Malignant hyperthermia susceptibility: anaesthetic implications and
Transcription
Malignant hyperthermia susceptibility: anaesthetic implications and
QJ /Vfec/1997; 90:13-18 Review QJM Malignant hyperthermia susceptibility: anaesthetic implications and risk stratification R. BEN ABRAHAM, A. CAHANA, R.M. KRIVOSIC-HORBER1 and A. PEREL From the Department of Anesthesiology, Sheba Medical Center, Sackler School of Medicine, Tel-Aviv University, Israel, and ^ Department d 'Anesthesie Reanimation Chirurgicale I, Hospital B, Centre Hospitalier Regional Universitaire, 59037 Lille Cedex, France Received 71 June 7996 and in revised form 22 September 7996 Summary anaesthesia machine should be carefully washed to remove traces of halogenated agents, and the use of fresh disposable anaesthetic circuits is recommended. Early diagnosis of the syndrome by alert, informed anaesthesiologists, and the immediate administration of dantrolene and other supportive measures, has reduced mortality. Patients with MH susceptibility should be instructed to alert the anaesthesiologist about their condition whenever anaesthesia is needed. Although people diagnosed with MH susceptibility should not change their lifestyle in general, military service is limited. Introduction Malignant hyperthermia susceptibility (MHS) manifests when a susceptible individual is given general anaesthesia using triggering agents, such as any of the potent volatile anaesthetics, and a depolarizing muscle relaxant (succinylcholine). Malignant hyperthermia (MH) is a syndrome of intense and abrupt striated muscle hypermetabolic reaction, resulting in hyperthermia and rhabdomyolysis. The clinical picture is often dramatic, with intense tachycardia, overproduction of CO 2 , muscular rigidity, respiratory and metabolic acidosis, hyperkalaemia and terminal haemodynamic collapse. The pathophysiology of the MH reaction involves inherited oversensitivity to triggering agents which, when used on MHS patients, can cause rapid accumulation of calcium in striated muscle myoplasm, resulting in muscle contracture followed by rhabdomyolysis and an intense heatproducing reaction. Due to its abrupt onset and violent character, an MH reaction is a medical emergency requiring immediate action from the anaesthesiologist. The main treatment is a drug called dantrolene, which is a non-specific muscle relaxant. It probably acts by blocking the release of calcium from the sarcoplasmic reticulum of skeletal muscle cells.1 Before dantrolene was used in the treatment of an MH reaction, mortality was well above 50%. 2 Improved awareness and understanding of the MH syndrome, better pre-anaesthetic identification of MHS patients, together with much better intra- and post-operative Address correspondence to Dr A. Cahana, Department of Anesthesiology, Sheba Medical Center, Sackler School of Medicine, Tel-Aviv University, Israeli Center for MH Research and Treatment, Tel-Hashomer, Israel 52621 © Oxford University Press 1997 Downloaded from by guest on December 22, 2014 Malignant hyperthermia (MH) is a rare autosomal dominant trait that predisposes individuals to great danger when exposed to certain anaesthetic triggering agents, such as potent volatile anaesthetics and succinylcholine. Sudden hypermetabolic reaction occurs in skeletal muscle, leading to hyperthermia and massive rhabdomyolysis. Precautions must be taken before the anaesthesia of M H susceptible patients. No triggering agents should be administered, central body temperature and ETCO2 should be carefully monitored, and dantrolene must be immediately available. In addition, the 14 R. Ben Abraham et al. Anaesthesia for MHS patients An individual with known or suspected MHS should not be denied general anaesthesia on this basis alone. Elective surgery should however be done only in hospitals equipped with the knowledge and expert- ise needed to treat an MH reaction.16 Although it has been recommended in the past that out-patient surgery should be avoided in these patients,17 it is now clear that out-patient surgery can be performed safely in MHS patients, provided that careful postoperative monitoring is continued for at least 4 h. In addition to routine pre-operative evaluation, baseline ECG and CPK levels are desired. Preparation in the operating room (OR) The OR must be free of anaesthetic vapours, and the anaesthesia machine should not be contaminated with volatile anaesthetics. Since keeping a dedicated anaesthesia machine reserved for MHS patients only is expensive, a protocol was suggested for preparing the anaesthesia machine in case of an MH episode.18 This can be done by removing vapourizers, flushing the machine with oxygen at a rate of 10 1/min for 5 min, replacing the fresh gas outlet hose and using a new disposable circuit. Reservoir bags, ventilator bellows and soda lime should also be changed, since all volatile anaesthetics, and especially halothane, have a high solubility in rubber, and by removing parts of the circle system a more rapid washout can be accomplished. 