Malignant hyperthermia

Isoflurane Alters Presynaptic Endoplasmic Reticulum Calcium Dynamics in Wild-Type and Malignant Hyperthermia-Susceptible Rodent Hippocampal Neurons

Volatile anesthetics reduce excitatory synaptic transmission by both presynaptic and postsynaptic mechanisms which include inhibition of depolarization-evoked increases in presynaptic Ca2+ concentration and blockade of postsynaptic excitatory glutamate receptors. The presynaptic sites of action leading to reduced electrically evoked increases in presynaptic Ca2+ concentration and Ca2+-dependent exocytosis are unknown. Endoplasmic reticulum (ER) of Ca2+ release via ryanodine receptor 1 (RyR1) and uptake by SERCA are essential for regulation intracellular Ca2+ and are potential targets for anesthetic action. Mutations in sarcoplasmic reticulum (SR) release channels mediate volatile anesthetic-induced malignant hyperthermia (MH), a potentially fatal pharmacogenetic condition characterized by unregulated Ca2+ release and muscle hypermetabolism. However, the impact of MH mutations on neuronal function are unknown. We used primary cultures of postnatal hippocampal neurons to analyze volatile anesthetic-induced changes in ER Ca2+ dynamics using a genetically encoded ER-targeted fluorescent Ca2+ sensor in both rat and mouse wild-type (WT) neurons and in mouse mutant neurons harboring the RYR1 T4826I MH-susceptibility mutation. The volatile anesthetic isoflurane reduced both baseline and electrical stimulation-evoked increases in ER Ca2+ concentration in neurons independent of its depression of presynaptic cytoplasmic Ca2+ concentrations. Isoflurane and sevoflurane, but not propofol, depressed depolarization-evoked increases in ER Ca2+ concentration significantly more in mouse RYR1 T4826I mutant neurons than in wild-type neurons. The RYR1 T4826I mutant neurons also showed markedly greater isoflurane-induced reductions in presynaptic cytosolic Ca2+ concentration and synaptic vesicle (SV) exocytosis. These findings implicate RyR1 as a molecular target for the effects of isoflurane on presynaptic Ca2+ handling.

Rhabdomyolysis: A syndrome to be considered

Rhabdomyolysis is characterized by the release of intracellular elements after the destruction of skeletal muscle. Is characterized by the presence of muscle pain, weakness, and dark urine, associated with elevated creatine kinase (CK). The causes related to this syndrome are varied, being traumatic etiology, immobilization, sepsis, drugs and alcohol the most frequent. CK values are used for diagnosis and prognosis, being renal dysfunction the most serious complication. Treatment is based on early and intensive fluid therapy to avoid kidney complications.

Malignant Hyperthermia in Bariatric Surgery: A Case Study With Clinical, Pathophysiological, Biochemical and Biophysical Correlations

Malignant hyperthermia (MH) is an acute pharmacogenetic disorder, which while uncommon is potentially fatal. MH is a calcium channelopathy of skeletal muscle in which a constant increase of intracytoplasmic Ca2+ concentration occurs causing a change in cellular metabolism. A hypermetabolic state develops when susceptible patients are exposed to halogenated volatile inhalational anesthetic agents and depolarizing muscle relaxants and/or extreme physical activity in hot environments. MH presents variable clinical expression. During an episode of MH, the patient may present clinical signs and laboratory findings including masseter muscle spasm, tachycardia, rise in end-tidal CO2 (EtCO2), tachypnea, hyperthermia, cyanosis, metabolic acidosis, rhabdomyolysis, hyperkalemia, myoglobinuria, hyperlactacidemia, and acute renal failure. The aim of this case report is to describe an episode of MH associated with the use of halogenated anesthetic during bariatric surgery. A 29-year-old Brazilian man was admitted to the hospital to undergo a bariatric surgery. The patient's relevant medical history included morbid obesity grade III, allergy to sulfa-based drugs and severe obstructive sleep apnea. Preoperative evaluations with cardiopulmonary exercise testing, echocardiogram and electrocardiogram showed no anatomical and functional changes of the patient's heart. Surgical procedures lasted for 4 h, without complications, but the evolution of the patient's condition indicated oliguria and acute breathing insufficiency. Five hours after the patient was placed under mechanical ventilation in the intensive care unit, he started to present clinical signs of hypermetabolic state, with tremors, excessive sweating, and rapid body temperature increases. In the postoperative period, the patient had hyperglycemia, hypocalcemia, hypernatremia, hyperkalemia, changes in creatine phosphokinase (CPK), aspartate transaminase (AST), alanine aminotransferase (ALT), urea and creatine concentrations, and metabolic and respiratory acidosis. Urinalysis showed traces of proteinuria, presence of ketones, leukocytes, red blood cells, and urobilinogen. In our case report, MH crisis was diagnosed late; the dantrolene was not administrated because it was not available and the patient died. This detailed case report of MH episode triggered by isoflurane anesthetic during bariatric surgery allowed us to describe the severity and lethality of this hypermetabolic syndrome. Dantrolene should be mandatory in all operating rooms. Knowledge of the symptoms, an early diagnosis and an adequate treatment can prevent the death of patients in MH crisis.

