Key Findings of the ARDSNet Trial on Ventilation Strategies for ARDS
The ARDSNet trial demonstrated that a low tidal volume ventilation strategy (6 ml/kg predicted body weight) with plateau pressure ≤30 cmH2O significantly reduced mortality in ARDS patients compared to traditional ventilation strategies with higher tidal volumes (12 ml/kg predicted body weight). 1
Primary Findings
- The trial showed a 22% relative reduction in mortality using 6 ml/kg predicted body weight tidal volume compared to 12 ml/kg predicted body weight 2
- Plateau pressure was limited to ≤30 cmH2O in the low tidal volume group, compared to ≤50 cmH2O in the traditional ventilation group 1
- The low tidal volume strategy became the foundation for lung-protective ventilation in ARDS patients 1, 3
Ventilation Parameters from ARDSNet
- Tidal volume: 4-8 ml/kg predicted body weight (targeting 6 ml/kg) 1
- Plateau pressure: maintained ≤30 cmH2O 1, 4
- Predicted body weight calculation:
- Males = 50 + 0.91[height (cm)-152.4] kg
- Females = 45.5 + 0.91[height (cm)-152.4] kg 1
- Respiratory rate: adjusted to maintain adequate minute ventilation for pH control 3
Mechanism of Benefit
- Lower tidal volumes and plateau pressures reduce ventilator-induced lung injury (VILI) by preventing alveolar overdistension 1, 4
- The strategy attenuates systemic and pulmonary inflammatory cytokine responses 1
- Driving pressure (plateau pressure minus PEEP) has been identified as an important predictor of outcomes in ARDS 1
Implementation and Adoption
- Despite strong evidence, implementation of low tidal volume ventilation in clinical practice was initially slow 2
- A 2004 study showed that after publication of ARDSNet results, mean tidal volumes decreased from 12.3 ml/kg to 10.6 ml/kg, but still remained above the recommended 6 ml/kg 2
- The efficacy of low tidal volume ventilation was consistent across different clinical risk factors for ARDS (sepsis, pneumonia, aspiration, trauma) 5
Additional Insights and Subsequent Research
- The ARDSNet trial excluded patients with elevated intracranial pressure, potentially limiting generalizability to certain populations like subarachnoid hemorrhage patients 1
- Subsequent research has explored even lower tidal volumes (approximately 3 ml/kg) with extracorporeal CO2 removal, showing potential benefits in more hypoxemic patients 6
- Later studies have investigated combining low tidal volume with other strategies like recruitment maneuvers and higher PEEP levels 7
- Driving pressure (plateau pressure minus PEEP) has emerged as possibly a better predictor of outcomes than tidal volume or plateau pressure alone 1
Clinical Implications
- Low tidal volume ventilation is now recommended for all ARDS patients by major respiratory and critical care societies 1, 3
- For severe ARDS, additional strategies like prone positioning for >12 hours/day are strongly recommended 1
- The ARDSNet protocol has influenced ventilation strategies beyond ARDS, with many clinicians adopting lower tidal volumes for all mechanically ventilated patients 3
- Airway pressure release ventilation (APRV) has been studied as an alternative strategy that may further reduce ventilation duration in ARDS 8
Common Pitfalls to Avoid
- Using actual body weight instead of predicted body weight for tidal volume calculations can lead to excessive volumes 3
- Failing to adjust tidal volumes for patients with decreased functional lung size (baby lung concept) 1
- Allowing plateau pressures to exceed 30 cmH2O, which increases risk of barotrauma 4
- Inadequate sedation leading to ventilator dyssynchrony and potentially higher plateau pressures 3
The ARDSNet trial fundamentally changed mechanical ventilation practices for ARDS patients, establishing lung-protective ventilation as a standard of care that continues to influence critical care practice today.