Low-birth-weight neonates exhibit a physiological set-point to regulate CO2: an untapped potential to minimize volutrauma-associated lung injury

The objective of this article is to determine whether low-birth-weight (LBW) infants have the capacity to modulate minute ventilation to achieve a CO (2) set-point within ranges acceptable to clinicians during a procedure designed to identify the best dynamic compliance loops. By using dynamic flow-loop mechanics, we performed a prospective stepwise reduction of tidal volume (by reduction of peak inspiratory pressure, keeping end-expiratory pressure constant), in a group of LBW infants to identify the steepest slope of the dynamic flow-loop. We used flow-synchronized, assist-control mechanical ventilation with termination sensitivity set at 5%. Vital signs and blood gases were assessed every 15 minutes at each stepped-pressure change during the first hour after enrollment and after 12 hours, to evaluate oxygenation and ventilation. Peak inspiratory pressure (PIP) was selected at the lowest level that achieved target range blood gases. The acute reduction of PIP and the resulting lower tidal volume was initially associated with an increase in the spontaneous respiratory rate in the first hour that also was associated with a significant decrease in patient-selected inspiration time. After 12 hours, the spontaneous respiratory rate returned to baseline; the peak PaCO(2) was 43.8 +/- 2.03 (mean +/- SEM). LBW infants have the capacity to alter respiratory rate to change minute ventilation in response to a reduction of tidal volume created by lowering the PIP. Using this model of endogenous CO(2) challenge in ventilated infants, we conclude that LBW neonates have the capacity to select a CO(2) set-point. This approach suggests an important avenue through which a clinician can minimize volutrauma through a reduction of PIP and use of expiratory trigger to limit excessive PIP and an overall lower mean airway pressure.