The Dose-Response Relationship and Regional Distribution of Lactate After Intramuscular Injection of Halothane and Caffeine in Malignant Hyperthermia-Susceptible Pigs

The current status of malignant hyperthermia

Malignant hyperthermia (MH) is a rare and life-threatening pharmacogenetic disorder triggered by volatile anesthetics, the depolarizing muscle relaxant succinylcholine, and rarely by strenuous exercise or environmental heat. The exact prevalence of MH is unknown, and it varies from 1:16 000 in Denmark to 1:100 000 in New York State. The underlying mechanism of MH is excessive calcium release from the sarcoplasmic reticulum (SR), leading to uncontrolled skeletal muscle hyper-metabolism. Genetic mutations in ryanodine receptor type 1 ( RYR1) and CACNA1S have been identified in approximately 50% to 86% and 1% of MH-susceptible (MHS) individuals, respectively. Classic clinical symptoms of MH include hypercarbia, sinus tachycardia, masseter spasm, hyperthermia, acidosis, muscle rigidity, hyperkalemia, myoglobinuria, and etc. There are two types of testing for MH: a genetic test and a contracture test. Contracture testing is still being considered as the gold standard for MH diagnosis. Dantrolene is the only available drug approved for the treatment of MH through suppressing the calcium release from SR. Since clinical symptoms of MH are highly variable, it can be difficult to establish a diagnosis of MH. Nevertheless, prompt diagnosis and treatments are crucial to avoid a fatal outcome. Therefore, it is very important for anesthesiologists to raise awareness and understand the characteristics of MH. This review summarizes epidemiology, clinical symptoms, diagnosis and treatments of MH and any new developments.

Ultrasound Elastography for Rapid, Real-time Detection of Localized Muscular Reaction in Malignant Hyperthermia-susceptible Pigs

WHAT WE ALREADY KNOW ABOUT THIS TOPIC

WHAT THIS ARTICLE TELLS US THAT IS NEW: BACKGROUND:: Halothane and caffeine induce excessive sarcoplasmic calcium liberation and skeletal muscle contracture in patients susceptible to malignant hyperthermia (MH) and are utilized for diagnosis in the in vitro contracture test. Intramuscular injection previously caused a marked local lactate increase in MH-susceptible but not in MH-nonsusceptible individuals in vivo. Using shear-wave elastography, this study evaluated localized changes in muscle stiffness after intramuscular injection of halothane and caffeine.

METHODS

Microdialysis probes were placed into the gracilis muscle of 16 pigs (9 MH-susceptible and 7 MH-nonsusceptible). After local injection of either halothane or caffeine in different concentrations, changes of tissue elasticity surrounding the probe were examined by quantitative shear-wave elastography. Local lactate concentrations were analyzed spectrophotometrically.

RESULTS

Ultrasound elastography detected a temporary increase in local muscle rigidity in MH-susceptible but not in MH-nonsusceptible pigs after 2.5 and 5 vol% halothane and after 10, 40, and 80 mM caffeine, whereas there were no differences in the control groups (median [interquartile range] for maximum effect after 5 vol% halothane: MH-susceptible: 97 [31 to 148] vs. MH-nonsusceptible: 5 [-6 to 18] kPa; P = 0.0006; maximum effect after 80 mM caffeine: 112 [64 to 174] vs. -3 [-6 to 35] kPa; P = 0.0002). These effects were seen rapidly within 5 min. Local lactate concentrations were higher in MH-susceptible versus nonsusceptible pigs after 1 and 2.5 vol% halothane and 10, 40, and 80 mM caffeine (2.5 vol% halothane: MH-susceptible: 2.8 [1.9 to 4.4] vs. MH-nonsusceptible: 0.6 [0.6 to 0.7] mmol/l; P < 0.0001; 80 mM caffeine: 5.2 [4.1 to 6.3] vs. 1.6 [1.2 to 2.4] mmol/l; P < 0.0001). After 10 vol% halothane, rigidity and lactate levels were increased in both MH-susceptible and MH-nonsusceptible animals.

