The novel rapid formulation of intravenous dantrolene (NPJ5008) versus standard dantrolene (Dantrium®): A clinical part-randomised phase 1 study in healthy volunteers

BACKGROUND

Delays in treating anaesthesia-induced malignant hyperthermia increase risks of complications and death. NPJ5008 is a novel formulation of the indicated treatment, dantrolene sodium, developed to shorten preparation and administration times compared with the reference formulation Dantrium®. The two formulations have been compared preclinically.

OBJECTIVES

Assess bioequivalence of overall dantrolene (free acid) exposure of NPJ5008 versus Dantrium® and ascertain similarities in their pharmacokinetics and safety/tolerability profiles. Evaluate preparation/administration time savings for the new formulation.

DESIGN

Part 1 of this open-label trial in humans was a 1 : 1 randomised crossover study; part 2 was a single-arm study. Trial pharmacy data and laboratory simulations assessed preparation/administration step timings.

SETTING

Single clinical centre in the UK, April to July 2021.

PARTICIPANTS

Twenty-one healthy male and female individuals.

INTERVENTIONS

Part 1: single intravenous 60 mg dose of NPJ5008 or Dantrium®, sequentially. Part 2: single intravenous 120 mg dose of NPJ5008. Simulation: five vials per formulation using paediatric and adult cannulas.

MAIN OUTCOME MEASURES

Overall drug exposure to last measurable concentration (AUC 0 to last ) and extrapolated to infinity (AUC 0 to ∞ ) were primary endpoints. Other pharmacokinetic, clinical and muscle-function parameters, and adverse events, were monitored.

RESULTS

Adjusted geometric mean ratios of NPJ5008 versus Dantrium® were 90.24 and 90.44% for AUC 0 to last and AUC 0 to ∞ , respectively, with the 90% confidence intervals (CI) within the 80 to 125% acceptance interval, establishing bioequivalence. No new safety issues emerged: any adverse events were of a similar magnitude across treatments and related to pharmacological properties of dantrolene. Pharmacy and simulation data revealed that every step in preparation and administration was 26 to 69% faster for NPJ5008 than Dantrium®.

CONCLUSION

NPJ5008 showed comparable pharmacokinetic and safety profiles to Dantrium®, while reducing dantrolene dose preparation/administration times, potentially reducing patient complications/healthcare resourcing in malignant hyperthermia.

TRIAL REGISTRATION

EudraCT Number: 2020-005719-35, MHRA approval.

The Anesthesiologists' Perception of Malignant Hyperthermia and Availability of Dantrolene in China: A Cross-Sectional Survey

Background

Malignant hyperthermia (MH) is a hypermetabolic syndrome with high mortality rates. Early detection and prompt intravenous administration of dantrolene are crucial for effective management of MH. However, there is currently a lack of comprehensive nationwide surveys on the availability of dantrolene and anesthesiologists' understanding of MH in China.

Methods

A nationwide survey was conducted between January 2022 and June 2022. Online questionnaires on the cognition of MH among anesthesiologists in China were sent through social platforms to anesthesiologists in mainland China. Data regarding participants' perception of MH-related knowledge, availability of domestic dantrolene, and reported MH cases were collected in this study.

Results

Responses were collected from a total of 11,354 anesthesiologists representing 31 provinces across the Chinese mainland. Among the 11 scoring questions, the highest accuracy rates were observed for the question regarding therapeutic drugs for MH (99.3%) and the characteristics of MH (98.0%). Conversely, the question pertaining to the earliest clinical signs of MH had the lowest accuracy rate (23.5%). Significant variations were observed in the scores among different professional titles (P=0.003), academic degree (P<0.001), hospital classification (P<0.001), and urban hierarchy (P<0.001). Of the respondents, 919 (8.1%) anesthesiologists reported dantrolene availability in their hospitals, and 631 (5.6%) indicated unclear. A total of 136 hospitals in this survey reported at least one previous case of MH.

Conclusion

Mainland China faces challenges such as insufficient experience in diagnosing and treating MH, as well as difficulty in obtaining dantrolene. To improve the public awareness of MH, it is imperative to establish and promote a refined MH training system. Additionally, a streamlined and rapid dantrolene linkage emergency system should be implemented to ensure prompt access to the drug.

Muscle fibre mitochondrial [Ca2+ ] dynamics during Ca2+ waves in RYR1 gain-of-function mouse

AIM

A fraction of the Ca2+ released from the sarcoplasmic reticulum (SR) enters mitochondria to transiently increase its [Ca2+ ] ([Ca2+ ]mito ). This transient [Ca2+ ]mito increase may be important in the resynthesis of ATP and other processes. The resynthesis of ATP in the mitochondria generates heat that can lead to hypermetabolic reactions in muscle with ryanodine receptor 1 (RyR1) variants during the cyclic releasing of SR Ca2+ in the presence of a RyR1 agonist. We aimed to analyse whether the mitochondria of RYR1 variant muscle handles Ca2+ differently from healthy muscle.

METHODS

We used confocal microscopy to track mitochondrial and cytoplasmic Ca2+ with fluorescent dyes simultaneously during caffeine-induced Ca2+ waves in extensor digitorum longus muscle fibres from healthy mice and mice heterozygous (HET) for a malignant hyperthermia-causative RYR1 variant.

