Increased carbon dioxide production in two patients with malignant hyperpyrexia and its control by dantolene

An Assessment of Penetrance and Clinical Expression of Malignant Hyperthermia in Individuals Carrying Diagnostic Ryanodine Receptor 1 Gene Mutations

BACKGROUND

Malignant hyperthermia (MH) is a potentially lethal disorder triggered by certain anesthetics. Mutations in the ryanodine receptor 1 (RYR1) gene account for about half of MH cases. Discordance between the low incidence of MH and a high prevalence of mutations has been attributed to incomplete penetrance, which has not been quantified yet. The authors aimed to examine penetrance of MH-diagnostic RYR1 mutations and the likelihood of mutation carriers to develop MH, and to identify factors affecting severity of MH clinical expression.

METHODS

In this multicenter case-control study, data from 125 MH pedigrees between 1994 and 2017 were collected from four European registries and one Canadian registry. Probands (survivors of MH reaction) and their relatives with at least one exposure to anesthetic triggers, carrying one diagnostic RYR1 mutation, were included. Penetrance (percentage of probands among all genotype-positive) and the probability of a mutation carrier to develop MH were obtained. MH onset time and Clinical Grading Scale score were used to assess MH reaction severity.

RESULTS

The overall penetrance of nine RYR1 diagnostic mutations was 40.6% (93 of 229), without statistical differences among mutations. Likelihood to develop MH on exposure to triggers was 0.25 among all RYR1 mutation carriers, and 0.76 in probands (95% CI of the difference 0.41 to 0.59). Penetrance in males was significantly higher than in females (50% [62 of 124] vs. 29.7% [30 of 101]; P = 0.002). Males had increased odds of developing MH (odds ratio, 2.37; 95% CI, 1.36 to 4.12) despite similar levels of exposure to trigger anesthetics. Proband's median age was 12 yr (interquartile range 6 to 32.5).

CONCLUSIONS

Nine MH-diagnostic RYR1 mutations have sex-dependent incomplete penetrance, whereas MH clinical expression is influenced by patient's age and the type of anesthetic. Our quantitative evaluation of MH penetrance reinforces the notion that a previous uneventful anesthetic does not preclude the possibility of developing MH.

Disorders of Temperature Control: Hyperthermia, Part II

Malignant hyperthermia and neuroleptic malignant syndrome, two hyperthermic syndromes, are discussed with respect to their pathogenesis, pathophysiological factors, diagnosis, differential diagnosis, and treatment. Malignant hyperthermia is a drug- or stress-induced hypermetabolic syndrome characterized by vigorous muscular contractures and cardiovascular collapse. Neuroleptic malignant syndrome results primarily from an imbalance of central neurotransmitters caused by neuroleptic drug use and characterized by mental status changes and muscular rigidity. Recognition and prompt treatment of these disorders reduces their morbidity and mortality.

Management of malignant hyperthermia susceptible parturients

The management of eleven women susceptible to malignant hyperthermia during twenty deliveries is presented. These women were managed over a six-year period following guidelines that were established in 1990. Initial problems identified were the management of labour and caesarean section, the use of sympathomimetics and potential problems for the newborn, viz placental transfer of drugs and the possibility of a stress-induced malignant hyperthermia reaction in the newborn. There was little evidence that the stress of labour produced hypermetabolic responses in either mother or neonates and the use of sympathomimetics increased throughout the six-year period with no evidence of adverse effects. A caesarean section using general anaesthesia was not required but the management of this situation is described in both the protocol and discussion sections of this paper.

Effect of dantrolene sodium on contractility of isolated human uterine muscle

The administration of intravenous dantrolene in a parturient susceptible to malignant hyperthermia has been associated with post partum uterine atony. We examined the effect of dantrolene sodium for injection (Dantrium Intravenous) on spontaneous contractility of uterine smooth muscle from women in term pregnancy in an isolated preparation. Dantrolene sodium for injection at 5 microg/ml and 10 microg/ml had no effect on the spontaneous contractility of the uterine muscle preparations. At a cumulative concentration of 20 microg/ml, a mild depression (16 +/- 14%) in the frequency of spontaneous contractions was noted. However, a similar depression in the muscle preparations treated with mannitol suggests that the depression observed with the dantrolene was likely due to the mannitol that was included in the dantrolene formulation rather than to dantrolene sodium itself. We conclude that dantrolene sodium has no effect on the spontaneous contractility of uterine smooth muscle. The depression of uterine muscle activity observed with dantrolene for injection appears attributable to the mannitol.

