A comparison of fresh gas flows during anesthesia with nitrous oxide in the dog

Nine healthy mixed-breed dogs weighing between 15 and 28 kg were anaesthetized with 33% oxygen, 67% nitrous oxide and halothane. Oxygen flow rates of 10, 20 and 30 ml/kg per minute were administered with appropriate nitrous oxide flow rates for three consecutive 45-minute periods. Inspired oxygen concentration was measured at five-minute intervals. There was a significant difference in the final inspired oxygen concentration among the three different flow rates and the rate of decrease in the inspired oxygen concentration also differed. The 10 and 20 ml/kg per minute oxygen flow rates do not appear to be adequate even for short procedures. Oxygen flow rates of 30 ml/kg per minute or greater are adequate since the drop in inspired oxygen concentration with time is not sufficient to be of any biological importance..