CONCLUSIONS

This pilot study revealed shear-wave elastography as a suitable technique for real-time detection of altered tissue elasticity in response to pharmacologic stimulation. By considering the variability of these results, further test protocol optimization is required before elastography could serve as a minimally invasive MH diagnostic test.

Metabolic effects as a cause of myotoxic effects of fluoroquinolones

OBJECTIVES

To investigate if fluoroquinolones (FQs) influence skeletal muscle metabolism of healthy and malignant hyperthermia susceptible (MHS) pigs.

MATERIALS AND METHODS

After approval from of the Animal Care Committee, 10 MHS pigs, and 6 MHS pigs were anesthetized with hemodynamic and systemic metabolic monitoring. Microdialysis catheters were placed intramuscularly. After equilibration, levofloxacin and ciprofloxacin were injected as a rapid bolus and continuous infusions. Lactate was measured in the dialysate and statistically analyzed was done (Wilcoxon-test; U-test; P < 0.05).

RESULTS

There were no differences in age, weight, and baseline lactate levels between the groups. Both applications of levofloxacin- and ciprofloxacin-induced an increase of local lactate levels in healthy and MHS pigs. No difference between the two groups was observed.

CONCLUSION

FQs influence skeletal muscle metabolism. Myotoxic effects of FQs can, therefore, be explained by an influence on the cellular energy balance.

The effect of succinylcholine on malignant hyperthermia events in susceptible swine

BACKGROUND

While the impact of volatile anaesthetics to induce malignant hyperthermia (MH) is abundantly clear, the role of succinylcholine still remains controversial. To evaluate the influence of succinylcholine on porcine MH events, the authors investigated the hemodynamic and metabolic responses in MH susceptible (MHS) and non-susceptible (MHN) swine following either succinylcholine or halothane application alone or a combination of both substances.

METHODS

With approval of the local animal care committee 27 MHS and 30 MHN pigs were anaesthetized and mechanically ventilated. Fiberoptic probes for continuous PCO2 measurement were inserted into the femoral vein and the triceps muscle. Group A received succinylcholine 4 mg/kg, group B incremental doses of halothane (0.5, 1.0 vol%) and group C succinylcholine and halothane simultaneously. Vital signs were recorded continuously.

RESULTS

Prior to drug application measured values did not differ between MHS and MHN. While MHN pigs did not show relevant alterations, succinylcholine, halothane and the combination of both lead to significant hemodynamic and metabolic changes in MHS swine.

CONCLUSIONS

Hemodynamic and metabolic alterations following succinylcholine were similar to halothane in MHS pigs. The combination of both pharmacological agents potentiated the observed effects. According to these results succinylcholine acted as an independent and supportive factor during onset of an MH episode.

A minimal-invasive metabolic test detects malignant hyperthermia susceptibility in a patient after sevoflurane-induced metabolic crisis

Malignant hyperthermia is a rare but life-threatening complication of general anesthesia in predisposed patients usually triggered by potent inhalation anesthetics and/or the depolarizing muscle relaxant succinylcholine. The authors present a case of delayed sevoflurane-induced malignant hyperthermia in a 21-year-old male patient that was sufficiently treated by discontinuation of trigger agent application and dantrolene infusion. After surviving an MH episode diagnostic procedures are indicated to increase patient safety. In the presented case, the use of a novel minimal-invasive metabolic test with intramuscular injection of halothane and caffeine successfully confirmed MH susceptibility and hence might be an alternative for invasive in vitro contracture testing in selected cases.

Evaluation of suspected malignant hyperthermia events during anesthesia

Background

Malignant hyperthermia (MH), a metabolic myopathy triggered by volatile anesthetics and depolarizing muscle relaxants, is a potentially lethal complication of general anesthesia in susceptible patients. The implementation of modern inhalation anesthetics that research indicates as less potent trigger substances and the recommended limitations of succinylcholine use, suggests there may be considerable decline of fulminant MH cases. In the presented study, the authors analyzed suspected MH episodes during general anesthesia of patients that were referred to the Wuerzburg MH unit between 2007 and 2011, assuming that MH is still a relevant anesthetic problem in our days.

Methods

With approval of the local ethics committee data of patients that underwent muscle biopsy and in vitro contracture test (IVCT) between 2007 and 2011 were analyzed. Only patients with a history of suspected MH crisis were included in the study. The incidents were evaluated retrospectively using anesthetic documentation and medical records.