19 Systems incorporating a nonrebreathing valve and a Bain system are not recommended for use in these cases, unless very high flow of O 2 can be provided. 20 Dantrolene therapy First discovered by Harrison to be of value in the therapy of MH crises in pigs,25 dantrolene was later confirmed as of value in a number of human MH episodes,26 and became the drug of choice in the prevention and treatment of acute MH crises. Dantrolene is a diphenylhydantoin analogue which is poorly soluble in water. Although the mechanism of action is still unclear, dantrolene appears to inhibit release of calcium from the sarcoplasmic reticulum to the myoplasm.25 Dantrolene is manufactured in a lyophilized formulation which also contains mannitol and sodium hydroxide. Each vial contains 20 mg dantrolene, 3 g mannitol and enough sodium hydroxide to raise the pH to 9.5. The lyophilized contents of each vial must be reconstituted with 60 ml sterile water. In an acute MH episode, a supply of at least 36 vials of dantrolene should be available for immediate use, which corresponds to a maximal dosage of 10 mg/kg in a 70 kg adult.21'22 Dantrolene should be administered repeatedly in 2-3 mg/kg doses every 5-10 min, until symptoms are controlled. The issue of dantrolene prophylaxis in MHS patients is unresolved and is still under current investigation.2'23'24 In view of the very low incidence Downloaded from by guest on December 22, 2014 monitoring and early use of dantrolene, has decreased mortality from acute fulminant MH episodes to 10%. 3 ' 4 The incidence of MH reaction during anaesthesia is estimated at from 1/15 000 in children, to 1/50 000 in adults.5 The acute MH syndrome is more prevalent in young individuals, with more than 50% of cases occurring before the age of 15.6 The MHS patient is normally in apparent good health, but suffers from subclinical myopathy which can be dramatically exposed when triggering agents are used during anaesthesia. The mode of inheritance of MHS is autosomal dominant with reduced penetrance and variable expressivity, although sporadic cases and recessive autosomal hereditary patterns have occasionally been seen.8 In recent years, a mutation in chromosome 19q13.1, linked to a mutation in the ryanodine receptor gene, was discovered to be linked to MHS. 9 Nevertheless, the exact nature of the molecular defect is still unknown. The population at risk for developing MH during anaesthesia is: (i) survivors of an MH reaction, or patients with a positive caffeine halothane contracture test (CHCT); (ii) first-degree relatives of such patients or members of known MHS families with neuromuscular disorders, with increased levels of creatine kinase (CPK) in serum;10 (iii) patients who suffer from Duchenne muscular dystrophy, King-Denborough syndrome or Central Core Myopathy, 10 this last being almost certainly related to MH; 1 1 (iv) patients who have exhibited masseter muscle spasm during anaesthesia with halothane and succinylcholine; 12 (v) patients with a history of Neuroleptic Malignant Syndrome or heat stroke, although the association with MHS may appear coincidental. 10 ' 14 ' 15 The in vitro caffeine halothane contracture test has been widely used to diagnose MH susceptibility.7 This test reveals abnormally high sensitivity of muscle from affected individuals to the contracture effect of halothane and caffeine. The test is not completely accurate and high specificity is often sacrificed to achieve high sensitivity.66 DNA-based diagnostic tests are currently available for those MH susceptible families (15%) in which a mutation in the RYR1 gene has been discovered.67 These diagnostic tests are however invasive and require freshly biopsied muscle, and therefore are done only in special centres dedicated to MH diagnosis. Malignant hyperthermia (0-0.62%) of MH reaction 26 ' 27 in MHS patients who receive a trigger-free anaesthetic for minor elective surgery, the common practice is not to use dantrolene pre-operatively on a routine basis.27'28 This eliminates the muscle weakness and nausea frequently associated with dantrolene treatment.29 Similarly, even in patients with one of the myopathies, dantrolene prophylaxis is not recommended because of its tendency to cause post-operative weakness and respiratory complications. 