Abstract
Background: Acute episodes of hypoxemia in ventilated preterm infants are triggered by changes in ventilation, lung volume (LV) and respiratory system compliance (CRS) that are not prevented by conventional synchronized intermittent mandatory ventilation (SIMV). Objective: To assess in a rabbit model of episodic hypoxemia the individual and combined efficacy of targeted tidal volume (VT) and minute ventilation (V’E) by automatic adjustment of peak inspiratory pressure (PIP) and ventilator rate, respectively. Methods: Six young New Zealand white rabbits were ventilated with SIMV, targeted VT, targeted V’E, and combined targeted V’E + VT in random sequence. Hypoxemia episodes were induced by apnea alone or by apnea combined with a reduction in LV and CRS. Apnea was induced by a bolus of propofol. The reduction in LV and CRS was induced by chest compression with a cuff. PaO2 and PaCO2 were measured continuously by an indwelling arterial electrode. Results: During SIMV, apnea caused a decrease in ventilation and PaO2. This was attenuated during targeted V’E and targeted V’E + VT. Apnea plus a reduction in LV and CRS caused a greater decrease in ventilation and PaO2 during SIMV. These changes were attenuated during targeted VT and targeted V’E. The attenuation was more pronounced during targeted V’E + VT. Conclusion: In this animal model, targeted V’E was effective in reducing hypoxemia caused by apnea. When apnea was accompanied by a reduction in LV and CRS, the combined adjustment of PIP and ventilator rate was more effective than each individually. This combined strategy may be effective in ameliorating acute episodes of hypoxemia in preterm infants but this remains to be proven.
