Potassium

Question 1

What are the 3 ways of elimination of potassium ?

Answer 1

Kidneys, fecal excretion, and sweat

Question 2

What are the 3 major factors affecting K+ excretion in the distal tubule ?

Answer 2

• Plasma [K+] : if increased, K+ excretion
• Aldosterone (from RAAS, stimulated by Na+) : K+ excretion
• ADH : K+ excretion (prevent hyperK in dehydrated animals)
• Urine flow : K+ excretion

Question 3

What are the 2 major substances affecting the uptake of K+ by cells ?

Answer 3

• insuline : decrease plasma [K+] (TT of severe hyperK)
• catecholamines (adrenaline) : decrease plasma [K+]

Question 4

What is the impact of acidosis and alkalosis on plasma [K+] ?

Answer 4

K+/H+ symport
Acidosis : increase plasma [K+]
Alkalosis : decrease plasma [K+]

Question 5

What are the main hypothesis in case of refractory hypoK ?

Answer 5

• HypoMg
• Alkalosis
• Insulin secretion
• Catecholamine secretion

Question 6

Clinical effects of hypoK ?

Answer 6

Synchronous diaphragmatic flutter, muscle weakness, changes in ECG (increased P-wave amplitude, decreased T-wave, and prolonged PR interval)

Question 7

What is the maximal supplementation rate of K+ ?

Answer 7

0,5 mEq/kg/h
This is a maximal supplementation rate, independent of the rate of change of blood dosage (contrary to Na+)
The rate of increase or decrease of K+ is less important to control than for Na+.

Question 8

What are the steps to consider when faced with hypoK ?

Answer 8

1- Evaluate for causes of K+ shifting iC (insulin, catecholamines, alkalosis)
2- Evaluate for K+ losses (diuretics, fluid adm°, hypoMg, diarrhea, sweat)
3- Evaluate for decreased intake (anorexia)

Question 9

What is HYPP ?

Answer 9

Hyperkalemic Periodic Paralysis
Genetic disease affecting QH and related breeds, due to a defect in the Na+ channel (SCN4A)
Autosomal dominant with incomplete penetrance.
Major increase in the plasma [K+] until 9.0 mmol/L
Clinical signs : weakness, sweating, muscle fasciculations, prolapse of the 3rd eyelid

Question 10

What are the common causes of hyperK in horses ?

Answer 10

1- Transcellular shifting : rhabdomyolyis, hemolysis, HYPP
2- Urinary dysfunction : renal failure, bladder rupture
3- Increased intake : rapid IV adm°

Question 11

Clinical effects of hyperK ?

Answer 11

ECG changes (tall T-wave, flattened P-wave, prolonged QRS), arrhythmias, bradycardia

Question 12

What is pseudohyperkalemia ?

Answer 12

Leakage of K+ from iC space of RBC, WBC or platelets in a blood sample

Question 13

When and how to treat hyperK ?

Answer 13

When [K+] > 6.0 mmol/L
1- IV calcium adm° : provides protection from the myocardial effects of hyperK
2- IV dextrose and insulin : should be given concurrently with calcium
3- additional TT if ineffective : bicarbonate, β-agonists (inhaled), furosemide, IV fluid therapy
*The rate of increase or decrease of K+ is less important to control than for Na+. *

Question 14

DDX of synchronous diaphragmatic flutter

Answer 14

• Hypocalcemia
• Hypochloremic metabolic alkalosis
• Hypokalemia