Nurses urgently call the physician to evaluate a 62-year-old woman in the step-down unit due to progressive somnolence and respiratory distress. She was admitted 48 hours ago for community-acquired pneumonia and is currently receiving intravenous ceftriaxone and azithromycin. Temperature is 38.6°C (101.5°F), blood pressure is 85/54 mm Hg, pulse is 122/min, and respirations are 30/min. Pulse oximetry shows 89% on a 6 L/min simple face mask. Physical examination reveals a lethargic patient who only briefly opens her eyes to painful stimuli. She has marked intercostal retractions and diminished breath sounds with crackles at the right lung base.
| Laboratory Study | Result |
|---|---|
| Serum sodium | 138 mEq/L |
| Serum chloride | 102 mEq/L |
| Serum bicarbonate | 12 mEq/L |
| Blood urea nitrogen | 34 mg/dL |
| Serum creatinine | 1.7 mg/dL |
| Lactate | 5.6 mmol/L |
Arterial blood gas (on 6 L/min oxygen):
| Parameter | Result |
|---|---|
| pH | 7.24 |
| PaCO2 | 32 mm Hg |
| PaO2 | 62 mm Hg |
Which of the following is the most appropriate next step in management?
- Endotracheal intubation and mechanical ventilationAnswer
- BNoninvasive positive pressure ventilation
- CSwitch current antibiotics to intravenous piperacillin-tazobactam and vancomycin
- DIntravenous administration of sodium bicarbonate
- EIntravenous administration of furosemide
Answer
Endotracheal intubation and mechanical ventilation
This patient is experiencing septic shock secondary to community-acquired pneumonia, leading to severe lactic acidosis. In metabolic acidosis, the lungs normally compensate by hyperventilating to blow off CO2. Using Winter's formula (), the patient's expected PaCO2 should be between 24 and 28 mm Hg. The actual PaCO2 is 32 mm Hg. Even though 32 is lower than the normal range (35-45 mm Hg), it is inappropriately high for this degree of metabolic acidosis, indicating a concomitant primary respiratory acidosis. This relative CO2 retention, along with lethargy, hypoxia, and tachypnea, is a cardinal sign of respiratory muscle fatigue and impending respiratory failure. Because she has altered mental status and hemodynamic instability, noninvasive ventilation is contraindicated, making endotracheal intubation and mechanical ventilation the most appropriate next step.
Step-by-Step Solution
Key Concept
In patients with severe metabolic acidosis, the failure to mount adequate respiratory compensation (as calculated by Winter's formula) indicates impending respiratory muscle fatigue. If accompanied by altered mental status or hemodynamic instability, noninvasive ventilation is contraindicated, and endotracheal intubation is required.