Chapter 177. The Hypotonic Child

Patients with undiagnosed neuromuscular disorder and hypotonia frequently present for a muscle biopsy. Most patients present because they do not carry a diagnosis yet. Hence, there is always uncertainty about the underlying pathophysiology. The toddler with an undiagnosed hypotonia could have a mitochondrial myopathy or a muscular dystrophy, which would require a different anesthetic management.

Review of the patient’s extensive workup is essential. The neurologist’s note could be helpful. Review lactate levels, cardiac workup, and family history. Look for signs and symptoms of a cardiomyopathy and pulmonary aspiration.

Muscular dystrophy:

• Succinylcholine is contraindicated: risk of hyperkalemia and MH
• Avoid volatile anesthetics because of concerns for MH (only Evans myopathy, King syndrome, and central core disease are truly associated with MH, but in doubt, better to avoid any triggering agents)

Mitochondrial myopathy:

• Avoid propofol. (The long-chain fatty acids interfere with fatty acid oxidation and the mitochondrial respiratory chain. A clinical picture similar to propofol infusion syndrome may result.)

If the patient does not clearly fall in one of the above categories, a trigger-free, propofol-free technique should be considered:

• Midazolam 0.5–0.7 mg/kg po + N2O + remifentanil 0.1–0.3 μg/kg/min
• Mask airway
• Supplemented with iv midazolam or ketamine boluses
• Use NS; avoid LR, since patients may have lactic acidosis. Avoid hypoglycemia
• Consider a lateral femoral cutaneous nerve block

Most patients can be treated as outpatients. Acetaminophen is usually sufficient to control postoperative pain. Patients who are on noninvasive ventilation support at home should continue this support immediately postoperatively in the ICU or PACU.

In cases where an additional skin biopsy is needed, avoid infiltration with local anesthetic that will destroy the sample.