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

Summary

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⁻¹ (∆P₃₀₀).

Results

∆P across pediatric devices always exceeded ∆P across the corresponding devices for adult patients (all P < .001 [no 95% CI includes 0]). ∆P₃₀₀ across breathing system components for adults was always below 0.2 cmH₂O but reached up to 4.6 cmH₂O in a flow sensor for pediatric patients. ∆P₃₀₀ was considerably higher across the reusable compared to the disposable pediatric breathing systems (1.9 vs 0.3 cmH₂O, 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.

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