Anaesthesia for caesarean delivery of a malignant hyperthermia susceptible parturient

The anaesthetic management for Caesarean delivery of a parturient with a strong family history of malignant hyperthermia (MH) is presented. Before surgery an anaesthetic machine that was in regular use was prepared by replacing all rubber or disposable components and flushing with O2 at 10 L.min-1 for one hour. Dantrolene prophylaxis was not used, and the patient received a bupivacaine and fentanyl spinal anaesthetic. Hypotension was treated with ephedrine. Current management of the MH patient no longer mandates a dedicated vapour-free machine, dantrolene is not indicated as pre-treatment, and amide local anaesthetics are considered safe. The role of vasopressors and ergot preparations is less clear.

End-tidal carbon dioxide concentration, carbon dioxide production, heart rate, and blood pressure as indicators of induced hyperthermia

In 4 spontaneously breathing, barbiturate-anesthetized dogs, hyperthermia was induced with 2,4-dinitrophenol while rectal temperature, heart rate, mean blood pressure, end-tidal carbon dioxide, and carbon dioxide production (milliliters per minute) were measured continuously. The latter was determined with a pneumotachygraph (to obtain respired volume) and an infrared carbon dioxide analyzer that measured inspired and expired carbon dioxide concentration. Of the five physiologic measurements, the increase in carbon dioxide production preceded the increase in rectal temperature by more than 120 seconds. End-tidal carbon dioxide was an unreliable indicator in the spontaneously breathing animal of approaching hyperthermia during spontaneous breathing due to a transient tachypnea, which decreased end-tidal carbon dioxide. The carbon dioxide production (milliliters per minute) increased immediately and reached three to five times the control value. Blood pressure and heart rate were insensitive indicators of approaching hyperthermia.

[Management of a patient with malignant hyperthermia susceptibility during anesthesia and daily living]

Death from malignant hyperthermia (MH) still occurs in France. However, anaesthesia of the MH susceptible (MhS) patient is quite possible without any more risk than for patients who are not MhS. Guidelines have been worked out: "trigger" drugs such as volatile anaesthetics (halothane, enflurane, isoflurane) and depolarizing muscle relaxants must be imperatively avoided; "non-trigger" drugs should be used, such as nitrous oxide, barbiturates, benzodiazepines, propofol, opiates, non-depolarizing muscle relaxants, amide or ester local anaesthetics at the usual doses without adrenaline. Moreover, dantrolene should be available in all hospitals, 12 bottles being a minimum at hand, or, better, 30 (about 10 mg.kg-1). In some cases, such as emergencies, an unprepared operating theatre, or an unprepared ventilator, the patient should be premedicated with 2.5 mg.kg-1 dantrolene intravenously. The ventilator, the circuit and the operating theatre should not contain any trace of halogenated vapour. The usual parameters, as well as temperature and expired CO2 concentration, should be closely monitored. MhS patients must also be given counselling. This includes explanations about MH, its genetic features, the main laboratory tests used to detect susceptibility, as well as advice about lifestyle, the use of drugs other than general and local anaesthetics, and a discussion concerning the association of MH with other diseases. This counselling is not always easy to provide, because many answers are not, as yet, definitive.

Dantrolene in pregnancy: lack of adverse effects on the fetus and newborn infant

Twenty malignant hyperthermia-susceptible pregnant patients were given dantrolene sodium orally for 5 days before delivery and 3 days after delivery. When cesarean section was necessary, triggering agents were avoided. No patient had a malignant hyperthermia reaction. No adverse effect of dantrolene sodium was detected by extensive testing of the fetus and neonate. The maternal predelivery dantrolene level was correlated with the noenatal cord blood dantrolene level (r = 0.837). The mean maternal predelivery dantrolene level was 0.99 +/- 0.5 microgram/ml, and the mean neonatal cord blood dantrolene level 0.68 +/- 0.3 microgram/ml. The time from the last dose of dantrolene to delivery was correlated with both the maternal dantrolene level and the neonatal cord blood level (r = 0.65). The half-life of dantrolene in the neonatal circulation was 20 hours. The controversy of oral dantrolene prophylaxis and the implications of this study with regard to further investigation are discussed.

