Subcutaneous Microdialysis Biomarkers Correlate With Intramuscular Biomarkers and Can Be Used to Detect Acute Compartment Syndrome in a Porcine Model

BACKGROUND: Acute compartment syndrome (ACS) is a time-sensitive diagnosis, with mortality rates as high as 15%. Diagnosis relies on clinical evaluation and intracompartmental pressure (ICP) measurements, which are only 68% accurate. Microdialysis has been shown to be reliable in detecting flap ischemia before clinically evident. Therefore, we hypothesized that intramuscular (IM) microdialysis could detect early ACS with high diagnostic test accuracy (DTA). Given IM perforators supply overlying skin, we further hypothesized that subcutaneous (SC) biomarkers closely correlate with IM metabolic changes and can detect ACS in a swine model. METHODS: Eleven Yorkshire swine (male, ~50 kg) were used to model tourniquet-induced ACS in the bilateral anterior hind limbs (n=22). ACS was induced for 6 hours. Microdialysis probes were placed in both IM and SC tissue compartments to collect interstitial fluid for analysis of glucose, pH, and lactate. Tissue oxygenation (SrO2) and hindlimb temperature were also monitored. Maximal diagnostic test accuracy and correlation coefficients were calculated for these metrics. RESULTS: ICP increased immediately after tourniquet inflation [preinflation: 15.6±4.7 mm Hg vs. postinflation: 53.0±38.2 mm Hg (P=0.0012)]. IM glucose decreased significantly at hour 2, while SC glucose decreased significantly at hour 3. SC glucose below 6.6 mg/dL had a DTA of 75%. Both IM and SC pH decreased significantly at hour 2. SC pH below 7.17 had a DTA of 78%. IM and SC lactate increased over the course of the experiment, but these changes were not statistically significant. SC lactate above 3.85 mg/dL had a DTA of 70%. SrO2 decreased significantly immediately after tourniquet inflation (DTA 100% below 58.5%), and hindlimb temperature decreased significantly within 30 minutes (DTA 99.6% below 27.8 °C). SC and IM glucose had the closest correlation (R2=0.931), followed by pH (R2=0.911), while lactate showed a less reliable correlation (R2=0.667). CONCLUSIONS: In a porcine model of ACS, SC biomarkers closely correlate with IM biomarkers and exhibit a high DTA with pH, having the highest accuracy. SrO2, and surface temperature also decreased rapidly and significantly. Future research should investigate these modalities in pilot clinical trials.