DELCLAUX 2000: Pressure Support vs. Controlled Ventilation in ARDS (2000)

“In patients with ARDS, a ventilatory strategy combining pressure support and low tidal volume, as compared with assist-control ventilation and high tidal volume, reduced the duration of weaning from mechanical ventilation.”

— The Delclaux et al. Study Group

1. Publication Details

  • Trial Title: Pressure Support with Low Tidal Volume vs. Controlled Ventilation with High Tidal Volume for ARDS: A Randomized Trial.
  • Citation: Delclaux C, L’Her E, Alberti C, et al. Pressure support with low tidal volume vs. controlled ventilation with high tidal volume for ARDS: a randomized trial. Am J Respir Crit Care Med. 2000;161(1):87-94. doi:10.1164/ajrccm.161.1.9903091.
  • Published: January 1, 2000, in the American Journal of Respiratory and Critical Care Medicine.
  • Author: Christophe Delclaux, M.D.
  • Funding: French Ministry of Health.

2. Keywords

Acute Respiratory Distress Syndrome (ARDS), Mechanical Ventilation, Pressure Support Ventilation (PSV), Low Tidal Volume, Weaning, Lung Protective Ventilation.

3. The Clinical Question

In adult patients with ARDS (Population), does a strategy of pressure-support ventilation with a low tidal volume target (Intervention) compared to assist-control ventilation with a high tidal volume (Comparison) reduce the duration of weaning from mechanical ventilation (Outcome)?

4. Background and Rationale

  • Existing Knowledge: At the time, the optimal way to ventilate patients with ARDS was highly debated. Many centers used assist-control ventilation (ACV) with high tidal volumes (e.g., 10-15 mL/kg) to normalize blood gases. However, evidence was emerging that these high volumes could cause ventilator-induced lung injury (VILI).
  • Knowledge Gap: It was unclear if using a spontaneous breathing mode like pressure support ventilation (PSV), combined with a lower tidal volume target, could be a safer and more effective strategy, potentially leading to faster liberation from the ventilator.
  • Proposed Hypothesis: The authors hypothesized that a ventilation strategy using PSV with a low tidal volume would shorten the duration of weaning compared to a strategy of ACV with a high tidal volume.

5. Study Design and Methods

  • Design: A prospective, multicenter, randomized, controlled trial.
  • Setting: 16 intensive care units in France.
  • Trial Period: Enrollment from November 1995 to December 1997.
  • Population:
    • Inclusion Criteria: Patients with ARDS, defined by standard criteria (acute onset, bilateral infiltrates, PaO2/FiO2 ratio < 200 mm Hg, and no evidence of left atrial hypertension).
    • Exclusion Criteria: Age < 16 years, chronic respiratory failure, brain death, or contraindications to PSV (e.g., deep sedation, paralysis).
  • Intervention: PSV-low Vt Group: Ventilated with pressure support targeting a tidal volume (Vt) of 6 to 10 mL/kg of predicted body weight.
  • Control: ACV-high Vt Group: Ventilated with assist-control volume-cycled ventilation with a set Vt of 10 to 12 mL/kg of predicted body weight.
  • Management Common to Both Groups: Sedation was managed with a common protocol aiming for patient comfort and interaction. PEEP and FiO2 were adjusted according to a standardized table.

6. Key Results

  • Enrollment and Baseline: 106 patients were randomized, with 100 included in the final analysis (50 in the PSV-low Vt group, 50 in the ACV-high Vt group). The groups were well-matched at baseline.
  • Trial Status: The trial was completed as planned.
  • Primary Outcome: The median duration of weaning was significantly shorter in the PSV-low Vt group compared to the ACV-high Vt group (3 days vs. 5 days; P=0.03).
  • Secondary Outcomes: There was no significant difference in 60-day mortality (38% in the PSV-low Vt group vs. 44% in the ACV-high Vt group; P=0.53). The incidence of barotrauma was also similar between the groups.

7. Medical Statistics

  • Analysis Principle: An intention-to-treat analysis was performed.
  • Statistical Tests Used: The primary outcome (weaning duration) was analyzed using the log-rank test. Mortality was compared using a chi-square test.
  • Key Statistic(s) Reported:
    • Primary Outcome (Weaning Duration): Hazard Ratio (HR) for successful weaning 1.75 (95% CI, 1.05 to 2.92; P=0.03).
    • Secondary Outcome (60-day mortality): Relative Risk (RR) 0.86 (95% CI, 0.53 to 1.41; P=0.53).
  • Interpretation of Key Statistic(s):
    • Hazard Ratio (HR) for Weaning:
      • Formula: Conceptually, HR = (Probability of event in Intervention Group) / (Probability of event in Control Group) at any given time point.
      • Calculation: The paper reports the HR as 1.75.
      • Clinical Meaning: A hazard ratio of 1.75 means that at any given time, a patient in the PSV-low Vt group had a 75% higher chance of being successfully weaned from the ventilator compared to a patient in the ACV-high Vt group.
    • Confidence Interval (CI):
      • Formula: Conceptually, CI = (Point Estimate) ± (Margin of Error).
      • Calculation: The reported 95% CI was 1.05 to 2.92.
      • Clinical Meaning: Since the 95% CI does not cross 1.0, the result is statistically significant, suggesting the observed benefit is unlikely to be due to chance.
    • P-value:
      • Calculation: The reported p-value was 0.03.
      • Clinical Meaning: The p-value of 0.03 is less than the conventional threshold of 0.05, further confirming that the observed difference is statistically significant.
  • Clinical Impact Measures (for Mortality – Interpreted with caution as the outcome was not significant):
    • Absolute Risk Reduction (ARR):
      • Formula: ARR = (Risk in Control Group) – (Risk in Intervention Group).
      • Calculation: ARR = 44% – 38% = 6%.
      • Clinical Meaning: There was a non-significant 6% absolute reduction in mortality in the PSV-low Vt group. This finding could be due to chance.

