Safety of general anesthesia in patients previously tested negative for malignant hyperthermia susceptibility

Malignant Hyperthermia Susceptibility and Related Diseases

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

Administration of Anaesthetic Triggering Agents to Patients Tested Malignant Hyperthermia Normal and Their Relatives in New Zealand: An Update

Testing for malignant hyperthermia in New Zealand involves two tests—in vitro contracture testing of excised lateral quadriceps muscle and DNA analysis. In vitro contracture testing is regarded as the gold standard in malignant hyperthermia diagnosis but several publications have questioned the reliability of a normal result. Analysis of 479 anaesthetic records in 280 patients or their descendants throughout New Zealand who had tested negative for malignant hyperthermia, demonstrated there was no evidence of malignant hyperthermia episodes in this group who had been administered anaesthetic triggering agents. A wide range of anaesthetics were used over the study period. Analysis of each anaesthetic record was undertaken using the malignant hyperthermia grading scale which determines the likelihood that an anaesthetic event represents a malignant hyperthermia episode. Confirmation of the negative results was further supported by normal DNA analysis of patients in 48% of anaesthetics. There are advantages to using inhalational agents in certain situations and although demonstrating a zero risk of a malignant hyperthermia episode is not statistically possible, evidence in this large series suggests that the risk of an episode in these patients is extremely low and may be negligible. We suggest that anaesthetic triggering agents can be used safely in patients with normal in vitro contracture tests, and in their descendants.

Safety of exposure of malignant hyperthermia non-susceptible patients and their relatives to anaesthetic triggering agents

As the reliability of malignant hyperthermia normal in vitro contracture test results has been questioned, this study set out to determine the reliability of malignant hyperthermia normal results in New Zealand. Three hundred and twenty-nine anaesthetics were administered to malignant hyperthermia normal patients, identified through the Palmerston North Hospital malignant hyperthermia database. Anaesthetic records were retrieved and scrutinised for a malignant hyperthermia reaction using the Malignant Hyperthermia Clinical Grading Scale. Patients were exposed to one or more of eight triggering agents and multiple anaesthetic agents were administered in 41% of cases. Six variables were analysed, and although a minority of variables were abnormal in a small number of patients, none of the findings supported a malignant hyperthermia reaction. While the analysis was limited by the adequacy of the anaesthesia records, it was supported by negative DNA analysis in 55% of patients. This study supports several previous studies in demonstrating that patients in New Zealand tested non-susceptible to malignant hyperthermia can safely be given triggering agents.

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.

Follow-up of patients tested for malignant hyperthermia susceptibility

BACKGROUND AND OBJECTIVE

Malignant hyperthermia is an inherited disorder of skeletal muscle characterized by muscle contracture and hypermetabolic crisis following exposure to halogenated anaesthetics and depolarizing muscle relaxants. We planned this follow-up to get more information about the safety of non-triggering anaesthesia in susceptible patients; the safety of the use of trigger agents in non-susceptible patients and any minor sequelae following the biopsy.

METHODS

A questionnaire was sent to 244 patients tested for susceptibility between 1998 and 2004 enquiring about sequelae from the biopsy, subsequent experience with anaesthesia and difficulties encountered because of the investigation.

RESULTS

Replies were received from 129 patients. Thirty-four complained about sequelae from the biopsy: 10 reported headache and nausea; 16 experienced pain and a lack of strength in the biopsed leg and 8 found the scar less than satisfactory. Ten patients found it difficult to find a diagnostic centre. Eighteen reported problems and/or delay when they had needed a subsequent anaesthetic. Fourteen patients found the anaesthesiologist reluctant to anaesthetize them and four experienced a delay. Forty-three patients received anaesthesia since their biopsy. Complete medical records were available for 24 anaesthetic exposures in 23 patients. No documented perioperative complications occurred. Only three non-susceptible patients received one trigger agent.

CONCLUSIONS

It is safe to use trigger-free anaesthesia in susceptible patients. The difficulties encountered by patients to be anaesthetized and the management of the majority of non-susceptible patients during general anaesthesia show the need of more accurate educational programmes and methods for promoting patient-centred care.

