Tracheobronchial consequences of the use of heat and moisture exchangers in dogs

Purpose: To determine the effect of heat and moisture exchange (HME) on the tracheobronchial tree (TBT) using a unidirectional anesthesic circuit with or without CO2 absorber and high or low fresh gas flow (FGF), in dogs. Methods: Thirty-two dogs were randomly allocated to four groups: G1 (n = 8) valvular circuit without CO2 absorber and high FGF (5 L.min(-1)); G2 (n = 8) as G1 with HME; G3 (n = 8) circuit with CO, absorber with a low FGF (I L .min(-1)); G4 (n = 8) as G3 with HME. Anesthesia was induced and maintained with pentobarbital. Tympanic temperature (TT), inhaled gas temperature (IG T), relative (RH) and absolute humidity (AH) of inhaled gas were measured a t 15 (control), 60, 120 and 180 min of controlled ventilation. Dogs were eu thanized and biopsies in the areas of TBT were performed by scanning electr on microscopy. Results: The G2 and G4 groups showed the highest AH (> 20 mgH(2)O.L-1)and G I the lowest(< 10 mgH(2)OL(-1)) and G3 was intermediate (< 20 mgH(2)O.L-1) (P < 0.01). There was no difference of TT and IGT among groups. Alteration s of the mucociliary system were greatest in G1, least in G2 and G4, and in termediate in G3. Conclusion: In dogs, introduction of HME to a unidirectional anesthetic cir cuit with/without CO2 absorber and high or low FGF preserved humidity of in spired gases. HME attenuated but did not prevent alterations of the mucocil iary system of the TBT.