Pressure-flow characteristics of breathing systems and their components for pediatric and adult patients.

Background: Breathing circuits connect the ventilator to the patients' respiratory system. Breathing tubes, connectors, and sensors contribute to artificial airway resistance to a varying extent. We hypothesized that the flow-dependent resistance is higher in pediatric breathing systems and their components compared to respective types for adults.

Aims: We aimed to characterize the resistance of representative breathing systems and their components used in pediatric patients (including devices for adults) by their nonlinear pressure-flow relationship.

Methods: We used a physical model to measure the flow-dependent pressure gradient (∆P) across breathing tubes, breathing tube extensions, 90°- and Y-connectors, flow- and carbon dioxide sensors, water traps and reusable, disposable and coaxial breathing systems for pediatric and for adult patients. ∆P was analyzed for usual flow ranges and statistically compared at a representative flow rate of 300 mL∙s (∆P ).

Results: ∆P across pediatric devices always exceeded ∆P across the corresponding devices for adult patients (all P < .001 [no 95% CI includes 0]). ∆P across breathing system components for adults was always below 0.2 cmH O but reached up to 4.6 cmH O in a flow sensor for pediatric patients. ∆P was considerably higher across the reusable compared to the disposable pediatric breathing systems (1.9 vs 0.3 cmH O, P < .001, [95% CI -1.59 to -1.56]).

Conclusion: The resistances of pediatric breathing systems and their components result in pressure gradients exceeding those for adults several fold. Considering the resistance of individual components is crucial for composing a breathing system matching the patient's needs. Compensation of the additional resistance should be considered if a large composed resistance is unavoidable.