Objective: To compare cardiopulmonary function during spontaneous breathing with three continuous-flow breathing circuits. The major difference between these circuits was the degree of flow resistance offered by the exhalation valve.
Design: Randomized crossover trial.
Patients: Twelve infants less than 12 months of age recovering from respiratory failure of variable etiology. Only patients weighing 3 to 10 kg were studied.
Interventions: The patients were connected to each respiratory circuit in a random sequence, with 15 min allowed for equilibration before assessment of cardiopulmonary function. Airway pressure (Paw) and FIO2 were maintained unchanged.
Measurements and main results: Ventilation, gas exchange, or circulatory function were not altered significantly by changing the breathing circuit. However, Paw and esophageal pressure fluctuations were altered and were largest during breathing with the circuit that had an exhalation valve with high-flow resistance. The Paw fluctuation recorded while the patient was breathing with the flow-resistor circuit increased with weight and exceeded 2 cm H2O in all patients weighing greater than 4.5 kg. Paw fluctuation could be decreased by greater than 2 cm H2O in ten of 12 patients by using the threshold-resistor circuit.
Conclusions: The results indicate a need for evaluating the characteristics of respiratory circuits used for spontaneous breathing in infants and children, to avoid unnecessary equipment-related increase in respiratory work.