Pressure- versus volume-cycled ventilation in liquid-ventilated neonatal piglet lungs

Background/Purpose: If the goal of partial liquid ventilation (PLV) with perfluorocarbons in the management of respiratory failure is to improve dynamic lung compliance (C dyn ) and pulmonary vascular resistance (PVR) while sustaing O 2 delivery, the optimal ventilatory management is unclear. The authors asked if volume-cycled or pressure-limited ventilation had different effects on PVR, cardiac index (CI), and C dyn in uninjured and injured neonatal piglet lungs. Methods: Anesthetized piglets (6 to 8 kg) were ventilated after tracheostomy. C dyn was measured by in-line Fleisch pneumotach/PC data acquisition terminal. Thermodilution instrumentation allowed determination of both Cl and PVR. Volume-control or pressure-limited ventilation was established in uninjured or injured (surfactant deficiency induced by saline lavage at 18 mL/kg) animals. After a stable 30-minute baseline, animals were assigned randomly to one of four groups: group I (n = 9), uninjured animals plus volume-cycled ventilation (intermittent mandatory ventilation [IMV], 10 bpm; tidal volume [TV], 15 mL/kg, positive end-expiratory pressure [PEEP], 5 cm H 2 O; Fio 2 , 1.0; and PLV for 150 minutes); group II (n = 9), uninjured animals plus pressure-limited ventilation (IMV, 10 bpm; peak inspiratory pressure (PIP), 25 cm H 2 O, PEEP, 5 cm H 2 O, Fio 2 , 1.0; and PLV for 150 minutes); group III (n = 7), injured animals plus volume-cycled ventilation (IMV, 10 bpm; TV, 15 mL/kg; PEEP, 5 cm H 2 O; Fio 2 , 1.0 for 30 minutes, followed by saline injury for 30 minutes, followed by PLV rescue for 120 minutes); group IV (n = 7), injured animals plus pressure-limited ventilation (IMV, 10 bpm; PIP, 25 cm H 2 O; PEEP, 5 cm H 2 O; Fio 2 , 1.0 for 30 minutes, followed by saline injury, and PLV rescue). Comparison within and between groups was accomplished by repeated measures analysis of variance (ANOVA) with Tukey correction. Results: There was no significant difference between volumecycled or pressure-limited ventilation in healthy lungs; however, in the setting of lung injury, dynamic compliance was 1.44 ± 0.15 after 180 minutes in the volume-cycled group and 0.91 ± 0.10 in the pressure-limited group after the same interval (mL/cm H 2 O · kg ± SEM). Similarly, PVR was 100 ± 6 in the volume-cycled group and 145 ± 12 in the pressurelimited group after 180 minutes of lung injury (mm Hg/L/kg · min ± SEM). Cardiac index declined significantly in all groups independent of ventilatory mode. Conclusions: These results suggest that in the setting of lung injury, C dyn and PVR improved significantly when volume-cycled, compared with pressure-limited ventilation was used. Although no difference existed between ventilatory modes in healthy lungs, pressure-limited ventilation, when combined with PLV in injured lungs, had adverse effects on lung compliance and pulmonary vascular resistance. Volume-cycled ventilation may optimize the ability of perfluorocarbon to recruit collapsed or atelectatic lung regions.