Intramuscular injection of sevoflurane detects malignant hyperthermia predisposition in susceptible pigs

BACKGROUND: The authors hypothesized that intramuscular sevoflurane injection allows diagnostic differentiation between malignant hyperthermia-susceptible (MHS) and -nonsusceptible (MHN) pigs by measurement of intramuscular lactate and carbon dioxide partial pressure (PCO2), and that dantrolene reduces the sevoflurane-induced PCO2 increase. METHODS: With approval of the local animal care committee, microdialysis probes with attached microtubing for sevoflurane injection were placed in the adductor muscles of nine MHS and six MHN pigs, and PCO2 probes with microtubing were positioned in the triceps muscle of eight MHS and six MHN pigs. After equilibration, sevoflurane boluses at different concentrations and a sevoflurane-dantrolene bolus were injected synchronously. Lactate, pyruvate, and glucose as well as PCO2 were measured spectrophotometrically, and the rate of PCO2 increase was calculated. RESULTS: Intramuscular sevoflurane injection increased local lactate and PCO2 dose dependently, and significantly higher in MHS than in MHN pigs. Measurement of the rate of PCO2 increase allowed a distinct differentiation between single MHS and MHN pigs. No significant increase in PCO2 was found with sevoflurane and dantrolene. CONCLUSIONS: Local sevoflurane induces a hypermetabolic reaction measured by PCO2 and lactate increases. The reduced PCO2 increase in MHS after sevoflurane and dantrolene injection is likely to be a result of the sevoflurane-mediated calcium release and its antagonism by dantrolene. Sevoflurane may be useful for a less invasive diagnostic test for malignant hyperthermia in humans.     

A minimally invasive metabolic test with intramuscular injection of halothane 5 and 6 vol% to detect probands at risk for malignant hyperthermia

We hypothesised that intramuscular halothane injection increases local Pco(2) concentrations in malignant hyperthermia susceptible (MHS) but not in non-susceptible (MHN) individuals. Pco(2) probes with attached microtubing catheters for halothane injection were placed into the lateral vastus muscle of eight MHS and eight MHN probands. Following equilibration, a single bolus of 200 microl halothane 5 and 6 vol% was injected. Pco(2) was measured spectrophotometrically. Baseline Pco(2) concentrations were similar between groups. Maximum Pco(2) and maximum rate of Pco(2) increase was significantly enhanced by halothane 5 and 6 vol% in MHS compared to MHN probands. Systemic haemodynamic and metabolic parameters did not differ between both groups. Local halothane application induces a hypermetabolic reaction with a significant Pco(2) increase in MHS compared to MHN probands, indicating a susceptibility to malignant hyperthermia. Intramuscular halothane injection with Pco(2) measurement seems to be a suitable method for the development of a minimally invasive metabolic test to diagnose malignant hyperthermia susceptibility.     

The dose-response relationship and regional distribution of lactate after intramuscular injection of halothane and caffeine in malignant hyperthermia-susceptible pigs

We hypothesized that IM halothane and caffeine injection increases local lactate concentration dose-dependently in malignant hyperthermia-susceptible (MHS) and nonsusceptible (MHN) pigs and that the hypermetabolic reaction measured by regional distribution of lactate and carbon dioxide is limited to a small muscle volume. Microdialysis probes were placed in the hindlimbs of 7 MHS and 7 MHN pigs and perfused with Ringer's solution. After equilibration, boluses of increasing halothane and caffeine concentrations were injected. For the second hypothesis regarding regional distribution, microdialysis probes were positioned in 7 MHS and 6 MHN pigs at the injection site for halothane and caffeine and at a distance of 10 mm and 25 mm. Lactate was measured in the dialysate by spectrophotometry. In addition, PCO2 was measured in the halothane experiments. Halothane and caffeine increased IM lactate dose-dependently in MHS pigs significantly more than in MHN pigs. Lactate and PCO2 were increased only at the injection site but not at 10 mm and 25 mm distance. MH susceptibility leads to a leftward shift of the dose-response curve for IM lactate after local injection of halothane and caffeine. The increase of lactate and carbon dioxide levels after local MH trigger injection is limited to a small area around the probe.     

