ARDS: Should We Be Prone to Prone?

**Corey Narry**, MSN, RN, NP

The buzz in critical care circles these days is the recent publication of the results of the PROSEVA Study Group in the New England Journal of Medicine. This European study begs to answer the question long-debated by critical care professionals over the years - is there a benefit to prone positioning in Acute Respiratory Distress Syndrome (ARDS)? Prior to the release of the PROSEVA results, trials that tested this hypothesis have failed to show a beneficial effect on patient outcomes.

Before going further on the topic, allow me to refresh our memories and establish an understanding of what happens in ARDS, a life-threatening condition many of us critical care professionals have encountered in our practice. In normal individuals, oxygen enters our respiratory tract into air filled sacs in our lungs called alveoli. Capillaries run through the walls of each alveoli exchanging carbon dioxide with oxygen which is then carried into our bloodstream to supply our organs with this life-sustaining gas.

ARDS develops in the lungs of patients for multiple reasons, infection and trauma being common. The lungs become injured by fluid accumulating in the patient's alveoli thus preventing them from filling with air. The capillaries that run through the alveolar walls are not able to exchange carbon dioxide for oxygen to be delivered into the bloodstream. As we all know, our organs such as the brain, heart, and kidneys are hungry for oxygen and the effect of prolonged absence of oxygen-rich blood affects their function.

In Medicine, a diagnosis of ARDS is made when the following criteria are met: (1) acute onset, (2) bilateral infiltrates on chest x-ray, (3) PAWP

Mechanically ventilated lungs suffer from further injury because of the artificial nature of positive pressure ventilation which forces a volume of air into alveolar sacs causing undue strain. Recumbent positioning creates dependent areas of fluid-filled alveoli centered in the posterior segments of the lungs. Forced air follows the path of least resistance so that a set volume of oxygen delivered by the ventilator can potentially over-distend the remaining healthy alveoli. This causes a vicious cycle of further lung injury. Prone positioning, in theory, allows for a homogenous distribution of stress and strain within all the alveoli.

The investigators in the PROSEVA study had astounding results. 466 Adult ICU patients in France and Spain were enrolled in the study and randomized to Supine Group (n-229) and Prone Group (n-237). At 28 days, patients who were placed in prone position for 16 hours daily had 16% mortality compared to 32.8% in the patients who remained in semi-recumbent position. At 90 days, mortality for the patients who were placed in the prone position was 23.6% vs 41% in the group who remained supine. Successful extubation was higher in the prone group at 80.5% at 90 days compared to 65% in the supine group. Length of stay and let me gasp for a minute...incidence of complications such as accidental extubations and cardiac arrests were insignificant between the two groups. Results were adjusted based on severity of symptoms and organ failure.

It should be mentioned that the centers who participated in the study all have experience with prone positioning at a minimum of 5 years and that no specialized beds or contraptions were used in all the ICU's that participated. All patients were laid on standard ICU beds and the technique of prone positioning was standardized across all the participating centers. Anyone interested in the technique should log into their hospital's free access to the New England Journal of Medicine articles to see a video depicting the technique used. I guarantee that you will get a kick out of hearing a male voice speaking in a French accent explaining the steps while three young women dressed in white who look like nurses perform the prone positioning on a patient.

The PROSEVA study has its share of criticisms just like any other new piece of evidence. Foremost among them is the fact that the centers enrolled in the study have all been shining stars in terms of mastering prone positioning as a modality in ARDS. Not every center in Europe, much less the US, could say the same thus making reproducibility of results precarious to say the least in centers with very little experience on the technique. For obvious reasons, the study is not blinded. Fluid volume status, an essential consideration in ARDS outcomes was not mentioned in the results. Body mass index in both groups averaged at 29, a number not quite consistent with a svelte figure but the mere thought of morbidly obese American patients with higher BMI's being proned truthfully makes my heart skip a beat...and I'm not judging here!

Nevertheless, the results of the PROSEVA study will undoubtedly cause a jolt of excitement within the critical care community and many an intensivists will want to replicate the results in their practice. As a nursing professional with years of practice at the bedside in the ICU, my hope is that any plan to introduce such a practice change in our respective ICU's be met with heavy input from nurses at the bedside. The huge burden of manpower required for implementing such modality calls for adequate staffing levels and involvement of a dedicated team of respiratory therapists. Let me know your thoughts, are you now prone to prone?

ARDS: Should We Be Prone to Prone?

About Corey Narry, MSN, RN, NP

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