Results

Between 2007 and 2011 a total of 124 patients were tested. 19 of them were referred because of suspected MH events; 7 patients were diagnosed MH-susceptible, 4 MH-equivocal and 8 MH-non-susceptible by IVCT. In a majority of cases masseter spasm after succinylcholine had been the primary symptom. Cardiac arrhythmias and hypercapnia frequently occurred early in the course of events. Interestingly, dantrolene treatment was initiated in a few cases only.

Conclusions

MH is still an important anesthetic complication. Every anesthetist must be aware of this life-threatening syndrome at any time. The rapid onset of adequate therapy is crucial to avoid major harm and possibly lethal outcome. Dantrolene must be readily available wherever MH triggering agents are used for anesthesia.

Minimally invasive metabolic testing for malignant hyperthermia susceptibility: a systematic review of the methodology and results

IMPORTANCE OF THE FIELD

Malignant hyperthermia (MH) is a potentially lethal hypermetabolic syndrome that develops in susceptible individuals exposed to volatile anesthetics or depolarizing neuromuscular blocking agents. Because genetic screening is successful only in 30 - 50% of all suspected cases, contracture testing following an open muscle biopsy is performed to diagnose MH susceptibility. Two different protocols exist, the in vitro contracture test (IVCT) for Europe and the caffine halothane contracture test for the US. As replacement for the IVCT, an in vivo metabolic test might allow an equal discrimination of MH susceptible individuals. In this systematic review, all available metabolic testing methods are analyzed.

WHAT THE READER WILL GAIN

The reader will gain insight in methods and results of alternative approaches to diagnose MH.

AREAS COVERED IN THIS REVIEW

Relevant studies involving in vivo metabolic testing were systematically searched (Medline) and reviewed. Their ability to discriminate MH susceptible individuals was analyzed and compared. Any systemic or local side effects were documented and evaluated in order to allow more robust conclusions based on larger sample sizes than the single trials.

TAKE HOME MESSAGE

All discussed study protocols allowed an adequate discrimination of MH susceptible individuals. The latest study protocol reaches a specificity of 79% with a sensitivity of 100%. No severe systemic or local adverse effects could be seen in the pooled analysis. Minimally invasive metabolic testing is a promising novel approach to diagnose MH. Further multi-center studies have to be conducted to optimize the results in order to replace the IVCT.

Screening test for malignant hyperthermia in patients with persistent hyperCKemia: a pilot study

INTRODUCTION

Persistently elevated serum creatine kinase (CK) is frequently associated with predisposition to malignant hyperthermia (MH). We investigated whether a minimally invasive metabolic test is suitable to diagnose MH susceptibility among patients with hyperCKemia.

METHODS

Thirty-nine participants were included: 10 were MH susceptible (MHS); 21 MH were non-susceptible (MHN); and 8 had MHN with persistent hyperCKemia >500 U/L. Microdialysis probes were inserted into the vastus lateralis muscle, and halothane or caffeine was injected via an attached microtubing catheter. Lactate concentrations in dialysis samples were measured spectrophotometrically.

RESULTS

Baseline lactate did not differ between the groups. After local application of halothane or caffeine, a significant lactate increase was detected only in the MHS group.

CONCLUSIONS

Test results were not influenced by hyperCKemia. To avoid risks and complications of a surgical muscle biopsy this microdialysis test might be a useful screening tool for MH susceptibility among patients with persistent CK elevation.

Minimally invasive monitoring of skeletal muscle hypermetabolism induced by the phosphodiesterase-III-inhibitor milrinone and sodium fluoride

OBJECTIVES

We hypothesized that the phosphodiesterase-III-inhibitor milrinone and the non-specific G-protein activator sodium fluoride increase the skeletal muscular lactate levels as a sign of a hypermetabolic response.

METHODS

With approval of the local animal care committee Sprague-Dawley rats were killed and artificially perfused either with Ringer's solution or sodium fluoride 110 mM, while milrinone 1.32 mM or Ringer's solution at 1 μl/min was applied via microdialysis probes in both hind limbs. Lactate was measured spectrophotometrically in the dialysate.