Australian Scorpion Hormurus waigiensis Venom Fractions Show Broad Bioactivity Through Modulation of Bio-Impedance and Cytosolic Calcium

Scorpion venoms are a rich source of bioactive molecules, but characterisation of toxin peptides affecting cytosolic Ca2+, central to cell signalling and cell death, is limited. We undertook a functional screening of the venom of the Australian scorpion Hormurus waigiensis to determine the breadth of Ca2+ mobilisation. A human embryonic kidney (HEK293) cell line stably expressing the genetically encoded Ca2+ reporter GCaMP5G and the rabbit type 1 ryanodine receptor (RyR1) was developed as a biosensor. Size-exclusion Fast Protein Liquid Chromatography separated the venom into 53 fractions, constituting 12 chromatographic peaks. Liquid chromatography mass spectroscopy identified 182 distinct molecules with 3 to 63 components per peak. The molecular weights varied from 258 Da-13.6 kDa, with 53% under 1 kDa. The majority of the venom chromatographic peaks (tested as six venom pools) were found to reversibly modulate cell monolayer bioimpedance, detected using the xCELLigence platform (ACEA Biosciences). Confocal Ca2+ imaging showed 9/14 peak samples, with molecules spanning the molecular size range, increased cytosolic Ca2+ mobilization. H. waigiensis venom Ca2+ activity was correlated with changes in bio-impedance, reflecting multi-modal toxin actions on cell physiology across the venom proteome.

CaATP prolongs strong actomyosin binding and promotes futile myosin stroke

Calcium plays an essential role in muscle contraction, regulating actomyosin interaction by binding troponin of thin filaments. There are several buffers for calcium in muscle, and those buffers play a crucial role in the formation of the transient calcium wave in sarcomere upon muscle activation. One such calcium buffer in muscle is ATP. ATP is a fuel molecule, and the important role of MgATP in muscle is to bind myosin and supply energy for the power stroke. Myosin is not a specific ATPase, and CaATP also supports myosin ATPase activity. The concentration of CaATP in sarcomeres reaches 1% of all ATP available. Since 294 myosin molecules form a thick filament, naïve estimation gives three heads per filament with CaATP bound, instead of MgATP. We found that CaATP dissociates actomyosin slower than MgATP, thus increasing the time of the strong actomyosin binding. The rate of the basal CaATPase is faster than that of MgATPase, myosin readily produces futile stroke with CaATP. When calcium is upregulated, as in malignant hyperthermia, kinetics of myosin and actomyosin interaction with CaATP suggest that myosin CaATPase activity may contribute to observed muscle rigidity and enhanced muscle thermogenesis.

Serotonin Syndrome: Pathophysiology, Clinical Features, Management, and Potential Future Directions

Serotonin syndrome (SS) (also referred to as serotonin toxicity) is a potentially life-threatening drug-induced toxidrome associated with increased serotonergic activity in both the peripheral (PNS) and central nervous systems (CNS). It is characterised by a dose-relevant spectrum of clinical findings related to the level of free serotonin (5-hydroxytryptamine [5-HT]), or 5-HT receptor activation (predominantly the 5-HT_1A and 5-HT_2A subtypes), which include neuromuscular abnormalities, autonomic hyperactivity, and mental state changes. Severe SS is only usually precipitated by the simultaneous initiation of 2 or more serotonergic drugs, but the syndrome can also occur after the initiation of a single serotonergic drug in a susceptible individual, the addition of a second or third agent to long-standing doses of a maintenance serotonergic drug, or after an overdose. The combination of a monoamine oxidase inhibitor (MAOI), in particular MAO-A inhibitors that preferentially inhibit the metabolism of 5-HT, with serotonergic drugs is especially dangerous, and may lead to the most severe form of the syndrome, and occasionally death. This review describes our current understanding of the pathophysiology, clinical presentation and management of SS, and summarises some of the drugs and interactions that may precipitate the condition. We also discuss the newer novel psychoactive substances (NPSs), a growing public health concern due to their increased availability and use, and their potential risk to evoke the syndrome. Finally, we discuss whether the inhibition of tryptophan hydroxylase (TPH), in particular the neuronal isoform (TPH2), may provide an opportunity to pharmacologically target central 5-HT synthesis, and so develop new treatments for severe, life-threatening SS.

