[Anesthesia breathing systems with CO2 absorption, circle valve circuit: comparison of thermal behavior of coaxial system and conventional system with different fresh gas flows.]. / Sistemas respiratórios com absorção de CO2, circulares, valvulares: comparação do comportamento térmico entre sistema coaxial e convencional com diferentes fluxos de gás fresco.

BACKGROUND AND OBJECTIVES: The adequate maintenance of inhaled gases temperature during anesthetic procedures is critical to prevent perioperative respiratory complications. This study aimed at comparing the ability to warm up inhaled gases of coaxial breathing system and conventional system, by varying fresh gas flows (FGF). METHODS: Breathing systems were tested in a lung simulator ventilated with 600 mL tidal volume and respiratory frequency of 10 bpm. The model simulated human CO2 production by delivering 250 mL.min-1 of CO2 flow. Then, exhaled gas from the model was directed to a pre-warmed humidifier to simulate human exhaled gas. Both systems were classified as circle, valve circuits with CO2 absorption. In the coaxial system (model A), the inspiratory branch was enveloped by the expiratory branch, whereas the conventional one (model B) presented separated respiratory branches. Inhaled gas temperature was measured at the following moments: 0, 5, 10, 20, 30, 40, 50, 60 and 90 minutes, with low (0.5 and 1 L.min-1) and high (3 and 6 L.min-1) FGF. RESULTS: Model A presented significant thermal variation between beginning and end of experiment (22.47 +/- 1.77 masculineC and 24.27 +/- 3.52 masculineC respectively, p < 0.05). Both models A and B produced similar temperatures at the end of the study (24.27 +/- 3.52 masculineC and 23.61 +/- 1.93 masculineC respectively). There was no difference between final temperatures of both models and environmental temperature (21.25 +/- 1.20 masculineC and 21.81 +/- 1,87 masculineC respectively). Low FGF has produced similar temperatures to those observed at the end of the study with higher flows in both models (A: 25.53 +/- 4.78 masculineC and 23.02 +/- 0.80 masculineC; B: 24.50 +/- 0.85 masculineC and 22.72 +/- 2.36 masculineC, respectively). CONCLUSIONS: The coaxial system presented significant thermal variation between beginning and end of experiment, while this was not observed in the conventional one. No difference was observed in final temperatures when comparing both systems, regardless of the FGF.