Tracheal gas insufflation-augmented continuous positive airway pressure in a spontaneously breathing model of neonatal respiratory distress

Respiratory distress syndrome (RDS) in neonates is characterized by labored breathing and poor gas exchange, often requiring ventilatory support. Continuous positive airway pressure (CPAP) is a preferred intervention to support spontaneous ventilatory efforts by sustaining lung volume recruitment, while it prevents derecruitment during exhalation by maintaining end-expiratory pressure. However, CO2 retention during CPAP often results in the need for mechanical ventilation. Since tracheal gas insufflation (TGI) promotes CO2 elimination by reducing prosthetic dead space, we hypothesized that TGI used with CPAP may reduce the need for more invasive therapies. The objective of this study was to evaluate the physiologic effect of TGI with CPAP in a spontaneously breathing model of acute lung injury with respect to gas exchange and pulmonary mechanics. Nineteen spontaneously breathing neonatal pigs (2.4 +/- 0.4 kg) were anesthetized, sedated, instrumented, and placed on CPAP at 5 cmH2O. All piglets were injured with intravenous oleic acid (0.08 ml/kg), and then randomized to receive CPAP with TGI (TGI; n = 9) or CPAP alone (control; n = 10). FiO2 was titrated at 0.05 every 15 min during the protocol to maintain SaO2 > 93%. Vital signs, arterial blood gases, pulmonary mechanics, and thoracoabdominal motion (TAM) were evaluated 30 min after injury and at 1-hr intervals for 4 hr. Following the 4-hr measurement, the piglets were sacrificed and the lungs were grossly examined. After initiation of treatment, we found that the PaCO2 was lower (33.1 +/- 5.0 vs. 47.0 +/- 10.3 mmHg; P < 0.01), while the oxygenation indices were greater (PaO2, SaO2, a/A ratio; P < 0.01) in the TGI group than with control animals. Subsequently, the pH was greater (7.45 +/- 0.08 vs. 7.36 +/- 0.08; P < 0.01) and closer to baseline values with TGI. By 4 hr, the FiO2 was titrated lower (0.37 +/- 0.06 vs. 0.49 +/- 0.15; P < 0.05) and ventilation was accomplished with a lower minute ventilation (MV) in the TGI group than in the control group (445 +/- 113 vs. 581 +/- 223 ml/kg/min; P < 0.01). Respiratory compliance was greater with TGI than control (0.76 +/- 0.13 vs. 0.63 +/- 0.11 ml/cmH2O/kg; P < 0.01), whereas resistance and TAM were similar between groups. We conclude that the use of TGI with CPAP in the treatment of RDS results in improved gas exchange and pulmonary mechanics. As such, TGI-augmented CPAP may prevent infants from requiring more invasive ventilation by reducing CO2 retention.