RESULTS

Mitochondrial Ca2+ -transient peaks trailed the peak of cytoplasmic Ca2+ transients by many seconds with [Ca2+ ]mito not increasing by more than 250 nM. A strong linear relationship between cytoplasmic Ca2+ and [Ca2+ ]mito amplitudes was observed in HET RYR1 KI fibres but not wild type (WT).

CONCLUSION

Our results indicate that [Ca2+ ]mito change within the nM range during SR Ca2+ release. HET fibre mitochondria are more sensitive to SR Ca2+ release flux than WT. This may indicate post-translation modification differences of the mitochondrial Ca2+ uniporter between the genotypes.

Application of the Bair Hugger™ core body temperature at wrist region with upper body warming blanket: a prospective observational study

BACKGROUND

Body temperature monitoring is essential during the perioperative period. However, core body temperature measurement requires invasive device that may cause complications. This study aimed to evaluate the accuracy of non-invasive Bair Hugger™ core body temperature monitoring system (BHTMS) at the wrist compared with esophageal temperature under general anesthesia.

METHODS

Twenty adult patients of the American Society of Anesthesiologists physical status I or II were enrolled. BHTMS sensor was applied at wrist region. After tracheal intubation, an esophageal probe was inserted. Bair Hugger™ upper body warming blankets were used. Esophageal temperature (Teso) and BHTMS at wrist (Twrist) were recorded every 10 min.

RESULTS

Total of 257 pairs of data sets were analyzed: Teso and Twrist had no statistically significant difference (P = 0.103). Median of Teso and Twrist were 36.5°C and 36.4°C. Bland-Altman analysis showed Teso - Twrist of 0.14°C ± 1.44. Subsequently, 99 pairs of 0-40 min data set were analyzed and showed significant difference at 0 and 10 min (P < 0.001) but no significant difference at 20, 30 and 40 min. Bland- Altman plot by times showed difference (Teso - Twrist) of 1.49°C ± 2.00, 0.82°C ± 1.30, 0.29°C ± 1.32, -0.03°C ± 0.84, and -0.12°C ± 0.82 at 0, 10, 20, 30 and 40 min respectively.

CONCLUSIONS

BHTMS at wrist area under the upper body warming blanket is a potential alternative other than esophageal temperature for monitoring body temperature after 30 min of anesthesia induction.

Critical illness aspects of heatstroke: A hot topic

Heatstroke represents the most severe end of the heat illness spectrum, and is increasingly seen in those undergoing exercise or exertion ('exertional heatstroke') and those exposed to high ambient temperatures, for example in heatwaves ('classical heatstroke'). Both forms may be associated with significant thermal injury, leading to organ dysfunction and the need for admission to an intensive care unit. The process may be exacerbated by translocation of bacteria or endotoxin through an intestinal wall rendered more permeable by the hyperthermia. This narrative review highlights the importance of early diagnosis, rapid cooling and effective management of complications. It discusses the incidence, clinical features and treatment of heatstroke, and discusses the possible role of intestinal permeability and advances in follow-up and recovery of this condition. Optimum treatment involves an integrated input from prehospital, emergency department and critical care teams, along with follow-up by rehabilitation teams and, if appropriate, sports or clinical physiologists.

R, Patel PH, Bazan DZ, Mora A, Samuel N, Mingle AC, Leon LR, Varon J, Surani S. Drug-Induced Hyperthermia Review

Humans maintain core body temperature via a complicated system of physiologic mechanisms that counteract heat/cold fluctuations from metabolism, exertion, and the environment. Overextension of these mechanisms or disruption of body temperature homeostasis leads to bodily dysfunction, culminating in a syndrome analogous to exertional heat stroke (EHS). The inability of this thermoregulatory process to maintain the body temperature is caused by either thermal stress or certain drugs. EHS is a syndrome characterized by hyperthermia and the activation of systemic inflammation. Several drug-induced hyperthermic syndromes may resemble EHS and share common mechanisms. The purpose of this article is to review the current literature and compare exertional heat stroke (EHS) to three of the most widely studied drug-induced hyperthermic syndromes: malignant hyperthermia (MH), neuroleptic malignant syndrome (NMS), and serotonin syndrome (SS). Drugs and drug classes that have been implicated in these conditions include amphetamines, diuretics, cocaine, antipsychotics, metoclopramide, selective serotonin reuptake inhibitors (SSRIs), tricyclic antidepressants (TCAs), and many more. Observations suggest that severe or fulminant cases of drug-induced hyperthermia may evolve into an inflammatory syndrome best described as heat stroke. Their underlying mechanisms, symptoms, and treatment approaches will be reviewed to assist in accurate diagnosis, which will impact the management of potentially life-threatening complications.

