Potassium
Hypokalemia
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Hypokalemia
, Hypokalemia Related EKG Changes
See Also
Serum Potassium
Hypokalemia due to Renal Potassium Loss
Hypokalemia due to Extrarenal Potassium Loss
Hypokalemia due to Transcellular Potassium Shift
Familial Periodic Paralysis
Potassium Replacement
Dietary Potassium
Pathophysiology
Approximate Total body
Potassium
= 55 meq/kg
Serum Potassium
decreased 0.3 mEq/L: 100 mEq K+ total body deficit
Serum Potassium
decreased 1 mEq/L: 350 mEq K+ total body deficit
Serum Potassium
less than 2 mEq/L: 1000 mEq K+ total body deficit
Causes
Hypokalemia due to Transcellular Potassium Shift
See
Transcellular Potassium Shift
Medications (Beta-agonists,
Insulin
excess)
Metabolic Alkalosis
Hypokalemic Periodic Paralysis
Thyrotoxicosis
Hypokalemia due to Renal Potassium Loss
See
Renal Potassium Loss
(
Hyperkaluria
)
Hypertension
: Obtain Plasma
Renin
and Aldosterone
Renin
high
Renovascular disease, renin secreting tumor or
Malignant Hypertension
Renin
normal
Liddle's Syndrome
Renin
low
Aldosterone High: Primary
Hyperaldosteronism
, Bilateral adrenal hyperplasia
Aldosterone Low:
Congenital Adrenal Hyperplasia
,
Cushing's Syndrome
, Ectopic ACTH
Normotensive: Obtain serum bicarbonate and
Urine Chloride
Serum Bicarbonate Low
Renal Tubular Acidosis
Serum Bicarbonate High
Urine Chloride
Low:
Vomiting
Urine Chloride
High: Barter's Syndrome, Normotensive primary
Hyperaldosteronism
,
Diuretic
use
Hypokalemia due to Extrarenal Potassium Loss
See
Extrarenal Potassium Loss
Normal Acid-Base Status or
Metabolic Alkalosis
Gastrointestinal or skin losses,
Hypomagnesemia
,
Penicillin
or
Aminoglycoside
s,
Acute Leukemia
Metabolic Acidosis
Diabetic Ketoacidosis
,
Diarrhea
,
Laxative
s
Other causes
Inadequate
Potassium
intake (typically in hospitalized patients)
Total Parenteral Nutrition
Anorexia
or Starvation
Dementia
Pseudohypokalemia
Delayed lab analysis of sample
Severe
Leukocytosis
(>75,000/mm3)
Findings
Symptoms and Signs (when
Serum Potassium
< 2.5 mEq/L)
Gene
ral
Malaise
Fatigue
Neurologic
Weakness
Decreased
Deep Tendon Reflex
es
Paresthesia
Cramps
Restless Legs Syndrome
Rhabdomyolysis
Paralysis
Gastrointestinal
Constipation
Ileus
Exacerbated
Hepatic Encephalopathy
Cardiovascular
Orthostatic Hypotension
Hypertension
Arrhythmia
s (rare in otherwise healthy patients)
Acute or recent
Myocardial Infarction
(5 fold increased risk of
Ventricular Fibrillation
if K+ <3.9 mEq/L)
Digoxin
use and Hypokalemia predisposes to
Arrhythmia
Renal
Metabolic Alkalosis
Polyuria
, Polydipsia
Decreased GFR
Glucose Intolerance
Labs
Serum Potassium
<3.5 mEq/L
Serum Magnesium
Confirm no
Hypomagnesemia
(Hypokalemia cause)
Complete Blood Count
Confirm no severe
Leukocytosis
(pseudohypokalemia)
24 hour
Urine Potassium
and
Urine Sodium
Most accurate evaluation of
Urine Potassium
excretion
However,
Urine Potassium
-to-
Creatinine
ratio is typically obtained instead
Sample should have total
Urine Sodium
> 100 meq
Urine Potassium
<20-30 meq/day
See
Extrarenal Potassium Loss
Urine Potassium
>20-30 meq/day
See
Renal Potassium Loss
Urine Potassium
-to-
Creatinine
ratio
Ratio <=1.5 mEq/mmol:
Hypokalemia due to Extrarenal Potassium Loss