KEY FINDINGS

Baseline lactate levels before drug application did not differ between hind limbs. Local infusion of milrinone via microdialysis did not significantly increase intramuscular lactate concentrations compared with the Ringer control group. Muscular perfusion with sodium fluoride resulted in a significant increase of lactate and was potentiated by combination with local milrinone.

CONCLUSIONS

Phosphodiesterase-III-inhibition alone does not significantly influence the lactate levels in skeletal muscle of sacrificed rats. Sodium fluoride infusion leads to an intramuscular lactate increase, which was further potentiated by local inhibition of phosphodiesterase-III. The fluoride-mediated hypermetabolic response following sodium fluoride could be a possible explanation for the observed myotoxic adverse effects in individuals treated by fluoride-containing agents.

Succinylcholine in malignant hyperthermia: evaluation of a novel in vivo model

INTRODUCTION

Malignant hyperthermia (MH) is a potentially lethal anesthetic complication characterized by muscle hypermetabolism and generalized rigor. The exact mechanism of succinylcholine as an MH trigger cannot be examined in existing in vitro models. Therefore, a novel in vivo model was used to examine the metabolic response to succinylcholine.

METHODS

With institutional review board approval, 6 MH susceptible (MHS) and 6 MH non-susceptible (MHN) pigs were anesthetized with hemodynamic and systemic metabolic monitoring. Microdialysis catheters were placed intramuscularly. After equilibration, succinylcholine, halothane, and Ringer solution were injected. Lactate was measured in the dialysate and statistically analyzed by Mann-Whitney U-test (significance level P < 0.05).

RESULTS

Hemodynamic and systemic metabolic parameters were not different between the groups throughout the experiment. In the MHS pigs, halothane induced a significant increase of lactate. In MHN pigs, no substance induced a reaction.

CONCLUSIONS

Halothane, but not succinylcholine, induced a hypermetabolic reaction in this model. Therefore, the role of succinylcholine as an MH trigger remains questionable.

Scientific advances in the genetic understanding and diagnosis of malignant hyperthermia

Malignant hyperthermia (MH), a potentially fatal disorder triggered by certain types of general anesthesia, has received much attention in the scientific literature. From the first case report in 1960 until the present, hundreds of studies have been conducted. The diagnosis of MH has evolved from subjective assumptions by family history and clinical diagnosis to more sophisticated laboratory testing. A genetic basis for MH was recognized in the early 1990s and, since then, complex genetic pathways have been demonstrated. The purpose of this paper is to summarize the research literature on what is known scientifically about the diagnosis and genetic basis of MH.

[In-vivo diagnosis of malignant hyperthermia susceptibility: a microdialysis study]

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.

An in-vivo metabolic test for detecting malignant hyperthermia susceptibility in humans: a pilot study

INTRODUCTION

In vitro contracture testing to diagnose malignant hyperthermia (MH) susceptibility requires a muscle biopsy, which may be associated with severe side effects for the patient. After investigation of several different protocols, we present a less invasive metabolic test that involves IM injection of caffeine and halothane, and subsequent measurement of interstitial lactate to differentiate between MH susceptible (MHS) and MH non-susceptible (MHN) individuals.

METHODS

Two microdialysis probes with attached microtubing for trigger injection were inserted into the lateral vastus muscle of eight previously diagnosed MHS patients (representing three genetic variants Gly2434Arg, Thr2206Met, and Arg614Cys), seven MHN patients, and seven control individuals. After equilibration and lactate baseline recording, a single bolus of 200 muL caffeine 80 mM and a suspension of 200 muL halothane 4%V/V in soy bean oil (triggers) were injected locally. Lactate was measured spectrophotometrically. Data are presented as medians and interquartile ranges.

RESULTS

Although baseline lactate values were similar in the investigated groups before trigger injection, caffeine increased local lactate in MHS patients significantly more (2.0 [1.8-2.6] mM) than in MHN (0.8 [0.6-1.1] mM) or in control individuals (0.8 [0.6-0.8 mM]). Similarly, halothane lead to a significant lactate increase in MHS compared to MHN and control individuals (8.6 [3.7-8.9] mM vs 0.9 [0.5-1.1] mM and 1.7 [0.9-2.3] mM, respectively). However, a relevant increase of lactate was observed in one MHN and in two control individuals. Systemic hemodynamic and metabolic variables did not differ between the investigated groups.

