How is alkalosis with volume contraction treated?

Treatment of Alkalosis with Volume Contraction

Isotonic saline (0.9% NaCl) administration is the first-line therapy for contraction alkalosis to correct both volume depletion and chloride deficit, which promotes renal bicarbonate excretion and suppresses the renin-angiotensin-aldosterone system. 1

Pathophysiology of Contraction Alkalosis

Contraction alkalosis is characterized by:

• Decreased extracellular fluid volume
• Elevated serum bicarbonate (>26 mEq/L)
• Hypochloremia (<98 mmol/L)
• Often accompanied by hypokalemia (<3.5 mEq/L)
• Elevated blood pH (>7.45)

The condition occurs when volume contraction leads to increased bicarbonate reabsorption in the kidneys. For alkalosis to persist, both generation and maintenance factors must be present, with volume depletion being the most common perpetuating factor 2.

Diagnostic Approach

Diagnosis is established by:

• Elevated arterial pH (>7.45)
• Elevated serum bicarbonate
• Compensatory elevation in pCO₂
• Signs of volume depletion

In older adults, volume depletion can be identified by:

• Postural pulse change ≥30 beats per minute when moving from lying to standing
• Severe postural dizziness resulting in inability to stand 3
• At least four of the following seven signs: confusion, non-fluent speech, extremity weakness, dry mucous membranes, dry tongue, furrowed tongue, sunken eyes 3

Treatment Algorithm

Step 1: Volume Repletion with Chloride

• First-line therapy: Administer isotonic saline (0.9% NaCl) to correct both volume depletion and chloride deficit 1
• Route of administration depends on severity:
  • Oral rehydration for mild cases
  • Nasogastric, subcutaneous, or intravenous for moderate to severe cases 3

Step 2: Address Potassium Deficiency

• Correct hypokalemia with potassium chloride supplementation
• For severe hypokalemia with symptoms or ECG changes: administer potassium chloride 0.25 mmol/kg over 30 minutes (maximum rate 20 mEq/hour via peripheral vein) 1
• Target potassium level: 4.0-5.0 mEq/L 1

Step 3: Manage Diuretic-Induced Alkalosis (if applicable)

• Reduce dose or discontinue the offending diuretic 1
• Consider adding potassium-sparing diuretics if continued diuretic therapy is necessary 1

Step 4: For Refractory Cases

• For severe metabolic alkalosis unresponsive to above measures:
  • Consider acetazolamide to enhance bicarbonate excretion 4
  • In emergency situations with severe alkalosis: consider hemodialysis with high chloride, low bicarbonate dialysate 2
  • For extreme cases: dilute hydrochloric acid (0.1-0.2 N) may be administered via central venous catheter, though this carries risk of hemolysis 5, 2

Monitoring and Follow-up

• Check serum electrolytes (potassium, sodium, chloride, bicarbonate) within 24 hours of initiating therapy 1
• Monitor more frequently for IV replacement
• Check magnesium levels and correct deficiency if present, as hypomagnesemia can perpetuate hypokalemia 1
• Adjust fluid and electrolyte therapy based on renal function 1

Important Considerations

• Chloride repletion can correct contraction alkalosis even without fully restoring plasma volume or glomerular filtration rate 6
• Potassium chloride is preferred over other potassium salts as it addresses both potassium and chloride deficiencies simultaneously 1
• Avoid correcting potassium too rapidly to prevent hyperkalemia 1
• In patients with kidney failure and severe alkalosis, consider low-bicarbonate dialysis 1

By addressing both the volume contraction and chloride deficit, this approach effectively treats contraction alkalosis while improving morbidity and mortality outcomes.