EFFECTS OF PROLONGED ISCHEMIA ON SKELETAL MUSCLE MICROCIRCULATION AS ASSESSED BY NEAR-INFRARED SPECTROSCOPY

BACKGROUND: The pathophysiology of ischemia-reperfusion injury has been subject of extensive studies in the last century, as it underlies to many clinical and surgical conditions. The most examined tissues during and after ischemia are the skeletal muscle, myocardium, nerves, skin, and the intestinal mucosa [1]. However, microvascular alterations during and following prolonged ischemia were investigated solely by anatomical and histological analysis, mainly in animal models [2]. Near-infrared spectroscopy (NIRS) has been used in last decades to detect in vivo microvascular alterations by means of a vascular occlusion test (VOT) [3,4]. We sought to analyse by NIRS the microcirculatory profile of patients undergoing prolonged tourniquet-induced ischemia for extremity surgery, and compare the results with time of ischemia and comorbidities. MATERIALS AND METHODS: We conducted a prospective observational study on 42 patients undergoing surgery of the upper limb, in which a prolonged tourniquet-induced ischemia was needed for surgical procedures. Regional anaesthesia was achieved before ischemia with a complete axillary brachial plexus block using 150 mg of levobupivacaine 0,5% as standard care. Ischemia was induced by a tourniquet (Zimmer ATS 2000, Zimmer Inc., Warsaw, USA) placed distal to the armpit and cuffed at 250 mmHg. The probe of a NIRS monitor (InSpectra 325, Hutchinson Technology Inc., Hutchiston, USA) was placed on the brachial muscle of the same arm, and muscle oxygen saturation (StO2) was recorded continuously before anaesthesia, during and after surgery, and analyzed with a dedicated software. The following variables were recorded: baseline StO2, StO2 desaturation slope during occlusion (dSlope, units/sec), resaturation rate of the reperfusion phase following the ischemic period (RR, units/sec), hyperaemic peak (peak, units), and duration of the hyperaemic period following ischemia (hyperaemic time, sec) (Figure 1). RESULTS: Patient’s characteristics are shown in Table 1. Values of dSlope were similar among all patients. Values of RR and hyperaemic time were correlated with the duration of ischemia (p = 0,022 SE = 0,003 and p = 0,019 SE = 0,58, respectively) but not with comorbidities (Figure 2). Grouping patients by duration of ischemia (30, 60, or 90 minutes), we found a significant decrease in RR after 60 and 90 minutes (Table 2, Figure 3). Hyperaemic peak was lower in the 90 minutes group whereas the hyperaemic time was significantly increased (Tables 3 and 4, Figure 3). CONCLUSION: Alterations of skeletal muscle microcirculation were correlated with the duration of ischemia, but not with comorbidities. We observed an initial impairment of the microcirculatory recovery at 90 minutes of ischemia.