Abstracts

Rationale: Sudden death in epilepsy (SUDEP) is a major cause of death in persons with epilepsy. The mech-anism(s) remain(s) unknown, but seizure-spread to brainstem areas serving autonomic and respiratory function appears to be critical. We established a mechanism for sudden death in epilepsy that involved seizure-induced laryngospasm due to seizures spreading into brainstem laryngomotor areas and causing obstr-uct-ive apnea, which could last sufficiently long to result in respiratory arrest. Based on these results we hypothesized that DBA/2 mice, a strain that displays severe generalized seizure activity that can be lethal, would be protected from death by implanting a tracheal tube to provide a surrogate airway.  Methods: DBA/2 mice (Jackson Labs, Bar Harbor, ME) were used. In pilot experi-ments, animals were implanted with T-shaped tracheal tubes under a combination of ketamine (85 mg/kg) and xylazine (15 mg/kg) anesthesia. A number of animals survived audiogenic seizures, but animals tested too early after surgery did not respond to the tone whereas long postoperative times before testing were associated with tracheal implant blockage. Isoflurane anes-thesia (2-4% in oxygen) during surgery permitted faster recovery and responsiveness to tone presentation. We were concerned about ictal spastic contractions of the thoracic skeletal musculature (thoracic spasm), a condition very similar to electrical asphyxiation, as a seizure-induced confound. Our pilot data suggested a low dose of ketamine and xylazine could moderate thoracic spasm. Our final 2x2 study design involved implant-ing every mouse, half with T-shaped tracheal tubes where the sidearm was open and half where the sidearm was closed. Thoracic spasm was modulated in half of the animals with a single 1/10th dose of ketamine and xylazine (8.5 mg/kg ketamine, 1.5 mg/kg xylazine IP) at 60 min postoperatively and the other half received no drug. Thus, animals received both treatments, one or the other treatment alone, or no treatments. Audiogenic seizures were induced by exposing animals for 60 sec to >100-dB noise from a personal alarm device, and the durations of behavioral seizure phases and recovery or death were measured.  Results: A total of 54 animals were divided into four groups. Twenty-seven animals each with either a closed or an open T-tube displayed a tonic-clonic seizure with full hindlimb extension during noise testing. Animals receiving both treatments had the highest survival rate, followed by animals receiving the open tube without ketamine and xylazine. A trend analysis was highly significant. Only one animal with a closed T-tube survived, whereas 13 animals with an open T-tube survived, indicating that the odds ratio for survival was more than twenty times higher with an open T-tube. No animals showed evidence of reflux or vomitus after seizure activity that was lethal or not lethal.  Conclusions: The results indicate that survival tracheostomy can prevent death in DBA/2 mice experiencing audiogenic seizure activity that would otherwise be lethal. Obstructive apnea due to laryngospasm was sufficient to cause death, but not necessary - some animals implanted with open tracheal tubes still died. The alternative mechanism to cause death was seizure-associated spastic contraction of the skeletal musculature of the thorax and, normally, these two mechanisms co-exist. Whereas the nominal dose of ketamine/xylazine appeared to reduce the contribution of thoracic spasm to apnea, it was neither necessary nor sufficicent for survival. Only eliminating laryngospasm with the surrogate airway saved lives.  Funding: NS104796