A 3-year retrospective analysis of elderly patients with heat illness

Background:

Heat illness in elderly patients has frequently occurred. Because of the difficulties in diagnosis and treatment, it is necessary for us to understand the clinical characteristics of elderly patients with heat illness.

Objective:

This study presents the demographic, clinical, and laboratory data for elderly patients who presented to our emergency department with heat illness and compares elderly group and non-elderly group to find out characteristics of elderly patient.

Methods:

We retrospectively analyzed the data of the elderly heat illness patients who had been presented to the emergency department of Jinshan Hospital, Fudan University, between 1 July 2014 and 1 October 2016.

Results:

There were 64 patients in the study in total and 25 elderly patients (39.1%). The mean age of the elderly patients was 72.8 ± 6.7 years; 18 cases (72%) were male and 7 cases (28%) were female. There were 5 mild cases (20%) and 20 severe cases (80%) in the elderly, which included 1 with heat cramps (5%), 4 with heat exhaustion (20%), and 15 with heat stroke (75%). Lactate dehydrogenase and creatine kinase were significantly higher in the elderly than in the non-elderly (p < 0.0001; t-value = −3.915 and −5.134, respectively). The Acute Physiologic Assessment and Chronic Health Evaluation II score and Modified Early Warning System score were significantly higher in the elderly than in the non-elderly (p < 0.0001; t-value = −6.411 and −4.705, respectively). Age was positively correlated with the Acute Physiologic Assessment and Chronic Health Evaluation II score and Modified Early Warning System score (r2 = 0.4939 and 0.3317, respectively; p value all <0.0001). The Acute Physiologic Assessment and Chronic Health Evaluation II score was positively correlated with lactate dehydrogenase and creatine kinase (r2 = 0.4103 and 0.4520, respectively; p value all <0.0001). The Modified Early Warning System score was positively correlated with lactate dehydrogenase and creatine kinase (r2 = 0.4759 and 0.5850, respectively; p value all <0.0001). There were 19 patients (76%) who improved and 6 patients (24%) who died in the elderly group.

Conclusion:

Chronic diseases and complications have increased rates in the elderly, who are also more likely to acquire severe heat illness, especially heat stroke. Lactate dehydrogenase and creatine kinase are positively correlated with Acute Physiologic Assessment and Chronic Health Evaluation II scores and Modified Early Warning System scores, which indicates that lactate dehydrogenase and creatine kinase could be good predictors of the severity of heat illness.

Associations of biochemical changes and maternal traits with mutation 1843 (C>T) in the RYR1 gene as a common cause for porcine stress syndrome

Stress syndrome is usually caused by a mutation in the ryanodine receptor gene (ryr1) and it is widely studied in humans and swine populations. The protein product of this gene plays a crucial role in the regulation of calcium transport in muscle cells. A G>T mutation in the human ryr1 gene, which results in the replacement of a conserved arginine at position 614 where a leucine occurs at the same position as the previously identified Arg→Cys mutation reported in all cases of porcine stress syndrome (PSS). Porcine stress syndrome affects biochemical pathways in stress-susceptible individuals during a stress episode and some biochemical parameters that were used as markers for diagnostic purposes. Also, PSS has remarkable influence on the maternal characteristics of sows. This study dealt with different genotypes for PSS and its association with possible biochemical changes and maternal traits of sows. Seventy-three reproductive sows genotyped for PSS by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) were included in this survey. Sixty of them were stress-free (NN), 11 were heterozygous carriers (Nn) and two animals were homozygous (nn) for the 1843 (C>T) mutation. Significant differences in non stress induced animals with different PSS genotypes were found in the values of creatine phoshokinase (CPK), lactate dehydrogenase (LDH), alkaline phosphatase (AP) and aspartate aminotransferase (AST). Regarding the maternal traits, our study showed that stress susceptible animals (nn) have an increased number of stillborn piglets and a reduced number of newborn piglets compared with heterozygous and normal animals.

Serotonin Syndrome: The Potential for a Severe Reaction Between Common Perioperative Medications and Selective Serotonin Reuptake Inhibitors

Selective serotonin reuptake inhibitors (SSRIs) are widely prescribed to patients of all ages. Although generally considered safe, therapy with SSRIs can be complicated by serotonin syndrome (SS), a life-threatening condition. We present a case of SS that developed in a young man who was receiving a stable dose of fluoxetine and then received several commonly used medications during an emergent appendectomy. Because polypharmacy in the perioperative setting may trigger SS, it is important for anesthesiologists to be cognizant of the interactions between SSRIs and common perioperative medications to formulate anesthetic plans that optimize patient safety.

