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 ([Formula: see text]) 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 HO 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]) [Formula: see text] of 54 (46-56) cm HO and median (IQR) PIP of 65 (58-73) cm HO; asystole at median (IQR) [Formula: see text] of 49 (36-54) cm HO and median (IQR) PIP of 60 (48-65) cm HO. Hemodynamic changes in the median artery pressure, cardiac output, and myocardial contractility were observed above the range of [Formula: see text] of 14 cm HO (PIP 25 and PEEP 10 cm HO). 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.