Malignant hyperthermia

Malignant hyperthermia is a hereditary trait characterized by hypercatabolic reactions induced by anesthetic drugs, or physical or emotional stress. Patients must be treated quickly and efficiently in order to prevent irreversible organ damage and death.

Use of capnography and transcutaneous oxygen monitoring during outpatient general anesthesia for oral surgery

The combination of the capnograph (respired CO2 monitor) and the transcutaneous oxygen monitor was evaluated as a non-invasive system for monitoring of respiratory function in 10 ASA class I patients undergoing ultralight general anesthesia for removal of third molars. Capnography proved to be a sensitive and accurate method for detecting apnea and airway obstruction using the continuous display of the CO2 waveform. All episodes of apnea or obstruction were immediately detected as the respired CO2 level fell to zero baseline. The end-tidal CO2 (PetCO2) obtained via nasal prong sampling was not significantly different from the PaCO2. PetCO2 values served as useful indicators of hypoventilation. During steady-state conditions of respiration, transcutaneous oxygen tensions (PtcO2) correlated well with simultaneously measured PaO2 (r = 0.93). However, during any period when oxygenation was rapidly changing (step increase in FIO2, step decrease in FIO2, or apnea) the PtcO2 lagged behind changes in PaO2 even after a five-minute equilibration period, thereby not accurately reflecting the true state of oxygenation. Consequently, the transcutaneous oxygen monitor does not appear to be optimal as a respiratory monitor in the setting of ultralight general anesthesia where rapid, critical changes in oxygenation must be detected without delay.

Treatment of porcine malignant hyperthermia: lactate gradient from muscle to blood

Treatment of MH was studied in 21 pigs, using an isolated perfused caudal body preparation (L1 transection). Halothane one per cent triggered MH; data included oxygen consumption, blood/muscle lactate levels, plasma potassium, acid-base balance. Three treatment protocols had two phases each: A-1, discontinue halothane, inject dantrolene 7.5 mg X kg-1; A-2, inject HCO3- (113 +/- 6 mEq). B-1, Discontinue halothane, inject HCO3- (118 +/- 13 mEq); B-2, inject dantrolene 7.5 mg X kg-1; X C-1, Continue halothane, inject dantrolene 7.5 mg X kg-1; C-2, discontinue halothane, inject HCO3- (101 +/- 8 mEq). Dantrolene and HCO3- acted separately and differently: dantrolene reversed the hypermetabolism, both aerobic and anerobic, and HCO3- reversed the extracellular metabolic acidosis. Semitendinosus muscle biopsies demonstrated that both red and white muscle are involved in MH, that muscle lactate (to 35 mumol X g-1) consistently exceeded blood lactate (to 22 mumol X ml-1), and that blood lactate levels were slow to diminish following treatment. One could expect continued release of muscle lactate into blood, despite adequate therapy of MH; this might suggest a recurrence even when such is not the case.

Dantrolene. A review of its pharmacodynamic and pharmacokinetic properties and therapeutic use in malignant hyperthermia, the neuroleptic malignant syndrome and an update of its use in muscle spasticity

Dantrolene sodium acts primarily by affecting calcium flux across the sarcoplasmic reticulum of skeletal muscle. Recently, dantrolene has been used very successfully in the treatment of several rare hypercatabolic syndromes which have previously been associated with high mortality rates. In malignant hyperthermia, where early diagnosis and treatment usually with intravenous dantrolene in association with other supportive measures (and often subsequent dantrolene therapy) is performed, recovery is seen in virtually 100% of patients. There is a rapid resolution of hyperthermia, dysrhythmias, muscle rigidity, tachycardia, hypercapnia, mottled or cyanotic skin, and metabolic acidosis, and a slower normalisation of myoglobinuria and elevated serum creatine phosphokinase levels. In patients with family history or previous episodes of malignant hyperthermia, prophylactic treatment with dantrolene prior to anaesthesia prevents the syndrome occurring in most cases. Where malignant hyperthermia has developed patients have been successfully treated with further dantrolene therapy. Dantrolene has also been used successfully in the treatment of a few cases of heat stroke and the neuroleptic malignant syndrome--both of which have many similarities to malignant hyperthermia. Dantrolene is well established in the treatment of patients with muscle spasticity where it generally improves at least some of the components of spasticity (i.e. hyper/hypotonia, clonus, muscle cramps and spasms, resistance to stretch and flexor reflexes, articular movement, neurological and motor functions and urinary control). However, in some patients, particularly those with multiple sclerosis, dantrolene may not be effective, and in many cases muscular strength may diminish. Long term dantrolene therapy has been associated with hepatic toxicity and may cause problems in patients treated for disorders of muscle spasticity. Thus, dantrolene offers a unique advance in the therapy available for the treatment of hypercatabolic disorders and is also useful in the treatment of muscle spasticity of various aetiology.

