Can a pregnant woman with hyperemesis (prolonged vomiting) develop metabolic acidosis?

Metabolic Acidosis in Pregnancy with Hyperemesis Gravidarum

Yes, a pregnant woman with hyperemesis gravidarum who has been vomiting for 4 days can develop metabolic acidosis with an anion gap of 24. While hyperemesis typically causes metabolic alkalosis due to loss of gastric acid, prolonged vomiting can lead to starvation ketoacidosis, resulting in a high anion gap metabolic acidosis 1, 2.

Pathophysiology of Acid-Base Disturbances in Hyperemesis

Hyperemesis gravidarum (HG) is characterized by intractable vomiting leading to:

• Dehydration
• Weight loss >5% of pre-pregnancy weight
• Electrolyte imbalances 3

The acid-base disturbances in hyperemesis can manifest in two primary ways:

1. Metabolic alkalosis (more common):

   • Due to loss of gastric acid from vomiting
   • Characterized by hypochloremia and hypokalemia
   • Can lead to compensatory respiratory acidosis 4

2. Metabolic acidosis (less common but serious):

   • Develops due to starvation ketoacidosis
   • Pregnancy is a diabetogenic state with enhanced lipolysis and ketogenesis
   • Short periods of starvation during pregnancy can precipitate ketoacidosis 2
   • Results in high anion gap metabolic acidosis

Clinical Presentation and Diagnosis

A pregnant woman with hyperemesis who develops metabolic acidosis may present with:

• Persistent vomiting (typically starting at 4-6 weeks, peaking at 8-12 weeks) 3
• Dehydration (orthostatic hypotension, decreased skin turgor, dry mucous membranes)
• Weight loss >5% of pre-pregnancy weight
• Altered mental status
• Laboratory findings:
  • Elevated anion gap (can reach 24 or higher)
  • Ketonuria and ketonemia
  • Electrolyte abnormalities (hyponatremia, hypokalemia, hypochloremia)
  • Elevated liver enzymes (seen in 40-50% of HG patients) 3

Management

Treatment should focus on rapid correction of the underlying metabolic disturbances:

1. Fluid resuscitation:

   • IV fluid and electrolyte replacement is the cornerstone of treatment 5
   • Dextrose-containing fluids are crucial to reverse ketoacidosis 2

2. Nutritional support:

   • IV thiamine supplementation (100 mg daily for minimum 7 days, followed by 50 mg daily) 5
   • Consider enteral or parenteral nutrition if severe 6

3. Antiemetic therapy:

   • Ondansetron (4-8 mg every 8 hours) for moderate to severe cases 5
   • Metoclopramide (5-10 mg orally every 6-8 hours) 5
   • Doxylamine and pyridoxine combination as first-line therapy 5

4. Monitoring:

   • Serial electrolyte measurements
   • Acid-base status
   • Fetal monitoring (metabolic disturbances can affect fetal well-being) 4

Complications and Prognosis

Untreated metabolic acidosis in pregnancy can lead to:

• Adverse impact on fetal neural development
• Impaired intelligence
• Fetal distress or demise 2
• Preterm delivery 4

With prompt and appropriate treatment, the prognosis is generally good. Rapid reversal of acidosis can be achieved with early administration of dextrose-containing fluids 2.

Important Considerations

• Metabolic disturbances can cross the placenta, affecting the fetus 4
• Early intervention is critical to prevent progression of HG and its metabolic complications 5
• Hospitalization is necessary for severe cases with significant dehydration, weight loss, and electrolyte imbalances 3, 5

In summary, while metabolic alkalosis is more commonly associated with hyperemesis gravidarum, starvation ketoacidosis leading to high anion gap metabolic acidosis is a recognized complication that requires prompt treatment to ensure maternal and fetal well-being.