Gregory C. Allen

Does forehead liquid crystal temperature accurately reflect "core" temperature?

Liquid crystal thermometry (LCT) is a non-invasive alternative to temperature monitoring. We evaluated the ability of forehead LCT, rectal temperature, and axillary skin temperature to trend distal oesophageal temperature during rapid warming on cardiopulmonary bypass. In 24 patients undergoing open heart surgery, temperatures were measured during the rapid warming phase on bypass (12–35 min). Scattergrams of temperature vs time for the four temperature sites each contained 150 data points. Polynomial regression analysis revealed that LCT, but not axillary or rectal temperatures, correlated with oesophageal temperature. We conclude that forehead LCT may be useful to monitor temperature trends and to detect rapid elevations in body temperature when more invasive temperature monitoring is inappropriate or unavailable.RésuméLa thermométrie à crystal liquide (LCT) est une alternative non-invasive pour surveiller la température corporelle. On a évalué durant la phase de rechauffement rapide lors d’une circulation extracorporelle, la capacité de la LCT mesurée au front, la température rectale, et la température cutanée axillaire, les comparant à la température œsophagienne distale. Chez 24 patients subissant une chirurgie cardiaque, les températures furent mesurées lors du réchauffement rapide par la CEC (12–35 minutes). Les courbes de dispersion de la température versus le temps pour les quatre sites de mesure de la température contenaient chacune 150 points de mesure. L’analyse de régression polynomiale a révélé que la LCT, mais non la température axillaire ou rectale, montrait une corrélation avec la température œsophagienne. On conclut que la mesure de la LCT au front peut être utile afin de mesurer la température et détecter une élévation rapide de la température corporelle quand d’autres moyens invasifs pour mesurer la température sont inappropriés ou non-disponibles.

Caffeine and halothane contracture testing in swine using the recommendations of the North American Malignant Hyperthermia Group.

Caffeine and halothane contracture testing is widely used to detect malignant hyperthermia (MH) susceptibility. The accuracy and reliability of the 3% halothane test and the incremental caffeine test, as recommended by the North American MH Group, were assessed in 11 swine (five MHS, six control). Nine swine were tested twice, 4-6 weeks apart. Accuracy of the in vitro diagnosis was also assessed by in vivo anesthetic challenge. Of all muscle bundles from MH-susceptible swine, 65% reacted positively to 3% halothane and 70% to 2 mM caffeine. Only 35% had a positive caffeine-specific concentration, and 25% developed an increase in baseline tension greater than or equal to 7% at 2 mM caffeine. However, when only the most positive response to 3% halothane or to 2 mM caffeine was used (a minimum of three fresh muscle strips is recommended), these two tests were highly sensitive and specific. In control swine one of 30 muscle bundles reacted positively to 3% halothane. A positive caffeine-specific concentration developed in one of 25 control muscle bundles exposed to caffeine. The variability in the results of these tests mandated that at least three muscle bundles be used for each test. Nonviable muscle bundles could not be relied upon to provide accurate results. In this porcine model, MH susceptibility could be detected by performing the Caffeine Halothane Contracture Test (CHCT) according to the guidelines of the North American MH Group. However, only the 3% halothane test and the response to 2 mM caffeine produced adequate diagnostic results in this breed of swine.

Phaeochromocytoma presenting as acute malignant hyperthermia — a diagnostic challenge

We report a case of acute hypermetabolism following the induction of general anaesthesia in an 11-yr-old boy. This episode was diagnosed and managed as an acute malignant hyperthermia crisis. However, severe hypertension during the episode led to the discovery of an unsuspected phaeochromocy-toma. A hypermetabolic state during anaesthesia has several aetiologies, but correct diagnosis during the acute episode may be difficult.RésuméOn rapporte le cas d’une crise augue d’ hypermétabolisme après l’induction de l’anesthesie générate chez un enfant de II ans. Cet épisode fut dianostiqué et traité comme une crise d’hyper-thermie maligne. Cependant l’hypertension sévère durant l’épisode a amené la découverte d’un phéochromocytome non diagnostiqué. Un état hypermétabolique durant l’anesthesie a plusieurs etiologies mais le diagnostic exact durant l’episode aigu peut etre difficile.

Malignant hyperthermia susceptibility in adult patients with masseter muscle rigidity.

