Influences of Macrohemodynamic Conditions on Systemic Microhemodynamic Changes in Burns

The clinical course after major burns is characterized by microcirculatory changes and consecutive capillary leakage. However, current clinical monitoring does not properly assess microcirculation, whereas macrohemodynamic changes are continuously evaluated. Here, we assess if macrohemodynamic and microhemodynamic parameters after burn trauma are correlated in a rat model.

Burn plasma harvested from donor rats 4 hours after thermal injury (30% total body surface area, 100 °C water, 12 seconds) was administered intravenously to healthy animals during 2 hours of intravital microscopy (burn group [BG]). Shamburn plasma (same procedure but water at 37°C) was transferred for negative controls (shamburn group [SBG]). Intravital microscopy was performed at 0, 60, and 120 minutes to assess capillary leakage measuring fluorescein isothiocyanate-albumin extravasation. Macrocirculation was assessed using mean arterial pressure and heart rate, whereas microcirculation was evaluated using red blood cell velocity, venular diameter, venular wall shear rate and plasma extravasation at 0, 60, and 120 minutes in postcapillary venules.

Thirty mesenteric venules (16 animals) in SBG and 31 mesenteric venules (15 animals) in BG were observed during intravital microscopy. Mean arterial pressure and heart rate remained within acceptable margins and showed no significant differences, neither within nor between groups. Significant correlations between macrohemodynamic and microhemodynamic conditions were neither observed for BG nor SBG, except from a significant correlation of MAP and plasma extravasation at T60. However, at T120 mesenteric venules in the BG clearly showed microvascular burn edema, whereas venules in SBG did not.

Stabilization of macrohemodynamic conditions may not necessarily have positive effects on microcirculatory derangements-a fact that has not been shown for burns yet, that is-however, well described for sepsis. Further studies are required to show whether distinct monitoring of microcirculation may offer new approaches for burn trauma treatment.