Effect of Prone Positioning on the Survival of Patients with Acute Respiratory Failure

Summary by Kelsey, Lawrence DO, 8.8.23
https://www.nejm.org/doi/full/10.1056/NEJMoa010043


Effect of Prone Positioning on the Survival of Patients with Acute Respiratory Failure


Clinical Hypothesis: A predefined strategy of prone positioning will improve the survival of patients with acute lung injury/ARDS since it is known that prone positioning improves oxygenation. Clinical relevance was defined as a 20% decrease in the mortality rate with the use of prone positioning.

Take Home Message:

  • - There was no significant difference in mortality rates at 10 days, ICU discharge, or at 6 months. This study does not suggest any improved survival overall in patients with ARDS.

  • - However, the use of the prone position improved oxygenation in more than 70 percent of the instances in which it was used, with about 70 percent of the effect occurring during the first hour of pronation.

  • - Prone positioning of patients at the highest risk may result in a survival advantage that was subsequently lost at the time of discharge from the ICU. Authors believe that this may have been the result of simply delaying the inevitable outcome of death.

  • - This study confirms that prone positioning improves arterial oxygenation and prone positioning may be useful in patients with severe hypoxemia, but other uses are limited. At the time of publishing this paper, there was a need for another trial to clarify the role of prone positioning in patients with particularly severe ARDS.

Summary:

  • Background: A landmark 1976 study showed that prone positioning dramatically improved the oxygenation of patients with ARDS. Mechanisms for this improvement may include increased end-expiratory lung volume, better ventilation-perfusion matching, and alterations in chest wall mechanics. Additionally, animal models have shown that prone positioning protects against ventilator-induced lung injury. However, the effect it has on overall survival is unknown.

  • Study Design: Multicenter, randomized trial that compared conventional treatment in the supine position with prone positioning for 6 or more hours a day for 10 days. 304 patients total were enrolled; 152 in each group.

-Physicians caring for patients in the prone position were asked not to change ventilatory settings during pronation in order to standardize the assessment of the changes in gas exchange afforded by the maneuver.

Methods:

Inclusion criteria: Patients were eligible if they met the following modified criteria for acute lung injury or ARDS: a ratio of partial pressure of arterial oxygen (PaO2) to fraction of inspired oxygen (FiO2) of 200 or less with a positive end-expiratory pressure of at least 5 cm of water, or a PaO2:FiO2 ratio of 300 or less with a positive end-expiratory pressure of at least 10 cm of water, radiographic evidence of bilateral pulmonary infiltrates, and (if measured) a pulmonary-capillary wedge pressure of 18 mm Hg or less or the absence of clinical evidence of left atrial hypertension.

Exclusion criteria: Patients were excluded from the study if they were younger than 16 years of age; had evidence of cardiogenic pulmonary edema, cerebral edema, or intracranial hypertension; or had clinical conditions that might have contraindicated the use of the prone position, such as fractures of the spine or severe hemodynamic instability.

Primary outcome: Primary endpoints were death at 10 days (the end of the period involving prone positioning), at the time of discharge from the intensive care unit, and 6 months after randomization.

- The survival rate was analyzed according to the Kaplan-Meier method

Secondary outcome: Secondary endpoints were improvement in respiratory failure and improvement in organ dysfunction at 10 days.

  • - Each morning, patients were assessed for respiratory and biochemical variables that are used to monitor patients for non-pulmonary organ failure as defined in the ARDSnet trial.

  • - Patients were also divided into quartiles based on their PaO2:FiO2 ratios and tidal volumes.


Results: The mortality rate did not differ significantly between the prone group and the supine group at the end of the 10-day study period (21.1% vs 25%), at the time of discharge from the ICU (50.7% vs 48%), or at 6 months (62.5% vs 58.6%).

  • - There was a significant difference in respiratory variables such as the PaO2:FiO2 ratio and tidal volume

  • - There was no statistically significant difference in the incidence of dysfunction of the various organ systems considered.

  • There was a significantly lower 10-day mortality rate in the prone group in the quartile with the lowest PaO2:FiO2 ratio (23.1% vs 47.2%) as well as the quartile with the highest tidal volume (18.2% vs 41%). However, these differences in mortality did not persist beyond discharge from the ICU. 

Discussion/conclusion: There was no significant difference in mortality rates at 10 days, ICU discharge, or at 6 months. This study does not suggest any improved survival overall in patients with ARDS.

  • - However, the use of the prone position improved oxygenation in more than 70 percent of the instances in which it was used, with about 70 percent of the effect occurring during the first hour of pronation.

  • - Prone positioning of patients at the highest risk may result in a survival advantage that was subsequently lost at the time of discharge from the ICU. Authors believe that this may have been the result of simply delaying the inevitable outcome of death.

  • - This study confirms that prone positioning improves arterial oxygenation and prone positioning may be useful in patients with severe hypoxemia, but other uses are limited. At the time of publishing this paper, there was a need for another trial to clarify the role of prone positioning in patients with particularly severe ARDS.