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 effects in the newborn. A reliable technique for epidural catheterization in the guinea pig was developed to allow use of this model to evaluate the effects of epidural labor analgesics on neonates. Catheters were implanted in two open pilot animals and 19 time-dated pregnant animals 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 to 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 placement was evaluated, using a bupivacaine test dose in 17 animals and postmortem histologic examination in 20 animals. One animal died immediately after surgery. Epidural placement was confirmed histologically in 15 of 20 animals. Failed catheters were either subdural, with one catheter found to be penetrating the spinal cord (intraspinal), or intramuscular. Response to epidurally administered bupivacaine was variable but was typically characterized by normal alertness and ability to use the forelimbs; depression of the panniculus reflex in the dorsal lumbar region; and hind limb motor impairment, with ataxia, loss of the placing reflex, and a tendency to drag the hind limbs. Subdural placement was associated with CNS depression, recumbency, shallow breathing, and sensory block ascending to the level of the ears.(ABSTRACT TRUNCATED AT 250 WORDS)