A 60-year-old man is brought to the emergency department due to fever, chills, and confusion. The patient was fishing in the ocean yesterday and cut his foot on a jagged rock while wading through shallow water. He was unable to clean the wound right away, and overnight, it became increasingly red and painful. The patient was awakened several times by fever and chills, and this morning, his wife found him disoriented. Medical history includes hypertension. Temperature is 38.8 C (101.8 F), blood pressure is 86/62 mm Hg, pulse is 118/min, and respirations are 24/min. On physical examination, the patient is in moderate distress. Heart sounds are rapid and regular with no murmurs. The lungs are clear to auscultation. Breathing is fast and shallow. The right foot shows a laceration with purulent drainage and erythema spreading to the midshin. The results of arterial blood gas testing on room air are as follows: Which of the following best describes the acid-base status of this patient?

Question

A 60-year-old man is brought to the emergency department due to fever, chills, and confusion.  The patient was fishing in the ocean yesterday and cut his foot on a jagged rock while wading through shallow water.  He was unable to clean the wound right away, and overnight, it became increasingly red and painful.  The patient was awakened several times by fever and chills, and this morning, his wife found him disoriented.  Medical history includes hypertension.  Temperature is 38.8 C (101.8 F), blood pressure is 86/62 mm Hg, pulse is 118/min, and respirations are 24/min.  On physical examination, the patient is in moderate distress.  Heart sounds are rapid and regular with no murmurs.  The lungs are clear to auscultation.  Breathing is fast and shallow.  The right foot shows a laceration with purulent drainage and erythema spreading to the midshin.  The results of arterial blood gas testing on room air are as follows:  Which of the following best describes the acid-base status of this patient?

Quizplus · Accepted Answer

11ec25c8_d4ea_3bdc_bc81_cb6698d928ed_MD0003_00 A mixed acid-base disorder involves ≥2 primary disturbances and may be suggested by either a very abnormal pH (eg, <7.2 or >7.6) or a near-normal pH despite significant abnormalities in serum bicarbonate (HCO₃⁻) and PaCO₂. Acid-base status is best evaluated in a stepwise fashion: ⁻ Evaluate the pH (normal: 7.4): This patient's low pH of 7.08 indicates acidosis.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 serum HCO₃⁻ is low (shifted toward acidity), indicating metabolic acidosis.Determine the compensation: Primary metabolic disturbances are quickly compensated via adjustments in alveolar ventilation and CO₂ removal. The expected compensation for this patient's metabolic acidosis is respiratory alkalosis with a PaCO₂ of approximately 26 mm Hg (estimated using Winters formula). However, this patient's PaCO₂ of 42 mm Hg is much higher than expected (inappropriate compensation) (Choice A), indicating respiratory acidosis as a second primary disturbance. Evaluate the pH (normal: 7.4): This patient's low pH of 7.08 indicates acidosis. Evaluate the pH (normal: 7.4): This patient's low pH of 7.08 indicates acidosis. 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 serum HCO₃⁻ is low (shifted toward acidity), indicating metabolic acidosis. 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 serum HCO₃⁻ is low (shifted toward acidity), indicating metabolic acidosis. ⁻ ⁻ Determine the compensation: Primary metabolic disturbances are quickly compensated via adjustments in alveolar ventilation and CO₂ removal. The expected compensation for this patient's metabolic acidosis is respiratory alkalosis with a PaCO₂ of approximately 26 mm Hg (estimated using Winters formula). However, this patient's PaCO₂ of 42 mm Hg is much higher than expected (inappropriate compensation) (Choice A), indicating respiratory acidosis as a second primary disturbance. Determine the compensation: Primary metabolic disturbances are quickly compensated via adjustments in alveolar ventilation and CO₂ removal. The expected compensation for this patient's metabolic acidosis is respiratory alkalosis with a PaCO₂ of approximately 26 mm Hg (estimated using Winters formula). However, this patient's PaCO₂ of 42 mm Hg is much higher than expected (inappropriate compensation) (Choice A), indicating respiratory acidosis as a second primary disturbance. compensation The clinical presentation should then be examined to ensure that all primary disturbances are explained. This patient has sepsis due to lower extremity cellulitis (eg, fever, hemodynamic instability), which explains primary metabolic acidosis due to lactic acidosis. The marked acidemia caused by severe sepsis creates high ventilatory demand that a patient may be unable to meet. This patient's rapid, shallow breathing suggests respiratory muscle fatigue and hypoventilation, which constitutes respiratory failure and accounts for primary respiratory acidosis. In addition to antibiotics and intravenous fluids for sepsis, such patients often require intubation and mechanical ventilation. primary disturbances (Choice B) Compensated respiratory acidosis is typical of chronic hypoventilation (eg, obesity hypoventilation syndrome). Low pH, elevated PaCO₂, and an appropriate compensatory increase in HCO₃⁻ are expected. ⁻ (Choice D) Mixed metabolic acidosis and respiratory alkalosis could occur with sepsis due to pneumonia. Consistent acid-based findings are near-normal pH (opposing processes), low HCO₃⁻, and PaCO₂ that is lower than the expected respiratory compensation. ⁻ (Choice E) Mixed metabolic alkalosis and respiratory acidosis could occur with severe vomiting and opioid overdose. Consistent findings are near-normal pH, elevated HCO₃⁻, and higher-than-expected PaCO₂. ⁻ Educational objective: Mixed acid-base disorders involve ≥2 primary disturbances and can be recognized by inappropriate compensation for the initial primary disturbance. Sepsis with respiratory failure is a common cause of mixed metabolic and respiratory acidosis. References: A stepwise approach to acid-base disorders. Practical patient evaluation for metabolic acidosis and other conditions. (http://www.ncbi.nlm.nih.gov/pubmed/10728149) A practical approach to acid-base disorders. (http://www.ncbi.nlm.nih.gov/pubmed/1843849)

A 60-Year-Old Man Is Brought to the Emergency Department Due