A 2-year-old female with a history of failure to thrive, hypotonia, and seizures is scheduled for a muscle biopsy for suspected mitochondrial disease. Her serum chemistries, creatine kinase (CK), and lactate level are normal. There is no family history of myopathy or adverse reactions to anesthesia.
Hypotonic patients should be carefully evaluated for respiratory insufficiency, cardiomyopathy, conduction defects, and difficulty swallowing. They may be at increased risk of aspiration, airway complications, and difficult intubation. Echocardiogram, electrocardiogram, chest x-ray, and serum chemistries are often evaluated preoperatively.
Anesthetizing the child with hypotonia of unknown etiology is problematic due to the unknown risk of malignant hyperthermia (MH), anesthesia-induced rhabdomyolysis (AIR), and lactic acidosis. Patients at higher risk for each complication are listed here:
MH: RYR1 mutations (King-Denborough syndrome, central core disease, mini-multicore disease with RYR1)
AIR: Duchenne’s and Becker’s muscular dystrophy
Lactic acidosis: Mitochondrial myopathy
Although the causes of hypotonia are diverse, and most are due to a central cause rather than to myopathy, clues to one of the previously named diagnoses should be actively sought by history and consultation with the primary pediatrician, neurologist, and geneticist. A positive family history of myopathy and elevated CK may point to muscular dystrophy or myopathy with RYR1 mutation. In these patients, volatile anesthetics should be avoided. Multiple organ involvement, especially of the central nervous system, and metabolic disturbances such as hypoglycemia and elevated lactate may point to a mitochondrial disorder.
Mitochondrial diseases are genotypically and phenotypically diverse and usually affect organs of high energy utilization (brain, skeletal muscles, kidneys, and liver). Common lab abnormalities include elevated pre- and postprandial lactate and hypoglycemia. MRI can show lytic lesions in the basal ganglia and thalamus. These patients are at risk of metabolic decompensation, including lactic acidosis and encephalopathy with preoperative fasting, perioperative stress, and pain.
Avoid prolonged fasting. IV fluids should contain dextrose.
Lactated Ringer’s solution should be avoided. Conversion of lactate to bicarbonate (a process that requires oxidative phosphorylation) may be impaired in patients with mitochondrial myopathy.
Premedication is helpful in decreasing stress if an awake IV or IV placement with 50% nitrous oxide is planned. The patient should be carefully monitored for respiratory depression.
Volatile anesthetics are not contraindicated in patients with mitochondrial myopathy, although some patients may be more sensitive to them. A mask induction with nitrous oxide and sevoflurane can be used.
Other commonly used agents for induction and maintenance include dexmedetomidine, ketamine, remifentanil, and midazolam.
As the muscle biopsy typically takes 30 minutes or less, the airway may not need to be instrumented. Mask, laryngeal mask airway, or intubation may be chosen depending on the patient’s respiratory status and risk for aspiration.
Careful padding of pressure points and patient positioning are essential, as a subclinical neuropathy may be present.
Monitor temperature closely and ...
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