Manage underlying losses
Ratio >1.5 mEq/mmol:
Hypokalemia due to Renal Potassium Loss
Elevated
Blood Pressure
or hypervolemia (mineralcorticoid excess)
Hyperaldosteronism
Renal Artery Stenosis
Cushing Syndrome
Congenital Adrenal Hyperplasia
Metabolic Acidosis
Type I and II
Renal Tubular Acidosis
Metabolic Alkalosis
Diuretic
s
Renal Tubular transport disorders (e.g. Bartter Syndrome)
Diagnostics
Electrocardiogram
Early changes
T Wave
s decreased amplitude to flattened
Later changes
Prominent
U Wave
s
ST depression
T Wave Inversion
PR prolongation (first degree
AV Block
)
QTc Prolongation
Arrhythmia
s associated with Hypokalemia
Sinus Bradycardia
Ventricular Tachycardia
or
Ventricular Fibrillation
Torsade de pointes
Management
Gene
ral
Potassium Replacement
Goal
Serum Potassium
>3.5 mEq/L (>4.0 in CAD, CHF)
Total body
Potassium
deficit
Serum Potassium
: <3.5 mEq/L = 100 meq total
Potassium
deficit
Serum Potassium
: 3.2 mEq/L = 200 meq total
Potassium
deficit
Serum Potassium
: 2.9 mEq/L= 300 meq total
Potassium
deficit
Serum Potassium
: 2.6 mEq/L = 400 meq total
Potassium
deficit
Avoid rebound
Hyperkalemia
(over-shooting replacement)
Hyperkalemia
with replacement is unlikely if normal
Renal Function
, adequate fluid intake
Dietary Potassium
(
Potassium
phosphate) is less efficient replacement than
Potassium
chloride
Most Hypokalemia is associated with concurrent chloride depletion
However
Potassium
chloride compliance is poor (
Dyspepsia
,
Dietary Potassium
tastes better)
Half of
Potassium Replacement
is typically excreted by the
Kidney
s
Aside from
Renal Failure
and dehydration, at least half of
Potassium Replacement
(esp. oral) is excreted
Approximate oral replacement
Serum Potassium
< 3.0 mEq/L (total body deficit 200-300 meq)
Start with KCl 20 meq orally every 2 hours for 4 doses and consider recheck level
Typically continue
Potassium Replacement
at 20 meq twice daily for 4-5 days
Serum Potassium
: 3.0 to 3.5 mEq/L(total body deficit 100-200 meq)
Give KCl 20 mEq orally every 2 hours for 2 doses OR KCl 40 mEq once
Typically continue
Potassium Replacement
at 20 meq twice daily for 2-3 days
Magnesium Replacement
(empirically or based on lab demonstrated
Hypomagnesemia
)
Especially consider empiric
Magnesium Replacement
in refractory Hypokalemia
Take oral
Magnesium
supplement 400-500 mg tabs 1-2 daily along with
Potassium
supplement
Emergent replacement indicated for serious findings or risks
EKG changes (esp.
QTc Prolongation
, see above)
Severe Hypokalemia (
Serum Potassium
<2.5 mEq/L)
Rapid onset Hypokalemia
Serious comorbidity (heart disease,
Cirrhosis
)
Consider pseudohypokalemia
Consider re-drawing lab for confirmation if delayed analysis
Confirm no severe
Leukocytosis
(WBC >75,000/mm3)
Consider
Transcellular Potassium Shift
See
Transcellular Potassium Shift
Hypokalemia from transcellular shift is typically transient
Management
Hospital Replacement Criteria
Hypokalemia with
Serum Potassium
<3.0 mEq/L AND
QTc Prolongation
>500 ms
Severe Hypokalemia with
Serum Potassium
<2.5 mEq/L
References
Orman and Slovis in Herbert (2018) EM:Rap 18(8): 4-5
Viera (2015) Am Fam Physician 92(6): 487-95 [PubMed]
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