Background <p>Lung ultrasound has been extensively used to assess the etiology of respiratory failure. Additionally, lung ultrasound-based scoring systems have been proposed to semi-quantify the loss of lung aeration in the ICU. The one most frequently used distinguishes four steps of progressive loss of aeration (scores from 0 to 3) and 3 scores mean tissue-like pattern. However, the burden of consolidation is not considered as tissue-like pattern is defined as 3 scores independently of its dimension. In this study, we present an ultrasound method for quantitative measurement of consolidation size and investigate the relationship between consolidation size and outcome in ICU patients with respiratory failure.</p> Methods <p>A total of 124 patients in ICU were prospectively enrolled and 13 patients were excluded due to failure to obtain LUS measurements. Among the remaining 111 patients, 17 patients were non-intubated, and 94 patients under sedation and analgesia were intubated. All patients underwent lung ultrasound examination for the measurement of lung consolidation size between 24 and 48&#xa0;h after ICU admission. Lung consolidation size was assessed by consolidation area index (CA), which was determined by tracing the maximum cross-sectional area of the region of consolidation. The Cox-regression model was constructed for 28- and 90-day mortality.</p> Results <p>Consolidation size was successfully evaluated in all patients. The CA was 24.2cm²[15.9–36.6] (median [25th -75th percentiles]). CA was negatively correlated with PaO₂/FiO₂ ratio (<i>r</i>=-0.26, <i>P</i> &lt; 0.0001). Upon univariate and multivariate analysis, only CA [Odds ratio (OR) 1.04, 95% CI 1.01–1.08, <i>P</i> = 0.004] and APACHEII (OR 1.14, 95% CI 1.05–1.25, <i>P</i> = 0.002) were the risk factors for ICU mortality. Patients with substantial CA (&gt; 29.4cm²) had a higher risk of death in 28-day [Hazard ratio (HR) 4.35, 95%CI 1.70-11.11; Log-rank <i>P</i> = 0.017] and 90-day mortality (HR 4.10, 95%CI 1.62–10.39; Log-rank <i>P</i> &lt; 0.01).</p> Conclusions <p>The proposed CA parameter, determined by lung ultrasound, was readily accessible at the bedside. It is noteworthy that a larger CA was correlated with impaired oxygenation and increased mortality rates among ICU patients. Further investigation is required to establish the merits of incorporating CA into lung ultrasound assessments in the ICU.</p> Trial registration <p>ClinicalTrial.gov, Identifier NCT05647967, Date: Dec 13, 2022, retrospectively registered.</p>