High laryngeal mask airway pressures resulting from nitrous oxide do not increase pharyngeal mucosal injury in dogs.

PURPOSE: During general anesthesia, nitrous oxide (N2O) diffuses rapidly into the air-filled laryngeal mask airway (LMA) cuff, increasing intracuff pressure. There is no clear correlation between LMA intracuff pressure and pressure on the pharynx. We have studied the effects of high LMA intracuff pressures secondary to N2O on the pharyngeal mucosa of dogs. METHODS: Sixteen mongrel dogs were randomly allocated to two groups: G1 (intracuff volume, 30 mL; n=8) breathed a mixture of O2 (l L x min(-1)) and air (l L x min(-1)) and G2 (intracuff volume, 30 mL; n=8) a mixture of O2 (l L x min(-1)) and N2O (l L x min(-1)). Anesthesia was induced and maintained with pentobarbitone. LMA cuff pressure was measured at zero (control), 30, 60, 90 and 120 min after #4 LMA insertion. The dogs were sacrificed, and biopsy specimens from seven predetermined areas of the pharynx in contact with the LMA cuff were collected for light (LM) and scanning electron microscopic (SEM) examination by a blinded observer. RESULTS: LMA intracuff pressure decreased with time in G1 (P <0.001) and increased in G2 (P <0.001). There was a significant difference between the groups (P <0.001). In both groups, the LM study showed a normal epithelium covering the pharyngeal mucosa and mild congestion in the subepithelial layer. There were no differences between the groups (P >0.10) or among the areas sampled (P >0.05). In both groups, the SEM study showed a normal pharyngeal mucosa with mild superficial desquamation. Few specimens in G1 and G2 showed more intense epithelial desquamation. CONCLUSION: High LMA intracuff pressures produced by N2O do not increase pharyngeal mucosal injury in dogs.

Effect of high laryngeal mask airway intracuff pressure on the laryngopharyngeal mucosa of dogs.

OBJECTIVES: To evaluate the effect of increased of laryngeal mask airway (LMA) intracuff pressures on the laryngopharyngeal mucosa. STUDY DESIGN: Animal model. METHODS: Sixteen mixed-breed dogs were randomly allocated to two groups, G1 (intracuff volume, 30 mL; n = 8) and G2 (intracuff volume, 54 mL; n = 8), to produce, respectively, high or very high intracuff pressures. Anesthesia was induced and maintained with pentobarbital. Intracuff pressures were measured immediately after insertion and inflation of a No. 4 laryngeal mask airway (LMA) and 30, 60, 90, and 120 minutes thereafter. The dogs were euthanized, and biopsy specimens from eight predetermined areas of the laryngopharynx in contact with LMA cuff were collected for light microscopic (LM) and scanning electron microscopic (SEM) examination. RESULTS: Initial LMA cuff inflation in G1 and G2 resulted in intracuff pressures of 119 mm Hg +/- 4 mm Hg and 235 mm Hg +/- 13 mm Hg, respectively. Over a 2-hour period, the intracuff pressure decreased significantly in G1 (P < .001) and G2 (P < .01), and there was a significant difference between the groups over time (P < .001). The LM study of laryngopharyngeal mucosa in both groups showed mild congestion in the subepithelial layer. There were no differences between the groups (P > .10) or among the areas sampled (P > .10). In some areas of G2, the SEM study showed epithelial desquamation that was more intense than that in G1. CONCLUSIONS: The increase in LMA intracuff pressure caused only mild alterations in the laryngopharyngeal mucosa of the dog.

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 x min(-1)); G2 (n=8) as G1 with HME; G3 (n=8) circuit with CO2 absorber with a low FGF (1 L x min(-1)); G4 (n=8) as G3 with HME. Anesthesia was induced and maintained with pentobarbital. Tympanic temperature (TT), inhaled gas temperature (IGT), relative (RH) and absolute humidity (AH) of inhaled gas were measured at 15 (control), 60, 120 and 180 min of controlled ventilation. Dogs were euthanized and biopsies in the areas of TBT were performed by scanning electron microscopy. RESULTS: The G2 and G4 groups showed the highest AH (>20 mgH2O x L(-1)) and G1 the lowest (< 10 mgH2O x L(-1)) and G3 was intermediate (< 20 mgH2O x L(-1)) (P < 0.01). There was no difference of TT and IGT among groups. Alterations of the mucociliary system were greatest in G1, least in G2 and G4, and intermediate in G3. CONCLUSION: In dogs, introduction of HME to a unidirectional anesthetic circuit with/without CO2 absorber and high or low FGF preserved humidity of inspired gases. HME attenuated but did not prevent alterations of the mucociliary system of the TBT.