TGI MH Friday, April 9, 2021
Good morning and welcome to another addition of TGI MH Friday. Thanks for your patience this week while I sorted out some health issues. This morning’s issue of PAAD was written by Robbie Shaw from the University of Wisconsin. He just started his first run of being a hotline consultant and I’m mentoring him. He received a great case that will be the subject for us today.
Our patient is a 3-year-old female with history of multiple congenital anomalies and arthrogryposis, undergoing repair of a tethered cord. She had uneventful previous anesthetics without any complication, including multiple exposures to triggering agents for MH. For this case she had sevoflurane, followed by rocuronium for intubation. Immediately following intubation, she felt rigid with rise in EtCO2 from baseline of 40s to mid 60s. Hand ventilation was maintained without changes in lung compliance or minute ventilation. The team then stopped the sevo and the patient was transitioned to TIVA for the remainder of the case. The patient was never tachycardic, hypertensive, or febrile. EtCO2 improved (32 at time of consultation) with normal ventilatory parameters after discontinuation of sevoflurane. The rest of the procedure continued uneventfully, and the patient was admitted postoperatively for further recovery. A genetics consultation was suggested to evaluate underlying myopathy or RYR1 receptor mutation.
Could this have been MH? What is arthrogryposis and its relationship to MH susceptibility?
Arthrogryposis (Greek, arthro:joint, gryp:curved) is a descriptive term for congenital contractures that affect two or more different areas of the body. The finding is present in 1 in 3,000 births, representing over 400 specific conditions, with 150 of these having respective gene alterations. The etiology of arthrogryposis is thought to be a result of fetal akinesia, with a direct correlation between onset of decreased fetal movement and contracture severity. This decrease in movement has been postulated to cause an increase in connective tissue around joints, disuse of muscles around the joint, and abnormal joint surfaces.
Fetal akinesia can result from a variety of causes. Neuromuscular disorders are of most interest in evaluating a patient with arthrogryposis and MH susceptibility. Congenital myopathies can be associated with arthrogryposis. These can be a result of mutations in genes encoding the ryanodine receptor (RYR1), fetal myosin heavy chain (MYH3), and skeletal-muscle thin filament proteins. Of specific concern to the pediatric anesthesia provider is the potential for RYR1 mutations, which have been reported in the literature, raising the risk for MH susceptibility.
There is no direct correlation between arthrogryposis and MH. A 1986 paper examined 398 anesthetics in 67 patients with arthrogryposis over a 32-year period (1952 to 1984), with multiple exposures to MH triggering agents (mostly halothane), and found no evidence of MH. A 1991 case series involved 2 patients with a hypermetabolic response (hyperthermia, tachycardia, hypercapnia) to MH triggering agents. The authors genetically tested one patient’s parents after presumed MH episode, and both were normal (the child was too young for contracture biopsy). The authors surmised that while patients with arthrogryposis can have a hypermetabolic response to MH triggering agents, it is distinct from MH.
These cases are difficult to know what to do…remember there is no bedside test for MH. The team did a great job assuming MH and treating accordingly. Her reaction to sevoflurane along with improvement after its discontinuation warrant further evaluation, especially genetic testing for RYR1 gene mutations.
We hope you have a great spring weekend, and wishing all those on call the chance to go outside for some sunshine.