Hypokalemia

Hypokalemia – Peter Thorne/Patrick Steadman

Background

  • Potassium (K+) < 3.5 mEq/L
  • 98% of total body K+ is intracellular (majority in muscle cells)
  • Goal: prevent life threatening complication (e.g. arrhythmia), replace deficit, elucidate cause
  • Insulin and catecholamines (Beta adrenoreceptors) are key drivers of transcellular shifts
  • H+ and K+ will trade places to maintain electroneutrality

 

Presentation

  • Malaise, weakness, myalgias, decreased gastrointestinal motility
  • EKG changes:
    • Mild: ST segment depression, decreased T wave amplitude
    • Severe: U-waves (most commonly seen in precordial leads V2 and V3)
  • Severe hypokalemia can lead to rhabdomyolysis

 

Evaluation

  • History: Consider decreased K+ intake, increased entry into cells (ex: Increased cell production, elevated beta-adrenergic activity, hypothermia), GI losses, urinary losses (diuretics, hypomagnesemia, RTA, tubular defects, hyperaldosteronism)
  • If concomitant metabolic alkalosis: Normal/low BP suggests diuretic use, vomiting or Gitelman/Bartter syndromes
  • Hypertension suggests renovascular disease or primary mineralocorticoid excess
  • Labs: BMP, CBC, VBG, urine electrolytes, magnesium, POC glucose, CK
  • Imaging: Renal US, CT A/P
  • Other: aldosterone, renin, cortisol

 

Management

  • Check Mg+2, replete to 2; Give empirically while waiting for serum Mg+2
  • K+ preparation (route); replete to 4
  • Choice of agent:
    • KCl is used for repletion in the hospital
        • PO tablets for mild asymptomatic hypokalemia
        • IV can be given through peripheral (rate is 10mEq/hr) or central access
    • K+ bicarbonate can be dissolved and put through G tube
        • Useful in pts with hypokalemia and metabolic acidosis
    • K+ acetate is given IV, rarely used (often additive to TPN)
  • Dose:
    • Normal renal function: 10 mEq K+ is expected to raise serum [K+] by 0.1 mEq/L
    • Significant CKD or AKI: at risk of overcorrection
        • Shortcut: multiply the mEq by the Cr = how much K+ expected to rise
    • Once K+ higher than 5.5, K+ increases much faster and rules above do not apply