Cystathionine β-synthase-derived hydrogen sulfide is involved in human malignant hyperthermia

Hydrogen sulfide is an endogenous gasotransmitter and its mechanism of action involves activation of ATP-sensitive K(+) channels and phosphodiesterase inhibition. As both mechanisms are potentially involved in malignant hyperthermia (MH), in the present study we addressed the involvement of the L-cysteine/hydrogen sulfide pathway in MH. Skeletal muscle biopsies obtained from 25 MH-susceptible (MHS) and 56 MH-negative (MHN) individuals have been used to perform the in vitro contracture test (IVCT). Quantitative real-time PCR (qPCR) and Western blotting studies have also been performed. Hydrogen sulfide levels are measured in both tissue samples and plasma. In MHS biopsies an increase in cystathionine β-synthase (CBS) occurs, as both mRNA and protein expression compared with MHN biopsies. Hydrogen sulfide biosynthesis is increased in MHS biopsies (0.128±0.12 compared with 0.943±0.13 nmol/mg of protein per min for MHN and MHS biopsies, respectively; P<0.01). Addition of sodium hydrosulfide (NaHS) to MHS samples evokes a response similar, in the IVCT, to that elicited by either caffeine or halothane. Incubation of MHN biopsies with NaHS, before caffeine or halothane challenge, switches an MHN to an MHS response. In conclusion we demonstrate the involvement of the L-cysteine/hydrogen sulfide pathway in MH, giving new insight into MH molecular mechanisms. This finding has potential implications for clinical care and could help to define less invasive diagnostic procedures.

Management of malignant hyperthermia: diagnosis and treatment

Malignant hyperthermia is a potentially lethal inherited disorder characterized by disturbance of calcium homeostasis in skeletal muscle. Volatile anesthetics and/or the depolarizing muscle relaxant succinylcholine may induce this hypermetabolic muscular syndrome due to uncontrolled sarcoplasmic calcium release via functionally altered calcium release receptors, resulting in hypoxemia, hypercapnia, tachycardia, muscular rigidity, acidosis, hyperkalemia, and hyperthermia in susceptible individuals. Since the clinical presentation of malignant hyperthermia is highly variable, survival of affected patients depends largely on early recognition of the symptoms characteristic of malignant hyperthermia, and immediate action on the part of the attending anesthesiologist. Clinical symptoms of malignant hyperthermia, diagnostic criteria, and current therapeutic guidelines, as well as adequate management of anesthesia in patients susceptible to malignant hyperthermia, are discussed in this review.

Muscle disorders: the latest investigations

Patients with muscle disorders can present a diagnostic challenge to physicians because of the different ways they can present and the large number of different underlying causes. Recognition of the 'myopathic phenotype' coupled with investigations usually including electrodiagnostic and histological investigations have been essential for diagnosing the underlying cause of a myopathy. Despite these standard investigations, some patients can remain undiagnosed. New tests including more specific antibody tests for immune-mediated myopathies and the introduction of next-generation sequencing promise to revolutionise diagnostic approaches for immune and inherited myopathies, but clinical expertise remains essential to choose the most appropriate tests and interpret the results. The aim of this review is to provide an overview of the different presentations to the neuromuscular clinic and the latest investigations that can be helpful in the diagnosis of muscle disorders.

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.

Multiple actions of phi-LITX-Lw1a on ryanodine receptors reveal a functional link between scorpion DDH and ICK toxins

We recently reported the isolation of a scorpion toxin named U1-liotoxin-Lw1a (U1-LITX-Lw1a) that adopts an unusual 3D fold termed the disulfide-directed hairpin (DDH) motif, which is the proposed evolutionary structural precursor of the three-disulfide-containing inhibitor cystine knot (ICK) motif found widely in animals and plants. Here we reveal that U1-LITX-Lw1a targets and activates the mammalian ryanodine receptor intracellular calcium release channel (RyR) with high (fM) potency and provides a functional link between DDH and ICK scorpion toxins. Moreover, U1-LITX-Lw1a, now described as ϕ-liotoxin-Lw1a (ϕ-LITX-Lw1a), has a similar mode of action on RyRs as scorpion calcines, although with significantly greater potency, inducing full channel openings at lower (fM) toxin concentrations whereas at higher pM concentrations increasing the frequency and duration of channel openings to a submaximal state. In addition, we show that the C-terminal residue of ϕ-LITX-Lw1a is crucial for the increase in full receptor openings but not for the increase in receptor subconductance opening, thereby supporting the two-binding-site hypothesis of scorpion toxins on RyRs. ϕ-LITX-Lw1a has potential both as a pharmacological tool and as a lead molecule for the treatment of human diseases that involve RyRs, such as malignant hyperthermia and polymorphic ventricular tachycardia.

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.