4-Chloro-m-cresol is a Trigger of Malignant Hyperthermia in Susceptible Swine

Background: 4-Chloro-m-cresol (4-CmC) induces marked contractures in skeletal muscle specimens from individuals susceptible to malignant hyperthermia (MHS). In contrast, 4-CmC induces only small contractures in specimens from normal (MHN) patients. 4-CmC is a preservative within a large number of commercially available drug-preparations (e.g., insulin, heparin, succinylcholine), and it has been suggested that 4-CmC might trigger malignant hyperthermia. This study was designed to investigate the effects of 4-CmC in vivo and in vitro in the same animals.

Methods: After approval of the animal care committee, six Pietrain MHS and six control (MHN) swine were anesthetized with azaperone 4 mg/kg intramuscularly and metomidate 10 mg/kg intraperitoneally. After endotracheal intubation, lungs were mechanically ventilated (inspired oxygen fraction 0.3) and anesthesia was maintained with etomidate 2.5 mg [middle dot] kg-1 [middle dot] h-1 and fentanyl 50 [micro sign]g [middle dot] kg-1 [middle dot] h-1. Animals were surgically prepared with arterial and central venous catheters for measurement of hemodynamic parameters and to obtain blood samples. Before exposure to 4-CmC in vivo, muscle specimens were excised for in vitro contracture tests with 4-CmC in concentrations of 75 and 200 [micro sign]M. Subsequently, pigs were exposed to cumulative administration of 3, 6, 12, 24, and 48 mg/kg 4-CmC intravenously. If an unequivocal episode of malignant hyperthermia occurred, as indicated by venous carbon dioxide concentration >or= to 70 mmHg, pH or= to 2 [degree sign]C, the animals were treated with dantrolene, 3.5 mg/kg.

Results: All MHS swine developed malignant hyperthermia after administration of 4-CmC in doses of 12 or 24 mg/kg. Venous carbon dioxide concentration significantly increased and pH significantly decreased. Temperature increased in all MHS animals more than 2 [degree sign]C. Blood lactate concentrations and creatine kinase levels were significantly elevated. All MHS swine were treated successfully with dantrolene. In contrast, no MHN swine developed signs of malignant hyperthermia. After receiving 4-CmC in a concentration of 48 mg/kg, however, all MHN animals died by ventricular fibrillation. The in vitro experiments showed that both concentrations of 4-CmC produced significantly greater contractures in MHS than in MHN specimens.     

In-vivo-Diagnostik einer malignen-Hyperthermie-Disposition

BACKGROUND: In malignant hyperthermia (MH), volatile anesthetics induce hypermetabolism, lactic acidosis and rhabdomyolysis in predisposed patients. The authors hypothesized that intramuscular caffeine and halothane application would increase local lactate concentration in MH susceptible (MHS) individuals more than in non-susceptible (MHN) subjects without initiating the full MH syndrome. METHODS: In 14 MHS, 12 MHN and 7 control individuals, microdialysis probes were placed in the rectus femoris muscle and perfused with Ringer's solution at 1 microl/min. After equilibration, 250 microl caffeine (80 mM) was injected through the first microdialysis probe, halothane 10 vol% dissolved in soybean oil was perfused through a second microdialysis probe and a third probe was used for control measurements. Dialysate samples were analyzed for lactate spectrophotometrically. Systemic hemodynamic and metabolic parameters were measured. Data are presented as median and quartiles. RESULTS: Intramuscular caffeine and halothane significantly increased local peak concentrations of lactate in MHS probands [5.0 mM (3.4-8.1 mM) and 3.7 mM (2.6-5.0 mM), respectively] compared to MHN [1.6 mM (1.3-2.0 mM) and 1.9 mM (1.6-2.0 mM)] or control individuals [2.1 mM (1.9-2.3 mM) and 2.0 mM (1.6-2.1 mM)]. This was accompanied by a higher serum creatine kinase level in the MHS group. Hemodynamic and metabolic parameters were normal in the investigated groups. CONCLUSION: Intramuscular caffeine and halothane application induces a temporary and abnormal increase of local lactate in MHS individuals. No serious systemic side effects occurred. This study presents evidence that metabolic monitoring with local stimulation by caffeine and halothane may allow a minimally invasive diagnosis of MH susceptibility.     

4-chloro-m-cresol is a trigger of malignant hyperthermia in susceptible swine.

