High‐frequency ventilation versus conventional ventilation for treatment of acute lung injury and acute respiratory distress syndrome
Abstract
Background
High frequency oscillation is an alternative to conventional mechanical ventilation that is sometimes used to treat patients with acute respiratory distress syndrome, but effects on oxygenation, mortality and adverse clinical outcomes are uncertain. This review was originally published in 2004 and was updated in 2011.
Objectives
To determine clinical and physiological effects of high frequency oscillation (HFO) in patients with acute lung injury (ALI) or acute respiratory distress syndrome (ARDS) compared to conventional ventilation.
Search methods
We electronically searched CENTRAL (Ovid), MEDLINE (Ovid), EMBASE (Ovid), and ISI (from inception to March 2011). The original search was performed in 2002. We manually searched reference lists from included studies and review articles; searched conference proceedings of the American Thoracic Society (1994 to 2010), Society of Critical Care Medicine (1994 to 2010), European Society of Intensive Care Medicine (1994 to 2010), and American College of Chest Physicians (1994 to 2010); contacted clinical experts in the field; and searched for unpublished and ongoing trials in clinicaltrials.gov and controlled‐trials.com.
Selection criteria
Randomized controlled clinical trials comparing treatment using HFO with conventional mechanical ventilation for children and adults diagnosed with ALI or ARDS.
Data collection and analysis
Three authors independently extracted data on clinical, physiological, and safety outcomes according to a predefined protocol. We contacted investigators of all included studies to clarify methods and obtain additional data. We used random‐effects models in the analyses.
Main results
Eight RCTs (n = 419) were included; almost all patients had ARDS. The risk of bias was low in six studies and unclear in two studies. The quality of evidence for hospital and six‐month mortality was moderate and low, respectively. The ratio of partial pressure of oxygen to inspired fraction of oxygen at 24, 48, and 72 hours was 16% to 24% higher in patients receiving HFO. There were no significant differences in oxygenation index because mean airway pressure rose by 22% to 33% in patients receiving HFO (P < 0.01). In patients randomized to HFO, mortality was significantly reduced (RR 0.77, 95% CI 0.61 to 0.98; P = 0.03; 6 trials, 365 patients, 160 deaths) and treatment failure (refractory hypoxaemia, hypercapnoea, hypotension, or barotrauma) was less likely (RR 0.67, 95% CI 0.46 to 0.99; P = 0.04; 5 trials, 337 patients, 73 events). Other risks, including adverse events, were similar. We found substantial between‐trial statistical heterogeneity for physiological (I2 = 21% to 95%) but not clinical (I2 = 0%) outcomes. Pooled results were based on few events for most clinical outcomes.
Authors' conclusions
The findings of this systematic review suggest that HFO was a promising treatment for ALI and ARDS prior to the uptake of current lung protective ventilation strategies. These findings may not be applicable with current conventional care, pending the results of large multi‐centre trials currently underway.
PICOs
Plain language summary
High frequency oscillation for the treatment of acute respiratory distress syndrome
Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are life‐threatening conditions. They are characterized by acute lung inflammation causing pulmonary congestion, stiff lungs that increase the work of breathing, and reduced ability of the lungs to adequately oxygenate the blood. Survivors can have a reduced quality of life. Patients with ALI or ARDS usually require mechanical ventilation in order to prevent death. High frequency oscillation (HFO) ventilation differs from conventional ventilation in that very small tidal volumes are delivered very rapidly with each breath (3 to15 Hz, or 180 to 900 breaths per minute). HFO facilitates the re‐expansion of collapsed lung tissue at a constant mean airway pressure. We performed a systematic review to determine whether HFO improves clinical outcomes (including preventing deaths) when compared to conventional mechanical ventilation of adults and children with ALI or ARDS.
We included eight randomized controlled trials enrolling 419 patients. HFO as an initial ventilation strategy reduced the risk of death in hospital by 23% in six trials enrolling 365 patients, and reduced the risk of treatment failure by 33% in five trials enrolling 337 patients. The ability of the lungs to oxygenate blood, measured at 24 to 72 hours of ventilation after randomization, was 16% to 24% better in patients receiving HFO. HFO had no effect on the duration of mechanical ventilation. The risk of adverse events, including low blood pressure or further injury to the lung due to high airway pressure, was not increased. We found substantial inconsistency for physiological outcomes such as oxygenation and carbon dioxide removal from the blood but not clinical outcomes. The quality of evidence is moderate at best for outcomes that would be most important to patients due to small numbers of trials, patients, and events. This indicates that randomized trials that are currently ongoing may change or impact these findings.