Movement disorders emergencies: a review

Movement disorders (MD) encompass acute and chronic diseases characterized by involuntary movements and/or loss of control or efficiency in voluntary movements. In this review, we covered situations in which the main manifestations are MDs that pose significant risks for acute morbidity and mortality. The authors examine literature data on the most relevant MD emergencies, including those related to Parkinson's disease, acute drug reactions (acute dystonia, neuroleptic malignant syndrome, serotonergic syndrome and malignant hyperthermia), acute exacerbation of chronic MD (status dystonicus), hemiballism and stiff-person syndrome, highlighting clinical presentation, demographics, diagnosis and management.

Malignant hyperthermia in the oral and maxillofacial surgery patient: an update

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, the depolarizing muscle relaxant succinylcholine, and, rarely in humans, to stresses, such as vigorous exercise and heat. The syndrome is likely to be fatal if untreated. Early recognition of the signs of MH provides the clinical diagnostic clues. Diagnostic testing relies on assessing the in vitro contracture response of biopsied muscle to halothane, caffeine, and other drugs. Dantrolene sodium is a specific antagonist of the pathophysiologic changes of MH and should be available wherever general anesthesia is administered. The prevention and treatment of acute episodes of this disorder is of paramount importance to the oral and maxillofacial surgeon. The management of such patients in the oral and maxillofacial surgery setting and the recent advances in the field of MH are presented.

Crisis checklists for the operating room: development and pilot testing

BACKGROUND

Because operating room crises are rare events, failure to adhere to critical management steps is common. We sought to develop and pilot a tool to improve adherence to lifesaving measures during operating room crises.

STUDY DESIGN

We identified 12 of the most frequently occurring operating room crises and corresponding evidence-based metrics of essential care for each (46 total process measures). We developed checklists for each crisis based on a previously defined method, which included literature review, multidisciplinary expert consultation, and simulation. After development, 2 operating room teams (11 participants) were each exposed to 8 simulations with random assignment to checklist use or working from memory alone. Each team managed 4 simulations with a checklist available and 4 without. One of the primary outcomes measured through video review was failure to adhere to essential processes of care. Participants were surveyed for perceptions of checklist use and realism of the scenarios.

RESULTS

Checklist use resulted in a 6-fold reduction in failure of adherence to critical steps in management for 8 scenarios with 2 pilot teams. These results held in multivariate analysis accounting for clustering within teams and adjusting for learning or fatigue effects (11 of 46 failures without the checklist vs 2 of 46 failures with the checklist; adjusted relative risk = 0.15, 95% CI, 0.04-0.60; p = 0.007). All participants rated the overall quality of the checklists and scenarios to be higher than average or excellent.

CONCLUSIONS

Checklist use can improve safety and management in operating room crises. These findings warrant broader evaluation, including in clinical settings.

Ryanodine receptors

Excitation-contraction coupling involves the faithful conversion of electrical stimuli to mechanical shortening in striated muscle cells, enabled by the ubiquitous second messenger, calcium. Crucial to this process are ryanodine receptors (RyRs), the sentinels of massive intracellular calcium stores contained within the sarcoplasmic reticulum. In response to sarcolemmal depolarization, RyRs release calcium into the cytosol, facilitating mobilization of the myofilaments and enabling cell contraction. In order for the cells to relax, calcium must be rapidly resequestered or extruded from the cytosol. The sustainability of this cycle is crucially dependent upon precise regulation of RyRs by numerous cytosolic metabolites and by proteins within the lumen of the sarcoplasmic reticulum and those directly associated with the receptors in a macromolecular complex. In addition to providing the majority of the calcium necessary for contraction of cardiac and skeletal muscle, RyRs act as molecular switchboards that integrate a multitude of cytosolic signals such as dynamic and steady calcium fluctuations, β-adrenergic stimulation (phosphorylation), nitrosylation and metabolic states, and transduce these signals to the channel pore to release appropriate amounts of calcium. Indeed, dysregulation of calcium release via RyRs is associated with life-threatening diseases in both skeletal and cardiac muscle. In this paper, we briefly review some of the most outstanding structural and functional attributes of RyRs and their mechanism of regulation. Further, we address pathogenic RyR dysfunction implicated in cardiovascular disease and skeletal myopathies.

