A 28-year-old primigravida woman is admitted to the hospital at 10 weeks gestation. Temperature is 36.7 C (98 F), pulse is 96/min, and respirations are 12/min. Arterial blood gas laboratory results are as follows: Which of the following is the most likely cause of this patient's abnormal arterial blood gas?

Question

A 28-year-old primigravida woman is admitted to the hospital at 10 weeks gestation.  Temperature is 36.7 C (98 F), pulse is 96/min, and respirations are 12/min.  Arterial blood gas laboratory results are as follows:  Which of the following is the most likely cause of this patient's abnormal arterial blood gas?

Quizplus · Accepted Answer

11ec25c8_da09_e106_bc81_c702ebf5be71_MD0003_00 Evaluating arterial blood gas results is a 3-step process: Evaluate the pH: This patient's increased pH of 7.49 (normal: 7.4) is indicative of alkalosis.Identify the primary process: Normal serum bicarbonate (HCO₃⁻) is 24 mEq/L and normal blood PaCO₂is 40 mm Hg. The parameter shifted in the direction that explains the change in pH represents the primary disturbance. This patient's serum HCO₃⁻ is high (shifted toward alkalinity), indicating that metabolic alkalosis is the primary disturbance.Determine the compensation: Primary metabolic disturbances are quickly compensated via adjustments in alveolar ventilation and CO₂ retention or removal. Compensation for a primary respiratory disturbance begins after several hours via adjustments in renal HCO₃⁻ excretion but requires several days (~72 hours) to complete. The compensatory response for metabolic alkalosis is respiratory acidosis. This patient's PaCO₂ of 54 mm Hg represents appropriate respiratory compensation. Evaluate the pH: This patient's increased pH of 7.49 (normal: 7.4) is indicative of alkalosis. Evaluate the pH: This patient's increased pH of 7.49 (normal: 7.4) is indicative of alkalosis. Identify the primary process: Normal serum bicarbonate (HCO₃⁻) is 24 mEq/L and normal blood PaCO₂is 40 mm Hg. The parameter shifted in the direction that explains the change in pH represents the primary disturbance. This patient's serum HCO₃⁻ is high (shifted toward alkalinity), indicating that metabolic alkalosis is the primary disturbance. Identify the primary process: Normal serum bicarbonate (HCO₃⁻) is 24 mEq/L and normal blood PaCO₂is 40 mm Hg. The parameter shifted in the direction that explains the change in pH represents the primary disturbance. This patient's serum HCO₃⁻ is high (shifted toward alkalinity), indicating that metabolic alkalosis is the primary disturbance. ⁻ ⁻ Determine the compensation: Primary metabolic disturbances are quickly compensated via adjustments in alveolar ventilation and CO₂ retention or removal. Compensation for a primary respiratory disturbance begins after several hours via adjustments in renal HCO₃⁻ excretion but requires several days (~72 hours) to complete. The compensatory response for metabolic alkalosis is respiratory acidosis. This patient's PaCO₂ of 54 mm Hg represents appropriate respiratory compensation. Determine the compensation: Primary metabolic disturbances are quickly compensated via adjustments in alveolar ventilation and CO₂ retention or removal. Compensation for a primary respiratory disturbance begins after several hours via adjustments in renal HCO₃⁻ excretion but requires several days (~72 hours) to complete. The compensatory response for metabolic alkalosis is respiratory acidosis. This patient's PaCO₂ of 54 mm Hg represents appropriate respiratory compensation. ⁻ compensation Severe vomiting involves the loss of hydrochloric acid (H⁺ and Cl⁻) and fluid volume from the gastrointestinal tract and is a common cause of metabolic alkalosis; therefore, hyperemesis gravidarum is the most likely cause of this patient's presentation. ⁻ (Choice A) The typical acid-base disturbance in asthma exacerbation is acute respiratory alkalosis (due to hyperventilation). Respiratory acidosis may develop in severe cases and suggests respiratory failure. (Choice C) Hypocapnia is a normal phenomenon of late pregnancy caused by a direct stimulatory effect of progesterone on the central respiratory center. This leads to increased respiratory drive, hyperventilation, and chronic respiratory alkalosis. (Choice D) Obesity can cause chronic hypoventilation (ie, obesity hypoventilation syndrome), leading to chronic respiratory acidosis. (Choice E) The most common acid-base disorder seen with pulmonary embolism is acute respiratory alkalosis due to hyperventilation. (Choice F) Severe diarrhea is commonly associated with nonanion gap metabolic acidosis (due to loss of HCO₃⁻and other organic anions in the stool). Metabolic alkalosis is not typical. ⁻ Educational objective: Severe vomiting (eg, hyperemesis gravidarum) is a common cause of metabolic alkalosis, which is characterized by elevated pH with elevated HCO₃⁻ and a compensatory elevation in PaCO₂. ⁻ References: Hyperemesis gravidarum-assessment and management. (http://www.ncbi.nlm.nih.gov/pubmed/17885701) Management strategies for hyperemesis. (http://www.ncbi.nlm.nih.gov/pubmed/19261546)

A 28-Year-Old Primigravida Woman Is Admitted to the Hospital at 10