Compartmental and muscular response to closed soft tissue injury in rats investigated by oxygen-to-see and intravital fluorescence microscopy

BACKGROUND: Closed soft tissue injury (CSTI) induces local inflammation and progressive microvascular dysfunction. The aim of the study was to evaluate and compare the microvascular changes systematically in a precompartmental tissue injury by oxygen-to-see (O2C), a combined laser Doppler flowmetry and spectrophotometry system, and intravital fluorescence microscopy (IVM). METHODS: Fourteen Wistar rats were subjected to a trauma and a control group (both n = 7). CSTI was performed on the left lower limb by means of a standardized impact device. Controls received a sham CSTI. Capillary blood flow (Q(RBC)), oxygen saturation (SO2), and postcapillary filling pressure (rHb) were measured noninvasively by O2C assessed in 2-mm and 8-mm depth underneath the skin. Measurements were done before and after trauma and hourly up to 24 hours. IVM of the soleus muscle was performed after 24 hours. RESULTS: Before CSTI, O2C parameters did not reveal a difference between both groups. Up to 2 hours after trauma, Q(RBC) was significantly increased in 8-mm tissue depth. No significant changes of SO2 and rHb were noted compared with controls. In 2-mm depth, significantly reduced Q(RBC) and rHb levels were observed compared with 8 mm but with no significant changes after CSTI. IVM showed a significant increase of postcapillary blood flow with decreased functional capillary density, increased macromolecular leakage, and increased nicotinamide adenine dinucleotide hydride. CONCLUSIONS: After CSTI in rats, there was an immediate increase of compartmental capillary blood flow with a slight increase of muscle oxygen saturation and unchanged postcapillary venous filling pressures as sign of a redistribution of blood between soft and muscle tissue. The severity of pathologic changes in the compartment was not reflected by O2C but by IVM. (J Trauma Acute Care Surg. 2012; 73: 73-79. Copyright (C) 2012 by Lippincott Williams & Wilkins)