High-Fat Diet Impairs Muscle Function and Increases the Risk of Environmental Heatstroke in Mice

Environmental heat-stroke (HS) is a life-threatening response often triggered by hot and humid weather. Several lines of evidence indicate that HS is caused by excessive heat production in skeletal muscle, which in turn is the result of abnormal Ca2+ leak from the sarcoplasmic reticulum (SR) and excessive production of oxidative species of oxygen and nitrogen. As a high fat diet is known to increase oxidative stress, the objective of the present study was to investigate the effects of 3 months of high-fat diet (HFD) on the HS susceptibility of wild type (WT) mice. HS susceptibility was tested in an environmental chamber where 4 months old WT mice were exposed to heat stress (41 °C for 1 h). In comparison with mice fed with a regular diet, mice fed with HFD showed: (a) increased body weight and accumulation of adipose tissue; (b) elevated oxidative stress in skeletal muscles; (c) increased heat generation and oxygen consumption during exposure to heat stress; and finally, (d) enhanced sensitivity to both temperature and caffeine of isolated muscles during in-vitro contracture test. These data (a) suggest that HFD predisposes WT mice to heat stress and (b) could have implications for guidelines regarding food intake during periods of intense environmental heat.

[Therapeutic effects of novel type1 ryanodine receptor inhibitor on skeletal muscle diseases]

Type 1 ryanodine receptor (RyR1) plays a key role in Ca²⁺ release from the sarcoplasmic reticulum (SR) during excitation-contraction coupling of skeletal muscle. Mutations in RyR1 hyperactivate the channel to cause malignant hyperthermia (MH). MH is a serious complication characterized by skeletal muscle rigidity and elevated body temperature in response to commonly used inhalational anesthetics. Thus far, more than 300 mutations in RyR1 gene have been reported in patients with MH. Some heat stroke triggered by exercise or environmental heat stress is also related to MH mutations in the RyR1 gene. The only drug approved for ameliorating the symptoms of MH is dantrolene, which has been first developed in 1960s as a muscle relaxant. However, dantrolene has several disadvantages for clinical use: poor water solubility which makes rapid preparation difficult in emergency situations and long plasma half-life, which causes long-lasting side effects such as muscle weakness. Here we show that a novel RyR1-selective inhibitor, 6,7-(methylenedioxy)-1-octyl-4-quinolone-3-carboxylic acid (Compound 1, Cpd1), effectively rescues MH and heat stroke in new mouse model relevant to MH. Cpd1 has great advantages of higher water solubility and shorter plasma half-life compared to dantrolene. Our data suggest that Cpd1 has the potential to be a promising new candidate for effective treatment of patients carrying RyR1 mutations.

The Ryanodine Receptor as a Sensor for Intracellular Environments in Muscles

The ryanodine receptor (RyR) is a Ca²⁺ release channel in the sarcoplasmic reticulum of skeletal and cardiac muscles and plays a key role in excitation-contraction coupling. The activity of the RyR is regulated by the changes in the level of many intracellular factors, such as divalent cations (Ca²⁺ and Mg²⁺), nucleotides, associated proteins, and reactive oxygen species. Since these intracellular factors change depending on the condition of the muscle, e.g., exercise, fatigue, or disease states, the RyR channel activity will be altered accordingly. In this review, we describe how the RyR channel is regulated under various conditions and discuss the possibility that the RyR acts as a sensor for changes in the intracellular environments in muscles.

A novel RyR1-selective inhibitor prevents and rescues sudden death in mouse models of malignant hyperthermia and heat stroke

Mutations in the type 1 ryanodine receptor (RyR1), a Ca²⁺ release channel in skeletal muscle, hyperactivate the channel to cause malignant hyperthermia (MH) and are implicated in severe heat stroke. Dantrolene, the only approved drug for MH, has the disadvantages of having very poor water solubility and long plasma half-life. We show here that an oxolinic acid-derivative RyR1-selective inhibitor, 6,7-(methylenedioxy)-1-octyl-4-quinolone-3-carboxylic acid (Compound 1, Cpd1), effectively prevents and treats MH and heat stroke in several mouse models relevant to MH. Cpd1 reduces resting intracellular Ca²⁺, inhibits halothane- and isoflurane-induced Ca²⁺ release, suppresses caffeine-induced contracture in skeletal muscle, reduces sarcolemmal cation influx, and prevents or reverses the fulminant MH crisis induced by isoflurane anesthesia and rescues animals from heat stroke caused by environmental heat stress. Notably, Cpd1 has great advantages of better water solubility and rapid clearance in vivo over dantrolene. Cpd1 has the potential to be a promising candidate for effective treatment of patients carrying RyR1 mutations.

Mutations in ryanodine receptor 1 (RyR1), a Ca2+ release channel in skeletal muscle, cause malignant hyperthermia (MH) and are involved in heat stroke. Here, the authors show that an oxolinic acid-derivative RyR1 inhibitor effectively prevents and treats MH and heat stroke in various MH mouse models.

Malignant hyperthermia, a rare perioperative complication: case series and literature review

Malignant hyperthermia is a rare complication of general anesthesia appearing as an acute and potentially lethal hypermetabolic state in people carrying a genetic anomaly expressed in skeletal muscles. Malignant hyperthermia has been scarcely described in sub-Saharan Africa. Herein, we present three cases of malignant hyperthermia occurring in the perioperative period in Cameroon. The authors wish to draw attention to the clinical presentation of this rare but potentially lethal emergency, for timely diagnosis, management and follow-up geared at preventing perioperative mortality.

