Distribution of technetium 99m-labeled red blood cells during isoflurane anesthesia in ferrets

Objective - To address the physiologic mechanism of isoflurane- associated reduction in hematologic variables in ferrets. Animals - 6 young adult female ferrets. Procedure -Distribution of ^99mTc-labeled autologous erythrocytes was measured by serial in vivo imaging. Data were recorded in 4 ferrets, using a gamma camera, immediately prior to anesthesia, 15 minutes after 2% isoflurane anesthesia in O₂ via endotracheal tube, 1 minute prior to and throughout a 10-minute phenylephrine infusion, 20 and 40 minutes after termination of the phenylephrine infusion, and 45 minutes after termination of anesthesia. Blood indices were also measured at times that paralleled those for imaging. One ferret served as a conscious control (no anesthetic administration), and another as an isoflurane control (no phenylephrine administration). Results -In ferrets under anesthesia, splenic radioactivity increased from baseline of 10.2 ± 2.0% to 38.4 ± 3.2% (mean ± SEM; P< 0.05) of the injected dose. Splenic radioactivity decreased to 13.4 ± 3.8% of the injected dose during phenylephrine infusion and to near baseline for the recovery image. Splenic radioactivity in the conscious control remained constant throughout the study, whereas that of the anesthetized control was persistently increased throughout administration of isoflurane. Percentage reduction of the 15-minute sample values, compared with baseline values for all hematologic indices, was: RBC count, 33% (P< 0.05); hemoglobin concentration, 34% (P< 0.05); hematocrit, 35% (P< 0.05); and plasma protein concentration, 20% (P < 0.05). All RBC variables returned to within 7 to 14% of baseline by 45 minutes after termination of anesthesia. Conclusion - Isoflurane anesthesia causes splenic sequestration of RBC in ferrets that is partially reversed by phenylephrine infusion or termination of anesthesia. Thus, investigators and clinicians should be cautious when interpreting hematologic findings in isoflurane-anesthetized ferrets, and accordingly, fluid treatment and transfusion should be planned.