Adverse drug reactions resulting in hyperthermia in the intensive care unit

Hyperthermia is frequently seen in the intensive care setting and is associated with significant morbidity and mortality. It is often initially misdiagnosed as fever associated with infection. Atypical presentations of classic syndromes are common. Clinical suspicion is the key to diagnosis. Adverse drug reactions are a frequent culprit. Syndromes include adrenergic "fever," anticholinergic "fever," antidopaminergic "fever," serotonin syndrome, malignant hyperthermia, uncoupling of oxidative phosphorylation, and withdrawal from baclofen. This review describes the pathophysiology of hyperthermia, as distinct from fever, and the physiology, diagnosis, and treatment of serotonin syndrome, neuroleptic malignant syndrome, malignant hyperthermia, and baclofen withdrawal. Much of the available evidence regarding the treatment of these disorders is based on single case reports, case series, or animal models. Therapeutic modalities consist of identification/withdrawal of possible offending agent(s), support directed at lowering temperature and preventing/treating complications, as well as targeted pharmacologic therapy directed at the specific cause. Early recognition and treatment using a multidisciplinary approach are essential to achieve the best possible outcome.

Thermal tolerance of contractile function in oxidative skeletal muscle: no protection by antioxidants and reduced tolerance with eicosanoid enzyme inhibition

Mechanisms for the loss of muscle contractile function in hyperthermia are poorly understood. This study identified the critical temperature, resulting in a loss of contractile function in isolated diaphragm (thermal tolerance), and then tested the hypotheses 1) that increased reactive oxygen species (ROS) production contributes to the loss of contractile function at this temperature, and 2) eicosanoid metabolism plays an important role in preservation of contractile function in hyperthermia. Contractile function and passive force were measured in rat diaphragm bundles during and after 30 min of exposure to 40, 41, 42 or 43 degrees C. Between 40 and 42 degrees C, there were no effects of hyperthermia, but at 43 degrees C, a significant loss of active force and an increase in passive force were observed. Inhibition of ROS with the antioxidants, Tiron or Trolox, did not inhibit the loss of contractile force at 43 degrees C. Furthermore, treatment with dithiothreitol, a thiol (-SH) reducing agent, did not reverse the effects of hyperthermia. A variety of global lipoxygenase (LOX) inhibitors further depressed force during 43 degrees C and caused a significant loss of thermal tolerance at 42 degrees C. Cyclooxygenase (COX) inhibitors also caused a loss of thermal tolerance at 42 degrees C. Blockage of phospholipase with phospholipase A(2) inhibitors, bromoenol lactone or arachidonyltrifluoromethyl ketone failed to significantly prevent the loss of force at 43 degrees C. Overall, these data suggest that ROS do not play an apparent role in the loss of contractile function during severe hyperthermia in diaphragm. However, functional LOX and COX enzyme activities appear to be necessary for maintaining normal force production in hyperthermia.

Enhanced excitation-coupled calcium entry in myotubes expressing malignant hyperthermia mutation R163C is attenuated by dantrolene

Dantrolene is the drug of choice for the treatment of malignant hyperthermia (MH) and is also useful for treatment of spasticity or muscle spasms associated with several clinical conditions. The current study examines the mechanisms of dantrolene's action on skeletal muscle and shows that one of dantrolene's mechanisms of action is to block excitation-coupled calcium entry (ECCE) in both adult mouse flexor digitorum brevis fibers and primary myotubes. A second important new finding is that myotubes isolated from mice heterozygous and homozygous for the ryanodine receptor type 1 R163C MH susceptibility mutation show significantly enhanced ECCE rates that could be restored to those measured in wild-type cells after exposure to clinical concentrations of dantrolene. We propose that this gain of ECCE function is an important etiological component of MH susceptibility and possibly contributes to the fulminant MH episode. The inhibitory potency of dantrolene on ECCE found in wild-type and MH-susceptible muscle is consistent with the drug's clinical potency for reversing the MH syndrome and is incomplete as predicted by its efficacy as a muscle relaxant.

Perioperative care of patients with neuromuscular disease and dysfunction

A variety of different pathologies result in disease phenotypes that are summarized as neuromuscular diseases because they share commonalty in their clinical consequences for the patient: a progressive weakening of the skeletal muscles. Distinct caution and appropriate changes to the anesthetic plan are advised when care is provided during the perioperative period. The choice of anesthetic technique, anesthetic drugs, and neuromuscular blockade always depends on the type of neuromuscular disease and the surgical procedure planned. A clear diagnosis of the underlying disease and sufficient knowledge and understanding of the pathophysiology are of paramount importance to the practitioner and guide optimal perioperative management of affected patients.

Fulminant-type malignant hyperthermia in Japan: cumulative analysis of 383 cases

We investigated the transition of clinical signs of fulminant-type malignant hyperthermia (f-MH) by analyzing a database consisting of 383 cumulative cases of f-MH from 1961 to 2004. The cases were divided by time period into group 1 (1961-1984), group 2 (1985-1994), and group 3 (1995-2004). The variables considered were age, sex, type of agents used (succinylcholine and volatile anesthetics), dantrolene administration, clinical signs, laboratory data, and mortality. The level of statistical significance was considered to be less than 5%. Groups 1, 2, and 3 consisted of 196, 127, and 60 cases, respectively. In groups 1, 2, and 3, the rates of dantrolene administration were 18.4%, 93.6%, and 86.7%; the rates of occurrence of ventricular arrhythmia were: 75.2%, 55.6%, and 35.0%; and the rates of generalized muscle rigidity were 64.7%, 60.9%, and 23.9%, respectively. The mortality rate decreased over time, from 42.3% in group 1, to 15.0% in group 2 and group 3. We considered that this decrease occurred because of the increased use of dantrolene and the early diagnosis of malignant hyperthermia in the latter two groups.

