Safe Inspiratory Pressures Threshold in Lung Recruitment Maneuvers: An In Vivo Neonatal ARDS Model

BACKGROUND: The aim of this study was to define the level of peak inspiratory pressure (PIP) and mean airway pressure (P̄_aw) at which a pneumothorax is produced in an in vivo ARDS neonate model. In addition, we analyzed the hemodynamic response and cerebral parameters during the progressive increase of intrathoracic pressure.

METHODS: We designed a prospective, experimental study with 11 Landrace × Large White pigs < 48 h from their birth. With the pigs under general anesthesia, tracheal intubation, invasive hemodynamic monitoring with a pediatric arterial thermodilution catheter, intracranial pressure, cerebral oximetry through near-infrared spectroscopy, and bilateral chest tube catheterization were performed. The ARDS model was developed with bronchoalveolar lavages. The rise in inspiratory pressure was performed achieved by increasing PEEP in stepwise increments at a constant driving pressure. PEEP was increased 5 cm H₂O every 2 min until a pneumothorax was observed. A descriptive analysis, a Kaplan-Meier curve, and a regression analysis by using a generalized estimation equation were performed.

RESULTS: A pneumothorax was observed in a median (interquartile range [IQR]) P̄_aw of 54 (46–56) cm H₂O and median (IQR) PIP of 65 (58–73) cm H₂O; asystole at median (IQR) P̄_aw of 49 (36–54) cm H₂O and median (IQR) PIP of 60 (48–65) cm H₂O. Hemodynamic changes in the median artery pressure, cardiac output, and myocardial contractility were observed above the range of P̄_aw of 14 cm H₂O (PIP 25 and PEEP 10 cm H₂O). Disturbances in intracranial pressure and cerebral oximetry through near-infrared spectroscopy appeared when deep hypotension and asystole occurred.

CONCLUSIONS: A progressive increase of PEEP at a constant driving pressure did not increase severe adverse events at the range of pressures that we routinely use in neonates with ARDS. Asystole, pneumothorax, and cerebral compromise appeared at high intrathoracic ranges of pressure. Hemodynamics must be strictly monitored in all patients during the performance of lung recruitment maneuvers because hemodynamic deflections emerge early, at a range of pressures commonly used in ventilated neonates with ARDS.