Ventilator-induced Lung Injury and Intra-abdominal Hypertension: Another Odd Couple?

Background: The respiratory role of the abdomen in intubated patients with acute lung injury (ALI) and Acute Respiratory Distress Syndrome (ARDS) is underexplored. Intra-abdominal hypertension (IAH) favors atelectasis, thus exposing the patients to the risk of ventilator-induced lung injury (VILI). Higher positive end-expiratory pressure (PEEP) values may reduce the risk of atelectasis but predispose to IAH. Objective: To clarify whether intra-abdominal pressure (IAP) as estimated by bladder pressure (Pblad) is correlated with intrathoracic pressures: pleural pressure (as estimated by esophageal pressure — Pes), transpulmonary pressure (PL) and airway pressures (PEEP and driving pressure —DP). Our secondary outcome was to evaluate the impact of IAH on 60-day mortality in patients with ALI. Methods: A reanalysis of EPVent and EPVent2 data focusing on patients with ARDS or ALI with Pblad available at baseline. Pes, PL, PEEP and Pblad were measured at the end of expiration. A linear regression analysis was conducted to study the correlation between intra-thoracic pressures and IAP. A logistic regression and a Cox regression were performed to evaluate the impact of IAH on 60-day mortality. Results: 141 patients were included. A positive correlation was found between Pes and Pblad (p < 0.001, r = 0.3532, R² = 0.1248). A negative correlation was found between PL and Pblad (p < 0.001, r = -0.2873, R² = 0.0825). For both correlations, the variance was better explained after adjusting for Body Mass Index (BMI) and extrapulmonary ALI. After adjusting for age, APACHE II score, BMI, Partial pressure of Oxygen (PaO2)/Fraction of Inspired Oxygen (FiO2) to PEEP ratio and protective PL at end expiration, IAH increased the odds of 60-day mortality without reaching statistical significance (Odds Ratio — OR 1.75, p=0.180, 95%CI 0.77-4.06); the adjusted Cox proportional hazards model showed a hazard ratio (HR) of non-surviving at 60 days of 1.56 (p = 0.151; 95% CI, 0.85–2.85) for patients with IAH. Conclusions: IAH correlates with high Pes and with concomitant low PL. Therefore, patients with IAH may be exposed to a higher risk of atelectrauma and VILI. Further studies are warranted to confirm our findings.