The syndrome of rhabdomyolysis: Pathophysiology and diagnosis

Rhabdomyolysis is defined as a pathological condition of skeletal muscle cell damage leading to the release of toxic intracellular material into the blood circulation. Its major causes include trauma, ischemia, drugs, toxins, metabolic disorders, and infections. The pathophysiological hallmark of the syndrome is an increase in intracellular free ionized calcium due to either cellular energy depletion, or direct plasma membrane rupture. The increased intracellular calcium activates several proteases, intensifies skeletal muscle cell contractility, induces mitochondrial dysfunction, and increases the production of reactive oxygen species, ultimately resulting in skeletal muscle cell death. Clinically, the syndrome presents with severe muscular pain, weakness and myoglobinuria. Increased myoglobin and creatine phosphokinase as a consequence of muscular cell death are the major laboratory findings, which, in combination with the clinical presentation, lead the clinician to the final diagnosis of the syndrome.

Rhabdomyolysis following shoulder arthroscopy

Fluid extravasation is not uncommon after shoulder arthroscopy. We report a case of massive fluid extravasation that resulted in rhabdomyolysis and renal shutdown following routine shoulder arthroscopic surgery. Compartment pressures in the deltoid, supraspinatus, and infraspinatus were normal. Magnetic resonance imaging of the shoulder revealed extensive subcutaneous edema and high-signal changes in the entire deltoid muscle. The patient made an uneventful recovery with adequate supportive treatment and renal dialysis. Repeat imaging studies 3 months later revealed complete restoration to normal of the deltoid muscle. In addition to extensive fluid extravasation in this patient, the use of nonsteroidal anti-inflammatory medication, the development of a transient allergic reaction to a prescribed antibiotic, and the inclusion of epinephrine in the infusion fluid may have collectively contributed to rhabdomyolysis. We recommend that the use of infusion pumps should be limited to the shortest time possible, and that gravity inflow should be used as much as possible. Inflow should preferably occur through the arthroscope itself, rather than through a separate portal cannula, which may dislodge, inadvertently causing infusion of high-pressure fluid into the surrounding tissue.

One-stage correction for blepharophimosis syndrome

PURPOSE

To classify the severity of blepharophimosis, describe associated features and their effects on the incidence of amblyopia and to recommend guidelines for surgical treatment and management of surgical complications.

METHODS

The case records of 23 patients with blepharophimosis syndrome were examined retrospectively. Patients' photographs and measurements were reviewed to analyse the severity of blepharophimosis, surgical techniques undertaken, surgical outcomes, and complications. Statistical analyses were performed using paired-sample t-tests to evaluate the surgical outcome and Spearman correlation to examine the influence of blepharophimosis on the interpalpebral fissure height (PFH).

RESULTS

Eighteen out of 23 (78%) patients underwent one-stage surgery before the age of 5 years. About 31% of these patients had amblyopia. Only two patients had a blepharophimosis ratio greater than 1.5 as poor result. Two out of 18 (11%) patients with PFHs more than 2 mm needed a repeat operation, but all five (100%) patients with s less than 2 mm (very severe ptosis) needed repeat operations.

CONCLUSIONS

The one-stage corrective procedure provided acceptable results both in function and cosmesis. However, patients with very severe ptosis required multiple stages of reconstruction for ptosis correction at an earlier age, after which correction of telecanthus and small horizontal palpebral fissure length followed at an older age.

An Assessment of a Point-of-Care Information System for the Anesthesia Provider in Simulated Malignant Hyperthermia Crisis

In this prospective, controlled study we compared the ability of anesthesia residents to diagnose and treat a simulated malignant hyperthermia (MH) scenario with and without the ability to use the On-Line Electronic Help (OLEH) information system or any other written guidelines. The OLEH is a point-of-care information system for the anesthesia provider in the operating room. The score for MH treatment after diagnosis based on clinical actions was significantly higher (P = 0.018) in the OLEH-user group (21.5 +/- 4.9) compared with a control group (15.5 +/- 7.6). This study demonstrates the possible value of a point-of-care information system in patient care; however, the significance of the results may be limited by the participants' anticipation of an acute event during training requiring the use of the OLEH.

