Effects of pH of cerebrospinal fluid and local anesthetic on the success rate of spinal anesthesia.

Forty-three ASA physical status I-II adult patients, receiving spinal anesthesia for lower abdominal or lower limb surgery, were allocated randomly to two groups. Group 1 patients (n = 21) were given heavy bupivacaine 12 mg and group 2 patients (n = 22) were given tetracaine 12 mg in 2.5 mL of 10% dextrose. Spinal anesthesia was performed in the lateral decubitus position the at L 3-4 interspace with a 25-G spinal needle. Radial artery blood samples were collected before and after spinal anesthesia fpr pH measurement using a NOVA Biomedical machine; CSF samples were collected before and after injection of local anesthetic, and local anesthetic was also collected at the same time, for pH measurement using a Radio pH meter. The time from injection to maximal cephalad spread of analgesia and level of spinal analgesia were measured by the pin-prick method. The result was regarded as a failure if pain sensation still existed at the level of the operation site after spinal anesthesia. There were 1 failure case in the bupivacaine group and 2 failures in tetracaine group. The pH of CSF and local anesthetic in these failures were compared with those in effective cases, and the results showed that there was no significant relationship between the pH value of CSF and the local anesthetic drug.