Effective gas exchange in paralyzed juvenile rabbits using simple, inexpensive respiratory support devices.

We have developed two devices: a high-amplitude bubble continuous positive airway pressure (HAB-CPAP) and an inexpensive bubble intermittent mandatory ventilator (B-IMV) to test the hypotheses that simple, inexpensive devices can provide gas exchange similar to that of bubble CPAP (B-CPAP) and conventional mechanical ventilation (CMV). Twelve paralyzed juvenile rabbits were intubated, stabilized on CMV, and then switched to CPAP. On identical mean airway pressures (MAPs), animals were unable to maintain pulse oximeter oxygen saturation (SpO2) >80% on conventional B-CPAP, but all animals oxygenated well (97.3 ± 2.1%) on HAB-CPAP. In fact, arterial partial pressures of O2 (Pao2) were higher during HAB-CPAP than during CMV (p = 0.01). After repeated lung lavages, arterial partial pressures of CO2 (Paco2) were lower with B-IMV than with CMV (p < 0.0001), despite identical ventilator settings. In lavaged animals, when HAB-CPAP was compared with CMV at the same MAP and 100% O2, no differences were observed in Pao2, but Paco2 levels were higher with HAB-CPAP (70 ± 7 versus 50 ± 5 mm Hg; p < 0.05). Arterial blood pressures were not impaired by HAB-CPAP or B-IMV. The results confirm that simple inexpensive devices can provide respiratory support in the face of severe lung disease and could extend the use of respiratory support for preterm infants into severely resource-limited settings.

Noninvasive respiratory support of juvenile rabbits by high-amplitude bubble continuous positive airway pressure.

Bubble continuous positive airway pressure (B-CPAP) applies small-amplitude, high-frequency oscillations in airway pressure (DeltaPaw) that may improve gas exchange in infants with respiratory disease. We developed a device, high-amplitude B-CPAP (HAB-CPAP), which provides greater DeltaPaw than B-CPAP provides. We studied the effects of different operational parameters on DeltaPaw and volumes of gas delivered to a mechanical infant lung model. In vivo studies tested the hypothesis that HAB-CPAP provides noninvasive respiratory support greater than that provided by B-CPAP. Lavaged juvenile rabbits were stabilized on ventilator nasal CPAP. The animals were then supported at the same mean airway pressure, bias flow, and fraction of inspired oxygen (FiO2) required for stabilization, whereas the bubbler angle was varied in a randomized crossover design at exit angles, relative to vertical, of 0 (HAB-CPAP0; equivalent to conventional B-CPAP), 90 (HAB-CPAP90), and 135 degrees (HAB-CPAP135). Arterial blood gases and pressure-rate product (PRP) were measured after 15 min at each bubbler angle. Pao2 levels were higher (p<0.007) with HAB-CPAP135 than with conventional B-CPAP. PaCO2 levels did not differ (p=0.073) among the three bubbler configurations. PRP with HAB-CPAP135 were half of the PRP with HAB-CPAP0 or HAB-CPAP90 (p=0.001). These results indicate that HAB-CPAP135 provides greater respiratory support than conventional B-CPAP does.

The impact of imposed expiratory resistance in neonatal mechanical ventilation: a laboratory evaluation.

BACKGROUND: Small endotracheal tubes (ETTs) and neonatal ventilators can impact gas exchange, work of breathing, and lung-mechanics measurements in infants, by increasing the expiratory resistance (R(E)) to gas flow. METHODS: We tested two each of the Babylog 8000plus, Avea, Carestation, and Servo-i ventilators. In the first phase of the study we evaluated (1) the imposed R(E) of an ETT and ventilator system during simulated passive breathing at various tidal volume (V(T)), positive end-expiratory pressure (PEEP), and frequency settings, and (2) the intrinsic PEEP at various ventilator settings. In the second phase of this study we evaluated the imposed expiratory work of breathing (WOB) of the ETT and ventilator system at various PEEP levels during simulated spontaneous breathing using an infant lung model. Pressure and flow were measured continuously, and we calculated the imposed R(E) of the ETT and each ventilator, and the intrinsic PEEP with various PEEP, V(T), and frequency settings. We measured the imposed expiratory WOB with several PEEP levels during a simulated spontaneous breathing pattern. RESULTS: The ventilator's contribution to the imposed R(E) was greater than that of the ETT with nearly all of the ventilators tested. There were significant differences in ventilator-imposed R(E) between the ventilator brands at various PEEP, V(T), and frequency settings. The Babylog 8000plus consistently had the lowest ventilator-imposed R(E) in the majority of the test conditions. There was no intrinsic PEEP (>1 cm H(2)O) in any of the test conditions with any ventilator brand. There were also no significant differences in the imposed expiratory WOB between ventilator brands during simulated spontaneous breathing. CONCLUSIONS: The major cause of R(E) appears to be the ventilator exhalation valve. Neonatal ventilators that use a set constant flow during inhalation and exhalation appear to have less R(E) than ventilators that use a variable bias flow during exhalation. Clinical studies are needed to determine whether the imposed R(E) of these ventilator designs impacts gas exchange, lung mechanics, or ventilator weaning.