What is alkalosis?

Alkalosis: Definition, Types, and Management

Alkalosis is defined as a condition characterized by an abnormally high pH (>7.45) in the blood, resulting from either excess bicarbonate (metabolic alkalosis) or decreased carbon dioxide (respiratory alkalosis). 1

Types of Alkalosis

1. Metabolic Alkalosis

Metabolic alkalosis is characterized by:

• Primary elevation of serum bicarbonate (HCO3-)
• Blood pH > 7.45
• Compensatory increase in PaCO2 (respiratory compensation)
• Often associated with hypochloremia and hypokalemia 2, 3

2. Respiratory Alkalosis

Respiratory alkalosis is characterized by:

• Primary decrease in PaCO2 due to hyperventilation
• Blood pH > 7.45
• Compensatory decrease in bicarbonate concentration
• Results from dysfunction of the respiratory control center 2, 4

Pathophysiology

Metabolic Alkalosis

For metabolic alkalosis to develop and persist, two processes must occur:

1. Generation phase: Gain of bicarbonate or loss of acid
2. Maintenance phase: Kidney's failure to excrete excess bicarbonate 5

Common mechanisms include:

• Gastrointestinal causes: Vomiting, nasogastric suction (loss of HCl)
• Renal causes: Diuretic use, mineralocorticoid excess, hypokalemia
• Exogenous alkali administration: Bicarbonate, citrate, lactate, acetate

Respiratory Alkalosis

Caused by hyperventilation leading to excessive CO2 elimination, which can result from:

• Central nervous system disorders
• Hypoxemia
• Pulmonary disorders
• Anxiety/panic attacks
• Sepsis
• Liver disease
• Pregnancy 4

Clinical Manifestations

Alkalosis can affect multiple organ systems:

• Neurological: Confusion, seizures, tetany, paresthesias
• Cardiovascular: Arrhythmias, decreased cardiac output
• Musculoskeletal: Muscle weakness, cramps
• Respiratory: Compensatory hypoventilation in metabolic alkalosis
• Electrolyte abnormalities: Hypokalemia, hypocalcemia, hypophosphatemia

Diagnosis

The diagnosis of alkalosis is established by arterial blood gas analysis:

• pH > 7.45
• For metabolic alkalosis: Elevated HCO3- with compensatory elevation in PaCO2
• For respiratory alkalosis: Decreased PaCO2 with compensatory decrease in HCO3-

Additional laboratory tests to consider:

• Serum electrolytes (potassium, chloride, calcium)
• Urinary chloride (helps distinguish chloride-responsive from chloride-resistant metabolic alkalosis)
• Plasma renin and aldosterone levels (if mineralocorticoid excess is suspected)

Management

Metabolic Alkalosis

Treatment depends on the underlying cause and severity:

1. Chloride-responsive alkalosis (urinary chloride <20 mEq/L):

   • Volume repletion with normal saline
   • Potassium replacement if hypokalemic
   • Discontinuation of causative medications (diuretics)

2. Chloride-resistant alkalosis (urinary chloride >20 mEq/L):

   • Address underlying cause (e.g., hyperaldosteronism)
   • Consider potassium-sparing diuretics

3. Severe cases (pH >7.60 or symptomatic):

   • In emergency situations, dilute hydrochloric acid (0.1 N HCl) may be infused intravenously, though this carries risk of hemolysis 3
   • Acetazolamide (carbonic anhydrase inhibitor)
   • Hemodialysis with low bicarbonate bath for refractory cases

Respiratory Alkalosis

Treatment focuses on addressing the underlying cause:

• Anxiety-induced hyperventilation: Reassurance, rebreathing techniques
• Hypoxemia: Oxygen therapy
• Mechanical ventilation: Adjustment of ventilator settings
• Treatment of underlying infections, liver disease, or other causes

Special Considerations

Bartter Syndrome

A rare genetic disorder characterized by renal salt wasting and metabolic alkalosis. Multiple types exist, all presenting with alkalosis, but with varying severity and age of onset 1.

Drug-Induced Alkalosis

Several medications can cause or exacerbate alkalosis:

• Diuretics (especially loop and thiazide diuretics)
• Mineralocorticoid receptor antagonists
• Exogenous bicarbonate administration
• Antacids 1

Pitfalls and Caveats

1. Pseudo-alkalosis: Laboratory error or improper specimen handling can falsely elevate pH.

2. Mixed acid-base disorders: Patients may have concurrent acidosis and alkalosis, complicating diagnosis and treatment.

3. Compensation vs. primary disorder: Distinguishing between primary alkalosis with compensation and mixed disorders requires careful interpretation of blood gases.

4. Overcorrection risks: Rapid correction of chronic metabolic alkalosis can lead to metabolic acidosis and other complications.

5. Mortality risk: Mortality increases as pH increases in metabolic alkalosis, particularly in critically ill patients 5.