Functional analysis of newly identified RYR1 variants in patients susceptible to malignant hyperthermia

PURPOSE

This study aimed to evaluate whether the three ryanodine receptor type 1 (RYR1) variants (p.Ser2345Thr, p.Ser2345Arg, and p.Lys3367Arg) which we identified in Japanese malignant hyperthermia (MH) patients with a clinical grading scale rank of 6 were causative for MH.

METHODS

We prepared human embryonic kidney (HEK)-293 cells transfected with wild-type RYR1 or one of the RYR1 variants, along with myotubes cultured from muscle pieces. Calcium kinetics were examined by calculating the 340/380-nm ratio under various caffeine and 4-chloro-m-cresol (4CmC) concentrations with the ratiometric dye Fura-2 AM. Half-maximal effective concentration (EC₅₀) values were calculated from dose-response curves. Statistical analysis was based on one-way analysis of variance with a Dunnett's multiple comparison test, using a P value < 0.05 as evidence of statistical significance.

RESULTS

In functional analysis using HEK-293 cells, we found significant reductions in the EC₅₀ of p.Ser2345Thr and p.Ser2345Arg in comparison with wild-type RYR1 (P < 0.001), while the EC₅₀ of p.Lys3367Arg was not significantly different (P = 0.062 for caffeine and P > 0.999 for 4CmC). On the other hand, functional analysis using myotubes showed significant differences in the EC₅₀ values for all variants (P < 0.001 for all comparisons).

CONCLUSIONS

p.Ser2345Thr and p.Ser2345Arg appear capable of causing a calcium metabolism disorder that leads to the onset of MH, and p.Ser2345Arg can be considered as a diagnostic mutation, because it meets the European Malignant Hyperthermia Group criteria. However, patients with p.Lys3367Arg might have mutations in genes other than RYR1 that are capable of causing MH.

Permeabilised skeletal muscle reveals mitochondrial deficiency in malignant hyperthermia-susceptible individuals

BACKGROUND

Individuals genetically susceptible to malignant hyperthermia (MH) exhibit hypermetabolic reactions when exposed to volatile anaesthetics. Mitochondrial dysfunction has previously been associated with the MH-susceptible (MHS) phenotype in animal models, but evidence of this in human MH is limited.

METHODS

We used high resolution respirometry to compare oxygen consumption rates (oxygen flux) between permeabilised human MHS and MH-negative (MHN) skeletal muscle fibres with or without prior exposure to halothane. A substrate-uncoupler-inhibitor titration protocol was used to measure the following components of the electron transport chain under conditions of oxidative phosphorylation (OXPHOS) or after uncoupling the electron transport system (ETS): complex I (CI), complex II (CII), CI+CII and, as a measure of mitochondrial mass, complex IV (CIV).

RESULTS

Baseline comparisons without halothane exposure showed significantly increased mitochondrial mass (CIV, P=0.021) but lower flux control ratios in CI+CII_(OXPHOS) and CII_(ETS) of MHS mitochondria compared with MHN (P=0.033 and 0.005, respectively) showing that human MHS mitochondria have a functional deficiency. Exposure to halothane triggered a hypermetabolic response in MHS mitochondria, significantly increasing mass-specific oxygen flux in CI_(OXPHOS), CI+CII_(OXPHOS), CI+CII_(ETS), and CII_(ETS) (P=0.001-0.012), while the rates in MHN samples were unaltered by halothane exposure.

CONCLUSIONS

We present evidence of mitochondrial dysfunction in human MHS skeletal muscle both at baseline and after halothane exposure.

Safety and efficacy of propofol anesthesia for pediatric target-controlled infusion in children below 3 years of age: a retrospective observational study

BACKGROUND

Although the requirement of propofol in children is increasing, propofol for induction and maintenance of anesthesia below 3 years old has not been approved in Korea. This study can provide a clinical evidence to increase the range of approval.

RESEARCH DESIGN AND METHODS

We reviewed the medical records of patients below 3 years of age who underwent surgery between September 2013 and December 2016. Safety was evaluated on the basis of vital signs, and laboratory findings and efficacy were evaluated on the basis of the bispectral index (BIS). Adverse events were examined.

RESULTS

A total of 109 patients anesthetized with propofol (propofol group) were compared with 109 patients with volatile anesthetics (volatile group) after propensity score matching. There was a difference in the proportion of patients showing decreased systolic pressure (P < 0.001) and heart rate (P = 0.03), but there was no difference in diastolic pressure (P = 0.238), mean arterial pressure (P = 0.175) during surgery. After surgery, there was no difference in all vital signs and the proportion patients who experienced adverse events of two groups.

CONCLUSIONS

Propofol anesthesia by target-controlled infusion was effective and didn't show serious propofol-related perioperative adverse events.

Malignant Hyperthermia Susceptibility and Related Diseases

This review identifies disease states associated with malignant hyperthermia susceptibility based on genotypic and phenotypic findings, and a framework is established for clinicians to identify a potentially malignant hyperthermia–susceptible patient.

