Last month I discussed the difficulty of understanding how MH susceptibility relates to heat stroke, muscle breakdown with exercise and MH without anesthesia. This is an exceedingly complex and murky topic.
However, even in the operating room with sophisticated monitoring and laboratory tests available, the diagnosis of MH during anesthesia is sometimes difficult to establish. This is so because the signs of MH do not always appear in the manner the textbooks describe. For example, although increased heart rate and increased exhaled carbon dioxide are early signs of MH, they may be signs of other problems as well. As hotline consultants we are sometimes challenged in answering the simple question, “Is this MH?” One of the reasons this is so, is probably a good one. When a clinician sees unexplained increases in heart rate and carbon dioxide levels with increasing acid content in the blood, he/she may choose to switch to a nontriggering agent or ask the surgeon to reschedule the procedure if it is elective rather than risk an overlooked case of MH that might cause the patient problems. That is appropriate in most situations.
The hotline consultant then makes the best estimate of what might have happened and suggests a course of treatment for the patient based on the best information available. In questionable cases the hotline consultant may post the case on our closed MHdiscussion list for comments by other hotline consultants. It’s amazing some time how we cannot be definitive in a diagnosis. What makes the issue more complicated is that we don’t have a diagnostic test that is easily available and appropriate for all cases. The most accurate, reliable test is the muscle biopsy contracture test. However in the US, there are only a few testing centers. In addition, many insurance companies do not recognize the test for reimbursement and the test involves a trip to the hospital and the operating room. Although the DNA test can be useful on many occasions, it should be reserved for cases where the patient or a family member has had a muscle biopsy contracture test, or the episode was almost certainly indicative of MH. Furthermore, the DNA also is expensive (about $900 for the basic test) and reimbursement for many genetic tests is often inadequate.
Let me cite a few examples of real world situations that confront the hotline expert.
A 10 week old neonate was scheduled for colon surgery. The anesthetic consisted in part of sevoflurane, one of the known MH triggers. Almost immediately following induction of anesthesia the carbon dioxide levels skyrocketed and the patient’s heart rate rose to about 200 beats per minute (very elevated). In addition acidosis was noted. It took about 20 minutes of ventilation by the anesthesiologist to get the carbon dioxide levels back to normal. Fortunately the patient suffered no ill consequences. But was this indicative of MH? Hard to know because the child may have had lung disease or the endotracheal tube may not have been seated in just the right place. The consultant felt that it was unlikely to be MH given the context of the situation. There was no rigidity, no temperature elevation, no increase in potassium levels and the increase in acid content was a respiratory one, rather than metabolic which is more characteristic of MH. All the hotline consultant could do was give his best advice after listening carefully to the clinician and asking questions which might have revealed that there was an indication suggestive of MH. Since this was a young child, muscle biopsy was not appropriate, nor was it an “almost certain” case of MH so DNA testing was not recommended.
I think however, the clinician at the other end of the phone was grateful to have an expert to discuss the case with and reassure him that he was not missing something or reacting inappropriately.
A 32 year old female underwent hand surgery under general anesthesia using a mask (actually a laryngeal mask airway device) with one of the MH triggering agents. When carbon dioxide levels went up, the patient was intubated with the aid of the paralyzing, MH trigger agent, succinylcholine. The patient experienced acidosis and elevated carbon dioxide levels and the clinician thought that the patient was experiencing asthma. The patient’s status was controlled and in about two days, the patient was found to have muscle destruction (rhabdomyolysis). This led the anesthesiologist to call the hotline to ask whether the patient should receive dantrolene. Could this have been a manifestation of MH? Perhaps, but the patient might also have some underlying metabolic problem with her muscle, particularly with acidosis and stress of surgery and asthma or may have resulted from the administration of succinylcholine itself. The hotline consultant using his best judgment thought that dantrolene was not indicated since there were no ongoing signs of MH other than muscle breakdown. Administering dantrolene would virtually label the patient as MH susceptible and effect future anesthetics for her and her family. As it turned out, this was one of those times when the hotline consultant was able to follow the patient with the help of the clinician and found out that with time the muscle breakdown resolved.
If there were a simple, straightforward, available diagnostic test for MH this patient would have been a good candidate. Unfortunately that is not the case for questionable situations such as this one.
With every such difficult case the experts learn a little more. Furthermore our hotline calls are entered into a database (without patient identifiers) for potential future studies.
Fortunately not every hotline call is so complex, sometime the diagnosis of MH is very clear cut in other situations, the presentation is clearly not indicative of MH.
MHAUS and the volunteer hotline consultants are happy to assist anesthesia providers as well as nurses, intensivists, surgeons, neurologists and other caregivers in sorting out complex issues even though the answers are not always clear cut. Our knowledge of MH however grows incrementally and even though it is not always possible to be definitive in terms of diagnosis, these difficult situations teach us that MH still happens regularly and that the diagnosis and treatment is often complex. In my opinion it underlines the need for MHAUS to continue to push the agenda of education and research related to MH.
Your comments are appreciated as well as suggestions for future blogs.