Neuraxial anesthesia affords a less interventional way to desensitization of the lower body for surgical procedures. After introduction of neuraxial anesthesia, vasodilatation of body part below the anesthetic level is theoretically appeared as the sympathetic nerve efferent is blocked. The vasodilatation effect is related to hypotension, hypothermia, shivering and the response of volume redistribution. It is believed that vasodilatation leads to better regional tissue perfusion and better regional tissue oxygenation. Previous reports of laser doppler flowmetry and thermography showed their effectiveness on monitoring blocked level but they were not easily available in the operation room. Recently Near-infrared spectroscopy(NIRS) demonstrates real-time tissue oxygen saturation(rSO2) which is applied generally in non-invasive brain oximeter. We use NIRS in spinal anesthesia to monitor the tissue oxygenation change over the upper and lower limbs during the induction of neuraxial anesthesia.

In patients who were planned to receive an operation with intrathecal anesthesia, NIRS (INVOS Cerebral Oximeter Model 5100B; Somanetics, Troy, MI, USA) with two adhesive patches was used to monitor rSO2. One patch was applied over the biceps brachii muscle,(the body part above the anaesthetic level), and the other patch was applied over the medial side of the gastrocnemius muscle of the non-surgical leg,(the body part below the anaesthetic level). In both extremities, rSO2 was monitored continuously and recorded every minute from before intrathecal bupivacaine injection until 15 min after injection. Isobaric bupivacaine 0.5% 10-15 mg was injected intrathecally and the level of anaesthesia was examined 10 min later by loss of cold sensation to alcohol swab by an anaesthetist not involved in the study. the changes of rSO2 of upper and lower extrimities were recorded and analysed.

Inclusion Criteria:

• patients who receive operations under spinal anesthesia

Exclusion Criteria:

• neurological, cardiovascular diseases

Patients who receive operations under spinal anesthesia