[Evaluation of malignant hyperthermia episodes with the Clinical Grading Scale]

The Clinical Grading Scale (CGS) was introduced to predict malignant hyperthermia (MH) susceptibility in adverse anaesthetic events. Because many of the clinical symptoms that occur during MH episodes are nonspecific, the CGS was designed as a tool to estimate the qualitative likelihood of MH. The purpose of this study was to compare the results of the CGS with the established in vitro contracture test (IVCT).

92 patients with a personal history for MH were tested for MH susceptibility with the IVCT according to the protocol of the European MH Group. All patients were also evaluated with the CGS. Clinical indicators for the CGS are rigidity, muscle breakdown, respiratory acidosis, temperature increase and cardiac involvement. There are additional indicators in case of a family history for MH. For each indicator 3-15 points are added to build a raw score; this raw score corresponds to a MH rank in the CGS that describes the likelihood of MH in the suspected event. The higher the raw score rank, the higher the likelihood of MH and vice versa.

From 92 patients, 32 (35%) were diagnosed as MH-susceptible (MHS) with the IVCT, 47 (51%) were MH-normal (MHN), and 13 (14%) were MH-equivocal (MHE). One patient with MH-rank 1 (MH almost never) in the CGS was diagnosed as MHS; on the other hand no patient with MH-rank 6 (MH almost certain) in the CGS was diagnosed as MHN. However, the majority of patients (72%) were assigned to ranks 3 and 4 (MH somewhat less than likely/MH somewhat greater than likely). The qualitative likelihood of MH could therefore not be clearly estimated.

Our study shows that the MH-rank of the CGS corresponds poorly with the results of the IVCT. In any case the evaluation of an MH suspicious event depends on the availability of data of that event. It is often difficult to obtain sufficient data, especially if the event occurred a long while ago. In these cases the MH rank may underestimate the likelihood of MH susceptibility. On the other hand, overestimation is also possible because some of the scoring indicators depend on the anaesthesiologist's judgement only. At present, the use of the CGS is neither validated nor clinically feasible. The CGS cannot replace IVCT.