EPIDURAL CATHETER PLACEMENT FOR TESTING OF OBSTETRICAL ANALGESICS IN FEMALE GUINEA-PIGS

The pregnant guinea pig may be a useful model for the study of drug ef fects in the newborn. A reliable technique for epidural catheterizatio n in the guinea pig was developed to allow use of this model to evalua te the effects of epidural labor analgesics on neonates. Catheters wer e implanted in two open pilot animals and 19 time-dated pregnant anima ls on days 59 to 62 of gestation. After establishing a surgical plane of isoflurane-induced anesthesia, an incision was made over the dorsal lumbar part of the spine. The L3-4 intervertebral space was exposed t o allow introduction of a caudally directed 27-gauge catheter into the epidural space. The catheter was capped and implanted subcutaneously, then the animal was allowed to recover from anesthesia. Catheter plac ement was evaluated, using a bupivacaine test dose in 17 animals and p ostmortem histologic examination in 20 animals. One animal died immedi ately after surgery. Epidural placement was confirmed histologically i n 15 of 20 animals. Failed catheters were either subdural, with one ca theter found to be penetrating the spinal cord (intraspinal), or intra muscular. Response to epidurally administered bupivacaine was variable but was typically characterized by normal. alertness and ability to u se the forelimbs; depression of the panniculus reflex in the dorsal lu mbar region; and hind limb motor impairment, with ataxia, loss of the placing reflex, and a tendency to drag the hind limbs. Subdural placem ent was associated with CNS depression, recumbency, shallow breathing, and sensory block ascending to the level of the ears. Administration of the test dose was fatal in the one animal that had intraspinal cath eter placement. Using the afore-described technique, epidural catheter ization can be performed reliably in the guinea pig. Correct catheter placement can be confirmed by use of an antemortem test dose of local anesthetic and by postmortem histologic examination.