BACKGROUND: 4-Chloro-m-cresol (4-CmC) induces marked contractures in skeletal muscle specimens from individuals susceptible to malignant hyperthermia (MHS). In contrast, 4-CmC induces only small contractures in specimens from normal (MHN) patients. 4-CmC is a preservative within a large number of commercially available drug-preparations (e.g., insulin, heparin, succinylcholine), and it has been suggested that 4-CmC might trigger malignant hyperthermia. This study was designed to investigate the effects of 4-CmC in vivo and in vitro in the same animals. METHODS: After approval of the animal care committee, six Pietrain MHS and six control (MHN) swine were anesthetized with azaperone 4 mg/kg intramuscularly and metomidate 10 mg/kg intraperitoneally. After endotracheal intubation, lungs were mechanically ventilated (inspired oxygen fraction 0.3) and anesthesia was maintained with etomidate 2.5 mg x kg(-1) x h(-1) and fentanyl 50 microg x kg(-1) x h(-1). Animals were surgically prepared with arterial and central venous catheters for measurement of hemodynamic parameters and to obtain blood samples. Before exposure to 4-CmC in vivo, muscle specimens were excised for in vitro contracture tests with 4-CmC in concentrations of 75 and 200 microM. Subsequently, pigs were exposed to cumulative administration of 3, 6, 12, 24, and 48 mg/kg 4-CmC intravenously. If an unequivocal episode of malignant hyperthermia occurred, as indicated by venous carbon dioxide concentration > or = 70 mmHg, pH < or = 7.25, and an increase of temperature > or = 2 degrees C, the animals were treated with dantrolene, 3.5 mg/kg. RESULTS: All MHS swine developed malignant hyperthermia after administration of 4-CmC in doses of 12 or 24 mg/kg. Venous carbon dioxide concentration significantly increased and pH significantly decreased. Temperature increased in all MHS animals more than 2 degrees C. Blood lactate concentrations and creatine kinase levels were significantly elevated. All MHS swine were treated successfully with dantrolene. In contrast, no MHN swine developed signs of malignant hyperthermia. After receiving 4-CmC in a concentration of 48 mg/kg, however, all MHN animals died by ventricular fibrillation. The in vitro experiments showed that both concentrations of 4-CmC produced significantly greater contractures in MHS than in MHN specimens. CONCLUSIONS: 4-CmC is in vivo a trigger of malignant hyperthermia in swine. However, the 4-CmC doses required for induction of malignant hyperthermia were between 12 and 24 mg/kg, which is about 150-fold higher than the 4-CmC concentrations within clinically used preparations.     

In Vitro and In Vivo Effects of the Phosphodiesterase-III Inhibitor Enoximone on Malignant Hyperthermia-susceptible Swine

Background: In human skeletal muscles, the phosphodiesterase-III inhibitor enoximone induces in vitro contracture development, and it has been suggested that enoximone could trigger malignant hyperthermia (MH). In this study, the in vitro and in vivo effects of enoximone in MH-normal (MHN) and MH-susceptible (MHS) swine were investigated.

Methods: Malignant hyperthermia trigger-free general anesthesia was performed in MHS and MHN swine. Skeletal muscle specimens were excised for an in vitro contracture test with 0.6 mm enoximone. Thereafter, MHS and MHN swine were exposed to cumulative administration of 0.5, 1, 2, 4, 8, 16, and 32 mg/kg enoximone intravenously. Clinical occurrence of MH was defined by a Pco2 greater than 70 mmHg, a pH less than 7.20, and an increase in body temperature of more than 2.0[degrees]C.

Results: Enoximone induced marked contractures in all MHS muscle specimens in vitro. In contrast, only small or no contracture development was observed in MHN muscle specimens, without an overlap in contractures between MHS and MHN muscles. However, in vivo, no clinical differences were found between MHS and MHN swine following cumulative enoximone doses. According to the defined criteria, none of the swine developed MH during the experiment. Furthermore, high enoximone doses induced progressive circulatory insufficiency, and after receiving 32 mg/kg enoximone, all animals died of cardiovascular failure.     

