Acute exacerbation of interstitial lung disease in the intensive care unit

Stress-strain curve and elastic behavior of the fibrotic lung with usual interstitial pneumonia pattern during protective mechanical ventilation

Patients with acute exacerbation of lung fibrosis with usual interstitial pneumonia (EUIP) pattern are at increased risk for ventilator-induced lung injury (VILI) and mortality when exposed to mechanical ventilation (MV). Yet, lack of a mechanical model describing UIP-lung deformation during MV represents a research gap. Aim of this study was to develop a constitutive mathematical model for UIP-lung deformation during lung protective MV based on the stress-strain behavior and the specific elastance of patients with EUIP as compared to that of acute respiratory distress syndrome (ARDS) and healthy lung. Partitioned lung and chest wall mechanics were assessed for patients with EUIP and primary ARDS (1:1 matched based on body mass index and PaO2/FiO2 ratio) during a PEEP trial performed within 24 h from intubation. Patient's stress-strain curve and the lung specific elastance were computed and compared with those of healthy lungs, derived from literature. Respiratory mechanics were used to fit a novel mathematical model of the lung describing mechanical-inflation-induced lung parenchyma deformation, differentiating the contributions of elastin and collagen, the main components of lung extracellular matrix. Five patients with EUIP and 5 matched with primary ARDS were included and analyzed. Global strain was not different at low PEEP between the groups. Overall specific elastance was significantly higher in EUIP as compared to ARDS (28.9 [22.8-33.2] cmH2O versus 11.4 [10.3-14.6] cmH2O, respectively). Compared to ARDS and healthy lung, the stress/strain curve of EUIP showed a steeper increase, crossing the VILI threshold stress risk for strain values greater than 0.55. The contribution of elastin was prevalent at lower strains, while the contribution of collagen was prevalent at large strains. The stress/strain curve for collagen showed an upward shift passing from ARDS and healthy lungs to EUIP lungs. During MV, patients with EUIP showed different respiratory mechanics, stress-strain curve and specific elastance as compared to ARDS patients and healthy subjects and may experience VILI even when protective MV is applied. According to our mathematical model of lung deformation during mechanical inflation, the elastic response of UIP-lung is peculiar and different from ARDS. Our data suggest that patients with EUIP experience VILI with ventilatory setting that are lung-protective for patients with ARDS.

Acute Exacerbations of Interstitial Lung Diseases: Focus on Biomarkers

Interstitial lung diseases (ILDs) are a large group of pulmonary disorders characterized histologically by the cardinal involvement of the pulmonary interstitium. The prototype of ILDs is idiopathic pulmonary fibrosis (IPF), an incurable disease characterized by progressive distortion and loss of normal lung architecture through unchecked collagen deposition. Acute exacerbations are dramatic events during the clinical course of ILDs, associated with high morbidity and mortality. Infections, microaspiration, and advanced lung disease might be involved in the pathogenesis of acute exacerbations. Despite clinical scores, the prediction of the onset and outcome of acute exacerbations is still inaccurate. Biomarkers are necessary to characterize acute exacerbations better. We review the evidence for alveolar epithelial cell, fibropoliferation, and immunity molecules as potential biomarkers for acute exacerbations of interstitial lung disease.

Interstitial Lung Disease: A Focused Review for the Emergency Clinician

BACKGROUND

Interstitial lung disease (ILD) is a group of restrictive pulmonary diseases associated with diffuse interstitial and parenchymal inflammation. Patients can present to the emergency department with severe exacerbation.

OBJECTIVE

This narrative review provides emergency clinicians with the most recent evidence concerning acute exacerbation of ILD (AE-ILD).

DISCUSSION

AE-ILD can present as acute respiratory distress in a patient with a pre-existing ILD diagnosis or as a de novo presentation of ILD, and is associated with significant morbidity and mortality. A variety of underlying triggers may result in AE-ILD. Emergency clinicians must first assess for extraneous causes of respiratory decompensation prior to diagnosing AE-ILD. For a de novo presentation of ILD, emergency physicians should also assess for possible reversible causes. AE-ILD is managed with systemic steroids, immunosuppressants, intravenous antibiotics, supplemental oxygen, and extracorporeal membrane oxygenation in severe cases. Given the high mortality rates in the absence of lung transplantation, early referral to transplant centers is essential to increase chances of survival.

CONCLUSIONS

Emergency clinician knowledge of AE-ILD can improve the evaluation and management of these patients.