30 ' 31 Dantrolene prophylaxis is also avoided in obstetric patients since it can cause uterine atony leading to excessive blood loss.32 It also crosses the placenta, causing neonatal weakness. If elective caesarean section is planned for MHS patients, regional anaesthesia is preferred, and if emergency caesarean section is carried out, than a rapid sequence induction using safe agents with a high dose of nondepolarizing muscle relaxants for relaxation is recommended.22 Supportive treatment Premedication The MHS patient should be the first on the OR program in order to minimize stress and anxiety, and to reduce exposure time to vapors of volatile anaesthetics.22 Pre-operative sedation with barbiturates, benzodiazepines and opiates to reduce anxiety is an important part of the anaesthetic management. Phenothiazines should be avoided because of the possible association between MH and the neuroleptic malignant syndrome (NMS).14 The use of atropine is not recommended because it can enhance sympathomimetic activity which can induce a hypermetabolic reaction.22 In addition there are reports of increased rigidity and mortality when MH reactions occur in the presence of atropine.33 Parasympatholytic drugs like atropine and glycopyrrolate, however, have been used safely in MHS patients,34 especially in children where administration of atropine offers certain advantages, such as prevention of bradycardia during induction. Some authors recommend that an i.v. infusion should be started several hours before opera- tion, to minimize the emotional stress associated with vein puncture. Expanding blood volume before induction of anaesthesia is also advisable to prevent hypotension, since the use of vasopressor agents is contraindicated in these cases.33 Induction and maintenance of anaesthesia Anaesthesia for MHS patients should be as stressfree as possible. Careful monitoring of central temperature (rectal or oesophageal) and ETCO2 is mandatory. Elevation of ETCO2 is an early sign of a possible impending reaction.35'36 Whenever suitable, local or regional anaesthesia is advisable because these techniques are reported to be safer.37 All volatile anaesthetics, including the newer agents such as desflurane and sevoflurane, must be avoided. 38 The use of depolarizing relaxants is also absolutely forbidden. Non-triggering anaesthetics All authors agree that barbiturates are non-triggering agents and suggest that they might even play a role in protection and inhibition of MH crises in humans, as it was shown in pigs.3 Similarly, benzodiazepines are also considered safe agents to be used in the anaesthesia of MHS patients.3 Etomidate was shown experimentally not to cause MH syndrome in susceptible pigs but compared to thiopental it has less protective effect.40 Several studies suggest that propofol is safe for MHS patients: it did not cause an MH episode in MHS pigs,41'42 and has been given many times to MHS patients without any reported side-effects.43 Furthermore, there are many reports on the use of propofol in patients with myopathies which may be related to MH, without untoward effects.44 Because of the rapid recovery time, propofol seems an ideal choice for short procedures in MHS patients under general anaesthesia. Ketamine use in MHS patients remains controversial. Most experts do not recommend its use because of its sympathomimetic effects. On the other hand, all opiates are considered safe non-triggering agents.46 It has been reported that diagnostic muscle biopsies are taken in England and North America under general anaesthesia using fentanyl without any adverse reactions.16 This was further reported for alfentanyl 47 and for sufentanil.48 Nitrous oxide (NO2) is considered a safe agent in MHS patients although one report mentioned the possibly of a slight triggering effect.49 However, it has been used many times in MHS patient without any problems.50 Although one report suggests that d-tubocurarine and gallamine may be unsafe in MHS patients,51 authors agree about the safety of other non- Downloaded from by guest on December 22, 2014 A set of drugs for the acute treatment of MH crises must be kept at the OR. These should include procainamide, sodium bicarbonate, furosemide, mannitol, regular insulin, 50% glucose and propranolol. Full equipment for resuscitation, insertion of arterial and central lines, bladder catheterization and a cooling machine with blankets should be prepared, as well as an ample supply of tubes, syringes and means of taking multiple arterial and venous blood samples. It is recommended that cool saline solution and ice are to hand. 15 16 R. Ben Abraham et al. Emergence and extubation Emergence and extubation should be smooth and stress-free as possible in MHS patients undergoing surgery. If residual neuromuscular block persists, or if dantrolene in doses higher than 3.5 mg/kg was given, it is recommended to continue with mechanical ventilation until full spontaneous recovery occurs.22 Episodes of hypoxia or hypercarbia should be avoided, as they can trigger an MH reaction. MH reactions have been reported to occur in the postoperative period, even if non-triggering anaesthesia was used.56 Therefore, continued supervision in the recovery room for at least 4 h, including monitoring of heart rate and temperature is recommended.57 MH consultation and risk stratification The MH reaction is fortunately rare. However, in recent years awareness of this syndrome has greatly increased, and an increased number of CHCT resulted in more patients diagnosed as MHS. Since primary prevention is an important issue in MH, it should be