Dr. Kwetny argues that contracture testing has limited usefulness in the management of patients who might be susceptible to malignant hyperthermia (MH). As a biologic test, 98% sensitivity is commendable. Very few commonly used diagnostic screening tests approach that level of accuracy. We formulate anesthesia plans on a daily basis using tests with much poorer positive predictive value (e.g. , electrocardiogram, echocardiogram, creatinine, hematocrit).
Furthermore, contracture testing has been a useful tool to identify genetic mutations in 60–80% of MH families. Because the number of identified causative mutations in MH families has increased over the past decade we now can offer noninvasive and less expensive genetic testing to many MH families.
In addition, we disagree that a nontriggering anesthetic is 100% safe (e.g. , propofol infusion syndrome, awareness). Volatile anesthetics have real and unique benefits. We wonder whether, because of his belief that a nontriggering anesthetic is 100% safe, Dr. Kwetny provides nontriggering anesthetics to all of his patients, regardless of MH status.
What is most disturbing is the reticence not to consider the test at all and label a patient MH-susceptible based solely on clinical criteria, especially when those criteria are minimal. Permitting patients to be labeled MH-susceptible by individual clinicians who might not have the requisite expertise can subject that patient and his or her family to the hardship of finding clinicians who will care for them.
We counsel numerous patients referred for potential testing with vague personal or family history of potential MH. These are patients who have tried to obtain anesthetic care in the community and have been told that they cannot be anesthetized until they have been tested for MH. We are at a loss to explain why so many anesthesiologists are reluctant to provide nontriggering anesthetics before a biopsy procedure, especially if that is exactly what they will provide after the biopsy.
Finally, various factors influence a patient's decision to undergo contracture testing, including: size of family and pedigree, profession, fear, budget, insurance, and location of the closest laboratory. Anesthesiologists who exclusively favor or disfavor contracture testing have a quite simple paternalistic view, which may be appropriate in some locales but not others.
We echo Dr. Kwetny's call for evidence-based data on the usefulness of contracture testing—but that goal will only be accomplished when we have accumulated enough contracture testing data, which in turn requires muscle biopsy and the contracture test, the very test Dr. Kwetny so fervently wants to ignore and discard.
Dr. Giordiano and colleagues rightly point out a limitation in our presentation of causes of increased end-tidal carbon dioxide. Under normal circumstances, a faulty inspiratory valve will produce a capnogram that differs from the stylized version shown in our figure—a version that is more typically seen with malfunction of the expiratory valve.
As we mentioned in the text, and is pointed out by Giordiano et al. , a faulty inspiratory valve would lead to an increased amount of carbon dioxide in the inspired gas, although the nadir of the inspired carbon dioxide would approach or equal 0. We hasten to add, however, that under certain conditions (e.g. , low fresh gas flow and low tidal volumes), the inspired carbon dioxide might not reach 0 when an inspiratory valve malfunctions.
*University of California, Davis, Davis, California. firstname.lastname@example.org