Experimental intra-abdominal hypertension influences airway pressure limits for lung protective mechanical ventilation

BACKGROUND: Intra-abdominal hypertension (IAH) and abdominal compartment syndrome (ACS) may complicate monitoring of pulmonary mechanics owing to their impact on the respiratory system. However, recommendations for mechanical ventilation of patients with IAH/ACS and the interpretation of thoracoabdominal interactions remain unclear. Our study aimed to characterize the influence of elevated intra-abdominal pressure (IAP) and positive end-expiratory pressure (PEEP) on airway plateau pressure (P_PLAT) and bladder pressure (P_BLAD). METHODS: Nine deeply anesthetized swineweremechanically ventilated via tracheostomy: volume-controlled mode at tidal volume (VT) of 10mL/kg, frequency of 15, inspiratory-expiratory ratio of 1:2, and PEEP of 1 and 10 cm H₂O (PEEP1 and PEEP10, respectively). A tracheostomy tube was placed in the peritoneal cavity, and IAP levels of 5, 10, 15, 20, and 25 mm Hg were applied, using a continuous positive airway pressure system. At each IAP level, P_BLAD and airway pressure measurements were performed during both PEEP1 and PEEP10. RESULTS: P_BLAD increased as experimental IAP rose (y = 0.83x + 0.5; R² = 0.98; p G 0.001 at PEEP1). Minimal underestimation of IAP by P_BLAD was observed (j2.5 T 0.8 mm Hg at an IAP of 10-25 mm Hg). Applying PEEP10 did not significantly affect the correlation between experimental IAP and P_BLAD. Approximately 50% of the P_BLAD (in cm H₂O) was reflected by changes in P _PLAT, regardless of the PEEP level applied. Increasing IAP did not influence hemodynamics at any level of IAP generated. CONCLUSION: With minimal underestimation, P_BLAD measurements closely correlated with experimentally regulated IAP, independent of the PEEP level applied. For each PEEP level applied, a constant proportion (approximately 50%) of measured PBLAD (in cm H₂O) was reflected in P_PLAT. A higher safety threshold for P_PLAT should be considered in the setting of IAH/ACS as the clinician considers changes in V_T. A strategy of reducing V _T to cap P_PLAT at widely recommended values may not be warranted in the setting of increased IAP.