Background and Goal of Study: 
Spinal anesthesia for inguinal hernia repair in day surgery necessitates short-acting local anesthetics. Chloroprocaine is a well-known local anesthetic with a beneficial pharmacodynamic/-kinetic profile and suitable in ambulatory surgery. The primary goal of this study was the determination of the minimum local analgesic dose (MLAD) of Chloroprocaine with 2.5 µg of sufentanil administered intrathecally for inguinal herniorrhaphy in outpatients. 

Materials and Methods: 
After ethical committee approval and written patient informed consent,12 patients were recruited. The intrathecal dose was administered by a combined spinal-epidural technique (CSE) at the L3-4 or L4-5 intervertebral space. The first spinal dose of chloroprocaine 1% was 50mg and the testing interval was 2 mg. The analgesic efficacy was assessed as successful by getting a sensory block at or above the T6 dermatome bilateral and by a score lower than 30mm on a 100 mm visual analogue pain scale at the beginning of surgery. Chloroprocaine 3% was administered epidurally in case of insufficient analgesia. The up-down sequential allocation method has been chosen for study setup and statistical analysis of the results. 

Results and Discussion: 
11 patients were finally included in the analysis. The up-down sequence of doses of chloroprocaine is demonstrated in figure 1.
Using the isotonic regression estimator method, the ED50 (95% CI) of spinal chloroprocaine 1% was calculated to be 56 ( 52 – 58 ) mg. Figure 2 shows PAVA-adjusted dose response curve.

Conclusion(s):
The present results suggest an ED50 of chloroprocaine 1% for hernia repair in outpatients of 56 mg. Further research is necessary to determine the full-dose response curve of spinal chloroprocaine.


04 / Determination of the minimum local anesthetic dose (MLAD) of spinal chloroprocaine for inguinal herniorrhaphy in ambulatory surgery, preliminary results.