Attenuation of serotonin–induced contractures in skeletal muscle from malignant hyperthermia–susceptible patients with dantrolene

Background : Porcine malignant hyperthermia (MH) can be triggered by administration of certain serotonin₂ receptor agonists. Pretreatment with dantrolene completely abolished serotonininduced MH. The purpose of this study was to investigate the effects of the serotonin₂ receptor agonist l–(2,5–dimethoxy–4–iodophenyl)–2–aminopropane (DOI) in skeletal muscle specimens from MH–susceptible (MHS) and MH–nonsusceptible (MHN) patients following pretreatment with dantrolene.
Results : Administration of DOI 0.02 mM induced contractures in muscle specimens from MHS and MHN patients. Contracture development started significantly earlier in MHS than in MHN specimens. In MHS muscle the maximum contracture was significantly greater than in MHN. Pretreatment with dantrolene significantly delayed the start of contracture development in MHS muscles, whereas in MHN muscles no contractures were observed after dantrolene. The contracture maximum was significantly reduced in MHS.
Conclusion : The acceleration of DOI–induced contracture development in skeletal muscle specimens from MHS patients indicates that an altered serotonin system might be involved in human MH. Dantrolene effectively delayed serotonin–induced contractures. Further investigations are needed to determine whether serotonin₂ receptors of skeletal muscle from MHS subjects are altered in function or structure, or whether this response is a secondary phenomenon.
Method : We used muscle specimens surplus to diagnostic requirements from 12 MHS and 13 MHN patients in this study. In the first experiment, DOI 0.02 mM was added to the organ bath. In the second experiment, muscle specimens were preincubated with dantrolene 0.5 μM or 1.0 nM, respectively, for 10 min before DOI 0.02 mM was administered.     

Alterations of inositol polyphosphates in skeletal muscle during porcine malignant hyperthermia

Malignant hyperthermia (MH) may result from increased intracellular calcium concentrations. Increased 1,4,5-IP3 concentrations could mediate this increase in Ca2+. In this study we measured inositol polyphosphates in selectively bred MH susceptible (MHS) and MH non- susceptible (MHN) swine. MH crisis was induced by halothane challenge, and dantrolene was administered in order to measure inositol polyphosphates after MH reversal. Muscle biopsies of skeletal muscles of the hind limbs were obtained in random order and inositol polyphosphates determined by high pressure liquid chromatography using a metal dye detection method. Inositol polyphosphates were determined in three groups: (1) MHS vs MHN basal, (2) during MH crisis induced by halothane and (3) following treatment with dantrolene after halothane challenge. Clinical variables (P(_)VO2, P(-)VCO2, PE'CO2 and pH) indicated that MH was readily induced in MHS swine. Basal concentrations of all inositol polyphosphates were higher in MHS swine compared with MHN swine. After halothane challenge, 1,3,4-IP3, 1,3,4,6- IP4 and 1,3,4,5-IP4 concentrations increased in MHS animals compared with the respective baseline values, whereas no changes in MHN animals could be detected. Dantrolene administration decreased inositol polyphosphate concentrations in MHS swine. MHN swine showed no changes in inositol polyphosphates after dantrolene. These findings indicate that inositol polyphosphates may be involved in metabolic changes after triggering and treatment of MH.      

Effects of the Serotonin sub 2 Receptor Agonist DOI on Skeletal Muscle Specimens from Malignant Hyperthermia-susceptible Patients

Background: Administration of serotonin2 (5-HT2) receptor agonists in pigs triggers malignant hyperthermia (MH) and psychotic-like behavior. Both can be reduced by 5-HT2 receptor antagonists. Furthermore, an increase in the plasma concentration of 5-HT has been found during onset of halothane-induced MH in pigs. Therefore, in this study, the in vitro effects of the 5-HT2 receptor agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) were investigated in muscle specimens from MH-susceptible (MHS) and -negative (MHN) patients.

Methods: After MH classification using the caffeine-halothane contracture test (CHCT), surplus muscle specimens from 23 MHS and 17 MHN patients were used to examine the effects of DOI. In the first study, DOI was added to the bath in a concentration of 0.02 mM. In a second experiment, muscles were preincubated for 60 min with 0.02 mM DOI, and subsequently, halothane was added incrementally to the organ bath (0.11-0.22-0.44 mM) for 15 min according to the CHCT protocol. The in vitro effects of DOI on contracture development and muscle twitch were measured for 120 min in both investigations.