Malignant hyperthermia and myotonic disorders

Advances in physiology and molecular genetics have promoted greater understanding of the various clinical manifestations of muscle disorders. For example, myotonia or profound weakness may be observed in sodium channel disease (e.g., paramyotonia congenita or hyperkalemic periodic paralysis), depending on the specific channel defect or with slight changes in membrane potential. Observed effects of anesthetic techniques have been essential to elucidating the primary muscular nature of myotonia. Commonly used anesthetic medications have potentially lethal (e.g., MH) or serious (e.g., myotonic dystrophy) adverse effects. Conversely, lidocaine or propofol may have therapeutic benefit for patients with skeletal muscle sodium channel disorders. Additional investigation is required to improve our understanding of how age, gender, or other factors determine the phenotypic expression of malignant hyperthermia. Future research holds the promise for more accurate pre-anesthetic identification of persons with heritable myopathies, especially those who are asymptomatic. Enhanced awareness of multiple organ system involvement in myotonic dystrophy is essential for planning perioperative care. Patients with periodic paralysis require that we know factors that incite or inhibit the development of their attacks. Advances in bench research and detailed clinical studies will further improve our ability to provide optimal care for patients with muscle disorders.

Comparison between the European and North American protocols for diagnosis of malignant hyperthermia susceptibility in humans

We compared the diagnostic outcome of in vitro contracture tests for diagnosis of malignant hyperthermia susceptibility performed according to the European Malignant Hyperthermia Group protocol and the North American Malignant Hyperthermia Group protocol. The aim of the study was to compare the two major diagnostic tests of malignant hyperthermia susceptibility to have basic data for a common worldwide protocol. We evaluated 156 patients and 17 control individuals. The accordance in diagnostic outcome was 87%. The diverging outcomes between the two protocols were found in a group of patients reacting in few muscle strips and close to the cutoff limits. A 100% accordance in diagnostic outcome was found in individuals with contractures in at least five of six tested muscle strips. In both protocols, contractures close to the cutoff limits in a few muscle strips in scientific studies should be considered as unknown results.

IMPLICATIONS

We compared the two major protocols for investigating malignant hyperthermia susceptibility. There was 87% accordance in diagnostic outcome. The diverging outcomes were seen in individuals with less reproducible test results near the cutoff limits. In scientific studies, such results should be considered as unknown.

Malignant hyperthermia

Malignant hyperthermia is a rare autosomal dominant trait that predisposes affected individuals to great danger when exposed to certain anaesthetic triggering agents (such as potent volatile anaesthetics and succinylcholine). A sudden hypermetabolic reaction in skeletal muscle leading to hyperthermia and massive rhabdomyolysis can occur. The ultimate treatment is dantrolene sodium a nonspecific muscle relaxant. Certain precautions should be taken before anaesthesia of patients known to be susceptible to malignant hyperthermia. These include the prohibition of the use of triggering agents, monitoring of central body temperature and expired CO2, and immediate availability of dantrolene. In addition, careful cleansing of the anaesthesia machine of vapours of halogenated agents is recommended. If these measures are taken, the chances of an MH episode are greatly reduced. When malignant hyperthermia-does occur in the operating room, prompt recognition and treatment usually prevent a potentially fatal outcome. The most reliable test to establish susceptibility to malignant hyperthermia is currently the in vitro caffeine-halothane contracture test. It is hoped that in the future a genetic test will be available.

In vitro contracture test for diagnosis of malignant hyperthermia following the protocol of the European MH Group: results of testing patients surviving fulminant MH and unrelated low-risk subjects. The European Malignant Hyperthermia Group

BACKGROUND

Determination of sensitivity and specificity of the in vitro contracture test (IVCT) for malignant hyperthermia (MH) susceptibility using the European MH Group (EMHG) protocol has been performed in some laboratories but only on a small sample from the combined EMHG. Thus, the purpose of the present study was to determine combined EMHG sensitivity and specificity of the test.

METHODS

Results of IVCT of patients with previous fulminant MH and normal, low-risk subjects (controls) were collected from 22 centres of the EMHG. IVCT was performed according to the EMHG protocol. Patients were included in the study if the clinical crisis had a score of at least 50 points with the Clinical Grading Scale. Low-risk subjects were included provided they did not belong to a family with known MH susceptibility, they had not developed any signs of MH at previous anaesthetics, and they did not suffer from any neuromuscular disease. For inclusion of both MH patients and low-risk subjects, at least 1 muscle bundle in the IVCT should have twitches of 10 mN (1 g) or more. For evaluation of individual tests, only muscle bundles with twitch heights of 10 mN (1 g) or more were used.

RESULTS

A total of 1502 probands had undergone IVCT because of a previous anaesthesia with symptoms and signs suggestive of MH. Of these, 119 had clinical scores of 50 and above. From these 119 MH-suspected patients and from 202 low-risk subjects, IVCT data were collected. Subsequently, 14 MH-suspected patients were excluded from further analysis for the following reasons: In 3 patients, the suspected MH episode could be fully explained by diseases other than MH; in 11 MHS patients, IVCT was incomplete (n = 1), data were lost (n = 3), or none of the muscle bundles fulfilled twitch criteria (n = 7). Of the remaining 105 MH-suspected patients, 89 were MHS, 10 MHEh, 5 MHEc, and one MHN. Thus, we observed a diagnostic sensitivity of the IVCT of 99.0% if the MHE group is considered susceptible (95% confidence interval 94.8-100.0%). Of the 202 low-risk subjects, 3 were MHS, 5 MHEh, 5 MHEc, and 189 MHN. This gives a specificity of the IVCT of 93.6% (95% confidence interval 89.2-96.5%).

