FEATURE ARTICLES

Decrease in Paco₂ with prone position is predictive of improved outcome in acute respiratory distress syndrome*

Gattinoni, Luciano MD, FRCP; Vagginelli, Federica MD; Carlesso, Eleonora MSC; Taccone, Paolo MD; Conte, Valeria MD; Chiumello, Davide MD; Valenza, Franco MD; Caironi, Pietro MD; Pesenti, Antonio MD for the Prone-Supine Study Group

Author Information

From Istituto di Anestesia e Rianimazione (LG, FV, EC, PT, VC, DC, FV, PC), Università degli Studi di Milano, Ospedale Policlinico, IRCCS, Milan, Italy; and Istituto di Anestesia e Rianimazione (AP), Università di Milano-Bicocca, Ospedale S. Gerardo, Monza, Italy.

Supported, in part, by Hill-rom Italy, which supported investigators’ meetings and secretarial activities of the coordinating center.

Address requests for reprints to: Luciano Gattinoni, MD, FRCP, Istituto di Anestesia e Rianimazione, Ospedale Maggiore Policlinico, IRCCS, Via Francesco Sforza, 35 20122 Milano, Italy. E-mail: [email protected]

Members of the Prone-Supine Study Group and participating institutions are listed in the Appendix.

Independently of the ventilator setting, which was maintained unmodified, the patients who reacted to prone positioning with a decrease in Paco₂ had a better outcome than the patients who did not.

Critical Care Medicine 31(12):p 2727-2733, December 2003. | DOI: 10.1097/01.CCM.0000098032.34052.F9

Abstract

Objective

To determine whether gas exchange improvement in response to the prone position is associated with an improved outcome in acute lung injury (ALI)/acute respiratory distress syndrome (ARDS).

Design

Retrospective analysis of patients in the pronation arm of a controlled randomized trial on prone positioning and patients enrolled in a previous pilot study of the prone position.

Setting

Twenty-eight Italian and two Swiss intensive care units.

Patients

We studied 225 patients meeting the criteria for ALI or ARDS.

Interventions

Patients were in prone position for 10 days for 6 hrs/day if they met ALI/ARDS criteria when assessed each morning. Respiratory variables were recorded before and after 6 hrs of pronation with unchanged ventilatory settings.

Measurements and Main Results

We measured arterial blood gas alterations to the first pronation and the 28-day mortality rate. The independent risk factors for death in the general population were the Pao₂/Fio₂ ratio (odds ratio, 0.992; confidence interval, 0.986–0.998), the minute ventilation/Paco₂ ratio (odds ratio, 1.003; confidence interval, 1.000–1.006), and the concentration of plasma creatinine (odds ratio, 1.385; confidence interval, 1.116–1.720). Pao₂ responders (defined as the patients who increased their Pao₂/Fio₂ by ≥20 mm Hg, 150 patients, mean increase of 100.6 ± 61.6 mm Hg [13.4 ± 8.2 kPa]) had an outcome similar to the nonresponders (59 patients, mean decrease −6.3 ± 23.7 mm Hg [−0.8 ± 3.2 kPa]; mortality rate 44% and 46%, respectively; relative risk, 1.04; confidence interval, 0.74–1.45, p = .65). The Paco₂ responders (defined as patients whose Paco₂ decreased by ≥1 mm Hg, 94 patients, mean decrease −6.0 ± 6 mm Hg [−0.8 ± 0.8 kPa]) had an improved survival when compared with nonresponders (115 patients, mean increase 6 ± 6 mm Hg [0.8 ± 0.8 kPa]; mortality rate 35.1% and 52.2%, respectively; relative risk, 1.48; confidence interval, 1.07–2.05, p = .01).

Conclusion

ALI/ARDS patients who respond to prone positioning with reduction of their Paco₂ show an increased survival at 28 days. Improved efficiency of alveolar ventilation (decreased physiologic deadspace ratio) is an important marker of patients who will survive acute respiratory failure.