Results: Muscle specimens from all patients developed contractures after administration of DOI, characterized by a significantly earlier development of contracture in MHS (16.8+/-1.7 min) than in MHN (66.3+/-5.8 min) muscles (P < 0.05). There was no overlap between the groups in the range of times. The onset of contracture development after DOI was prolonged by halothane in specimens from MHN patients (89.7 +/-5.6 min) but not MHS patients. Preincubation with DOI increased the halothane-induced contractures in specimens from MHS patients compared to the results of the CHCT. The contracture development in specimens from MHS patients was larger than from MHN patients. At the end of the experiment, contractures had reached a maximum of 12.9+/-1.1 mN in specimens from MHS and 5.3+/-0.6 mN in MHN patients (P < 0.05). The additional administration of halothane led to significantly increased contractures in specimens from MHS individuals (15.9+/- 0.9 mN) at 120 min. However, the contracture development decreased significantly to 3.1+/-0.4 mN in MHN muscles. Muscle twitch after DOI administration was reduced significantly in specimens from MHS and MHN patients.     

Abnormal Action Potential Responses to Halothane in Heart Muscle Isolated from Malignant Hyperthermia-susceptible Pigs

Background: During human and porcine malignant hyperthermia (MH), cardiac dysrhythmias and altered myocardial function can be observed. It is unknown whether a primary abnormality in cardiac muscle contributes to the cardiac symptoms during MH. An abnormal response to halothane has recently been demonstrated in action potentials (APs) from MH-susceptible (MHS) human skeletal muscles. We investigated the electrophysiologic properties in trabeculae isolated from the right ventricles of normal (MHN) and MHS pigs.

Methods: The experiments were performed on electrically stimulated (1 Hz) trabeculae isolated from the right ventricles of MHS and MHN pigs. Resting membrane potentials, APs, and tension were measured with and without the presence of 1% of halothane. In addition, the halothane-equilibrated muscles were exposed to caffeine in increasing doses (1, 2, and 4 mM).

Results: In the absence of halothane, resting potential and AP characteristics in MHS and MHN muscles did not differ significantly. Halothane did not alter resting potentials but produced different alterations in the APs in MHS and MHN muscles, whereas the decrease in twitch tension was identical. In contrast to reductions in the AP amplitude and duration in MHN muscle, halothane produced an enlargement of the APs in MHS muscle. The addition of caffeine caused nearly identical prolongations of AP duration in MHS and MHN muscles.     

In vitro and in vivo effects of the phosphodiesterase-III inhibitor enoximone on malignant hyperthermia-susceptible swine

BACKGROUND: In human skeletal muscles, the phosphodiesterase-III inhibitor enoximone induces in vitro contracture development, and it has been suggested that enoximone could trigger malignant hyperthermia (MH). In this study, the in vitro and in vivo effects of enoximone in MH-normal (MHN) and MH-susceptible (MHS) swine were investigated. METHODS: Malignant hyperthermia trigger-free general anesthesia was performed in MHS and MHN swine. Skeletal muscle specimens were excised for an in vitro contracture test with 0.6 mm enoximone. Thereafter, MHS and MHN swine were exposed to cumulative administration of 0.5, 1, 2, 4, 8, 16, and 32 mg/kg enoximone intravenously. Clinical occurrence of MH was defined by a Pco(2) greater than 70 mmHg, a pH less than 7.20, and an increase in body temperature of more than 2.0 degrees C. RESULTS: Enoximone induced marked contractures in all MHS muscle specimens in vitro. In contrast, only small or no contracture development was observed in MHN muscle specimens, without an overlap in contractures between MHS and MHN muscles. However, in vivo, no clinical differences were found between MHS and MHN swine following cumulative enoximone doses. According to the defined criteria, none of the swine developed MH during the experiment. Furthermore, high enoximone doses induced progressive circulatory insufficiency, and after receiving 32 mg/kg enoximone, all animals died of cardiovascular failure. CONCLUSIONS: The cumulative enoximone doses used in this study were 30- to 50-fold higher than therapeutic doses in humans. Enoximone does not trigger MH in genetically determined swine. However, enoximone might be useful for in vitro diagnosis of MH.     

Induction of Malignant Hyperthermia in Susceptible Swine by 3,4-Methylenedioxymethamphetamine (Ecstasy)

Background: 3,4-Methylenedioxymethamphetamine (MDMA, "ecstasy") can mediate acute toxic effects such as muscle rigidity, metabolic acidosis, and hyperthermia. Because of close clinical similarities, an association between MDMA intoxication and malignant hyperthermia (MH) was suggested. The aim of this study was to investigate whether MDMA is a trigger of MH in susceptible swine.

