Type 1 Respiratory Failure
This patient has Type 1 (hypoxemic) respiratory failure, characterized by severe hypoxemia (PO2 59 mm Hg, SpO2 85%) with a low-normal PCO2 (25 mm Hg) and respiratory alkalosis (pH 7.54). 1, 2
Pathophysiologic Classification
The arterial blood gas definitively distinguishes between respiratory failure types:
- Type 1 respiratory failure presents with PaO2 <60 mm Hg (8 kPa) with normal or low PCO2, resulting from failure to maintain adequate oxygenation despite normal or increased ventilatory effort 1, 2
- Type 2 respiratory failure is distinguished by the presence of hypercapnia (PCO2 ≥45 mm Hg with pH <7.35) from alveolar hypoventilation 3, 4
This patient's PCO2 of 25 mm Hg (well below normal 35-45 mm Hg) with severe hypoxemia clearly indicates Type 1 failure 2, 3
Clinical Context Supporting Type 1 Failure
The clinical presentation strongly supports pneumonia causing Type 1 respiratory failure:
- Rust-colored sputum is pathognomonic for bacterial pneumonia (typically Streptococcus pneumoniae), which causes ventilation-perfusion mismatch and intrapulmonary shunting 5
- Tachypnea (RR 30/min) represents compensatory hyperventilation attempting to correct hypoxemia, which explains the low PCO2 and respiratory alkalosis 5
- Fever and dyspnea with bilateral infiltrates are hallmarks of severe community-acquired pneumonia leading to hypoxemic respiratory failure 5
Why Other Options Are Incorrect
Alveolar hypoventilation is physiologically impossible here—the patient is hyperventilating (RR 30/min, PCO2 25 mm Hg), not hypoventilating 2, 4
Primary respiratory acidosis requires elevated PCO2 with low pH; this patient has respiratory alkalosis (pH 7.54, PCO2 25 mm Hg) 3
Type 2 respiratory failure requires PCO2 ≥45 mm Hg with acidemia; this patient's PCO2 is 25 mm Hg 3, 4
Immediate Management Priorities
Given SpO2 85% (critically low), immediate oxygen therapy is mandatory:
- Start with reservoir mask at 15 L/min for initial SpO2 below 85%, targeting saturation 94-98% 5
- Measure arterial blood gases in all critically ill patients to guide ongoing management 5
- Consider high-flow nasal oxygen (HFNO) if standard oxygen fails to maintain SpO2 >93% with increasing respiratory rate 5
- Prepare for possible intubation if oxygenation cannot be maintained or work of breathing becomes unsustainable 6
Critical Pitfall to Avoid
Do not confuse the compensatory hyperventilation (low PCO2) with primary hyperventilation disorder—the severe hypoxemia (PO2 59 mm Hg) is the primary pathology driving the respiratory response 5, 2. The rust-colored sputum and fever confirm infectious pneumonia as the underlying cause requiring antimicrobial therapy in addition to oxygen support 5.