Canadian Journal of Anesthesia, Vol 27, 1-11, Copyright © 1980 by Canadian Anesthesiologists' Society

Effect of Temperature, Time and Fascicle Size on the Caffeine Contracture Test

¹ Department of Anaesthesia, University of Toronto; Department of Pharmacology, University of Toronto; Toronto General Hospital, Toronto, Ontario, Canada
² Department of Pharmacology, University of Toronto; Department of Preventive Medicine and Biostatistics University of Toronto Toronto, Ontario, Canada
³ Department of Anaesthesia

The caffeine contracture test is the most commonly used method of diagnosing malignant hyperthermia. We have examined some factors which may influence the results of this test. These have included the temperature of the bathing solution, the size of the muscle fascicles, and the combined effect of the passage of time and prior equilibration with caffeine or with caffeine plus halothane.

For both malignant hyperthermic susceptible (MHS) and normal fascicles, caffeine contractures were greater at 37° C than at 22° C, while halothane and caffeine plus halothane contractures were similar at 37° C and at 22° C. Good differentiation between the normal and the MHS fascicles were observed at both temperatures although the discrimination was slightly, although not always significantly, better at 22° C.

The weight, length or diameter of the fascicles had little or no effect on the height of the caffeine or the caffeine plus halothane contractures.

We compared caffeine plus halothane contractures exhibited by newly prepared muscle fascicles with caffeine plus halothane contractures manifested by fascicles which had already been equilibrated with either caffeine alone or with caffeine and halothane for at least one hour. Differences in contracture heights among the techniques were small and often not significant, particularly at 37° C. The greatest discrimination between the MHS and the normal muscle fascicles was provided by determining the caffeine plus halothane contracture curves at 22° C, using muscle fascicles which had previously been equilibrated with incremental doses of caffeine in the absence of halothane. Slightly less accurate but still reasonably satisfactory results were also obtained at 37° C using muscle strips which were either freshly prepared or which had prior exposure to caffeine or to caffeine in combination with halothane and, at 22° C, using either newly prepared muscle or muscle which had already been equilibrated with caffeine plus halothane.

The widest differentiation between the MHS and the normal muscle was given by the caffeine plus halothane contractures and the least by the halothane contractures. MHS patients whose muscle fascicles exhibited greater than normal caffeine plus halothane contractures but normal caffeine contractures and normal halothane contractures had had the most mild clinical reactions. On the other hand MHS patients whose muscle fascicles demonstrated halothane contractures, caffeine contractures and caffeine plus halothane contractures which were all greater than normal had had the most severe reactions.

It is concluded, therefore, that if the amount of muscle available is very small, a satisfactory caffeine contracture test can still be performed by doing the various parts of the test sequentially on the same fascicle. If the time available for performing the test is limited, then the several parts of the test should rather be performed simultaneously on separate muscle fascicles.