Evidence of Malignant Hyperthermia in Patients Administered Triggering Agents before Malignant Hyperthermia Susceptibility Identified: Missed Opportunities Prior to Diagnosis

Malignant hyperthermia (MH) is a hypermetabolic disorder of skeletal muscle triggered almost exclusively by potent inhalational agents and suxamethonium. Signs of an MH reaction are non-specific and may be confused with the presentation of other problems such as sepsis and overheating of a patient. A high index of suspicion is needed to be aware of an early presentation of MH. Nine patients are presented who showed abnormal signs with an earlier anaesthetic where the possible diagnosis of an MH reaction was missed. These patients either presented later with an MH reaction, confirmed by DNA analysis and in some cases in vitro contracture testing, or were diagnosed by the identification of a causative mutation confirming MH susceptibility. The MH clinical grading scale is helpful in determining the likelihood that clinical indicators indicate a possible MH reaction. Masseter muscle rigidity is a known sign of MH, confirmed in this report by positive in vitro contracture testing and DNA analysis. Several uncommon muscle disorders have a high association with MH, and postoperative myalgia unrelated to suxamethonium can be a sign which is associated with MH. These reports emphasise the importance of a thorough family history (as the MH status was known by the family in four patients), a high index of suspicion for MH, and documentation of the possibility of MH susceptibility in the anaesthesia record.

Malignant Hyperthermia in a Morbidly Obese Patient Depletes Community Dantrolene Resources: A Case Report

During resection of a duodenal carcinoid tumor, a 28-year-old morbidly obese woman developed suspected malignant hyperthermia. This hypermetabolic state posed a diagnostic challenge given the similar intraoperative presentation of carcinoid crisis and malignant hyperthermia. The patient's weight posed therapeutic challenges as massive doses and prolonged administration of dantrolene were required that quickly depleted the available supply. Current dantrolene dosing recommendations are based on actual body weight despite a paucity of literature in obese patients. We speculate that the prolonged need for dantrolene redosing was from the continuous release of the volatile anesthetic from the patient's adipose tissue.

Genotype-Phenotype Correlations of Malignant Hyperthermia and Central Core Disease Mutations in the Central Region of the RYR1 Channel

Type 1 ryanodine receptor (RYR1) is a Ca²⁺ release channel in the sarcoplasmic reticulum of skeletal muscle and is mutated in some muscle diseases, including malignant hyperthermia (MH) and central core disease (CCD). Over 200 mutations associated with these diseases have been identified, and most mutations accelerate Ca²⁺ -induced Ca²⁺ release (CICR), resulting in abnormal Ca²⁺ homeostasis in skeletal muscle. However, it remains largely unknown how specific mutations cause different phenotypes. In this study, we investigated the CICR activity of 14 mutations at 10 different positions in the central region of RYR1 (10 MH and four MH/CCD mutations) using a heterologous expression system in HEK293 cells. In live-cell Ca²⁺ imaging, the mutant channels exhibited an enhanced sensitivity to caffeine, a reduced endoplasmic reticulum Ca²⁺ content, and an increased resting cytoplasmic Ca²⁺ level. The three parameters for CICR (Ca²⁺ sensitivity for activation, Ca²⁺ sensitivity for inactivation, and attainable maximum activity, i.e., gain) were obtained by [³ H]ryanodine binding and fitting analysis. The mutant channels showed increased gain and Ca²⁺ sensitivity for activation in a site-specific manner. Genotype-phenotype correlations were explained well by the near-atomic structure of RYR1. Our data suggest that divergent CICR activity may cause various disease phenotypes by specific mutations.

The pathophysiological basis and consequences of fever

There are numerous causes of a raised core temperature. A fever occurring in sepsis may be associated with a survival benefit. However, this is not the case for non-infective triggers. Where heat generation exceeds heat loss and the core temperature rises above that set by the hypothalamus, a combination of cellular, local, organ-specific, and systemic effects occurs and puts the individual at risk of both short-term and long-term dysfunction which, if severe or sustained, may lead to death. This narrative review is part of a series that will outline the pathophysiology of pyrogenic and non-pyrogenic fever, concentrating primarily on the pathophysiology of non-septic causes.

Low-dose Simvastatin Increases Skeletal Muscle Sensitivity to Caffeine and Halothane

Objective To determine whether the myotoxic side effects of statin simvastatin affect skeletal muscle's sensitivity to caffeine and halothane.Methods Primary cultured neonate rat skeletal myotubes were treated with 0.01-5.0 μmol/L simvastatin for 48 hours. MTT was used to evaluate cellular viability. The gross morphology and microstructure of the myotubes were observed with a light and electron microscope, respectively. The intracellular calcium concentrations ([Ca²⁺]i) at rest and in response to caffeine and halothane were investigated by fluorescence calcium imaging. Data were analyzed by analysis of variance (ANOVA) test.Results Simvastatin (0.01-5.0 μmol/L) decreased myotube viability, changed their morphological features and microstructure, and increased the resting [Ca²⁺]i in a dose-dependent manner. Simvastatin did not change myotube's sensitivity to low doses of caffeine (0.625-2.5 mmol/L) or halothane (1.0-5.0 mmol/L). In response to high-dose caffeine (10.0 mmol/L, 20.0 mmol/L) and halothane (20.0 mmol/L, 40.0 mmol/L), myotubes treated with 0.01 μmol/L simvastatin showed a significant increase in sensitivity, but those treated with 1.0 μmol/L and 5.0 μmol/L simvastatin showed a significant decrease. The sarcoplasmic reticulum Ca²⁺ storage peaked in the myotubes treated with 0.01 μmol/L simvastatin, but it decreased when cells were treated with higher doses of simvastatin (0.1-5.0 μmol/L).Conclusions The myotoxic side effect of simvastatin was found to change the sensitivity of myotubes in response to high-dose caffeine and halothane. When dose was low, sensitivity increased mainly because of increased Ca²⁺ content in the sarcoplasmic reticulum, which might explain why some individuals with statin-induced myotoxic symptoms may show positive caffeine-halothane contracture test results. However, when the dose was high and the damage to the myotubes was severer, sensitivity was lower. It is here supposed that the damage itself might put individuals with statin-induced myotoxic symptoms at greater risks of presenting with rhabdomyolysis during surgery or while under anesthesia.

