Regional anesthesia and pain medicine vol. 24 no. 3 may-june supplement 1999 analgesic spread and segmental dosing requirements for thoracic epidural block

Introduction. Oft quoted dosing recommendations for thoracic epidural analgesia are based on data from lumbar epidural studies combined with clinical expertise . This abstract reports data from a thoracic epidural dosing study that was designed to establish initial dosing guidelines such as those previously reported . Segmental dosing requirements (SDR) were calculated for each group (vol(ml)/seg). Methods. After IRB approval at Portsmouth Naval Medical Center all suitable ASA 1-3 patients ages 18-80, scheduled for thoracic or upper abdominal surgery were offered enrollment in the study; consenting patients were then placed in group 1(1855 years) or group 2 (56-80 years) depending on their age. After placement of IV and A-line, a thoracic epidural catheter was placed in an interspace between T6 and T10, and secured 3 cm into the epidural space. The patient was positioned supine and given a 3 ml test dose of 2% lidocaine. After three minutes the randomized additional study dose (2 ml(A) or 6 ml(B) of 2% lidocaine) was given (time 0) and the patient was assessed for evidence of epidural blockade. Dermatomal spread of blockade was measured bilaterally in the mid-clavicular line starting at the level of catheter placement and moving caudad and cephalad. Analgesia to pinprick was recorded 1 level inside of the dermatome where the pin felt as sharp as over an unblocked dermatome. Extent of blockade was then measured every five minutes for thirty minutes. If bilateral blockade was not evident by 15 minutes, the study was terminated and the patient readied for surgery. Results. Group # of pts total Vol (ml) Max Seg Analgesia Mean±SD Minutes to Max Spread ±SD Segment Dosing Req (ml/seg) Mean ±SD 1A 10 5 10. 9 + 4. 0 14. 5 ±4. 4 0. 53 ±0. 22 1B 10 9 13. 9 + 4. 5 21. 0 + 7. 0 0. 71 ±0. 25 2A 14 5 14. 1 ±5. 6 18. 6±6. 9 0. 41+0. 18 2B 14 9 17. 4 + 5. 1 22. 1+5. 5 0. 55+0. 14 In each age group the differences in maximum segments blocked (approx 3 seg) between volumes were similar because there was no interaction effect between age group and volume. The difference between groups and volumes was significant with p=0. 0239 and p=0. 0280 respectively (2-way ANOVA). Likewise, there was no interaction effect for the calculated SDRs; the differences between groups (p=0. 0194) or volumes (p=0. 0062) were significant (2-way ANOVA). The difference in time to reach maximum spread was significant between volumes but not groups (p=0. 0086, p=0. 1477 respectively, 2-way ANOVA). Conclusions. Using lumbar catheters, many authors have demonstrated greater segmental epidural blockade for a given dose in older patients3'4. Data from this study confirms the effect of age on epidural spread in the thoracic region. The segmental dosing requirements for 2% lidocaine are approximately . 5 and . 6 ml per segment for young and old patients respectively in the midthoracic area. The spread of analgesia peaked at approximately 15-20 minutes, (see fig. ).