Proportional effects of hypothermia, neural block, interstizial fluid changes and sedation on skeletal muscle oxygenation and microcirculation.

Introduction SIRS and sepsis are characterized by factors each of which plays a specific role in determining tissue oxygenation and microcirculatory function. Hyperthermia itself and the action of sedative drugs as well as the increased interstitial tissue fluid play also a major role in microcirculatory upregulation. Knowing how each factor influences the microcirculatory regulation and tissue oxygenation can provide useful information to induce a change in therapeutic approach thus influencing sepsis morbidity and mortality. Aim This study was aimed to evaluate non invasively with near infrared spectroscopy changes in skeletal muscle oxygenation and microcirculatory function induced by regional hyperthermia, neuronal block, volume changes of the interstitial fluid and sedatives drugs. Protocols The study was performed on four experimental conditions. 1. Regional hyperthermia was studied on the brachioradial muscle of 15 healthy volunteers during 20 min of selective heating emitted through electromagnetic waves (SMARTY Far infrared system: FUJIKA, Tokyo Japan). The skin temperature did not exceed 42°C. 2. The abolishing of neuronal tone was studied on the calf of 20 pts receiving spinal anaesthesia with 15 mg of 0.75% levobupivacaine for orthopaedic surgery. 3. Change in interstitial fluid volume was investigated on the calf of 10 pts with a history of end-stage renal disease before and after dialysis. 4. The effects of a continuous infusion of 5.5 mg*kg-1*h of propofol and 0.3 mg kg-1 of remifentanil were studied on the brachioradial muscle of 20 pts (ASAI)receiving. Measurements were performed before anaesthesia (baseline) and 30 min thereafter. NIRS variables: Oxygenated haemoglobin ([HbO2]) and de-oxygenated haemoglobin ([HHb]). The total haemoglobin concentration ([HbT]), haemoglobin oxygen saturation (StO2:[HbO2] to [HbT]) and tissue oxygen content (CtO2: 1.36* StO2/100*[HbT]*0.645/100) were calculated. muscle blood flow (mBF), oxygen consumption (mVO2), and microvascular compliance (compliance) were measured during repeated vein occlusions. Conclusion All four experimental conditions we investigated by NIRS in subjects without acute or chronic injuries induced specific pattern in skeletal muscle oxygenation and microcirculatory function that varied in intensity. The information we provide on their precise contribution should help in designing appropriate therapeutic measures to reduce their deleterious effects in patients with sepsis and septic shock