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Unexpected Metabolic Acidosis in Pregnancy

November 1st, 2010 by Patrick

At the American Society of Anesthesiology 2010 conference in San Diego I presented this medically challenging case.

A 38 year-old multiparous parturient at 37 weeks gestation presented for a repeat Cesarean section. History was notable for several prior Cesareans and anemia during pregnancy. The patient was NPO for nine hours, was on liquid diet two days prior, and had an enema the evening before surgery.

Spinal anesthesia was induced with bupivicaine 0.75%, preservative-free morphine, and fentanyl. After delivery and approximately 1000 mL of blood loss a venous blood gas was checked. The pH was 7.26 and Hct was 26. A repeat arterial blood gas found similar results. The patient remained awake and hemodynamically stable.

As pregnant patients approach term, their oxygen consumption and metabolism increase steadily, leading to an increase in base excess.
The term “base excess” refers to the excess or deficit of base in the blood stream. In the same way that CO2 levels demonstrate the degree of respiratory acidosis, the base excess shows the degree of metabolic acidosis.

Possibly due to the patient’s limited diet, her body began breaking down fatty acids and producing ketone bodies, creating an acidemia. Also, the patient’s home enema treatments reduced her bicarbonate levels.

For treatment, the patient was started on D5W with 140 mEq bicarbonate at 125 mL/hr. Potassium and phosphate were repleted. An arterial line was placed to monitor ABGs and the patient was transferred to the MICU. Within 12 hours her pH normalized and she returned to the postpartum floor.

The D5W/NaHCO3 drip provides substrate for anaerobic metabolism and helps restore lost bicarbonate. It is notable that the patient’s acidemia worsened for several hours after treatment began, demonstrating the time required to correct such a severe imbalance.

References

  1. Marx GF, Desai PK, Habib NS, “Detection and Differentiation of Metabolic Acidosis in Partrurients,” Anesth Analg 1980 Dec; 59(12):929-31. PMID 7192513.
  2. Toth HL and Greenbaum LA, “Severe Acidosis caused by Starvation and Stress”, Am J Kid Dis 2003 Nov; 42(5):E16-19. PMID 14582074.
  3. Levraut J and Grimaud D, “Treatment of metabolic acidosis”, Curr Opin Crit Care. 2003 Aug;9(4):260-5. PMID 12883279.

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