Intramuscular partial oxygen tension monitoring in compartment syndrome–an experimental study

Measuring intracompartmental pressure is a well-accepted method in evaluating a compartment syndrome, which may occur after limb ischaemia followed by reperfusion. As a compartment syndrome is paralleled by a decreased microcirculation it should be possible also to evaluate a compartment syndrome by measuring intramuscular partial oxygen tension (p_O2). In this study, anaesthetized 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 p_O2 catheter. Besides a sham operated group, three experimental groups were subjected to either 2, 4 or 6 h of ischaemia followed by 4 h of reperfusion. One further group was also subjected to 4 h of ischaemia and 4 h of reperfusion but received a fasciotomy at the time of reperfusion. Compartment pressure and intramuscular p_O2 were recorded every 15 min. For histological examination muscle specimens were obtained after each experiment. Two hours of ischaemia followed by 4 h of reperfusion did not result in any morphological changes and also in no significant change in compartment pressure during both phases, whereas p_O2significantly dropped during ischaemia (from 19.0 mmHg to 3.0-5.0 mmHg) and returned to normal during reperfusion. In prolonged ischaemia (4 h) morphologically a severe interstitial oedema was evident, compartment pressure increased during reperfusion (from 2.0 mmHg to 8.8 mmHg) and p_O2 dropped during ischaemia to 3.0 mmHg and did not return to normal during reperfusion (10.5 mmHg versus 19.0 mmHg normal). In the case of 6 h ischaemia, partial necrosis and no interstitial oedema was found morphologically. There was no significant change in compartment pressure throughout the study, and p_O2 remained significantly decreased even during reperfusion (2.0-3.0 mmHg). Normal compartment pressure could mislead to false negative interpretation of microcirculatory disorders preceding or following compartment syndrome, whereas P_O2 clearly identifies the microcirculatory state of the muscle. Thus, intramuscular P_O2 monitoring presents a valuable method in evaluating compartment syndrome, especially where there are suspected clinical signs and risk of ischaemia but normal compartment pressure.