Elevated intracompartmental pressure (ICP) results in tissue damage due to impaired microcirculatory function. The nature of microcirculatory impairment in elevated ICP is not well understood. This study was designed to measure the effects of increased ICP on skeletal muscle microcirculation, inflammation and cell viability using intravital videomicroscopy.

Twenty adult male Wistar rats were randomised to four groups: the control group (control) had no intervention; while three experimental groups had elevated ICP maintained for fifteen (15m), 45 (45m), or ninety (90m) minutes. Compartment pressure was continuously monitored and controlled between 30¡V40mmHg in the posterior hindlimb using saline infusion into the anterior hindlimb. Mean arterial pressure was maintained between 80 and 120mmHg. Fasciotomy was then performed and the Extensor Digitorum Longus muscle studied using intravital videomicroscopy. Perfusion was measured by comparing the numbers of continuous, intermittent, and nonperfused capillaries. Inflammation was measured by counting the number of activated (rolling and adherent) leukocytes in post-capillary venules. Muscle cellular Injury was measured using fluorescent vital staining of injured cell nuclei.

Perfusion: The number of continuously perfused capillaries decreased from 77 ± 3/mm (control) to 46 ± 10/mm (15m),40±10/mm(45m)and27±8/mm(90m)(p< 0.05). Non-perfused capillaries increased from 13 ± 1 (control) to 16 ± 4 (15m), 30 ± 7 (45m), and 39 ± 5 (90m) (p< 0.05). Inflammation: Activated leukocytes increased from 3.6 ± 0.7/(100ƒÝ)2 (control) to 5.9 ± 1.3 (15m), 8.6 ± 1.8 (45m), and 10.9 ± 3.0/(100ƒÝ)2 (90m) (p< 0.01). Injury: The proportion of injured cells increased from 5 ± 2 % in the control group to 12 ± 3 (15m), 16 ± 7 (45m) and 20 ± 3 % (90m) (p< 0.05).

As little as fifteen minutes of 30mmHg ICP caused irreversible muscle damage and microvascular dysfunction. With increased duration, further decreases in capillary perfusion and increases in injury are noted. A severe inflammatory response accompanies elevated ICP. The role of inflammation in compartment syndrome is unknown, but may contribute to cell injury and reduced capillary perfusion.