CPAP in the Perioperative Setting: Evidence of Support

OSA is a commonly encountered comorbid condition in surgical patients. The risk of cardiopulmonary complications is increased by two to threefold with OSA. Among the different treatment options for OSA, CPAP is an efficacious modality. This review examines the evidence regarding the use of CPAP in the preoperative and postoperative periods in surgical patients with diagnosed and undiagnosed OSA.

A case of malignant hyperthermia that was difficult to be differentiated from oral antipsychotic polypharmacy-associated neuroleptic malignant syndrome

Malignant hyperthermia (MH) occurred during anesthesia with volatile inhalation anesthetics in a patient under treatment with multiple oral antipsychotic drugs and with a history of multi-acting receptor-targeted antipsychotic drug (MARTA)-induced elevation of serum creatine kinase (CK). Since the patient was considered to be at high risk for neuroleptic malignant syndrome (NMS) based on this history, differential diagnosis between MH and NMS was difficult at the time of onset. Later, the patient was found to be predisposed to MH based on abnormal high rate of the Ca²⁺-induced Ca²⁺ release (CICR). We concluded that MH was induced by the volatile inhalation anesthetics.

Malignant hyperthermia, a Scandinavian update

BACKGROUND

Malignant Hyperthermia (MH) is a rare pharmacogenetic disorder, triggered by halogenated anesthetics and/or succinylcholine. In susceptible individuals, these drugs can activate an explosive life threatening clinical reaction. Leading symptoms are hypercarbia, muscle rigidity, and metabolic acidosis. MH is inherited in an autosomal-dominant manner and linked to mutations in the large ryanodine 1 gene (RYR1) gene in the majority of cases. Very few MH patients have been found to carry mutations in the CACNA1S gene.

METHODS

For this review a large litterature search was carried out and the Swedish MH database consisting of 436 probands who have undergone in vitro muscle contraction test (IVCT) during 1984-2014 was analyzed.

RESULTS

Twelve different MH causative mutations have been found in Swedish patients so far. These mutations lead to a disturbed calcium balance in striated muscle tissue. A muscle biopsy for the IVCT or finding of an approved causative mutation are required for the diagnosis.

CONCLUSION

A Malignant Hyperthermia susceptible (MHS) patient should be anesthetized with trigger-free anesthesia. There are a few reports of MH-like reactions in patients unrelated to anesthesia. The outcome is dependent on early recognizing of the reaction and fast disconnection of the trigger agents and administration of dantrolene.

Malignant hyperthermia: a review

Malignant hyperthermia (MH) is a pharmacogenetic disorder of skeletal muscle that presents as a hypermetabolic response to potent volatile anesthetic gases such as halothane, sevoflurane, desflurane, isoflurane and the depolarizing muscle relaxant succinylcholine, and rarely, in humans, to stressors such as vigorous exercise and heat. The incidence of MH reactions ranges from 1:10,000 to 1: 250,000 anesthetics. However, the prevalence of the genetic abnormalities may be as great as one in 400 individuals. MH affects humans, certain pig breeds, dogs and horses. The classic signs of MH include hyperthermia, tachycardia, tachypnea, increased carbon dioxide production, increased oxygen consumption, acidosis, hyperkalaemia, muscle rigidity, and rhabdomyolysis, all related to a hypermetabolic response. The syndrome is likely to be fatal if untreated. An increase in end-tidal carbon dioxide despite increased minute ventilation provides an early diagnostic clue. In humans the syndrome is inherited in an autosomal dominant pattern, while in pigs it is autosomal recessive. Uncontrolled rise of myoplasmic calcium, which activates biochemical processes related to muscle activation leads to the pathophysiologic changes. In most cases, the syndrome is caused by a defect in the ryanodine receptor. Over 400 variants have been identified in the RYR1 gene located on chromosome 19q13.1, and at least 34 are causal for MH. Less than 1 % of variants have been found in CACNA1S but not all of these are causal. Diagnostic testing involves the in vitro contracture response of biopsied muscle to halothane, caffeine, and in some centres ryanodine and 4-chloro-m-cresol. Elucidation of the genetic changes has led to the introduction of DNA testing for susceptibility to MH. Dantrolene sodium is a specific antagonist and should be available wherever general anesthesia is administered. Increased understanding of the clinical manifestation and pathophysiology of the syndrome, has lead to the mortality decreasing from 80 % thirty years ago to <5 % in 2006.

