Ventilator-associated lung injury in patients without acute lung injury at the onset of mechanical ventilation*

TLDR

Ventilation with small tidal volumes is recommended for acute lung injury, yet many patients receive variable tidal volumes to normalize blood gases. The study tested whether acute lung injury that develops after mechanical ventilation is linked to risk factors for ventilator‑induced lung injury, particularly large tidal volume. A retrospective cohort of 332 patients from four ICUs who received ≥48 h of invasive ventilation in 2001 was analyzed, with ventilator settings, hemodynamics, and risk factors extracted from the APACHE III database and medical records. Among these patients, 24 % developed acute lung injury within five days, with larger tidal volume, blood transfusion, acidemia, and restrictive lung disease independently predicting its onset, highlighting the importance of tailoring tidal volume to height and gender and limiting large tidal volumes even in patients at risk.

Abstract

Although ventilation with small tidal volumes is recommended in patients with established acute lung injury, most others receive highly variable tidal volume aimed in part at normalizing arterial blood gas values. We tested the hypothesis that acute lung injury, which develops after the initiation of mechanical ventilation, is associated with known risk factors for ventilator-induced lung injury such as ventilation with large tidal volume.Retrospective cohort study.Four intensive care units in a tertiary referral center.Patients who received invasive mechanical ventilation for > or = 48 hrs between January and December 2001.None.The main outcome of interest, acute lung injury, was assessed by independent review of daily digital chest radiographs and arterial blood gases. Ventilator settings, hemodynamics, and acute lung injury risk factors were extracted from the Acute Physiology and Chronic Health Evaluation III database and the patients' medical records. Of 332 patients who did not have acute lung injury from the outset, 80 patients (24%) developed acute lung injury within the first 5 days of mechanical ventilation. When expressed per predicted body weight, women were ventilated with larger tidal volume than men (mean 11.4 vs. 10.4 mL/kg predicted body weight, p <.001) and tended to develop acute lung injury more often (29% vs. 20%, p =.068). In a multivariate analysis, the main risk factors associated with the development of acute lung injury were the use of large tidal volume (odds ratio 1.3 for each mL above 6 mL/kg predicted body weight, p <.001), transfusion of blood products (odds ratio, 3.0; p < 0.001), acidemia (pH < 7.35; odds ratio, 2.0; p =.032) and a history of restrictive lung disease (odds ratio, 3.6; p =.044).The association between the initial tidal volume and the development of acute lung injury suggests that ventilator-associated lung injury may be an important cause of this syndrome. Height and gender should be considered when setting up the ventilator. Strong consideration should be given to limiting large tidal volume, not only in patients with established acute lung injury but also in patients at risk for acute lung injury.