General anesthesia impairs muscle microvascular compliance

Introduction Drugs used to induce and maintain general anesthesia have deep effects on the cardiovascular system. To our knowledge there are no studies investigating microvascular compliance during general anesthesia with a noninvasive approach based on near-infrared spectroscopy (NIRS) technology. Methods We randomized 36 healthy subjects undergoing maxillofacial surgery to receive general anesthesia with a sevofluorane–remifentanil (Group S) or a propofol–remifentanil association (Group P). We collected noninvasive measures of hemoglobin concentration from the gastrocnemius muscle of the subjects using a NIRS device (NIMO, NIROX srl, Italy), which performs quantitative assessments of the [HbO2] and [Hb] exploiting precise absorption measurements close to the absorption peak of the water. Data were collected during a series of venous occlusions at different cuff pressures, before and after 30 minutes from induction of general anesthesia. The muscle blood volume and microvascular compliance were obtained with a process previously described elsewhere [1]. Data were analyzed with a one-way analysis of variance test. Results Demographic data of the 36 subjects were similar in both Groups S and P. General anesthesia reduced the heart rate and mean arterial pressure and increased the total muscle blood volume in both groups (Group S: from 2.4 ± 0.9 to 3.2 ± 1.2 ml/ 100 ml; Group P: from 2.4 ± 1.2 to 3.5 ± 1.8 ml/100 ml; P < 0.05). During general anesthesia, despite no differences in muscle blood volume between the two groups, sevofluorane– remifentanil significantly decreased microvascular compliance (from 0.15 ± 0.08 to 0.09 ± 0.04 ml/mmHg/100 ml; P = 0.001) whereas propofol–remifentanil did not (from 0.15 ± 0.08 to 0.16 ± 0.11 ml/mmHg/100 ml; P = 0.39).