Hypothesis: exertional heat stroke-induced myopathy and genetically inherited malignant hyperthermia represent the same disorder, the human stress syndrome

Exertional heat stroke is usually experienced as a result of a prolonged and intensive exercise. It is a life-threatening condition that is characterized by an increase in core body temperature and rhabdomyolysis. The associated hyperkalemia and metabolic acidosis may lead to an acute renal, cardiac, and hemostatic failure. Exactly, the same symptoms are noticed in case of the anesthesia-induced malignant hyperthermia (MH), an inherited disorder of the skeletal muscle ryanodine receptor. This receptor is a Ca(2+) channel that is activated by the volatile anesthetic agents and depolarizing muscle relaxant. The presence of MH-associated ryanodine receptor variant in the individuals who suffered from EH and improvement of the symptoms with dantrolene has frequently raised the question as to whether the two disorders actually represent one and the same disease. Nevertheless, an exact explanation of the susceptibility of the genetically predisposed MH individuals to ER remains elusive. We have attempted to review the published clinical reports to explore the possibility that ER and EH represent one and the same disorder.

Divergent Activity Profiles of Type 1 Ryanodine Receptor Channels Carrying Malignant Hyperthermia and Central Core Disease Mutations in the Amino-Terminal Region

The type 1 ryanodine receptor (RyR1) is a Ca²⁺ release channel in the sarcoplasmic reticulum of skeletal muscle and is mutated in several diseases, including malignant hyperthermia (MH) and central core disease (CCD). Most MH and CCD mutations cause accelerated Ca²⁺ release, resulting in abnormal Ca²⁺ homeostasis in skeletal muscle. However, how specific mutations affect the channel to produce different phenotypes is not well understood. In this study, we have investigated 11 mutations at 7 different positions in the amino (N)-terminal region of RyR1 (9 MH and 2 MH/CCD mutations) using a heterologous expression system in HEK293 cells. In live-cell Ca²⁺ imaging at room temperature (~25 °C), cells expressing mutant channels exhibited alterations in Ca²⁺ homeostasis, i.e., an enhanced sensitivity to caffeine, a depletion of Ca²⁺ in the ER and an increase in resting cytoplasmic Ca²⁺. RyR1 channel activity was quantitatively evaluated by [³H]ryanodine binding and three parameters (sensitivity to activating Ca²⁺, sensitivity to inactivating Ca²⁺ and attainable maximum activity, i.e., gain) were obtained by fitting analysis. The mutations increased the gain and the sensitivity to activating Ca²⁺ in a site-specific manner. The gain was consistently higher in both MH and MH/CCD mutations. Sensitivity to activating Ca²⁺ was markedly enhanced in MH/CCD mutations. The channel activity estimated from the three parameters provides a reasonable explanation to the pathological phenotype assessed by Ca²⁺ homeostasis. These properties were also observed at higher temperatures (~37 °C). Our data suggest that divergent activity profiles may cause varied disease phenotypes by specific mutations. This approach should be useful for diagnosis and treatment of diseases with mutations in RyR1.

Clonidine withdrawal induced sympathetic surge

A 30-year-old man with a history of epilepsy and substance misuse presented to the hospital with status epilepticus. Difficult seizure control necessitated anaesthetising the patient followed by intubation and ventilation. A clonidine infusion was started as the patient developed withdrawal syndrome and was difficult to wean off mechanical ventilation. Once the withdrawal syndrome was controlled, the clonidine was abruptly stopped. Two hours after stopping the infusion, the patient developed high-grade fever, severe hypertension, tachycardia, profound sweating and lacrimation. The patient then developed respiratory distress syndrome secondary to acute pulmonary oedema. Clonidine withdrawal as a cause of such response was proposed. Reversal of symptoms and successful reweaning was achieved by restarting a low-dose clonidine infusion followed by slow downward titration and use of oral clonidine as a step-down measure. The patient was subsequently discharged from the intensive care unit.

Drug-induced hyperthermia in critical care

Fever is common in critically ill patients and the cause is frequently not infection. Drug fevers occur in the intensive care and there are many pharmacological agents, by a variety of mechanisms, which increase body temperature beyond normal range. This article is a review of the common classes of drugs that can induce hyperthermia, highlighting the deleterious effects of a sustained high temperature and outlining available treatments.

Next-generation DNA sequencing of a Swedish malignant hyperthermia cohort

Malignant hyperthermia (MH)-related mutations have been identified in the ryanodine receptor type 1 gene (RYR1) and in the dihydropyridine gene (CACNA1S), but about half of the patients do not have causative mutations in these genes. We wanted to study the contribution of other muscle genes to the RYR1 phenotypes. We designed a gene panel for sequence enrichment targeting 64 genes of proteins involved in the homeostasis of the striated muscle cell. Next-generation sequencing (NGS) resulted in >50,000 sequence variants which were further analyzed by software filtering criteria to identify causative variants. In four of five patients we identified previously reported RYR1 mutations while the fifth patient did not show any candidate variant in any of the genes investigated. In two patients pathogenic variants were found in other genes known to cause a muscle disorders. All but one patient carried likely benign rare polymorphisms. The NGS technique proved convenient in identifying variants in the RYR1. However, with a clinically variable phenotype-like MH, the pre-selection of genes poses problems in variant interpretation.

