Shortened Automatic Lung Recruitment Maneuvers in an In Vivo Model of Neonatal ARDS.

BACKGROUND: The aim of this study was to assess the safety and efficacy of 2 protocols for automatic lung recruitment maneuvers (LRMs) using stepwise increases in PEEP in a neonatal ARDS model. These protocols were designed with lower maximum opening pressures than traditional methods and differ each one in the duration of the opening phases (short vs prolonged). We described hemodynamic changes through invasive monitoring, and we analyzed if the behavior of the variables depends on the duration of the opening phase of the LRM. METHODS: We designed a prospective, experimental study with 10 Landrace x Large White pigs < 48 h old. Under general anesthesia, tracheal intubation, invasive hemodynamic monitoring with a pediatric arterial thermodilution catheter was performed. An ARDS model was developed with bronchoalveolar lavages. Two types of LRMs were performed in each piglet, with a maximum peak inspiratory pressure (PIP) of 30 cm H2O and a PEEP 15 cm H2O applied during 8.5 s in the short LRM and 17 s in the prolonged LRM. A comparative analysis by virtue of the Wilcoxon signed-rank test and a regression analysis using generalized estimation equation were performed. RESULTS: We found that both LRMs were effective regarding oxygenation and respiratory mechanics. Shortening the duration of the opening phase and lowering the maximum opening pressures to PIP 30 and PEEP 15 cm H2O were above the critical opening pressure to reverse alveolar collapse in our neonatal ARDS model. Although we observed hemodynamic variations during both types of LRMs, these were well tolerated. CONCLUSIONS: Our LRM protocols exceeded critical opening pressures to reverse alveolar collapse in our neonatal ARDS model. This range of pressures might involve less hemodynamic disturbance. Duration of the maximum opening pressure step is a determining factor for hemodynamic alterations.

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 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]) [Formula: see text] of 54 (46-56) cm H2O and median (IQR) PIP of 65 (58-73) cm H2O; asystole at median (IQR) [Formula: see text] 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 [Formula: see text] 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.