Pediatric emergency medicine trisk 2861 2861
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such as diuretics, laxatives, and β-agonists. The laboratory assessment of
hypokalemia should include serum electrolytes, magnesium, calcium,
serum bicarbonate, renal function, and glucose. In addition to urinalysis and
urine pH, urine electrolytes and osmolality should be submitted to assess
the renal response to hypokalemia.
Clinical manifestations. The clinical manifestations of hypokalemia are
generally proportionate to the severity and duration of the disorder and
result from hyperpolarization of the cell membrane. Unless the serum
potassium falls rapidly or is associated with digitalis use, symptoms are
typically not apparent until the serum level is below 2.5 mEq/L. Symptoms
may also vary depending on the concentration of other ions, including
calcium, magnesium, and hydrogen. Clinically relevant signs and symptoms
of hypokalemia relate to abnormal neuromuscular function and
cardiovascular effects, and monitoring of muscle strength and
electrocardiogram (ECG) are indicated to assess the functional
consequences of hypokalemia. Neuromuscular dysfunction typically
manifests as skeletal muscle weakness in an ascending pattern with
worsening hypokalemia. Lower extremity muscles are initially affected
with progression to the trunk and upper extremities. Respiratory weakness
may develop and lead to respiratory failure. Smooth muscle dysfunction can
lead to nausea, vomiting, constipation, and voiding dysfunction with
urinary retention. Significant hypokalemia produces characteristic changes
on the ECG. As the serum potassium drops, T-wave amplitude declines, U
waves develop, and ST segment depression may result. With more profound
hypokalemia the QRS complex may widen and the PR and QT intervals
may prolong. Supraventricular and ventricular dysrhythmias may develop,
especially in patients taking digitalis and in patients with congestive heart
failure and coronary ischemia. Hypokalemia may also lead to an impaired
ability to concentrate urine, an acquired form of nephrogenic diabetes
insipidus.
Management. The therapeutic approach to hypokalemia will depend on
severity, acuity, associated clinical signs, and underlying conditions. In
general, potassium replacement is indicated when there has been potassium
loss. If hypokalemia is redistributive in nature but associated with either
severely depressed levels or clinical signs, supplementation may be
required. However, supplementation during a redistributive process should
