Is a PaO2 (partial pressure of arterial oxygen) goal of 55-80 mmHg acceptable for Acute Respiratory Distress Syndrome (ARDS) patients?

Oxygenation Goals in Acute Respiratory Distress Syndrome (ARDS)

A PaO2 target range of 70-90 mmHg (or SpO2 92-97%) is recommended for patients with ARDS, rather than the lower range of 55-80 mmHg, due to potential safety concerns with more conservative oxygenation targets. 1, 2

Evidence-Based Oxygenation Targets

Current Recommendations

• The most recent guidelines from critical care societies recommend maintaining PaO2 between 70-90 mmHg or SpO2 between 92-97% in ARDS patients 1, 2
• This represents a slightly higher target than the previously suggested range of 55-80 mmHg from the ARDS Clinical Trials Network

Safety Concerns with Lower Targets

• The LOCO2 trial (2020) compared conservative oxygen therapy (PaO2 55-70 mmHg; SpO2 88-92%) with liberal oxygen therapy (PaO2 90-105 mmHg; SpO2 ≥96%) 3
• This trial was stopped early due to safety concerns and showed:
  • No difference in 28-day mortality (34.3% vs 26.5%)
  • Higher 90-day mortality in the conservative-oxygen group (44.4% vs 30.4%)
  • Five mesenteric ischemic events occurred in the conservative-oxygen group 3

ARDS Severity and Oxygenation Management

ARDS Classification

• ARDS severity is classified based on PaO2/FiO2 ratio:

  • Mild: 201-300 mmHg
  • Moderate: 101-200 mmHg
  • Severe: ≤100 mmHg 2

• Some evidence suggests that a PaO2/FiO2 threshold of 150 mmHg may be useful for risk stratification, with patients below this threshold having higher mortality (OR 1.6,95% CI 1.1-2.4) 4

Management Based on Severity

• For mild ARDS: Basic lung-protective ventilation with PEEP 5-10 cmH2O
• For moderate ARDS: Higher PEEP, consider neuromuscular blockers
• For severe ARDS (PaO2/FiO2 <150 mmHg): Higher PEEP, prone positioning, neuromuscular blockers 1, 2

Ventilation Strategies to Improve Oxygenation

Core Principles

• Use lung-protective ventilation with tidal volumes of 6 mL/kg predicted body weight 1, 2
• Maintain plateau pressures ≤30 cmH2O 1, 2
• Apply appropriate PEEP to prevent alveolar collapse at end-expiration 1

Advanced Strategies for Refractory Hypoxemia

• For patients with PaO2/FiO2 <150 mmHg:

  • Prone positioning (strong recommendation, moderate quality evidence) 1, 2
  • Neuromuscular blocking agents for ≤48 hours 1, 2
  • Recruitment maneuvers before PEEP selection 1, 5

• Combined prone positioning and recruitment maneuvers have shown marked oxygenation improvement in studies 5

Practical Implementation

Monitoring Approach

• Regularly assess arterial blood gases to monitor PaO2 levels
• Use pulse oximetry for continuous monitoring, targeting SpO2 92-97%
• Calculate PaO2/FiO2 ratio under standardized ventilatory settings (PEEP ≥10 cmH2O and FiO2 ≥0.5) for more accurate risk stratification 6

Avoiding Common Pitfalls

• Avoid excessive oxygen administration: Physicians often prescribe higher FiO2 levels than necessary, which may increase the risk of oxygen toxicity 7
• Avoid excessively low oxygenation targets: The LOCO2 trial suggests potential harm with very conservative targets (PaO2 55-70 mmHg) 3
• Avoid delayed implementation of advanced strategies: For severe ARDS with PaO2/FiO2 <150 mmHg, promptly consider prone positioning and neuromuscular blockade 1, 2

Fluid Management and Adjunctive Therapies

• Implement a conservative fluid strategy for established ARDS without evidence of tissue hypoperfusion 1, 2
• Elevate the head of the bed to 30-45 degrees to reduce ventilator-associated pneumonia risk 1, 2
• Minimize sedation and implement a weaning protocol when appropriate 1, 2

In conclusion, while the ARDS Network previously suggested a PaO2 target of 55-80 mmHg, more recent evidence supports targeting a PaO2 of 70-90 mmHg or SpO2 of 92-97% to balance the risks of hypoxemia and oxygen toxicity.