Maternal blood gas physiology

The arterial blood gas provides vital information regarding acid-base balance, oxygenation, and ventilation. Clinically, a blood gas is most commonly used to identify and monitor treatment of acid-base disturbances and evaluate the response to therapeutic interventions. This chapter focuses on fundamental physiology, analytic considerations, the effective interpretation of an arterial blood gas, and acid-base disturbances. Disturbances in acid-base balance are classified according to whether the underlying process results in an abnormal rise or fall in arterial pH. The accuracy of a blood gas determination relies on many factors, including blood collection techniques, specimen transport, and laboratory equipment. The chapter highlights considerations for obtaining a blood sample and potential sources of error, and briefly describes laboratory methods. Metabolic acidosis is diagnosed on the basis of a decreased serum bicarbonate and arterial pH. The baseline bicarbonate concentration during pregnancy should be kept in mind when interpreting the bicarbonate concentration.