Just over 10% of patients in intensive care units around the world have Acute Respiratory Distress Syndrome, a condition that continues to have a high mortality rate despite advances in care, according to one of the biggest studies ever conducted in critical care. However, the study involving more than 450 ICUs in 50 countries on five continents found that that ARDS is under-recognised and under-treated, said Dr John Laffey, the lead author and chief anesthesiologist at St Michael’s Hospital in Toronto.
“We know that 40% of patients with ARDS die, either of this syndrome or their primary illness or injury, so this new, global understanding of this important public health issue and how we are treating it is enormously important for patients and clinicians,” said Laffey, who is also a scientist with the hospital’s Keenan Research Centre for Biomedical Science.
ARDS occurs in in patients with critical illnesses such as severe infections or following severe injuries. An uncontrolled inflammatory response damages the lining of the lungs causing fluid to build up in the tiny, elastic air sacs in the lungs known as alveoli, reducing the amount of oxygen that reaches the bloodstream. Patients with ARDS are unable to breathe on their own and require artificial ventilation.
The LUNG SAFE (Large observational study to UNderstand the Global impact of Severe Acute respiratory FailurE ) study was carried out by the European Society of Intensive Care Medicine, and enrolled 29,144 patients admitted to 459 ICUs in 2014. It found that while 10.4% of those patients developed ARDS – about six patients per ICU bed per year – 40% of all cases were not diagnosed. The number of patients who died in hospital was 34%, 40.3% and 46.1% for mild, moderate and severe ARDS respectively.
Laffey said the reasons for failing to recognise ARDS are likely complex, and include the fact there is no single test for diagnosing a syndrome made up of many symptoms. But making the diagnosis is important because it influences the care delivered. Another finding of the study was that approaches to managing patients with ARDS are inconsistent, indicating perhaps that more research is needed to provide evidence that certain treatments are effective.
For example, less than two-thirds of ARDS patients received “protective” forms of mechanical ventilation known to cause less damage to the lungs. The study defined “protective” tidal volumes – the volume of air inhaled or exhaled at a time – as being based on a person’s ideal weight rather than his or her actual weight. Lung size is related to ideal weight, which is derived from height, not actual body weight.
The study found that clinicians used lower-than-expected levels of PEEP, or positive-end expiratory pressure, the amount of pressure applied by the ventilator at the end of an exhalation. This was somewhat surprising, especially for patients with more severe ARDS, Laffey said, raising concerns that these patients may not have had enough PEEP to prevent parts of their lungs from collapsing.
Only 14.5% of patients in the study received ventilation while lying in the prone position, which improves oxygenation in most patients with ARDS.
The study also found geographic differences in the recognition and treatment of ARDS, although not as large as they expected. The highest incidence of ARDS was in Australia and New Zealand, followed by Europe and North America.
Importance: Limited information exists about the epidemiology, recognition, management, and outcomes of patients with the acute respiratory distress syndrome (ARDS).
Objectives: To evaluate intensive care unit (ICU) incidence and outcome of ARDS and to assess clinician recognition, ventilation management, and use of adjuncts—for example prone positioning—in routine clinical practice for patients fulfilling the ARDS Berlin Definition.
Design, Setting, and Participants: The Large Observational Study to Understand the Global Impact of Severe Acute Respiratory Failure (LUNG SAFE) was an international, multicenter, prospective cohort study of patients undergoing invasive or noninvasive ventilation, conducted during 4 consecutive weeks in the winter of 2014 in a convenience sample of 459 ICUs from 50 countries across 5 continents.
Exposures: Acute respiratory distress syndrome.
Main Outcomes and Measures: The primary outcome was ICU incidence of ARDS. Secondary outcomes included assessment of clinician recognition of ARDS, the application of ventilatory management, the use of adjunctive interventions in routine clinical practice, and clinical outcomes from ARDS.
Results: Of 29 144 patients admitted to participating ICUs, 3022 (10.4%) fulfilled ARDS criteria. Of these, 2377 patients developed ARDS in the first 48 hours and whose respiratory failure was managed with invasive mechanical ventilation. The period prevalence of mild ARDS was 30.0% (95% CI, 28.2%-31.9%); of moderate ARDS, 46.6% (95% CI, 44.5%-48.6%); and of severe ARDS, 23.4% (95% CI, 21.7%-25.2%). ARDS represented 0.42 cases per ICU bed over 4 weeks and represented 10.4% (95% CI, 10.0%-10.7%) of ICU admissions and 23.4% of patients requiring mechanical ventilation. Clinical recognition of ARDS ranged from 51.3% (95% CI, 47.5%-55.0%) in mild to 78.5% (95% CI, 74.8%-81.8%) in severe ARDS. Less than two-thirds of patients with ARDS received a tidal volume 8 of mL/kg or less of predicted body weight. Plateau pressure was measured in 40.1% (95% CI, 38.2-42.1), whereas 82.6% (95% CI, 81.0%-84.1%) received a positive end-expository pressure (PEEP) of less than 12 cm H2O. Prone positioning was used in 16.3% (95% CI, 13.7%-19.2%) of patients with severe ARDS. Clinician recognition of ARDS was associated with higher PEEP, greater use of neuromuscular blockade, and prone positioning. Hospital mortality was 34.9% (95% CI, 31.4%-38.5%) for those with mild, 40.3% (95% CI, 37.4%-43.3%) for those with moderate, and 46.1% (95% CI, 41.9%-50.4%) for those with severe ARDS.
Conclusions and Relevance: Among ICUs in 50 countries, the period prevalence of ARDS was 10.4% of ICU admissions. This syndrome appeared to be underrecognized and undertreated and associated with a high mortality rate. These findings indicate the potential for improvement in the management of patients with ARDS.