DIAPHRAGMATIC MICROCIRCULATION DURING HALOTHANE AND ISOFLURANE EXPOSURE IN PENTOBARBITAL-ANESTHETIZED RATS

We investigated the effects of halothane and isoflurane on diaphragmatic microcirculation in pentobarbital-anesthetized rats by in vivo video microscopy. After a baseline period, rats were randomly allocated into three groups according to administration of 0.5, 0.75, and 1 minimal alveolar concentration (MAC) of either halothane (group Hal, n = 16), isoflurane (group Iso, n = 14), or no halogenated agent (group C, n = 20) in three succeeding steps of 15 min. Mean arterial blood pressure (MAP), arteriolar diameters, and functional capillary density were analyzed in the last 3 min of each step. MAP remained unchanged in group C but decreased in a dose-dependent manner in both halogenated receiving groups. MAP was significantly lower in rats breathing Hal compared with those breathing Iso. Arterioles were classified in second (A2, n = 39), third (A3, n = 24), and fourth (A4, n = 30) order according to their relative location in the network. No changes in A2 and A3 diameters were noted in either group. A4 diameters remained unchanged in groups C and Iso, whereas a significant reduction was found in group Hal at 0.75 and 1 MAC exposure (P < 0.05 compared with baseline and with groups C and Iso, respectively). During Iso exposure, functional capillary density was not significantly different when compared with baseline and group C, whereas in group Hal it decreased significantly at 0.5, 0.75, and 1 MAC, amounting to 61.1 +/- 9, 30.7 +/-10.3, and 22.8 +/- 6.3%, respectively, of baseline (P < 0.01 vs. baseline and P < 0.05 vs. groups Iso and C for 0.75 and 1 MAC). Thus fourth-order arteriolar diameter and functional capillary density were markedly reduced during Hal breathing, whereas no changes in these parameters were observed during Iso breathing.