May 1997
Volume 61 |
Number 5
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Recent Trends
in the Clinical Presentation of MH:
Report from the MH Hotline Database |
Steven M. Karan, M.D.
Carolyn P. Greenberg, M.D.
The Malignant Hyperthermia Hotline was established in 1982 by
the Malignant Hyperthermia Association of the United States (MHAUS)
to provide immediate MH-related advice and assistance to the medical
community. Twenty-four hours a day, seven days a week, 365 days
a year, three volunteer anesthesiologists with special expertise
in MH accept calls. Recently, advancing technology and assistance
from ASA have helped the MH Hotline to establish a prospective
electronic database of calls. The database will be used to identify
trends in the presentation and treatment of MH and to develop
educational programs.
The strength of the database, however, will depend on how well
the data represent all MH cases in North America. The recent advances
in monitoring technology, availability of dantrolene, educational
emphasis on MH in training and continuing education programs on
MH issues have resulted in many cases of MH now being diagnosed
and treated without assistance from the hotline. The hotline database
currently represents only 25 percent to 33 percent of all MH cases,
according to estimates; therefore, we ask for your help and support
to report voluntarily any case in which MH is suspected to the
MH Hotline in order to gain a better understanding of this disease.
From January 1990 to December 1996, more than 4,000 calls were
received by the MH Hotline. One-third of the calls involved the
clinical management of an MH-suspicious case. The remainder of
the calls represented questions related to MH. Table
1 lists the 10 most frequently asked questions about MH. Table
2 lists the breakdown, by year, of the case management calls
through June 1996.
Case calls are classified into one of four categories by the
MH Hotline consultant taking the call. The categories include:
1) not enough information: a diagnosis of MH could not be confirmed
or refuted with the available data; 2) not MH: there is no clinical
evidence to support the diagnosis of MH; 3) isolated masseter
muscle rigidity (MMR): increased jaw tension without signs of
increased metabolism; or 4) MH: diagnosis of MH was likely.
The fourth category is further subdivided into three groups:
a) acute MH: unquestionable clinical MH episode; b) MMR to MH:
increased jaw tension that progressed to an unquestionable clinical
MH episode; and c) suspect MH: MH is likely but not certain. The
data are reviewed for accuracy and consistency by two additional
hotline consultants prior to submission for analysis.
The data indicate that the hotline is used not only to help manage
acute MH episodes, but also to rule out the diagnosis of MH (21
percent MH versus 49 percent not MH). An isolated temperature
elevation was the only clinical sign in half of the not-MH cases.
The case data also reflect that a small percentage of MH cases
are preceded with MMR. Incomplete data at the time of the event
(call) and a low response to follow-up questionnaires influence
the size of the suspect MH category (34 percent of the total MH
episodes). Likewise, rapid actions taken by clinicians during
suspicious episodes frequently reverse signs and symptoms before
a firm diagnosis can be documented by abnormal laboratory test
results. In both the total MH and not-MH groups, there was over-representation
by gender (>male) and type of surgery (>otolaryngology,
general surgery and orthopedic cases). However, the chronology
of the episode and age at presentation differed between these
groups [Table 3].
Although the number of total MH cases reported was relatively
constant on average (40 cases per year), the exposure to triggering
agents has changed. From 1990 to 1993, triggering agent exposure
was constant with 87 percent of cases exposed to potent inhaled
agents and 65 percent exposed to succinylcholine. Since 1994,
succinylcholine exposure has decreased each year: 45 percent in
1994, 30 percent in 1995 and 21 percent in 1996. However, exposure
to potent inhaled agents has remained constant at 87 percent.
This trend suggests that the frequency of MH episodes may not
be altered significantly even if succinylcholine administration
is avoided.
The number of isolated MMR cases reported also has significantly
decreased, particularly in the pediatric age group [Figure
1]. In addition, reports of cardiac arrest in children following
succinylcholine have decreased. These data suggest that practice
changes in the use of succinylcholine in children may be responsible
for the decrease in the number of isolated MMR and cardiac arrest
cases reported to the MH Hotline.
