EBQ:ARDSnet Trial

incomplete Journal Club Article

Brower RG, et al. "Ventilation With Lower Tidal Volumes As Compared With Traditional Tidal Volumes For Acute Lung Injury And The Acute Respiratory Distress Syndrome". The New England Journal of Medicine. 2000. 342(18):1301-1308.
PubMed Full text PDF

Clinical Question

Does a lung protective strategy of low tidal volumes in patients with Acute Lung Injury (ALI) and Acute Respiratory Distress Syndrome (ARDS) decrease mortality and ventilator-free days when compared to traditional ventilation strategies.

Conclusion

In patients with ALI/ARDS, lower tidal volumes of 6mL/kg ideal body weight reduces mortality and decreases length of time on mechanical ventilation.

Major Points

• Acute Respiratory Distress Syndrome results from alveolar damage and barotrauma are associated with elevated plateau pressures and higher tidal volume ventilations
• The trial was stopped early when patients in the low tidal volumes arm showed a significant decrease in mortality and more ventilator-free days compared to the traditional tidal volumes arm.

Guidelines

See Surviving Sepsis 2012

Design

• Multicenter, randomized trial of 861 patients in parallel-group in 10 university-affiliated ARDSNet centers
  • Low tidal volumes: Starting at 6ml/kg PBW and plateau pressure ≤30cmH2O (n=432)
  • Traditional tidal volumes: starting at 12ml/kg PBW and plateau pressure of ≤50cmH2O (n=429)
• Enrollment: March 1996 to March 1999 (terminated early after the fourth interim analysis)
• Follow-up: 180 days or until home breathing independently

Population

Inclusion Criteria

• Age ≥18 years
• Receiving mechanical ventilation
• Diagnosis of ALI/ARDS ≤36h prior to enrollment; defined as:
  • Acute decrease in PaO2/FiO2ratio to ≤300
  • CXR: Bilateral pulmonary infiltrates
  • PCWP of ≤18mmHg without evidence of left atrial hypertension

Exclusion Criteria

• Pregnancy
• Increased ICP, neuromuscular disease imparing spontaneous breathing, sickle cell disease, or severe chronic respiratory disease
• Weight more than 1kg/cm of height
• Burns >30% of BSA
• Estimated 6-month mortality rate >50%
• History of bone marrow or lung transplantation
• Child-Pugh class C liver disease
• Participation in other trials w/in 30 days

Baseline Characteristics

• Mean age: 51.5 years
• Gender: Female (40.5%)
• Ethnicity:
  • White: 73%
  • Black: 17.5%
  • Hispanic: 6%
• APACHE III score: 82.5
• Mean PaO2:FiO2: 136
• Mean tidal volume: 670 mL
• Mean minute ventilation: 13.4 vs. 12.7 L/min (P=0.01)

Interventions

Patients randomly assigned to receive mechanical ventilation (volume-assist-control mode) with following strategies for tidal volume:

• Low tidal volumes (lung protective strategy): Starting at 6ml/kg PBW to maintain plateau pressure ≤30cm H₂O (n=432)
• Traditional tidal volumes: Starting at 12ml/kg to maintain plateau pressure of ≤50cm H₂O (n=429)

Patients monitored until day 28 or death for signs of system failure:

• Circulatory failure: SBP ≤90mmHg or need for vasopressor
• Coagulation failure: Platelets ≤80,000 mm3
• Hepatic failure: Bilirubin ≥2mg/dL
• Renal failure: Creatinine ≥2mg/dL

Outcomes

Primary Outcomes

180-day mortality

• 31.0% vs. 39.8% (RR 0.78; P=0.007)

Ventilator-free days (Days 1-28)

• 12 vs. 10 (P=0.007)

Breathing without assistance by day 28

• 65.7% vs. 55.0% (P<0.001; NNT 9)

Funding

The National Heart, Lung, and Blood Institute.

CME

1 According to the ARDSnet study, which of the following strategies is indicated?

	Tidal volumes of 10 ml/kg.
	Plateau pressure to be maintained at >45 cm
	Increase PEEP to achieve >90% oxygen saturation
	Maintain patient-ventilator synchrony

2 Pulmonary question: Which of the following are potential complications from endotacheal intubation and ventilatory management?

	cardiac dysfunction and hypotension
	barotrauma and pneumothorax
	elevated intracranial pressure
	ventilator-induced lung injury
	auto-PEEP

3 Regarding mechanical ventilation, all of the following statements are TRUE, EXCEPT:

	Acute respiratory failure can be defined by the presence of at least two of four criteria: 1) acute dyspnea, 2) PaO2<50mm at room air, 3) PaCO2>50mm, and 4) significant respiratory acidemia.
	One potential adverse effect of positive-pressure ventilation includes decreased venous return to the heart and decreased cardiac output.
	The best approach to use in patients with asthma is to use small tidal volumes (5-8ml/kg) and high inspiratory flow rates to reduce inspiratory time and peak airway pressures.
	When inadequate expiratory time is allowed in the COPD patient, air trapping is exacerbated with each inspiration and may eventually result in a high level of intrinsic PEEP (iPEEP or auto-PEEP) such that the inhaled volume cannot overcome the exhaled volume; the solution is to build adequate expiratory time into the ventilator settings.
	The ventilator rate for COPD patients should be titrated as high as possible with I/E ratios of 1:1.