The anaesthetic management of the malignant hyperthermia susceptible parturient

An overall management plan for malignant hyperthermia susceptible (MHS) parturients is presented based on the experience of managing 14 of these patients. A summary of the pertinent features of their deliveries and care plus a case report of one of these parturients is described. Discussion centres around the problems of diagnosis of malignant hyperthermia susceptibility in pregnancy, the differential diagnosis and management of fever and tachycardia in a MHS parturient during labour and the use of dantrolene prophylaxis. Management of the MHS parturient in labour includes temperature and heart-rate monitoring, provision for cooling, and ready availability of a vapour-free anaesthetic machine. A large-bore intravenous infusion for hydration and for potential therapy of a MH crisis is essential. Epidural analgesia, using 2-chloroprocaine, is recommended. Emergency and elective Caesarean section anaesthesia are discussed. The importance of being prepared for a potential crisis is stressed with particular emphasis on early diagnosis by monitoring of temperature at two sites, of heart rate and rhythm with a continuous ECG and of end-tidal carbon dioxide, should a general anaesthetic be required. Recommendations are made for appropriate anaesthetic agents for both regional and general anaesthesia. Treatment of a MH crisis is outlined, with emphasis on availability of appropriate resuscitative drugs.

End-tidal CO2 monitoring. Its use in the diagnosis and management of malignant hyperthermia

Two cases of malignant hyperthermia are described where the earliest sign was a rise in the end-tidal CO2 concentration. This led to nearly immediate detection and adequate treatment with sodium dantrolene. These cases demonstrate the efficacy of monitoring end-expired CO2 concentrations in patients at risk from malignant hyperthermia, as well as a means for following the adequacy of treatment.

Dantrolene sodium and dystrophia myotonica

A patient with dystrophia myotonica was given dantrolene sodium to try to provide muscle relaxation during a cholecystectomy. Dantrolene was used as it is accepted that the drug has a place in the control of spasticity and also causes muscle relaxation, whereas conventional muscle relaxants are unable to control myotonia of muscle origin. Dantrolene alone did not provide good enough intubating and operating conditions in this subject. Later studies showed that, after dantrolene, EMG recordings from the patient were not significantly altered, although an impression of a slight increase in the myotonic potentials was gained.

In vivo induced malignant hyperthermia in pigs. I. Physiological and biochemical changes and the influence of dantrolene sodium

The effects of an induced malignant hyperthermia (MH) crisis have been studied in the intact pig. Both physiological and biochemical changes in skeletal muscle were studied. MH was induced with 3% halothane plus a bolus injection of succinylcholine. In the prechallenge period a significant difference was observed in the concentration of certain muscle metabolites, comparing the MH-susceptible (MH+) with the non-susceptible (MH-) pigs. A lower level was measured for phosphocreatine (PCr), inosine monophosphate (IMP) and an increased level of lactate and creatine (Cr) in the susceptible pigs (MH+). The challenge caused a significant reduction of the level of PCr and adenosine in MH+ pigs, compared to the prechallenge period. After administration of dantrolene sodium, a significant decrease was measured in the level of lactate, compared to the prechallenge period as well as during the challenge. In contrast, in the control pigs no significant changes were observed in muscle metabolites, either after induction of MH or after the administration of dantrolene sodium. Enzyme activity determinations of muscle adenylate kinase and adenosine monophosphate (AMP)-deaminase did not show any difference in activity either before or during the MH crisis or after treatment with dantrolene sodium. The earliest physiological change during an induced MH crisis in our study was the rapid increase of the end-tidal CO2. Within 5 min after MH induction, end-tidal CO2 was doubled. It is concluded that the monitoring of the end-tidal CO2 is essential to diagnose MH at a very early stage.