Compartmental Pharmacokinetics of Dantrolene in Adults: Do Malignant Hyperthermia Association Dosing Guidelines Work?

Dantrolene is the only drug proven effective for prevention and treatment of malignant hyperthermia (MH). Current dosing recommendations are based on noncompartmental analyses and are largely empiric. They are also divergent, as evidenced by differing recommendations from the Malignant Hyperthermia Association of the United States (MHAUS) and European Sources. We determined the compartmental pharmacokinetics of dantrolene, simulated the concentration time course based on currently recommended dosing, and suggest an optimal regimen. Nine volunteers (55-89 kg) received IV infusions of dantrolene (5 mg/kg over 30 min followed by 0.05 mg.kg(-1) . h(-1) for 5 h). Venous blood samples were drawn for up to 60 h, and dantrolene plasma concentrations were determined by reverse phase, high-performance liquid chromatography. One, two, and three compartmental models were fitted to the data, and a covariate analysis was performed. All calculations were performed with NONMEM using the population approach. The data were adequately described by a two-compartment model with the following typical variable values (median +/- se): volumes of distribution V1= 3.24 +/- 0.61 L; V2= 22.9 +/- 1.53 L; plasma clearance CL el= 0.03 +/- 0.003 L/min; and distributional clearance CL dist= 1.24 +/- 0.22 L/min. All parameters were scaled linearly with weight. Simulations of European recommendations for treatment of MH lead to plasma concentrations converging to 14-18 mg/L within 24 h. Simulating MHAUS guidelines (intermittent bolus administration) yielded peak and trough plasma concentrations ranging from 6.7-22.6 mg/L. Based on our findings, we propose an infusion regimen adjusted to the initial bolus dose(s) required to control symptoms. This strategy maintains the individualized therapeutic concentrations and improves stability of plasma concentrations.

Paediatric anaesthesia and inhalation agents

Inhalation agents are amongst the mainstays of paediatric anaesthesia, as children are often induced by mask before venous access is obtained. Children do not like needles and obtaining venous access in an awake and moving child can be very demanding. Safety aspects are of particular importance in paediatric anaesthesia. Therefore, the possibility of monitoring end-tidal concentrations facilitates correct dosing in all patients, from the preterm infant weighing less than 1000 g to the adult-sized adolescent. For induction, sevoflurane has nearly universally replaced halothane, leading to increased cardiovascular safety. The main disadvantages of inhalation agents, especially sevoflurane and desflurane, are delirious behaviour and agitated states during emergence. In addition, there remains uncertainty regarding the relevance of the cerebral stimulating pattern of some of these agents. Inhalation anaesthesia has a long tradition, whereas the experience with propofol is comparatively small. The incidence and clinical relevance of the propofol infusion syndrome during clinical anaesthesia are still unknown. Inhalation anaesthesia is still considered to be the gold standard by the overwhelming majority of paediatric anaesthetists world-wide, however, intravenous techniques can be an attractive alternative in specific clinical situations.

Ryanodine receptor channelopathies

Ryanodine receptors (RyR) are the Ca2+ release channels of sarcoplasmic reticulum that provide the majority of the [Ca2+] necessary to induce contraction of cardiac and skeletal muscle cells. In their cellular environment, RyRs are exquisitely regulated by a variety of cytosolic factors and accessory proteins so that their output signal (Ca2+) induces cell contraction without igniting signaling pathways that eventually lead to contractile dysfunction or pathological cellular remodeling. Here we review how dysfunction of RyRs, most commonly expressed as enhanced Ca2+ release at rest (skeletal muscle) or during diastole (cardiac muscle), appears to be the fundamental mechanism underlying several genetic or acquired syndromes. In skeletal muscle, malignant hyperthermia and central core disease result from point mutations in RYR1, the skeletal isoform of RyRs. In cardiac muscle, RYR2 mutations lead to catecholaminergic polymorphic ventricular tachycardia and other cardiac arrhythmias. Lastly, an altered phosphorylation of the RyR2 protein may be involved in some forms of congestive heart failure.

Bench-to-bedside review: Rhabdomyolysis -- an overview for clinicians

Rhabdomyolysis ranges from an asymptomatic illness with elevation in the creatine kinase level to a life-threatening condition associated with extreme elevations in creatine kinase, electrolyte imbalances, acute renal failure and disseminated intravascular coagulation. Muscular trauma is the most common cause of rhabdomyolysis. Less common causes include muscle enzyme deficiencies, electrolyte abnormalities, infectious causes, drugs, toxins and endocrinopathies. Weakness, myalgia and tea-colored urine are the main clinical manifestations. The most sensitive laboratory finding of muscle injury is an elevated plasma creatine kinase level. The management of patients with rhabdomyolysis includes early vigorous hydration.