Fresh gas flow changes during controlled mechanical ventilation with the circle breathing system have significantly greater effects on the ventilatory parameters of toddlers compared with children

Abstract

Summary Fresh gas flow into a circle system can affect the delivered minute ventilation because fresh gas flow augments the flow delivered by the ventilator bellows during inspiration. After establishing a stable ventilatory pattern with 3.0 l·min-1 fresh gas flow into a circle system, changes in peak inflation pressure, minute ventilation and end-tidal carbon dioxide were measured at 1.5 l·min-1 and 6.0 l·min-1 in 10 toddlers (10–20 kg) and 10 children (30–60 kg). Changes in all variables were observed but these changes were greater in toddlers compared with children (P < 0.001). Some toddlers were noted to have as much as a 37% change in ventilatory parameters when fresh gas flow was altered between 1.5 and 6.0 l·min-1. Whenever changes are made in fresh gas flow, compensatory changes in minute ventilation should be considered to avoid unintended hyperventilation or hypoventilation. This is especially important during anaesthesia for toddlers.