Part 8: Advanced Challenges in Resuscitation
Section 1: Life-Threatening Electrolyte Abnormalities
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Electrolyte abnormalities are commonly associated with cardiovascular emergencies. These abnormalities may cause or contribute to cardiac arrest and may hinder resuscitative efforts. It is important to identify clinical situations in which electrolyte problems may be expected. In some cases therapy for life-threatening electrolyte disorders should be initiated even before laboratory results become available.
The magnitude of the potassium gradient across cell membranes determines excitability of nerve and muscle cells, including the myocardium. Minor changes in serum potassium concentration can have major effects on cardiac rhythm and function. Of all the electrolytes, rapid changes in potassium concentration can cause the most immediate life-threatening consequences.
Evaluation of serum potassium must consider the effects of changes in serum pH. When serum pH falls, serum potassium rises because potassium shifts from the cellular to the vascular space. When serum pH rises, serum potassium falls because potassium shifts intracellularly. In general, serum K+ decreases by approximately 0.3 mEq/L for every 0.1 U increase in pH above normal. Effects of pH changes on serum potassium should be anticipated during evaluation and therapy for hyperkalemia or hypokalemia. Correction of an alkalotic pH will produce an increase in serum potassium even without administration of additional potassium. If serum potassium is “normal” in the face of acidosis, a fall in serum potassium should be anticipated when the acidosis is corrected, and potassium administration should be planned.
Hyperkalemia is defined as serum potassium concentration above the normal range of 3.5 to 5.0 mEq/L. Hyperkalemia is most frequently caused by increased K+ release from cells or by impaired excretion by the kidneys (see Table 1⇓). The most common clinical presentation of severe hyperkalemia involves patients with end-stage renal failure. These patients may present with severe weakness or arrhythmias.
Medications may also contribute to development of …