CONCLUSION

The IVCT for diagnosis of MH susceptibility in Europe has a high sensitivity and a satisfactory specificity.

How controversial are anesthetic controversies?

STUDY OBJECTIVES

To determine how controversial the management of a number of clinical scenarios that are labeled as controversial (eg, how to induce anesthesia in the "open eye-full stomach" patient) are among those practicing anesthesia.

DESIGN

Written survey.

SETTING

A national anesthesiology review course.

SUBJECTS

575 anesthesiologists attending the review course.

INTERVENTIONS

Anesthesiologists were presented 11 scenarios regarding some specific controversies in anesthetic management; each scenario also described a suggested course of management. Two questions were asked for each scenario: "Is this acceptable practice?" and "Would you do this in your own practice?" The scenarios included using succinylcholine for an "open eye-full stomach" patient, not evaluating preoperatively the cardiac status of a patient after receiving adriamycin therapy, using triggering drugs after a negative muscle biopsy for malignant hyperthermia, ordering a pregnancy test preoperatively for all females of child-bearing age, and seven others.

MEASUREMENTS AND MAIN RESULTS

For each scenario, comparisons between the number of respondents who felt a particular management was acceptable practice and the number who would do this in their own practice were made using chi-square analysis; p < or = 0.05 was considered significant. 160 (27.8%) surveys were returned. In ten scenarios, there was 70% or less agreement about whether a technique was acceptable. In six scenarios, there was a significant difference between the number of respondents who felt a suggested management was acceptable practice and the number who would use it in their own practice.

CONCLUSIONS

This survey of anesthesiologists regarding these controversial clinical scenarios showed that (a) most scenarios were in fact controversial amongst those in practice, and (b) there were disparities between whether a technique is believed to be acceptable practice and whether it would be used in one's own practice.

Diagnosis of malignant hyperthermia: a comparison of the in vitro contracture test with the molecular genetic diagnosis in a large pedigree

Malignant hyperthermia (MH) is an inherited skeletal muscle disorder and is one of the major causes of death resulting from anaesthesia. MH is currently diagnosed by the in vitro contracture test performed on a muscle biopsy. Genetic linkage analysis on an Irish MH pedigree showed that when the thresholds for the standardised European protocol for MHS diagnosis was applied, linkage between the MHS phenotype and the RYR1 locus was excluded. When we raised the threshold values for assignment of MHS status and assumed MHN diagnosis in subjects where this threshold was not attained, tight linkage between MHS and RYR1 markers was observed, suggesting that MHS is linked to the RYR1 locus in this pedigree. Confirmation of these results was borne out by the fact that all of the MHS patients in the pedigree exceeding the raised threshold carried the known MHS Gly341Arg RYR1 mutation. The results obtained could be explained (1) by false positive diagnosis of MHS in the recombinant subjects, (2) by the presence of a mutation in a predisposing gene other than RYR1, or (3) by the presence of mild subclinical myopathies. The implications of these results for heterogeneity studies is discussed.

Evaluation of anaesthesias in malignant hyperthermia negative patients

In vitro contracture test is still the most reliable method for diagnosing malignant hyperthermia susceptibility. In order to investigate the reliability of Malignant Hyperthermia Negative (MHN) results, a questionnaire was sent to 237 persons of whom 133 were consecutively investigated and found to be MHN, together with 104 of their children. In 17 anaesthetics with triggering agents in 7 MHN patients and 7 children of MHN patients, no signs of malignant hyperthermia were observed in any patient. This material is, however, too small to draw any conclusion about the reliability of MHN test results. This can only be done in a large multicentre study or a metaanalysis of several studies.

Clinical effects of intravenously administered dantrolene

OBJECTIVE

To compare side effects after intravenous administration of dantrolene sodium in subjects susceptible to and those nonsusceptible to malignant hyperthermia (MHS and MHN, respectively).

DESIGN

We studied two groups, six patients thought to be MHS and six assumed MHN subjects, and analyzed their responses to intravenously administered dantrolene.

MATERIAL AND METHODS

Dantrolene (3 mg/kg) was administered slowly into an antecubital vein, and blood samples were withdrawn from the other arm at 5 and 25 minutes after infusion. Shortly thereafter, all subjects underwent a clinical neurologic assessment, and side effects were graded subjectively by the study participants.

