• Index of sympathectomy: photoplethysmography derived amplitude-baseline ratio from foot and hand; data measured at time 0, 5, 10 and 20 min following epidural; data expressed as % change from baseline and as area under time effect curve.
  

• 1. Other indices of sympathectomy:
  
• a. Photoplethysmography derived baseline change (ln (Blepi/Blo));
  
• b. Photoplethysmography derived time lag between pulse reaching hand and foot;
  
• c. Blood pressure (mean, systolic, diastolic);
  
• d. Skin temperature changes (finger and toe temperature change from baseline, toe-thigh and finger-arm temperature gradients).
  
• 2. Sensory level (pinprick, touch, cold)
  
• 3. Motor block (Bromage scale)
  
• All assessments made at 0, 5, 10 and 20 minutes after epidural drug administration.
  

There is controversy regarding the factors that determine the extent and intensity of epidural drug action. Most studies have focused on the inter-related triad of dose, concentration and volume.

We compare three groups: group A: 10ml of 0.5% bupivacaine; group B: 10ml of 0.25% bupivacaine and group C: 40ml of 0.0625% bupivacaine. When comparing these groups, groups A & B have the same volume of epidural drug, and groups B & C have the same total dose.

In particular this study compares different methods of assessing the sympathetic block (causing vasodilatation). These methods include skin temperature changes, hemodynamic changes and photoplethysmography.

Inclusion Criteria:

• Patients scheduled for extracorporeal shock wave lithotripsy (ESWL) under epidural anesthesia between March to September 1999

Exclusion Criteria:

• graded as ASA 3 or higher, below 18 or above 70 years of age, if they had peripheral vascular disease, baseline neurological deficit, or had any other contraindication for regional anesthesia.