Methods: MH-nontriggering general anesthesia was performed in six MH-susceptible (MHS) and six MH-normal swine. The animals were exposed to MDMA in cumulative doses of 0.5, 1, 2, 4, 8, and 12 mg/kg. The clinical occurrence of MH was defined by achievement of two of three conditions: central venous Pco2 >=75 mmHg, central venous pH <= 7.20, and increase of body core temperature >= 2.0[degrees]C. Once MH occurred, a standardized therapy with dantrolene, sodium bicarbonate, and hyperventilation with 100% oxygen was initialized.

Results: Administration of 8 mg/kg MDMA triggered MH in all MHS swine. The MH-normal swine also developed clinical signs of hypermetabolism, but even after administration of 12 mg/kg MDMA, changes were moderate compared with the MHS swine. Dantrolene therapy of MDMA-induced MH crisis in the MHS swine partially counteracted the clinical signs of MH immediately.     

Hypersensitivity of Malignant Hyperthermia-susceptible Swine Skeletal Muscle to Caffeine Is Mediated by High Resting Myoplasmic [Ca2+]

Background: Malignant hyperthermia (MH) is an inherited pharmacogenetic syndrome that is triggered by halogenated anesthetics and/or depolarizing muscle relaxants. MH-susceptible (MHS) skeletal muscle has been shown to be more sensitive to caffeine-induced contracture than muscle from nonsusceptible (MHN) subjects and is the basis for the most commonly used clinical diagnostic test to determine MH susceptibility.

Methods: We studied the effects of caffeine on myoplasmic free calcium concentration ([Ca2+]i) in MHN and MHS swine muscle fibers by means of Ca2+-selective microelectrodes before and after K+-induced partial depolarization.

Results: [Ca2+]i in untreated MHN fibers was 123 +/- 8 nm versus 342 +/- 33 nm in MHS fibers. Caffeine (2 mm) caused an increase in [Ca2+]i in both groups (296 +/- 41 nm MHN vs. 1,159 +/- 235 nm MHS) with no change in resting membrane potential. When either MHN or MHS, muscle fibers were incubated in 10 mm K+ [Ca2+]i transiently increased to 272 +/- 22 nm in MHN and 967 +/- 38 nm in MHS for 6-8 min. Exposure of MHN fibers to 2 mm caffeine while resting [Ca2+]i was elevated induced an increment in [Ca2+]i to 940 +/- 37 nm. After 6-8 min of exposure to 10 mm K+, [Ca2+]i returned to control levels in all fibers, and the effect of 2 mm caffeine on resting [Ca2+]i returned to control, despite continued partial membrane depolarization.     

Effects of a 5HT(2) receptor agonist on anaesthetized pigs susceptible to malignant hyperthermia

Background. The pathophysiology of the serotoninergic systemin malignant hyperthermia (MH) is not completely understood.The serotonin-2 (5HT_2A) receptor agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropanehydrochloride (DOI) induces typical MH symptoms, including skeletalmuscle rigidity, an increase in body temperature, hyperventilationand acidosis in conscious MH-susceptible (MHS) pigs. Whetherthese symptoms are directly generated in skeletal muscle, resultfrom central serotonergic overstimulation or from a porcinestress syndrome remains unresolved. In this study the in vivoeffects of DOI on anaesthetized (and thus stress-protected)MHS and MH-normal (MHN) pigs were investigated. Methods and results. DOI 1 mg kg^–1 was administered threetimes at 40-min intervals to five MHS and five MHN anaesthetizedpigs. Body temperature, heart rate, muscle tone, arterial carbondioxide pressure (Pa_CO2), pH and creatine kinase concentrationswere measured. The clinical occurrence of MH was defined byPa_CO2 above 70 mm Hg and an increase in body temperature ofmore than 2 °C. Intragroup differences were analysed withthe Friedman test as an overall non-parametric ANOVA and, incase of significance, with the Wilcoxon test. Intergroup comparisonswere performed with the Mann–Whitney U-test (statisticalsignificance P<0.05). MHS and MHN pigs developed muscle fasciculations,significant increases in body temperature and Pa_CO2 and a significantdecrease in pH after the administration of DOI. These changeswere comparable in both groups until the third dose of DOI,when in MHS pigs heart rate and Pa_CO2 rose significantly andpH fell significantly compared with MHN pigs. All MHS pigs fulfilledthe MH criteria. Body temperature increased by more than 2 °Cin all MHN pigs and Pa_CO2 exceeded 70 mm Hg in two. Thus, twoMHN pigs fulfilled the criteria of MH. Conclusions. The comparability of the clinical presentationfollowing DOI administration in MHS and MHN animals and theorder of the development of MH-like symptoms favour the hypothesisof a central serotonergic overstimulation, leading to a serotoninsyndrome. Br J Anaesth 2003; 91: 281–4     

