In Acute Brain Injury, Protective Ventilation Strategies May Not Affect Outcomes

In patients with acute brain injury receiving invasive mechanical ventilation (MV), use of low tidal volume (Vt) and/or moderate-to-high positive end expiratory pressure (PEEP) does not improve mortality or the incidence of acute respiratory distress syndrome (ARDS), according to systematic review and meta-analysis findings published in Critical Care.

Patients with brain injury who develop respiratory complications are at risk for a longer duration of MV and death. Study authors assessed how mortality and respiratory complications in patients with acute brain injury on MV were affected by the use of low Vt and/or moderate-to-high PEEP, the protective ventilation strategies recommended for patients with ARDS.  The primary study endpoint was in-hospital mortality or death at 28 days; duration of mechanical ventilation, incidence of ARDS, and the partial pressure of oxygen (PaO₂)/fraction of inspired oxygen (FiO₂) ratio were secondary endpoints.

Investigators conducted a systematic literature search of the Cochrane Controlled Clinical trials register, EMBASE, and PubMed databases through August 2022 for interventional and observational studies published in English or French. Relevant articles evaluated the association between lung protective strategies, moderate-to-high PEEP, low Vt, and outcomes among patients with brain injuries.

The 8 studies selected for meta-analysis involved adult patients (n=5639) at least 18 years of age (mean [SD] age, 54.9 [18.5] years; 39% women) with trauma (37%), subarachnoid hemorrhage (14%), or stroke (37%) who received invasive MV for at least 24 hours.

Protective ventilation was defined as PEEP less than 5cm H₂O and Vt less than 8mL/kg of ideal body weight (IBW). Investigators noted PEEP was less than 5cm H₂O in 50.9% of patients, and Vt was lower than 8mL/kg of IBW in 47.0% of patients.

No difference in mortality was found between protective and nonprotective ventilation strategies (odds ration [OR], 1.03; 95% CI, 0.93-1.15; P =.6; I²=11%), low- and moderate-to-high PEEP (OR, 0.8; 95% CI, 0.59-1.07; P =.13; I²=80%), or low and high tidal volume (OR, 0.88; 95% CI, 0.74-1.05; P =.16; I²=20%).

Investigators noted the occurrence of acute respiratory distress syndrome (ARDS) was not affected by protective ventilation (OR, 1.22; 95% CI, 0.94-1.58; P =.13; I²=22%) or individually by its components, moderate PEEP (OR, 0.98; 95% CI, 0.76-1.26; P =.9; I²=21%) or low Vt (OR, 0.74; 95% CI, 0.45-1.21; P =.23; I²=88%).

The PaO₂/FiO₂ ratio was improved with protective ventilation in the first 5 days of mechanical ventilation. Neither low Vt vs high Vt nor low PEEP vs high PEEP reduced the duration of mechanical ventilation.

Review and meta-analysis limitations include the use of nonrandomized trial studies and no assessment of the effect of MV settings on intra-cranial pressure or partial pressure of carbon dioxide (PaCO₂).

“Low tidal volume, moderate to high PEEP, or protective ventilation were not associated with mortality and lower incidence of ARDS in patients with acute brain injury undergoing invasive mechanical ventilation,” review authors concluded. They added that “protective ventilation improved oxygenation and could be safely considered in this setting.”

Disclosure: Some study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.