A 56-year-old man comes to the emergency department due to a 1-day history of fever, chills, shortness of breath, and productive cough. The patient has an episode of vomiting while in the emergency department. He has no prior medical conditions and takes no medications. The patient has smoked for several years and occasionally drinks alcohol. Temperature is 38.8 C (101.8 F), blood pressure is 90/60 mm Hg, and pulse is 102/min. Repeat blood pressure measurement after administration of 2 L of normal saline bolus is 120/80 mm Hg. Leukocyte count is 16,000/mm³. Arterial blood gas analysis on room air shows the following: Which of the following is the most likely acid-base status of this patient?

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11ec25c8_d4f9_f371_bc81_7f195131036a_MD0003_00 This patient's presentation is consistent with sepsis due to pneumonia, which may cause a variety of primary acid-base disturbances. The evaluation of acid-base status follows a stepwise process: disturbances Evaluate the pH (normal: 7.4): This patient's elevated pH of 7.49 indicates alkalosis.Identify the primary process: Analyze the metabolic component of acid-base balance, serum HCO₃⁻ (normal: 24 mEq/L), and the respiratory component, PaCO₂(normal: 40 mm Hg). The parameter shifted in the direction that explains the change in pH represents the primary disturbance. This patient's PaCO₂ is low (shifted toward alkalinity), indicating respiratory alkalosis as the primary disturbance. Evaluate the pH (normal: 7.4): This patient's elevated pH of 7.49 indicates alkalosis. Evaluate the pH (normal: 7.4): This patient's elevated pH of 7.49 indicates alkalosis. Identify the primary process: Analyze the metabolic component of acid-base balance, serum HCO₃⁻ (normal: 24 mEq/L), and the respiratory component, PaCO₂(normal: 40 mm Hg). The parameter shifted in the direction that explains the change in pH represents the primary disturbance. This patient's PaCO₂ is low (shifted toward alkalinity), indicating respiratory alkalosis as the primary disturbance. Identify the primary process: Analyze the metabolic component of acid-base balance, serum HCO₃⁻ (normal: 24 mEq/L), and the respiratory component, PaCO₂(normal: 40 mm Hg). The parameter shifted in the direction that explains the change in pH represents the primary disturbance. This patient's PaCO₂ is low (shifted toward alkalinity), indicating respiratory alkalosis as the primary disturbance. ⁻ ₂ Determine the compensation: A primary metabolic disturbance is quickly compensated via an adjustment in alveolar ventilation and CO₂ removal. In contrast, compensation for a primary respiratory disturbance begins after several hours via adjustments in renal HCO₃⁻ excretion but requires several days to complete. The compensatory response for respiratory alkalosis is metabolic acidosis. This patient's serum HCO₃⁻ of 24 mEq/L indicates that minimal metabolic compensation has taken place. Determine the compensation: A primary metabolic disturbance is quickly compensated via an adjustment in alveolar ventilation and CO₂ removal. In contrast, compensation for a primary respiratory disturbance begins after several hours via adjustments in renal HCO₃⁻ excretion but requires several days to complete. The compensatory response for respiratory alkalosis is metabolic acidosis. This patient's serum HCO₃⁻ of 24 mEq/L indicates that minimal metabolic compensation has taken place. ⁻ ⁻ Therefore, this patient has uncompensated respiratory alkalosis, which suggests hyperventilation due to pneumonia as the primary driver of his acid-base status. (Choices A and F) Sepsis is a common cause of primary metabolic acidosis due to lactic acidosis. Unlike this patient, laboratory results should demonstrate low pH and low HCO₃⁻. Respiratory compensation typically occurs quickly via increased respiratory rate with a decrease in PaCO₂; however, the compensation may be impaired or incomplete in patients with underlying lung disease or severe sepsis. ⁻ (Choices B and G) Vomiting may lead to primary metabolic alkalosis, with laboratory results showing high pH but high HCO₃⁻. Respiratory compensation via decreased respiratory rate with an increase in PaCO₂ is typically present. ⁻ (Choices D and H) Primary respiratory acidosis results from hypoventilation, as can occur with narcotic overdose or neuromuscular weakness. Laboratory results show low pH and high PaCO₂. If the respiratory acidosis is acute, minimal renal compensation is present; however, respiratory acidosis that persists for several days is compensated by an increase in serum HCO₃⁻. ⁻ (Choice E) This patient has acute respiratory alkalosis that is uncompensated. Primary respiratory alkalosis that persists for several days (eg, residing at high altitude) is compensated by a decrease in serum HCO₃⁻, with pH approaching normal. ⁻ Educational objective: Pneumonia triggers hyperventilation that can lead to primary respiratory alkalosis, which is indicated by high pH and low PaCO₂. Serum HCO₃⁻ remains near normal in the acute setting because full renal compensation requires several days to complete. ⁻

A 56-Year-Old Man Comes to the Emergency Department Due to a 1-Day