Mg2+ Dependence of Halothane-induced Ca2+ Release from the Sarcoplasmic Reticulum in Skeletal Muscle from Humans Susceptible to Malignant Hyperthermia

Background: Recent work suggests that impaired Mg2+ regulation of the ryanodine receptor is a common feature of both pig and human malignant hyperthermia. Therefore, the influence of [Mg2+] on halothane-induced Ca2+ release from the sarcoplasmic reticulum was studied in malignant hyperthermia-susceptible (MHS) or -nonsusceptible (MHN) muscle.

Methods: Vastus medialis fibers were mechanically skinned and perfused with solutions containing physiologic (1 mm) or reduced concentrations of free [Mg2+]. Sarcoplasmic reticulum Ca2+ release was detected using fura-2 or fluo-3.

Results: In MHN fibers, 1 mm halothane consistently did not induce sarcoplasmic reticulum Ca2+ release in the presence of 1 mm Mg2+. It was necessary to increase the halothane concentration to 20 mm or greater before Ca2+ release occurred. However, when [Mg2+] was reduced below 1 mm, halothane became an increasingly effective stimulus for Ca2+ release; e.g., at 0.4 mm Mg2+, 58% of MHN fibers responded to halothane. In MHS fibers, 1 mm halothane induced Ca2+ release in 57% of MHS fibers at 1 mm Mg2+. Reducing [Mg2+] increased the proportion of MHS fibers that responded to 1 mm halothane. Further experiments revealed differences in the characteristics of halothane-induced Ca2+ release in MHS and MHN fibers: In MHN fibers, at 1 mm Mg2+, halothane induced a diffuse increase in [Ca2+], which began at the periphery of the fiber and spread slowly inward. In MHS fibers, halothane induced a localized Ca2+ release, which then propagated along the fiber. However, propagated Ca2+ release was observed in MHN fibers when halothane was applied at an Mg2+ concentration of 0.4 mm or less.     

Histomorphologic Examination of Skeletal Muscle Preparations Does Not Differentiate between Malignant Hyperthermia-Susceptible and -Normal Patients

Background: It has been suggested that malignant hyperthermia (MH) can be diagnosed by specific myopathologic alterations. The purpose of this study was to investigate whether there are characteristic myopathologic changes in skeletal muscles of MH-susceptible (MHS) compared with MH-normal (MHN) patients.

Methods: Four hundred forty patients with clinical suspicion of MH were classified as MHN, MH equivocal (MHE), or MHS by the in vitro contracture test with halothane and caffeine. In addition, a small muscle sample excised from each patient was analyzed by histologic, histochemical, immunohistochemical, and computer-aided morphometric methods.

Results: MHN was diagnosed in 243 patients, MHE was diagnosed in 65, and MHS was diagnosed in 132. No myopathologic abnormalities were found in 53.5% of the MHN, 53.9% of the MHE, and 56.1% of the MHS patients. Thirty-five percent of all patients showed one, 9.8% showed two, and only 0.9% showed three different pathologic findings within skeletal muscle preparations. The frequency of pathologic findings did not differ between the MHN and the MHS patients; only fiber type I predominance was observed more often in MHN. MHE patients could not be assigned to a diagnostic group by detection of myopathologic alterations. In six clinically unaffected patients, a former unrecognized myopathy, such as central core disease, was diagnosed. This disease is characterized by a specific alteration (cores).     

