Generalized Seizure Activity in an Adult Rhesus Macaque (Macaca mulatta) during Ketamine Anesthesia and Urodynamic Studies

We report a case of a generalized seizure in an adult female rhesus macaque (Macaca mulatta) undergoing a urodynamic evaluation while she was anesthetized with continuous-infusion ketamine. The seizure presented with generalized tonic–clonic activity during bladder infusion with saline. The tonic–clonic phase was self-limited and was followed by focal facial twitching, which was interrupted by bolus administration of intravenous diazepam. The ictal event was documented as pressure oscillations during cystometrogram recordings and a period of external urethral sphincter muscle activation, which was detectable by electromyography. An acute decrease in urethral pressure was demonstrated at the end of the generalized seizures. Ketamine anesthesia combined with relatively rapid infusion of saline into the bladder may have contributed to the onset of seizures. In addition, this case highlights the value of having a fast-acting benzodiazepine agent available to stop continuous or residual seizure activity during diagnostic or experimental procedures in anesthetized nonhuman primates.Anesthetic agents are used to sedate and immobilize nonhuman primates for veterinary health care and experimental studies. For these purposes, ketamine, a dissociative general anesthetic, is the agent used most commonly in macaques. Several protocols have been developed for the safe administration of ketamine, either as a single agent or as part of a balanced anesthetic approach administered orally, per rectum, intramuscularly, or intravascularly.^9,16,18 Although ketamine and other anesthetic agents are known to suppress physiologic responses during experimental studies, reflexive micturition may still be evoked, as demonstrated by urodynamic recordings in anesthetized rats.^1,2,10 In addition, urodynamic studies have demonstrated that bladder reflexes are suppressed by anesthesia in nonhuman primates, although comparative studies on the effects of different anesthetic agents have suggested that ketamine may be a suitable anesthetic for cystometrograms in rhesus macaques.⁵Here, parenteral administration of ketamine was used to sedate and immobilize adult rhesus macaques for comprehensive urodynamic studies. In one subject, the infusion of saline into the urinary bladder was associated with the acute onset of a generalized seizure, characterized by a self-limited period of tonic–clonic activity, followed by focal facial twitching, which was relieved by prompt intravenous administration of diazepam, and voiding. The tonic–clonic phase of the event was documented by cystometrography and electromyography recordings. We suggest the administration of ketamine anesthesia and the relatively rapid infusion of saline into the bladder as possible factors that may have contributed to the ictal event in this rare case of a clinical seizure during a urodynamic study in a nonhuman primate.