Findings from the "Lung Safe" ARDS Epidemiology Study

29.08.2017
Author: Paul Garbarini MS, RRT, VP Product Research and Development US, Hamilton Medical, Inc., Reviewer: Mark Soucy

The Lung Safe study Epidemiology, Patterns of Care, and Mortality for Patients With Acute Respiratory Distress Syndrome in Intensive Care Units in 50 Countries (1) evaluated the recognition, incidence, mortality and management of ARDS in 450 ICU’s in 50 countries. The results of the study may be somewhat surprising in comparison to common perceptions.

Key findings:

  • ARDS patients accounted for 10.4% (3033 cases) of ICU admissions and 23.4% of ICU ventilator days; whereas the perception seems to be that ARDS is only a very small percentage of ventilator cases. These findings support the need for more recognition of ARDS patients both in terms of mortality and cost.
  • As defined by the Berlin ARDS criteria, 93% of patients with acute hypoxemic respiratory failure developed ARDS within 48 hrs; thus the need for early protective ventilation interventions.
  • The median duration of ventilation was 8 days and the ICU survival rate was 33% for all ARDS patients and 43% for severe ARDS patients. Of note is the year 2000 original ARDSnet study in which the primary intervention maintaining a 6 ml/kg IBW tidal volume in the treatment group. The mortality rate in the 6 ml group was 33%. So in the intervening 16 years it appears little, if any, progress has been made in reducing ARDS mortality. Additional study findings provide some explanation.
  • Ventilator management
    • The mean tidal volume for all ARDS patients (mild, moderate, severe) was 7.6 ml/kg and was about the same for severe ARDS, 7.5 ml/kg IBW. The difference between tidal volumes in patients recognized with ARDS vs. not recognized was not significantly different.
      35% of ARDS patients received a tidal volume greater than 8 ml/kg IBW.
      So the goal of 6 ml/kg IBW is not being achieved even if ARDS is recognized.
      (Albeit recent evidence supports using drive pressure (Plateau pressure – PEEP) as a better target to assess in reducing lung injury….more on this in our next issue)
    • The mean FiO2for severe ARDS patients was 0.90 yet the mean PEEP was only 10cm. This despite the ARDSnet protocol minimum PEEP setting being 14 cm if FiO2 0.90 and more recent evidence that higher PEEP and recruitment maneuvers may be beneficial in severe ARDS.
    • The ARDSnet goal to limit plateau pressure to less than 30 cm was unknown in the 60% of patients as plateau pressure was not measured (although in those measured, plateau pressures were 30 cm or less). So again, we are not routinely achieving protective ventilation goals.
    • ARDS was not recognized in 39.8% of ARDS patients; so these patients may help explain the low adherence to lung protective goals
    • In severe ARDS patients, 33% received recruitment maneuvers and 38% neuromuscular blockade.
      This, despite the accepted concept that PEEP is insufficient to recruit the lung and neuromuscular blockade, may be beneficial in the first 48 hrs of severe ARDS. Only 1.2% had esophageal monitoring despite recent evidence of the potential benefit. This is likely due to the lack of ventilators with this monitoring capability and clinicians’ understanding and training in transpulmonary pressures assessment.

The authors noted a major finding of the study was the under recognition of ARDS. This would suggest the need for identifying early markers of ARDS which might include assessment/trending of Static compliance, SpO2/FIO2 ratio or other ‘smart monitoring’.

Taking human factors out of adhering to goals for tidal volume, plateau pressure and driving pressure can be achieved with closed loop ventilation. Hamilton Medical’s ASV mode automatically implements ARDSnet compliant tidal volume goals in ARDS patients. Additionally, in Hamilton Medical’s IntelliVent-ASV (not available in all countries) allows the option to automatically implement ARDSnet PEEP goals and recruitment maneuvers.

As noted at the start of this discussion, the perception of many clinicians is that they don’t need ventilator ‘bells & whistles’ such as static pressure volume loops, automated recruitment maneuvers, and esophageal pressure since the incidence of ARDS is low. However, the findings of this study regarding the actual incidence of ARDS and adherence to lung protection strategies would suggest the need for more routine application of advanced techniques to manage ARDS patients.

References

  1. Epidemiology, Patterns of Care, and Mortality for Patients With Acute Respiratory Distress Syndrome in Intensive Care Units in 50 Countries. JAMA 2016 Feb 23; 315(8): 788-800

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ARDS, study, epidemiology, lung safe, criteria
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