explained to the patient that administration of general anaesthesia to MHS subjects is safe, providing that no triggering agents are used, routine monitoring including temperature is performed, and dantrolene is available in case of an MH episode. The meaning of autosomal dominant transmission of MH should be clarified to the patient, and the anaesthesiologist should encourage patients and their families to refer to special diagnostic centres. It should also be explained that MHS does not carry increased risk for heart disease, sudden infant death syndrome (SIDS) or stress reaction after sport activity. Sport is safe provided heat stroke is prevented.64 Certain professions, such as those involving exposure to halogenated hydrocarbons and organ solvents, and constant strenuous physical activities should be avoided. 65 In view of this, military authorities are reluctant to enlist MHS individuals, especially in field positions, although it seems reasonable to allow limited-activity military service. Anaesthesiologists are advised to adopt a strict monitoring regime including temperature and ETCO2/ since with adequate monitoring an MH reaction can be detected long before serious complications have occurred. In cases of suspected MH reaction, serum potassium, CPK and myoglobin levels should be documented. The patient should then be referred to an appropriate consultation after a full explanation about the MH episode from the anaesthesiologist in charge. Patients found to be positive to MH should be provided with a bracelet noting: 'malignant hyperthermia, no potent inhalation anaesthetics or succinylcholine', and should be instructed that whenever anaesthesia is needed, the anaesthesiologist must be notified of their special sensitivity. Cognizance and a high index of suspicion among anaesthesiologists remain the cornerstones of MH management. References 1. Gronert GA. Malignant Hyperthermia. Anaesthesiology 1980; 53:395-423. 2. Britt BA. Malignant hyperthermia. Can Anaesth SocJ 1985; 32:666-78. 3. Britt BA. Dantrolene. Can Anaesth SocJ 1984; 31:61-75. 4. Harrison GG. Dantrolene-dynamics and kinetics. Br J Anaesth 1988; 60:274-86. 5. Krivosic-Horber RM, Adnet PJ. L'hyperthermie maligne anesthesique: Un syndrome dont le taux de mortalite est inacceptable. La revue du Praticien. Medecine Generate 1992; 188:50-8. 6. Strazis KP, Fox AW. Malignant hyperthermia: A review of published cases. Anaesth Analg 1993; 77:297-304. 7. Ording H. Diagnosis of susceptibility to malignant hyperthermia in man. BrJ Anesth 1988; 60:287-302. 8. Mcpherson E, Taylor CA. The genetics of malignant hyperthermia: Evidence of heterogeneity. Am) Med Genet 1982; 11:273-85. 9. Mac-Lennan DH, Duff C, Zorzato F, era/. Ryanodine receptor gene is a candidate for predisposition to malignant hyperthermia. Nature 1990; 343:559-61. 10. Brownell AKW. Malignant hyperthermia: Relationship to other diseases. Br) Anaesth 1988; 60:303-8. 11. Krivosic-Horber R, Krivosic I. Myopathie axe central (central Downloaded from by guest on December 22, 2014 depolarizing muscle relaxants (NDMR), especially pancuronium, for which a possible protective effect was demonstrated in pigs.52 Atracurium was shown to be safe in pigs53 and in humans.34 Vecuronium is a safe agent in MHS patients.54 The safety of neuromuscular block reversal for MHS patients has also been questioned. Because of unpublished reports of the occurrence of asystole following reversal with neostigmine and atropine,55 some clinicians prefer to ventilate the patient until the neuromuscular junction recovers spontaneously, although others use it without hesitation.26'34 Agents with sympathomimetic activity, especially the alpha-agonist type, should not be used since they can aggravate crises of MH experimentally.2 The use of alpha-antagonists and beta blockers for arrhythmia is not restricted.2 All medication which can augment calcium concentration in the myoplasm should be avoided. This is true of digoxin, methylxanthines and calcium salts. However, in cases of severe asthma59'60 or the urgent need to treat life-threatening hyperkalaemia, aminophylline and calcium can be administered, respectively.61 The use of calcium channel blockers is contraindicated for fear of causing acute hyperkalaemia associated with dantrolene administration. 62 ' 63 Malignant hyperthermia core disease) associee une sensibilite I'hyperthermie maligne. Presse Med 1989; 18:828-31. 12. Ellis FR, Halsall JP. Suxamethonium spasm. A differential diagnostic conundrum. BrJ Anaesth 1984; 56:381-3. 13. Oflynn RP, Shutack JG, Rosenberg H, etal. Masseter muscle rigidity and malignant hyperthermia susceptibility in pediatric patients. Anesthesiology 1994; 80:1228-33. 14. Adnet PJ, Krivosic-Horber RM, Adamantidis M, etal. The association between the neuroleptic malignant syndrome and malignant hyperthermia. Acta Anaesthesiol Scan 1989; 33:676-80. 15. Bello N, Adnet PJ, Saulnier F, et al. 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