DISCUSSION

Metabolic monitoring of IM lactate after local caffeine and halothane injection may allow less invasive testing to detect MH susceptibility, without systemic side effects.

Effects of ryanodine on skeletal muscle lactate and pyruvate in malignant hyperthermia-susceptible and normal swine as assessed by microdialysis

BACKGROUND

The caffeine/halothane contracture test in North America and the in vitro contracture test in Europe are currently the only validated bioassays for diagnosing malignant hyperthermia susceptibility and phenotyping families. Both tests are invasive requiring surgical muscle biopsy. Here, we report first use of the selective ryanodine receptor type I agonist ryanodine in a percutaneous microdialysis protocol designed to test whether microdialysis-induced local metabolic responses of skeletal muscle due to ryanodine receptor activation can differentiate between malignant hyperthermia-sensitive and normal pigs.

METHODS

Six microdialysis catheters were implanted percutaneously into the adductor muscles of the right and left thighs of malignant hyperthermia-susceptible (n = 9) and normal (n = 8) anaesthetized (ketamine/propofol) and mechanically ventilated swine. Systemic blood gases, haemodynamic parameters and creatine kinase levels were measured before, during and after microdialysis perfusion of ryanodine. After a post-implantation equilibration period of 30 min, one catheter perfused (2 micro min-1) with 0.9% NaCl (control) and was compared with the remaining five catheters perfused with increasing concentrations of ryanodine (0.2-100 micromol). Lactate and pyruvate levels were measured enzymatically.

RESULTS

Continuous perfusion with ryanodine revealed dose-dependent sigmoidal increases in the dialysate lactate and lactate-pyruvate ratio parameters; these effects were greatly augmented in malignant hyperthermia-susceptible pigs compared to normal pigs (two- to threefold): estimated EC50 greatly decreased (>19-fold) while the maximum effect increased (>twofold) in the malignant hyperthermia-susceptible group.

CONCLUSION

The in vivo percutaneous microdialysis protocol for skeletal muscle, using ryanodine as the ryanodine receptor type I agonist and dialysed lactate-pyruvate parameters as metabolic index, can reproducibly differentiate between malignant hyperthermia-susceptible and normal swine.

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.

Elevated resting [Ca2+]iin myotubes expressing malignant hyperthermia RyR1 cDNAs is partially restored by modulation of passive calcium leak from the SR

Malignant hyperthermia (MH) is a pharmacogenetic disorder of skeletal muscle triggered in susceptible individuals by inhalation anesthetics and depolarizing skeletal muscle relaxants. This syndrome has been linked to a missense mutation in the type 1 ryanodine receptor (RyR1) in more than 50% of cases studied to date. Using double-barreled Ca2+microelectrodes in myotubes expressing wild-type RyR1 (WTRyR1) or RyR1 with one of four common MH mutations (MHRyR1), we measured resting intracellular Ca2+concentration ([Ca2+]i). Changes in resting [Ca2+]iproduced by several drugs known to modulate the RyR1 channel complex were investigated. We found that myotubes expressing any of theMHRyR1s had a 2.0- to 3.7-fold higher resting [Ca2+]ithan those expressingWTRyR1. Exposure of myotubes expressingMHRyR1s to ryanodine (500 μM) or (2,6-dichloro-4-aminophenyl)isopropylamine (FLA 365; 20 μM) had no effects on their resting [Ca2+]i. However, when myotubes were exposed to bastadin 5 alone or to a combination of ryanodine and bastadin 5, the resting [Ca2+]iwas significantly reduced ( P < 0.01). Interestingly, the percent decrease in resting [Ca2+]iin myotubes expressingMHRyR1s was significantly greater than that forWTRyR1. From these data, we propose that the high resting myoplasmic [Ca2+]iinMHRyR1 expressing myotubes is due in part to a related structural conformation ofMHRyR1s that favors “passive” calcium leak from the sarcoplasmic reticulum.