In general, a majority of cases are being diagnosed early in
the course of the episode and are responding rapidly to discontinuation
of triggering agents and early administration of dantrolene. However,
several difficult diagnostic presentations have been identified,
requiring special attention. These presentations include:
- intraoperative events in young children
- events during emergence from general anesthesia
- slowly progressing MH episodes
- MH-like events in the absence of triggering agents
Intraoperative events in young children: End-tidal carbon
dioxide (ETCO2) concentrations begin to rise one to
two hours into an otherwise uneventful anesthetic in a child under
5 years old. Despite increases in minute ventilation, ETCO2
rises to the mid 60s. Temperature, heart rate and blood pressure
are mildly to moderately elevated. Breath sounds appear to be
equal bilaterally. The response to discontinuation of triggering
anesthetic and dantrolene (5-10 mg/kg) is not impressive and the
child slowly improves over the next couple of hours. Airway obstruction,
secondary to mainstem bronchus intubation or a mucous plug in
the endotracheal tube or in the lung, occurs more frequently than
MH in this scenario. Even in light of clear bilateral breath sounds,
suctioning of the airway, irrigation of the airway with 3-5 ml
of saline or replacement of the endotracheal tube usually result
in dramatic improvement of ETCO2 concentrations and
a return to baseline minute ventilation requirements. MH should
be considered if the patient's condition does not improve following
these maneuvers.
MH on emergence: The differential diagnosis for emergence
delirium is extensive and can be difficult to distinguish from
MH. More than 50 percent of not-MH cases occur in the postoperative
period while less than 10 percent of MH cases occur during that
same time period. In many cases, the patient is treated with multiple
therapies (oxygen, controlled ventilation, re-establishment of
the airway, increasing the depth of the anesthetic, pharmacologic
reversal of anesthetic agents, dantrolene, etc.) and improves
before the cause of the episode is determined. These patients
usually exhibit tachycardia, hypertension, hypercarbia, acidosis,
temperature elevation and increased muscular tone. Halothane/caffeine
contracture testing is useful in determining the patient's susceptibility
in this setting.
Slow progression of the MH episode: All MH cases do not
progress at the same rate. Routine use of capnographic monitoring
enables clinicians to rapidly diagnose most MH episodes. However,
in cases that progress less rapidly, early intermittent increases
in minute ventilation can maintain the ETCO2 concentration
below 40 mm Hg, thereby masking an important clinical sign of
MH. In several cases, discontinuation of the potent inhaled agent
has reversed the increased minute ventilation requirement. Dantrolene
therapy is still indicated in these cases. When allowed to progress
with triggering agents, ETCO2 continues to rise despite
increases in minute ventilation, and other clinical signs of MH
become apparent. Laboratory confirmation of the diagnosis is difficult
since most values are normal and peak creatine kinase concentrations
are usually less than 3000 I.U.
MH-like events in absence of triggering agents: Events
reported in this category represent less than 2 percent of total
MH cases. Analysis of these types of cases is too complex for
the MH Hotline database format. Callers reporting these types
of cases are strongly encouraged to refer the patient and family
to an MH diagnostic center and to report the event to the North
American MH Registry using the Adverse Metabolic Reaction to Anesthetics
(AMRA) forms.
The MH Hotline has been a valuable aid to clinicians in the management
of actual or suspect cases of MH. In addition, the data have provided
an important perspective on the varied and changing presentations
of MH. The more than 30 hotline consultants who volunteer for
this endeavor deserve the thanks of anesthesiologists and their
patients for generously donating their time and expertise in helping
to reduce the morbidity and mortality from MH.
Steven M. Karan, M.D., is Assistant Professor
of Anesthesiology, Uniformed Services University of the Health
Sciences and Walter Reed Army Medical Center, Bethesda, Maryland.
E-mail the author.
Carolyn P. Greenberg, M.D., is Associate
Professor of Clinical Anesthesiology at Columbia University, New
York, New York.
E-mail the author.
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