HYPOKALEMIA

Salient Features 55 y/o male Diarrhea for several weeks to admission 3 days PTA: progressive weakness

Laboratory Findings:

Chemistry Profile

Actual Results Normal Values Remarks

Na+ 140 meq/L 136-145meq/L Normal

Cl- 110 meq/L 98-106 meq/L Increased

K+ 2. 0 meq/L 3.5-5.0 meq/L Decreased

Laboratory Findings:Arterial Blood Gas Profile:

Urine Potassium: 15 meq/L(NV: usually >15 meq/L)

Actual Results Normal Values Remarks

pH 7.28 7.38 - 7.44 Decreased

pCO2 39mmHg 35 - 45 mmHg Normal

HCO3 16 meq/L 21 - 30 meq/L Decreased

Guide Questions:

1.) Using an algorithm, discuss the diagnostic approach to hypokalemia. What is the cause of hypokalemia in this patient?

DIAGNOSTIC APPROACH TO HYPOKALEMIA

Urinary K+ Loss

<15 moml/d >15 mmol/d

Assess Acid-Base status Assess K+ secretion

Metabolic acidosis

Metabolic alkalosis

TTKG >4 TTKG <2

Lower GIT K+ loss

Remote diuretic useRemote vomitingK+ loss via sweat

Na+ wastingNephropathy

Osmotic diuresisDiuretic

Acid-Base status

Metabolic acidosis Metabolic alkalosis

HypertensionDiabetic ketoacidosisProximal Type 2 RTA

Distal Type 1 RTAAmphotericin B Mineralocorticoid excess

Liddle’s syndrome

VomitingBartter’s syndromeHypomagnesemia

Harrison’s Principles of Internal Medicine 16th ed. Vol.I, p.260

Causes of Hypokalemia

DecreaseIntake Increase Loss

Redistribution into Cells

A.Nonrenal

B.Renal

Causes of HypokalemiaI. Decreased intake

A. Starvation B. Clay Ingestion

II. Redistribution into Cells A. Acid-Base (Metabolic Alkalosis) B. Hormonal (Insulin, Beta agonist, Alpha

antagonist) C. Anabolic State (folic acid) D. Other (Hypothermia, Pseudohypokalemia)

Causes of Hypokalemia

III. Increased Loss

A. Nonrenal

1. Gastrointestinal Los (diarrhea)

2. Integumentary Loss (sweat)

B. Renal

Hypokalemia: Extrarenal loss

Cause of Hypokalemia in the patient:

Gastrointestinal losses diarrhea (secretory)

Urine potassium level less than 20 mEq/L suggests gastrointestinal loss

Stool has a relatively high potassium content, and fecal potassium losses could exceed 100 mEq per day with severe diarrhea.

Gastrointestinal Loss Hypokalemia is also due to increased K+

renal excretion Loss of Gastric contents results in volume

depletion and metabolic alkalosis, both of which promotes kaliuresis

Gastrointestinal Loss Stimulates aldosterone release=augments

K+ secretion by principal cells There is an increase in distal delivery of

NaHCO3 which enchances the electrochemical gradient favoring potassium loss in urine.

SIGNS & SYMPTOMS Fatigue Myalgia Muscular weakness & paralysis Hyporeflexia Dyspnea Arrhythmia Predispose to digitalis toxicity Constipation

SIGNS & SYMPTOMS

Risk of hyponatremia resultant confusion, headaches, & seizures

Irritable Nervousness anorexia Ileus

Adverse Medical Implications Muscle weakness and paralysis (more

negative resting membrane potential) Respiratory

Hypoventilation (due to respiratory muscle weakness or paralysis)

Gastrointestinal Paralytic ileus

Adverse Medical Implications Cardiac

ECG changes Due to delayed ventricular repolarization Early changes: flattening or inversion of T wave,

prominent U wave, ST-segment depression, prolonged QU interval

Severe K+ depletion: prolonged PR interval, decreased voltage and widening of QRS complex

A: Normal

B: flattening of T wave

C-F:U wave, ST-depression, prolonged QU interval

Adverse Medical Implications Cardiac

Increased risk for ventricular arrythmias Potential digitalis toxicity Risk for Hypertension

Exercising skeletal muscle insufficient blood flow increased risk for rhabdomyolysis

Metabolic acidosis (due to increased bicarbonate excretion)

Adverse Medical Implications Renal

Risk for renal cystic disease HypoK leads to increased ammoniagenesis which

may activate the complement system Mild Nephrogenic Diabetes Insipidus (NDI)

Defective activation of adenylate cyclase = decrease effect of vasopressin

Endocrine Glucose intolerance = due to decreased insulin

or insulin resistance

4. What is the significance of the urinary potassium

levels?

Potassium Regulation Kidney

K+ balance: Urinary K+ excretion= Dietary intake Decreased secretion: Low K+ diet, hypoaldosteronism,

acidosis, K+ sparing diuretics GIT

dietary K+ is absorbed in the small intestine by passive diffusion

K+ is secreted in the colon through aldosterone stimulation

in diarrhea, K+ secretion by the colon is increased

Urinary Potassium level NV = 25 - 100 meq/L patient has decreased urinary K+

(15meq/L) a decrease of:

<25meq/L - diarrhea >40meq/L - diuretics

What is the treatment?

TREATMENT

Therapeutic goals:

to correct the K+ deficit

to minimize on going losses

•It is safer to correct hypokalemia via oral route in order to prevent rebound hyperkalemia if given IV

•The plasma potassium concentration should be monitored frequently when assessing the response to treatment

TREATMENT

Emergency Treatment of Hypokalemia

A. Estimated Potassium Deficit

serum K <3 mEq/L= K deficit >300 mEq

serum K <2 mEq/L= K deficit >700 mEq

TREATMENT

B. Indications for Urgent Replacement

ECG abnormalities consistent with severe K+ depletion

myocardial infarction

hypoxia

digitalis intoxication

marked muscle weakness

respiratory muscle paralysis.

TREATMENT

IV infusion

- for severe hypokalemia or those who cannot take oral supplementation

- peripheral vein = 40 mmol/L (preferred) central vein = 60 mmol/L

- rate of infusion 20 mmol/hr - mixed in NSS

Continous ECG monitoring

Serum potassium determination every 3-6 hours

TREATMENT

Potassium chloride (KCl)

-drug of choice

- treat hypokalemia and metabolic alkalosis

Potassium bicarbonate and citrate

- more appropriate for hypokalemia associated with chronic diarrhea or RTA

Non-Emergency Treatment of Hypokalemia

-attempts should be made to normalize K+ levels if <3.5 mEq/L.

-oral supplementation is significantly safer than IV

-KCL elixir, 1-3 tablespoon every day.

TREATMENT

TREATMENT

ORAL ROUTE

1 mmol/L decrease in plasma K+ concentration

200-400mmol total body K+ deficit

=

Plasma levels <3 mmol/L require additional 600 mmol