Modulation of ryanodine-induced contractures in human skeletal muscle pretreated with dantrolene

Dantrolene seems to be the causal therapy in malignant hyperthermia (MH) crisis but the complex mechanisms of MH and dantrolene therapy are still not fully understood. The influence of dantrolene on ryanodine-induced contractures has been reported in animal studies only. In the present study 20 patients from] 7 families were tested for MH using the protocol of the European Malignant Hyperthermia Group. In addition ryanodine-induced contractures were evaluated following bolus application of 10.0 μmol · 1^-1 ryanodine. After pretreatment with 1 μimol · 1^-1 dantrolene ryanodine-provoked contractures developed significantly later in MHS (15.8±1.8 min) and MHN (46.0±4.2 min) muscle specimens than after ryanodine alone (MHS 4.8±0.7 min), (MHN 13.7±0.9 min). They were no longer observed in either group after pretreatment with 5 μimol · 1^-1 dantrolene. We conclude that dantrolene is able to attenuate ryanodine-induced contractures dose-dependendy, and therefore it is speculated that dantrolene could specifically act at the ryanodine receptor binding site.     

Effect of CO2, calcium, digoxin, and potassium on cardiac and skeletal muscle metabolism in malignant hyperthermia susceptible swine

The effects on whole body or cardiac metabolism of carbon dioxide, calcium, potassium, or digoxin were studied in 16 normal swine and 31 swine susceptible to malignant hyperthermia (MHS). Malignant hyperthermia (MH) was defined as an increase in metabolism that occurred in MHS but not in normal pigs. Whole body response: despite a sustained PaCO2 greater than 130 mmHg, MH did not develop in four intact MHS swine during thiopental-N2O anesthesia and controlled ventilation. Drugs given during total cardiopulmonary bypass: MH did not develop in five MHS pigs with blood ionized calcium to 15 mEq/l, in four MHS pigs with digoxin levels to 60 ng/ml, or in four normal pigs with potassium to 10 mEq/l. In six MHS pigs, oxygen consumption increased from 6.5 to 11.6 ml O2 X min-1 X kg-1 when potassium exceeded 6 mEq/l; lactate did not increase. Cardiac response (during extracorporeal right heart bypass): eight pigs (four normal, four MHS) with blood ionized calcium to 5 mEq/l and eight pigs (four normal, four MHS) with digoxin levels above 7.5 ng/ml had increased myocardial oxygen consumption. Cardiac potassium efflux or lactate production did not occur in normal or MHS pigs. Increased arterial potassium (7.4-8.5 mEq/l) did not alter myocardial oxygen consumption or lactate production in four MHS or four normal pigs. MH responses were initiated only by potassium and only in regard to whole body metabolism. Cardiac metabolism increased as a result of specific drugs (calcium, digoxin), unrelated to MH phenomena. Porcine inbreeding resulting in MH susceptibility of skeletal muscle does not imply abnormality in other tissues.     

Contractures in skeletal muscle of malignant hyperthermia susceptible patients after in vitro exposure to sevoflurane

BACKGROUND: Sevoflurane, a potent inhalational anaesthetic agent that is structurally similar to halothane, has some favourable characteristics, but may also be able to trigger malignant hyperthermia (MH) in susceptible patients. The diagnosis of malignant hyperthermia susceptibility relies on the in vitro contracture test on skeletal muscle. The present study was undertaken to investigate whether exposure to sevoflurane of muscles of malignant hyperthermia susceptible (MHS) patients would also cause an abnormal contracture. METHODS: Muscle fascicles obtained from three MHS patients, one malignant hyperthermia non-susceptible (MHN) patient, two control patients and one malignant hyperthermia equivocal (MHE) patient were exposed to sevoflurane instead of halothane in the in vitro contracture test, carried out according to the protocol of the European Malignant Hyperthermia Group. The muscle fascicles were surplus to diagnostic requirements. Sevoflurane concentrations in the testbath were measured using a headspace gas chromatographic technique. RESULTS: The kinetics of sevoflurane concentration in the testbath were similar to those of halothane. An in vitro contracture response of 2 mN or more was seen in all four MHS/MHE patients with sevoflurane but not in the three control/MHN patients. The magnitude of muscle contracture in the sevoflurane test was less than in the conventional halothane test at comparable testbath concentrations. CONCLUSIONS: Sevoflurane can trigger an abnormal contracture in human muscle in vitro. This is indicative of malignant hyperthermia susceptibility. Exposure to sevoflurane should be avoided in patients thought to be susceptible to malignant hyperthermia.