RESULTS

Side effects occurred in all subjects. Visual symptoms occurred more commonly in MHN than in MHS subjects. Subjective muscle weakness of the extremities, dizziness, and fatigue occurred more commonly and were more severe in MHS patients than in MHN subjects.

CONCLUSION

In patients recovering from an episode of malignant hyperthermia for which dantrolene has been administered, these side effects should be considered. Although the presence of side effects does not outweigh the usefulness of this drug in treating malignant hyperthermia, it may be a consideration in deciding whether to administer dantrolene prophylactically before surgical procedures in known or suspected MHS patients.

Malignant Hyperthermia

Malignant hyperthermia (MH) is a rare, genetically inherited hypermetabolic syndrome that remains dormant until triggered by exposure to certain conditions (emotional and physical stresses) or pharmacological agents (anesthetic gases and succinylcholine) in susceptible individuals. It is believed that MH is caused by a derangement in the control of intracellular calcium ions, which results in a hypermetabolic state from sustained muscle contractures. Without supportive measures and immediate treatment with the antidote, dantrolene, the mortality rate from MH can be as high as 70%. A complete personal and family medical history before surgery can show important clues that might alter the anesthetic regimen preoperatively and postoperatively (eg, the use of nontriggering agents) in MH-susceptible patients. Anesthesia personnel need to recognize the early signs of a MH crisis (eg, tachycardia, muscle stiffness, hypercapnia, and tachypnea), then monitor for other signs (eg, arrhythmias, blood pressure changes, fever, metabolic and respiratory acidosis, and mottling cyanosis), and initiate prompt treatment. Because immediate recognition and treatment of this potentially fatal hyperpyrexic episode increase a patient's chance of survival, other health care personnel (eg, nurses, pharmacists) play key roles in the emergency treatment of a MH crisis. A suspected episode of MH should be followed up with contracture testing to determine MH susceptibility (MHS). Reports of MH should be reported to the North American MH Registry.

Anterior mediastinal mass in a patient susceptible to malignant hyperthermia

We report a malignant hyperthermia-susceptible patient who required investigation for a large, symptomatic anterior mediastinal mass. Multiple attempts at tissue diagnosis under local anaesthesia were unsuccessful. Following awake fibreoptic tracheal intubation, general anaesthesia was administered using ketamine, midazolam, and nitrous oxide, maintaining spontaneous ventilation. Prophylactic dantrolene was not used, to avoid potential muscle weakness and respiratory compromise. Diagnostic mediastinotomy was performed without incident. We conclude that ketamine anaesthesia is appropriate for patients with anterior mediastinal masses, and is considered safe in malignant hyperthermia-susceptible patients.

Perioperative complications of anesthesia

An overview of several perioperative complications and their management strategies is presented. Operative hypothermia, malignant hyperthermia, bronchospasm, and side effects of spinal opioid agents are discussed. Ramifications of these complications may extend well beyond the operative period and influence patient outcome. Therefore, it is necessary that the surgeon have a fundamental understanding of the pathophysiology and modalities of treatment in the context of anesthesia and surgery.

Evaluation of 119 anaesthetics received after investigation for susceptibility to malignant hyperthermia

A questionnaire was sent to the first 371 patients investigated for MH susceptibility at the Danish MH Register, in order to assess sequelae from the muscle biopsy and possible subsequent anaesthetic complications. The purpose was to evaluate both the safety of anaesthetizing MH-susceptible (MHS) patients without the use of trigger agents, and the safety of giving trigger agents to non-susceptible (MHN) patients. Eighty-eight per cent of patients alive replied to the questionnaire. Of these, 22% complained about discomfort at the site of the biopsy, 2% had experienced problems when needing a subsequent anaesthetic, and 0.9% had had trouble when applying for life or accident insurance. The median observation period for all patients following the muscle biopsy was 5.5 years (range 27 months-11 years). During this period, 36 MHS patients had been anaesthetized 52 times (28 general and 23 regional anaesthetics, data missing in one case) without any MH-related complications. None of the patients had received prophylactic dantrolene. Three MHE patients had received non-trigger anaesthetic agents on three occasions without development of MH. Thirty-five MHN patients had been anaesthetized 64 times, and 13 of these MHN patients had received trigger agents 26 times without any signs of MH. An estimate of the probability of clinical MH developing in MHN patients subsequently anaesthetized with trigger agents was found to be 0-24.7% (95% confidence limits), whereas the probability of clinical MH developing in MHS patients anaesthetized with non-trigger agents was 0-9.7% (95% confidence limits).