8. Strengths of the Study

  • Randomized Controlled Design: The study used a strong methodology to compare the two ventilation strategies.
  • Important Clinical Question: It was one of the first trials to prospectively test a lower tidal volume strategy combined with a spontaneous breathing mode in ARDS.
  • Standardized Protocols: The use of standardized protocols for sedation and PEEP/FiO2 management helped to reduce confounding variables.

9. Limitations and Weaknesses

  • Small Sample Size: The trial was small and therefore underpowered to detect a difference in mortality.
  • Unblinded Design: Clinicians were aware of the treatment allocation, which could have introduced bias in co-interventions and weaning decisions.
  • Outdated Control Arm: The control group’s tidal volume (10-12 mL/kg) is now considered harmful and is no longer the standard of care.
  • Conflated Interventions: The trial tested two things at once: a different mode (PSV vs. ACV) and a different tidal volume (low vs. high), making it difficult to isolate which component was responsible for the observed effect on weaning.

10. Conclusion of the Authors

“A ventilatory strategy combining pressure support and low tidal volume, as compared with assist-control ventilation and high tidal volume, reduced the duration of weaning from mechanical ventilation without increasing morbidity or mortality.”

11. To Summarize

  • Impact on Current Practice: This trial was an important early signal in the move toward lung-protective ventilation. While it was quickly overshadowed by the larger and more definitive ARMA trial (published the same year), it provided evidence that a lower tidal volume strategy was not only safe but could also be beneficial for weaning. It supported the concept that avoiding high tidal volumes was a key component of ARDS management.
  • Specific Recommendations:
    • Patient Selection: For patients with ARDS who are able to trigger the ventilator.
    • Actionable Intervention: This trial supports the principle of targeting a lower tidal volume (6-10 mL/kg) in patients with ARDS.
    • Expected Benefit: A potential reduction in the duration of weaning from mechanical ventilation.
  • What This Trial Does NOT Mean: This trial does not prove that Pressure Support is a superior mode to Assist-Control for all patients with ARDS, especially in the early, severe phase. Its primary finding is related to weaning duration, not overall mortality.

12. Context and Related Studies

  • Building on Previous Evidence: This study built on preclinical data and smaller observational studies suggesting harm from high stretch (volutrauma) in ARDS.
  • Influence on Subsequent Research: This trial, along with others from the same era, contributed to a paradigm shift in mechanical ventilation. It was published in the same year as the landmark ARMA trial, which definitively showed that a low tidal volume strategy (6 mL/kg) significantly reduced mortality compared to a high tidal volume strategy (12 mL/kg). The ARMA trial’s larger size and mortality endpoint made it the more practice-changing study.

13. Unresolved Questions & Future Directions

  • Unresolved Questions: The optimal role and timing of spontaneous breathing modes like pressure support in the management of ARDS remains a topic of intense research and debate.
  • Future Directions: Subsequent research has focused on refining lung-protective strategies, including driving pressure, PEEP titration, and understanding the potential benefits and harms of spontaneous breathing efforts in early ARDS (the concept of patient self-inflicted lung injury, or P-SILI).

14. External Links

15. Framework for Critical Appraisal

  • Clinical Question: The question was highly relevant, addressing a key aspect of ARDS management at a time of major change in the field.
  • Methods: The randomized design was appropriate, but the small sample size and unblinded nature are significant limitations. The confounding of both mode and tidal volume makes it difficult to draw firm conclusions about either intervention in isolation.
  • Results: The primary outcome of reduced weaning time was statistically significant. However, the lack of a mortality benefit, combined with the small sample size, means the results should be interpreted with caution.
  • Conclusions and Applicability: The authors’ conclusion is a fair reflection of their data. While the specific comparison is no longer clinically relevant (as the control arm is outdated), the trial’s core principle—that avoiding high tidal volumes is beneficial—has been robustly confirmed and is a cornerstone of modern critical care.

16. Disclaimer and Contact

This summary is provided by the Academic Committee of ESBICM (ACE) to facilitate the understanding of this study; readers are advised to refer to the original trial document for a deeper understanding. If you find any information incorrect, or missing, or it needs an update or have a request for a specific critical care trial summary, kindly write to us at academics[at]esbicm.org.

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