Evaluation of the Surgical Pleth Index During Spinal and General Anesthesia

The Effects of Sedation and Analgesia on the Surgical Pleth Index (SPI)

The Surgical Pleth index (SPI) has been introduced as a non invasive tool to "measure" stress and pain during surgery. Preliminary studies were performed in patients under general anaesthesia with propofol and remifentanil. These trials showed a good correlation between SPI and aching procedures and a negative correlation between SPI and the remifentanil dosage. Hence, it was concluded that SPI may be a bedside tool to measure 'pain' during surgery. So far, no study investigated SPI during regional anaesthesia.

1. Spinal anaesthesia secures full pain relieve and muscle relaxation usually in the lower part of the body. Thus, SPI - a measure that reflects pain during surgery - may not exceed significantly compared to baseline. It may slightly increase only during administration of the block.
2. Increasing SPI values due to surgery under subarachnoid block may reflect intraoperative patient's stress mediated by activation of the autonomic nervous system, specifically sympathetic activation.
3. In consistence with previously published data no changes of SPI should occur due to standardized sedation with propofol.

Inclusion Criteria:

• surgical procedures feasible under general or spinal anesthesia
• duration between 30 and 90 min
• ASA status I,II or III

Exclusion Criteria:

• contraindications against one of the anesthesia methods
• age under 18
• emergencies
• chronical pain history
• lack of sinus rhythm