1 Jena, Germany 2 Toronto, Canada 3 Hamburg, Germany
EditorSchmidt and colleagues1 should be congratulated for their case presentation and the patients good outcome. We appreciated the detailed discussion on Duchenne muscular dystrophy (DMD) and perioperative complications. It is striking that preoperative echocardiography may not reflect the intraoperative ability of the diseased myocardium to respond to stressa situation we are quite often confronted with in clinical scenarios.
The authors raise the question of which intraoperative monitoring should be used for detection of cardiac abnormalities and for adjusting therapy. From our point of view the patient was adequately monitored, at least at the beginning of the operation. Nevertheless, we are surprised that the high arteriovenous PCO2 difference of 15 mm Hg, 30 min after induction of anaesthesia (Fig. 2 of Case Report 1) was not mentioned in the discussion. Given a normal ventilatory situation, should this difference not be interpreted as a hallmark of early cardiac decompensation?24 Carried forward to anaesthetic practice generally, an increased arteriovenous PCO2 difference demands clarification, and should be the trigger for more invasive haemodynamic monitoring such as transoesophageal echocardiography, pulmonary artery catheterization or pulse contour analysis.
W. Schummer
C. Schummer
Jena, Germany
EditorWe read with interest the case report by Schmidt and colleagues.1 The report describes a perioperative cardiac complication in a patient with DMD. As demonstrated in this case, intraoperative complications are predominantly cardiac whereas respiratory issues and rhabdomyolysis complicate recovery. Whilst we congratulate the authors on their case report, we question the sentence early in the text that states [perioperative complications] may be related to the administration of succinylcholine or halothane, as the disease is associated with malignant hyperthermia. This is a controversial issue.
Examination of the four references used for this statement provides no definitive conclusion. Sethnas review in 19885 of the anaesthetic complications of DMD presented four cases. Two were cardiac complications and the other two were not typical of malignant hyperthermia (MH). Although a rise in temperature was noted, there was no hypercapnia or acidosis. No dantrolene was used and no confirmation with in vitro caffeine/halothane contracture testing (CHCT) was mentioned. The second reference describes 18 complications in 65 general anaesthetics.6 Only one resembled MH with signs of muscle rigidity and tachycardia (but no fever nor acid base abnormality). No dantrolene was given, and no CHCT performed. The third reference discusses the pathophysiology of hyperkalaemic arrest in response to succinylcholine and volatile anaesthetics and did not discuss any association between MH and DMD.7 The fourth reference by Kleopa and colleagues8 describes a patient with Becker muscular dystrophy (BMD), not DMD. These are similar disease entities, but different nonetheless.
We reviewed the literature for any evidence that supports an association. There is no doubt that patients with DMD can have MH.9 Takagi10 evaluated 20 cases reported as MH-like episodes in DMD and BMD patients using a MH Clinical Grade Scale. Nine were classified as very likely MH. CHCT on skinned muscle fibres from 11 DMD and BMD patients produced five MH-susceptible and three MH-equivocal results. It is possible that MH-like episodes are under-recognized in DMD patients because of the absence of sufficient muscle mass to demonstrate conventional MH responses, such as muscle rigidity or metabolic acidosis, which are the classic findings.11
However, much of the evidence supporting an association is based on case reports of individual patients, often with ambiguous presentations and not always corroborated with CHCT. There are difficulties with CHCT as the diagnostic gold standard for MH. Standardization of CHCT was not in place until 1985 and global variations continue. North American and European procedures use slightly different methods, and the Japanese procedure uses a different muscle preparation. Not surprisingly, disconcordant results between centres have been documented for the same patient.12 Sensitivity thresholds are intentionally kept high with resulting loss of specificity; there is therefore the potential to see an association that does not exist. Additionally, muscle from patients with myopathies may display abnormal CHCT results.13
The balance of opinion has shifted from an association with MH to an anaesthesia-induced rhabdomyolysis (AIR). The two processes share common clinical and biochemical characteristics, such as hyperkalaemia, metabolic acidosis, myoglobinuria and elevated creatine kinase. However, the underlying mechanism of rhabdomyolysis is different, in that the anaesthetic agents stress a muscle cell membrane that is fragile or unstable because of the progressive X-linked myopathy (short arm of the X chromosome), not the autosomal dominant MH (long arm of chromosome 19). This further increases membrane permeability, resulting in a compensatory hypermetabolic response in an attempt to re-establish membrane stability and prevent calcium ion fluxes.14
Negative CHCT has been documented in patients with confirmed DMD.14 15 CHCT on dystrophin-deficient mdx mouse muscle demonstrated that the absence of dystrophin does not predispose to MH susceptibility.16 A recent large retrospective review of 444 anaesthetics in DMD and BMD patients found 15 complications, only one of which was thought to be MH.17 This was based on beer-coloured urine and an elevated creatine kinase, which could equally have been attributable to rhabdomyolysis.
In conclusion, it may seem trivial to dismiss this association especially when the triggering agents are the same for both MH and AIR. It is, however, important to be alert to the diagnostic differential. So great is the concern over the association with MH that some have advocated pretreatment with dantrolene.18 Dantrolene, although life-saving when used appropriately, is not without side-effects including muscular weakness (particularly undesirable in a patient with DMD). More importantly, dantrolene does not treat AIR and may detract from the more appropriate management course.
J. A. Hayes
W. A. Ames
Toronto, Canada
EditorThank you for the opportunity to reply to the interesting correspondence from Schummer and colleagues, and Hayes and colleagues to our case report about a boy with DMD who developed acute heart failure during spinal surgery.
Hayes and colleagues underline the controversial discussion about DMD and MH. We want to thank them for their clarification of this issue. Nevertheless, MH should be excluded when complications develop in patients with DMD. Despite the controversy in the literature, we use a trigger free anaesthetic for patients with DMD in our institution.
Schummer and colleagues are right to point out that the high arteriovenous PCO2 difference 30 min after induction of anaesthesia could be interpreted as a hallmark of cardiac decompensation. They suggest using arteriovenous PCO2 difference as a trigger for more invasive haemodynamic monitoring. We think this is a good idea. In our patient, in the absence of haemodynamic complications 30 min after induction of anaesthesia, we primarily interpreted the PCO2 difference as attributable to ventilation problems. Moreover, the sensitivity and specificity of the arteriovenous PCO2 difference is still unclear. In this case it was 15 mm Hg, 30 min after induction of anaesthesia and 12 mm Hg during the first, and 2 mm Hg during the second hypotensive event. When the high arteriovenous PCO2 difference was detected the boy was still in the prone position and surgery was started. Starting monitoring with transoesophageal echocardiography and pulmonary artery catheterization at this point in the surgery may have proved difficult. From our point of view, a parameter is required to estimate the cardiac risk preoperatively. Further studies should investigate the role of the arteriovenous PCO2 difference.
These two letters are very helpful, but they do not contradict our conclusion that a normal preoperative echocardiogram and electrocardiogram failed to predict the development of heart failure during anaesthesia in a patient with DMD undergoing major surgery.
G. N. Schmidt
M.-A. Burmeister
F. Wappler
P. Bischoff
Hamburg, Germany
References
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