CLINICS 2010;65(5):531-7 decreased by 10%, and the protocol was repeated following a 15 min anesthetic equilibration period. If there was purposeful movement in response to the stimulation, the end-tidal concentration was increased by 5%, and following equilibration, the stimulation was repeated. The site of the stimulations was changed slightly to prevent sensitization or desensitization to subsequent stimuli. The expiratory concentration of the agent halfway between that allowing and that not allowing movement in response was the MAC of that agent for each specific animal. After MAC determination, systemic hemodynamics, respiratory data and blood gases were collected at 0.5, 1.0 and 1.5 MAC, observing a 15 min equilibrium period after each concentration change. Histopathological analysis At the end of the experiment, while still under anesthesia, animals received a 1-g bolus of thiopental followed by 25 mEq of potassium chloride. Lung samples were collected from the left diaphragmatic lobe (from zones 1, 2 and 3). A sample from the middle portion of the trachea was also collected. The lung and trachea samples were prepared for optical analyses, fixed in 10% formaldehyde and stained with hematoxylin and eosin. The pathologist, who was blinded to the experimental protocol, described the analysis according to the combined assessment of neutrophils, eosinophils, mastocytes, and mononuclear cell accumulation, pulmonary interstitial edema, alveoli collapse, and congestion in the prepared sample lamina using an optical microscope at a magnification of 10x. In a subjective manner, the observer quantified the positive findings in the samples from different regions of the lung as none (0), discrete (1), moderate (2), or intense (3). Statistical analysis MAC values were analyzed using the Student´s t-test. Hemodynamic and other parametric data were analyzed within groups and between groups using an analysis of variance (ANOVA) for repeated measurements with two factors (SigmaStat 3.11, Systat Software Inc, San Jose, USA). When appropriate, post hoc analyses were performed with the Tukey test. P<0.05 was considered statistically significant. Values are presented as means (SD). RESULTS The MAC for the Sevo A group was 4.4% (0.5), whereas it was 4.1% (0.7) for the Sevocris group. Body weights, Copyright © 2010 CLINICS Sevoflurane MAC and hemodynamics in pigs Otsuki DA et al. MAC values and times to achieve sternal recumbence and to orotracheal intubation are presented in Table 1. Hemodynamic, respiratory and oxygenation parameters are described in Tables 2 and 3. Table 1 - Body weight, MAC, time to sternal recumbency and orotracheal intubation. Body weight (kg) MAC (%) Sternal recumbency (s) Orotracheal intubation (s) Mean (SD) Sevo A 31.3 (1.9) 4.4 (0.5) 116 (96) 659 (433) Sevocris 31.9 (1.9) 4.1 (0.7) 112 (36) 620 (275) Hemodynamic parameters presented significant differences in a dose-dependent pattern as expected, but did not differ between groups. Cardiac indices decreased significantly in both groups when the sevoflurane concentration increased from 0.5 to 1 and 1.5 MAC. We also observed a significant decrease in blood pressure and mean pulmonary artery pressure at all concentrations compared to 0.5 MAC. Heart rate decreased significantly when MAC was augmented from 0.5 to 1.0 and 1.5, but the values remained in the physiological range for this group of animals, and bradycardia was not verified. SvO2 and DO2I decreased significantly at 1.5 MAC when compared to 0.5 and 1.0 MAC. Regarding histopathological analyses, no evidence of neutrophils, eosinophils, mastocytes, mononuclear cell accumulation, pulmonary interstitial edema, alveoli collapse, or congestion was found in lung optical microscopy of both groups. Also, no histopathological changes were found in the trachea. DISCUSSION The main finding in this study was that hemodynamic and metabolic responses at equipotent doses were similar between water-added sevoflurane (Sevo A) and propylene glycol-added sevoflurane (Sevocris). Under the conditions of this study, the MAC of Sevo A was 4.4% (0.5), and the MAC of Sevocris was 4.1% (0.7). These values are higher than most published reports, in which sevoflurane MAC values range between 2.1% and 4.4% in pigs.8-13 Several factors may account for the variations in published sevoflurane MAC values, including different age groups of pigs, body temperature, pre-anesthetic and induction agents, the type and site of noxious stimulus and the defined end-point for determination of purposeful 533