Masseter spasm and malignant hyperthermia: a retrospective review of a hospital-based pediatric otolaryngology practice.

It has been claimed that the combination of halothane and succinylcholine, commonly used for anesthetic induction during short pediatric otolaryngologic procedures, is associated with a 1% incidence of masseter spasm (MS) which may be an early sign of malignant hyperthermia (MH). An 18-month retrospective chart review of all patients undergoing general anesthesia at the Children's Hospital of Pittsburgh (n = 14, 112) was conducted to assess the incidence of MS and its management. In addition, a separate subgroup of patients identified as being at risk for MH was also evaluated. In the otolaryngology service, the incidence of developing MS was 2 of 206 (1%) in children who were anesthetized with halothane and received succinylcholine, patients were identified in the MH high-risk group, and none developed MH. The findings affirmed the risks of using this combination of anesthetic and neuromuscular blocking agents during induction and the need for establishing management guidelines.     

The genetics of malignant hyperthermia

The genetic evaluation of the ryanodine type one receptor (RYR1) gene is unlikely to be a useful screening test of malignant hyperthermia susceptibility. But when significant suspicion of malignant hyperthermia has been raised by well-documented clinical events or strong family history, the genetic evaluation of RYR1 could secure a diagnosis and indicate appropriate treatment for both the index patient and many relatives of all ages, including the youngest.     

Screening of the entire ryanodine receptor type 1 coding region for sequence variants associated with malignant hyperthermia susceptibility in the north american population

BACKGROUND: Malignant hyperthermia (MH) is a life-threatening and frequently fatal disorder triggered by commonly used anesthetics. MH susceptibility is a genetically determined predisposition to the development of MH. Mutations in the ryanodine receptor type 1 (RYR1) gene are the major cause of MH susceptibility. The authors sought to develop a reliable genetic screening strategy based on efficient and relatively inexpensive mutation-detection procedures. METHODS: A cohort (n = 30) of North American MH patients and MH-susceptible individuals was studied. RNA and DNA extracted from muscle tissue or blood lymphocytes were used for analysis. The entire RYR1 coding region was amplified in 57 overlapping fragments and subjected to denaturing high-performance liquid chromatography analysis followed by direct nucleotide sequencing to characterize RYR1 alterations. RESULTS: Nine previously reported and nine unknown RYR1 mutations were identified in 21 of 30 studied patients (70%). Some of the new mutations were located outside of known mutational "hot spots," suggesting that RYR1 contains previously unknown mutation-prone areas requiring analysis. The North American MH/MH-susceptible population is characterized by a high RYR1 allelic heterogeneity. CONCLUSIONS: Denaturing high-performance liquid chromatography analysis of RNA samples extracted from the biopsied skeletal muscle followed by DNA sequencing is a highly efficient methodology for RYR1 mutation detection. This approach allows increasing the rate of mutation detection to 70% and identifying mutations in the entire RYR1 coding region.     

Is there a link between malignant hyperthermia and exertional heat illness?

Exertional heat illness (EHI) and malignant hyperthermia (MH) are two potentially lethal conditions. It has been suggested that a subset of MH susceptible persons may be predisposed to EHI. We examine the current understanding of these disorders and explore evidence of a relationship. Screening for the muscle type I ryanodine receptor gene should help clarify the relationship between MH and EHI.     

Mivacurium infusion during nitrous oxide-isoflurane anesthesia: a comparison with nitrous oxide-opioid anesthesia.

STUDY OBJECTIVE: To determine the potentiation of the neuromuscular blockade induced by a titrated infusion of mivacurium in the presence of isoflurane versus a nitrous oxide (N2O)-opioid anesthesia. DESIGN: An open-label, controlled study. SETTING: The inpatient anesthesia service of two university medical centers. PATIENTS: Thirty adults divided into two groups. INTERVENTION: An intravenous infusion of mivacurium during anesthesia with N2O-opioid or N2O-isoflurane. MEASUREMENTS AND MAIN RESULTS: A neuromuscular blockade was monitored by recording the electromyographic activity of the adductor pollicis muscle resulting from supramaximal stimulation at the ulnar nerve at 2 Hz for 2 seconds at 10-second intervals. The mivacurium infusion rate was significantly less in the presence of isoflurane [4.0 +/- 0.8 micrograms/kg/min (mean +/- SEM)] than during N2O-opioid anesthesia (6.4 +/- 0.6 micrograms/kg/min). The recovery rates did not differ between anesthetic groups. After the termination of the infusion, spontaneous recovery to T4/T1 of at least 0.75 occurred in an average of 17.9 +/- 1.5 minutes, with a mean recovery index (T25-75) of 6.0 +/- 0.7 minutes. CONCLUSION: Isoflurane anesthesia reduces the infusion rate of mivacurium required to produce about 95% depression of neuromuscular function.