[Intramuscular pO2 monitoring in compartment syndrome--an experimental study].

HYPOTHESIS

Measuring intracompartmental pressure is a well accepted method in evaluating a compartment syndrome, which may occur after limb ischemia followed by reperfusion. As a compartment syndrome is paralleled by a decreased microcirculation it should be possible to evaluate a compartment syndrome also by measuring intramuscular pO2.

METHODS

Anesthetized rats (spontaneous breathing via tracheotomy) were subjected to infrarenal ligation of the aorta. A pressure catheter was placed subfascial in the crural muscle group of one hind limb, whereas the contralateral side was prepared with a pO2 catheter. Besides a sham operated group, three experimental groups were subjected to either 2 hrs, 4 hrs or 6 hrs of ischemia followed by 4 hrs of reperfusion. One further group was also subjected to 4 hrs of ischemia and 4 hrs of reperfusion but received a fasciotomy at the time of reperfusion. Compartment pressure and intramuscular pO2 were recorded every 15 min. For histological examination muscle specimen were obtained after each experiment.

RESULTS

Two hours of ischemia followed by 4 hrs of reperfusion did not result in any morphological changes and also not in any significant change in compartment pressure during both phases, whereas pO2 significantly dropped during ischemia (from 19.0 mmHg to 3.0-5.0 mmHg) and returned to normal during reperfusion. In prolonged ischemia (4hrs) morphologically a severe interstitial edema was evident, compartment pressure increased during reperfusion (from 2.0 mmHg to 8.8 mmHg) and pO2 dropped during ischemia down to 3.0 mmHg and did not return to normal during reperfusion (10.5 mmHg versus 19.0 mmHg normal). In case of 6 hrs ischemia, partial necrosis and only little interstitial edema were found morphologically. There was no significant change in compartment pressure throughout the study; and pO2 remained significantly decreased even during reperfusion (2.0-3.0 mmHg).

DISCUSSION

Normal compartment pressure could mislead to false negative interpretation of compartment syndrome, whereas pO2 clearly identifies the microcirculatory state of the muscle. Thus, intramuscular pO2 monitoring presents a valuable method in evaluating compartment syndrome, especially in case of suspect clinical signs but normal compartment pressure.