What are the types of alkalosis?

Types of Alkalosis

Alkalosis is classified into two primary types based on the underlying mechanism: respiratory alkalosis and metabolic alkalosis. 1

Respiratory Alkalosis

Respiratory alkalosis occurs when excessive ventilation leads to decreased arterial CO2 levels (hypocapnia), resulting in elevated blood pH above 7.45. 2

Mechanism

• Hyperventilation causes excessive elimination of CO2, reducing carbonic acid formation and increasing pH 2
• The condition affects virtually every organ system in the body and produces multiple metabolic abnormalities 2

Key Metabolic Effects

• Changes in potassium, phosphate, and calcium handling 2
• Development of mild lactic acidosis 2
• Altered renal handling of electrolytes 2

Common Etiologies

• Pulmonary disorders: Direct lung pathology causing increased ventilation 2
• Extrapulmonary disorders: Conditions outside the lungs triggering hyperventilation 2
• Hyperventilation syndrome: A common cause in emergency settings, diagnosed by exclusion 1, 2
• Psychogenic disorders: Anxiety, panic disorders, and stress-related hyperventilation 1

Clinical Manifestations

• Cardiac effects including tachycardia, ventricular and atrial arrhythmias, and chest pain (both ischemic and nonischemic) 2
• Pulmonary vasodilation 2
• Gastrointestinal changes in perfusion, motility, and electrolyte handling 2
• Abnormal breathing patterns with abrupt onset of rapid, shallow breathing during exercise 1
• Decreased PetCO2 and PaCO2 levels 1

Diagnostic Features During Exercise Testing

• Impressive hyperventilation with abnormal increases in Ve, Ve/VCO2, and respiratory frequency 1
• Respiratory alkalosis evident by decreased PetCO2 and PaCO2 1
• Chronic respiratory alkalosis may show a downregulated PaCO2 set point at rest 1

Metabolic Alkalosis

Metabolic alkalosis is characterized by primary elevation of serum bicarbonate and arterial pH above 7.45, with compensatory increase in PaCO2 due to adaptive hypoventilation. 1, 3

Mechanism of Generation

• Gain of bicarbonate: Through oral or parenteral HCO3- administration, or via lactate, acetate, or citrate administration 4, 3
• Loss of acid: Either via gastrointestinal tract (vomiting) or kidney (diuretics) 4, 3

Factors Maintaining Metabolic Alkalosis

• Decreased glomerular filtration rate 5, 4
• Volume contraction 5, 4, 3
• Hypokalemia 5, 4, 3
• Hypochloremia 5, 4, 3
• Aldosterone excess 5, 4, 3
• Elevated arterial CO2 3

Major Clinical States

• Diuretic-induced: Most common in congestive heart failure patients, caused by chloruretic diuretics activating the renin-angiotensin system 6, 4
• Vomiting: Loss of gastric acid 4, 3
• Mineralocorticoid excess: Including primary hyperaldosteronism 4, 3
• Bartter syndrome: Genetic tubulopathy causing salt wasting, hypokalemia, and metabolic alkalosis with polyhydramnios in severe cases 1, 4, 3
• Gitelman syndrome: Similar genetic tubulopathy with later presentation 4, 3
• Licorice ingestion: Mineralocorticoid-like effects 4, 3
• Excess calcium-alkali ingestion 3

Clinical Significance

• Severe metabolic alkalosis (arterial pH ≥7.55) in critically ill patients is associated with significantly increased mortality 3
• Effects include central nervous system changes, myocardial dysfunction, skeletal muscle abnormalities, and hepatic effects 5, 4

Diagnostic Approach

• Urinary chloride excretion: Fractional chloride excretion usually >0.5% in conditions like Bartter syndrome helps distinguish renal from extrarenal salt losses 1, 7
• Paradoxical aciduria: May occur in hypokalemic metabolic alkalosis despite systemic alkalosis, due to enhanced hydrogen ion secretion in the distal tubule 7
• Serum electrolytes showing hypokalemia (typically <3.5 mmol/L), hypochloremia, and elevated bicarbonate 7, 6

Treatment Principles

• Eliminate generation and maintenance factors 6, 4
• Chloride and potassium repletion: Essential for correction 6, 4
• Acetazolamide: Enhances renal bicarbonate excretion 6, 4
• Hydrochloric acid: For direct titration of base excess in severe cases 6, 4
• Low-bicarbonate dialysis: When accompanied by kidney failure 6, 4
• Address underlying cause: Discontinue diuretics, treat vomiting, manage heart failure appropriately 6, 3

Important Caveats

• Potassium-sparing diuretics should be used cautiously in salt-wasting disorders like Bartter syndrome, as they may worsen volume depletion despite improving hypokalemia 7
• In congestive heart failure, aldosterone antagonists should be integral to the diuretic regimen 6
• Correction of volume depletion and electrolyte abnormalities (especially potassium and chloride) is essential rather than attempting to correct aciduria directly in paradoxical aciduria 7