Chapter 14 Hypokalaemia

14.1 Causes of hypokalaemia

  1. spurious
  2. distribution (ECF/ICF shifts)
  3. K loss (renal or extra-renal)

14.2 Causes of K loss
RENAL with metabolic alkalosis vomiting
with metabolic alkalosis diuretics
Gitelman
Bartter
true mineralocorticoid XS
apparent mineralocorticoid XS
RTAI
RTAII
RTAIII
DKA
Mg-depletion
non-reabsorbable anion
EXTRA-RENAL with normal acid-base anorexia
tea & toast diet
laxative abuse
diarrheoa
villous adenoma

14.3 Diagnostic approach

Stratify according to the following schemata:

or

14.4 Vomiting

In vomiting, K is lost through extra-renal and renal routes. Volume contraction stimulates aldosterone; contribution for chloride depletion and bicarbonaturia. A urinary pH and UCl may be informative.

The classical differential diagnosis for unexplained hypokalaemia when surruptious vomiting / laxitive use is suspected is as follows:

serum pH UNa UK UCa
laxative use acidosis < 10 mM < 20 mM
vomiting alkalosis < 10 mM < 20 mM < 25 mM
diuretic use alkalosis > 10 mM > 20 mM < 25 mM
Bartter alkalosis > 10 mM > 20 mM > 40 mM

Eating disorder suggested by alternating alkalosis (vomiting) and acidosis (RTA from hypokalaemic nephropathy).

14.5 Non-reasbsorbable anions

Hypokalaemia can be due to renal tubular K secretion in the presence of a non-reabsorbable anion (classically IV penicillins). Look for low U.Cl and treat with IV 0.9 % NaCl. Exacerbated in volume depletion (stimulates aldosterone).


14.6 Cola-induced hypokalaemia

Excessive cola production causes a predominatly caffeine-dependent hypokalaemia. This is mulfactorial with…

…2 mechanisms to shift K\(^+\) into cells:

  • caffeine > catecholamines > Na-K-ATPase stimulated
  • glucose load > insulin > ditto

…and 2 mechanisms to promote kaliuresis:

  • caffeine > diuresis
    • symps (+ block adenosine Rs) > + renin > + aldo


14.7 Hypokalaemic periodic paralysis

AD inheritance. Thought to be caused by K shifts between ICF and ECF. Associated with thyrotoxicosis in oriental males aged 20 – 50 yrs (in which case high risk of arrhythmias). In this case, treating the thyrotoxicosis will prevent paralysis (as will propranolol).

Triggers:

  • sleep
  • glucose / insulin / large CHO meal
  • EtOH
  • anxiety

Treatment:

  • attacks IV K supplements
  • prophylaxis K supplements & K-sparing diuretics