article191

HYPRESS

"Ventilation with Lower Tidal Volumes as Compared with Traditional Tidal Volumes for Acute Respiratory Distress Syndrome".The New England Journal of Medicine. 2015.

Clinical Question

Does driving pressure (ΔP) act as an independent variable associated with survival in patients with ARDS undergoing mechanical ventilation?

Bottom Line

Driving pressure (ΔP), calculated as tidal volume divided by respiratory-system compliance (VT/CRS) and reflective of the "functional" lung size, was the variable most strongly associated with survival. Decreases in ΔP due to ventilator settings were linked to increased survival in patients with ARDS.

Major Points

Among patients with ARDS, mechanical ventilation strategies using lower tidal volumes and higher positive end-expiratory pressures (PEEP) demonstrate survival benefits. However, the specific contributions of each variable remain uncertain. This analysis assessed whether ΔP, when adjusted for the severity of lung disease, could be a stronger predictor of outcomes than individual settings such as VT or PEEP.

Guidelines

As of the last knowledge update, there are no specific guidelines providing recommendations based on ΔP. Traditional guidelines for the management of ARDS highlight the role of low tidal volume ventilation and the application of PEEP.

Design

A multilevel mediation analysis of individual data from 3,562 patients with ARDS enrolled in nine randomized trials examining ΔP as an independent variable associated with survival.

Population

Patients with ARDS enrolled in nine previously reported randomized trials.

Interventions

Patients were mechanically ventilated with strategies involving different tidal volumes, plateau pressures, and PEEP as part of the randomized clinical trials.

Outcomes

ΔP, calculated as VT/CRS, was strongly associated with survival independent of predefined protective plateau pressures and VT. Changes in VT or PEEP were not independently associated with survival; they were beneficial only if associated with reductions in ΔP. ΔP mediated the beneficial effects of randomized interventions in both lower tidal volume and higher PEEP trials.

Criticisms

- The analysis was conducted post hoc and observational, requiring clinical trials designed to implement ventilator changes linked to ΔP for validation.
- The study is applicable only when the patient is not actively breathing, as ΔP interpretation becomes difficult with respiratory efforts.
- Findings may not apply beyond the ventilation ranges used in the trials: plateau pressures greater than 40 cm of water, PEEPs less than 5 cm of water, or respiratory rates above 35 per minute.
- Transpulmonary ΔP was not directly measured.

Funding

Supported by Fundação de Amparo e Pesquisa do Estado de São Paulo, Conselho Nacional de Pesquisa e Desenvolvimento, and Financiadora de Estudos e Projetos (FINEP).