Radiographic lung density assessed by computed tomography is associated with extravascular lung water content

Area of Science:

• Pulmonary medicine
• Medical imaging
• Critical care medicine

Background:

• Acute lung injury (ALI) is a critical condition affecting lung tissue and fluid balance.
• Accurate assessment of extravascular lung water (EVLW) is crucial for managing ALI.
• Quantitative computed tomography (CT) offers a non-invasive method to evaluate lung tissue volume.

Purpose of the Study:

• To investigate the association between lung tissue volume, determined by quantitative CT, and EVLW content in a sheep model of ALI.
• To compare CT-derived tissue volume index (TVI(CT)) with EVLW indexes obtained through single transpulmonary thermodilution (EVLWI(STD)), thermal-dye dilution (EVLWI(TDD)), and postmortem gravimetry (EVLWI(G)).

Main Methods:

• Seven sheep underwent oleic acid (OA) infusion to induce ALI; four served as controls.
• Quantitative CT scans were performed before and after ALI induction.
• Hemodynamics, oxygenation, and EVLW indexes (EVLWI(STD), EVLWI(TDD)) were measured.
• Linear regression analysis correlated EVLWI(STD), EVLWI(TDD), EVLWI(G), and TVI(CT).

Main Results:

• OA-induced ALI increased total lung volume and significantly expanded poorly and non-aerated lung regions.
• TVI(CT) nearly doubled in the OA group, indicating increased lung tissue volume.
• TVI(CT) showed significant correlations with EVLWI(STD), EVLWI(TDD), and EVLWI(G) (r values ranging from 0.85 to 0.90).
• TVI(CT) exhibited a mean bias of 4.0 +/- 6.0 ml/kg compared to EVLWI(G).

Conclusions:

• In ovine ALI, CT-derived lung tissue volume closely aligns with EVLW measurements from indicator dilution and gravimetry.
• Quantitative CT provides a valuable tool for assessing lung tissue changes in ALI.
• CT-based lung tissue volume assessment may overestimate actual lung fluid content.