Rhabdomyolysis: review of the literature

Rhabdomyolysis is a serious and potentially life threatening condition. Although consensus criteria for rhabdomyolysis is lacking, a reasonable definition is elevation of serum creatine kinase activity of at least 10 times the upper limit of normal followed by a rapid decrease of the sCK level to (near) normal values. The clinical presentation can vary widely, classical features are myalgia, weakness and pigmenturia. However, this classic triad is seen in less than 10% of patients. Acute renal failure due to acute tubular necrosis as a result of mechanical obstruction by myoglobin is the most common complication, in particular if sCK is >16.000 IU/l, which may be as high as 100,000 IU/l. Mortality rate is approximately 10% and significantly higher in patients with acute renal failure. Timely recognition of rhabdomyolysis is key for treatment. In the acute phase, treatment should be aimed at preserving renal function, resolving compartment syndrome, restoring metabolic derangements, and volume replacement. Most patients experience only one episode of rhabdomyolysis, mostly by substance abuse, medication, trauma or epileptic seizures. In case of recurrent rhabdomyolysis, a history of exercise intolerance or a positive family history for neuromuscular disorders, further investigations are needed to identify the underlying, often genetic, disorder. We propose a diagnostic algorithm for use in clinical practice.

Malignant hyperthermia: clinical and molecular aspects

CONTENT

Malignant hyperthermia (MH) is a potentially lethal pharmacogenetic disorder that affects genetically predisposed individuals. It manifests in susceptible individuals in response to exposure to Inhalant anesthetics, depolarizing muscle relaxants or extreme physical activity in hot environments. During exposure to these triggering agents, there is a rapid and sustained increase of myoplasmic calcium (Ca(2+)) concentration induced by hyperactivation of ryanodine receptor of skeletal muscle (RyR1), causing a profound change in Ca(2+) homeostasis, featuring a hypermetabolic state. RyR1, Ca(2+) release channels of sarcoplasmic reticulum, is the primary locus for MH susceptibility. Several mutations in the gene encoding the protein RyR1 have been identified; however, other genes may be involved. Actually, the standard method for diagnosing MH susceptibility is the muscle contracture test for exposure to halothane-caffeine (CHCT) and the only treatment is the use of dantrolene. However, with advances in molecular genetics, a full understanding of the disease etiology may be provided, favoring the development of an accurate diagnosis, less invasive, with DNA test, and also will provide the development of new therapeutic strategies for treatment of MH. Thus, this brief review aims to integrate molecular and clinical aspects of MH, gathering input for a better understanding of this channelopathy.

Continuous veno-venous hemofiltration for massive rhabdomyolysis after malignant hyperthermia: report of 2 cases

We present 2 cases of fulminant malignant hyperthermia (MH), complicated with massive rhabdomyolysis. The patients were successfully treated in the intensive care unit of our university teaching hospital, despite the lack of availability of dantrolene in our country, by early application of continuous veno-venous hemofiltration (CVVH). Both male patients developed fulminant malignant hyperthermia during anesthesia for oromaxillofacial surgery. CVVH was employed when the values of creatine phosphokinase (CPK), myoglobin (Mb), and lactate dehydrogenase (LDH) increased significantly. After emergency treatment and CVVH therapy, the values of CPK, Mb, and LDH in the blood plasma of the patients decreased significantly. The complications, including acute renal failure, disseminated intravascular coagulation, and acute respiratory distress syndrome were also treated without any obvious organ damage. Early detection and management are the keys to treat MH successfully. CVVH is a valuable therapeutic application in the initial/critical management of severe rhabdomyolysis. If these complications occur even with initial treatment with dantrolene, our experiences may be useful adjunctive treatments to consider.

Malignant hyperthermia

Malignant hyperthermia (MH) is an uncommon, life-threatening pharmacogenetic disorder of the skeletal muscle. It presents as a hypermetabolic response in susceptible individuals to potent volatile anesthetics with/without depolarizing muscle relaxants; in rare cases, to stress from exertion or heat stress. Susceptibility to malignant hyperthermia (MHS) is inherited as an autosomally dominant trait with variable expression and incomplete penetrance. It is known that the pathophysiology of MH is related to an uncontrolled rise of myoplasmic calcium, which activates biochemical processes resulting in hypermetabolism of the skeletal muscle. In most cases, defects in the ryanodine receptor are responsible for the functional changes of calcium regulation in MH, and more than 300 mutations have been identified in the RYR1 gene, located on chromosome 19q13.1. The classic signs of MH include increase of end-tidal carbon dioxide, tachycardia, skeletal muscle rigidity, tachycardia, hyperthermia and acidosis. Up to now, muscle contracture test is regarded as the gold standard for the diagnosis of MHS though molecular genetic test is used, on a limited basis so far to diagnose MHS. The mortality of MH is dramatically decreased from 70-80% to less than 5%, due to an introduction of dantrolene sodium for treatment of MH, early detection of MH episode using capnography, and the introduction of diagnostic testing for MHS. This review summarizes the clinically essential and important knowledge of MH, and presents new developments in the field.