We sought to determine the incidence of malignant hyperthermia (MH) susceptibility in adult patients with a previous episode of masseter muscle rigidity (MMR). The medical records and in vitro contracture test results of all patients over 15 years of age tested for MH because of previous MMR from 1985 to 1988 were reviewed. The number of children (age < 16 yr) tested for MH because of previous MMR was also determined for the same four-year period, for comparison of coincidence rates. Six of 24 adult patients (25 per cent) were proved MH-susceptible by in vitro contracture testing. No clinical sign associated with the episode of MMR was predictive of MH-susceptibility. Two of six MH-susceptible patients developed acute MH following MMR. In the same four-year period, 75 children were tested for MH-susceptibility because of previous MMR; 44 (59 per cent) had a positive in vitro contracture test. We conclude that the coincidence of MMR and MH-susceptibility is lower in adults than children. Episodes of acute MH do occur after MMR, but the onset of MH may be delayed. Conservative management of MMR in adult patients is recommended.RésuméOn a essayé de determiner l’incidence de susceptibilité à l’hyperthermie maligne (MH) chez des patients adultes ayant eu au préalable un épisode de rigidité musculaire au massetér (MMR). Les dossiers et les tests de contraction in vitro de tous les patients âgés de 15 ans et plus testés pour MH à cause a” un MMR préalable de 1985 à 1989 ont été revus. Le nombre d’enfants (age < 16 ans) testes pour MH à cause d’un MMR préalable a aussi été déterminé pour la même période afin de comparer les fréquences. Six des 24 patients adultes (25 pour cent) ont été prouvés comme étant susceptibles de développer du MH par des tests de contracture in vitro. Aucun signe clinique associé avec l’épisode de MMR pouvait prédire la susceptibilité au MH. Deux des six patients susceptibles au MH ont développé un syndrome d’ hyperthermie maligne aigu après un épisode de MMR. Pour la même période de quatre ans, 75 enfants ont été testés pour la susceptibilité au MH à cause d’un MMR préalable; 44 (59 pour cent) avaient un test de contracture in vitro positif. On conclut que la coïncidence de MMR et de susceptibilité au MH est plus basse chez les adultes que chez les enfants. Les épisodes d’hyperthermie maligne aiguë surviennent après MMR mais le début du MH peut être retardé. Une conduite conservative de patient adulte ayant présenté du MMR est recommandée.

Diagnosis of malignant hyperthermia in infants.

We read with interest the clinical report by Wilhoit et al. (1) describing a 7-wk-old male infant who developed acute rhabdomyolysis on exposure to halothane and succinylcholine. Subsequent muscle histopathology was consistent with Duchenne’s muscular dystrophy (DMD). There are several points here that deserve comment. First, based on the observed elevation of creatine kinase (CK)-MB isoenzymes in their patient, the authors discussed the possibility of myocardial damage secondary to DMD or malignant hyperthermia (MH). In fact, CK-MB elevation is commonly seen in DMD and can be traced to skeletal muscle in origin (2,3). This would help to explain why the infant had no cardiovascular instability and a normal echocardiogram. The authors question the effect of the relatively large dose of succinylcholine in terms of muscle membrane depolarization triggering MH. A recent study by Iaizzo et al. (4) showed that halothane-induced contractures in MHsusceptible porcine muscle are not associated with membrane depolarization. This suggests that membrane depolarization is not necessary for MH triggering. In vitro contracture testing would not be indicated in this child for two reasons. First, the amount of muscle required would leave a visible defect in the muscle belly. Second, control data from infants are lacking for comparison (5), making it difficult to interpret the results of the test. Generally, children under 4 yr of age or 20 kg body weight are not considered eligible for MH muscle biopsy. The relationship between the genetic inheritance of MH and DMD is not well understood (6) . Whereas DMD is an X-linked disorder (3), MH usually follows an autosomal dominant pattern (7). Although DMD patients may develop anesthetic-induced rhabdomyolysis, this may not be true of their close relatives. For this reason we recommend that the parents of such DMD patients be tested for MH. It is possible that the parents and unaffected siblings of such DMD patients are not at increased risk for MH. Obviously, this would be of importance to such families. Finally, in children who have had an adverse anesthetic reaction that may be due to a neuromuscular disease, the Muscular Dystrophy Association (MDA) may be able to provide financial assistance to some families. The MDA will cover MH testing in selected cases, provided that other tests, e.g., histopathology, are also performed. Several children with MH or other myopathies have been tested in our laboratory with the support of the MDA.

IMPORTANCE OF FASTING IN THE LYMPHOCYTE CALCIUM TEST FOR MALIGNANT HYPERTHERMIA

Anaesthetic‐induced increases in cytoplasmic free Ca2+ have been reported to be greater in lymphocytes from malignant hyperthermia (MH) susceptible patients than in those from controls, suggesting that this may be the basis for a less invasive test for MH susceptibility. In the present study the cytoplasmic Ca2+ concentrations of lymphocytes were monitored with indo‐1 in 14 control subjects (nine fasted and five nonfasted) and five fasted MH susceptible and three fasted nonsusceptible patients, diagnosed by the halothane and caffeine contracture tests. No relationship was observed between MH susceptibility and Ca2+ concentrations in lymphocytes in the absence or presence of halothane. There was, however, a relationship in control subjects between fasting and the response of lymphocytes to halothane, with the halothane‐induced Ca2+ increase being considerably larger in nonfasted subjects.