy mechanically-ventilated pigs and if there is any correlation between changes in FCD of ileal and sublingual mucosas during HHD.Methods:Sixteen domestic female pigs were anesthetized,mechanically-ventilated,and randomly assigned to the HHD (20 ml/(kg·h) Hartmann's solution for 3 h) or fluid restrictive (5 ml/(kg·h) Hartmann's solution for 3 h) group.Microcirculations of sublingual and ileal mucosas via ileostomy were visualized using sidestream dark-field (SDF) imaging at baseline conditions (t=0 h) and at selected time intervals of fluid therapy (t=1,2,and 3 h).Results:A significant decrease of ileal FCD (285 (278-292) cm/cm 2) in the HHD group was observed after the third hour of HHD when compared to the baseline (360 (350-370) cm/cm 2) (P<0.01).This trend was not observed in the restrictive group,where the ileal mucosa FCD was significantly higher after the third hour of fluid therapy as compared to the HHD group (P<0.01).No correlation between microhemodynamic parameters obtained from sublingual and ileal mucosas was found throughout the study.Conclusions:Prolonged HHD established by crystalloid solution significantly decreased ileal villus FCD when compared to restrictive fluid regimen.An inappropriate degree of HHD can be harmful during uncomplicated abdominal surgery.