CAUSES OF HYPOKALEMIA

Hypokalemia due to decreased potassium uptake:

-marked reduction in K+ intake is required to develop hypokalemia
-kidneys ability to conserve plasma [K+]
-kidneys ability to decrease urinary [K+] as low as 5 – 15 mEq/L
Hypokalemia due to increased potassium losses:

 Increased K+ losses be generally be from:
-renal loss: urinary [K+] > 20 mEq/L
ex. diuresis, chronic metabolic alkalosis, inc mineralcorticoid, antibiotics, RTA
-GI loss: urinary [K+] < 20 mEq/L
ex. vomiting, diarrhea, fistulas

Hypokalemia due to increased intracellular movements:

-acute alkalosis
-insulin therapy
-(2 agonist
-hypothermia
-vitamin B12 treatment

CLINICAL MANIFESTATIONS FOR HYPOKALEMIA:

-usually asymptomatic until [K+] < 3 mEq/L
Central nervous system:
possible encephalopathy due to:
-metabolic alkalosis
-advanced liver disease
-resultant decreased [K+] and increased ammonia levels
Cardiovascular system:
electrocardiogram changes include:
-flattening/inversion of T wave
-prominent U wave
-ST segment depression
-increased P wave
-prolonged PR interval
dysrhythmias may involve:
-increase in myocardial automaticity
-delayed ventricular repolarization
decreased cardiac contractility
labile mean arterial pressure
-secondary autonomic dysfunction
Respiratory system:
-possible compensatory acidosis (hypoventilation) secondary to metabolic alkalosis
Hepatic system:
-increased ammonia production
-intracellular acidosis
-H+ moves intracellular to compensate for intracellular K+ loss
Renal system:
-renal dysfunction includes:
-impaired concentrating ability
-ex. resistance to ADH (nephrogenic diabetes insipidus)

TREATMENT FOR HYPOKALEMIA:
 
Oral replacement:
-60 – 80 mEq/L ; generally the safest
Intravenous replacement:
reserved for:
-serious cardiac manifestation
-muscle weakness
Goal for intravenous treatment of hypokalemia:
-remove patient from immediate danger
-then replace the K+ PO
KCL is preferred in metabolic alkalosis especially in hypochloremic metabolic alkalosis
K+acetate or K+citrate: preferred for metabolic acidosis
K+phosph: preferred when both K+ and Phosphorus are decreased
peripheral intravenous line: replace K+ 8 mEq/hr due to venoirritation
central intravenous line: replace K+ 10 –20 mEq/hr
maximum K+ replacement/day: 240 mEq/day
 
ANESTHETIC CONSIDERATIONS FOR HYPOKALEMIA:

-lower limits of K+: 3 – 3.5 mEq/L without ECG changes
-generally does not appear to be significant anesthetic risk
-exception may occur in patients taking digoxin
-patients taking digoxin should have K+ maintained at 4 mEq/L
Anesthetic consideration decisions in hypokalemic patients may be based on:
-rate of K+ loss
-presence or absence of organ dysfunction
Intraoperative management in hypokalemic patients:
Provide intravenous K+ supplementation if:
-atrial dysrhytmias occur due to decreased K+ levels
-ventrilcular dysrhythmias occurs due to decreased K+ levels
avoid glucose containing solutions in hypokalemic patients
avoid hyperventilation in hypokalemic patients