Figure 9-9 The flow meter sequence is a potential cause of hypoxia. A and B, In the event of a flow meter leak, a potentially dangerous arrangement exists when nitrous oxide is located in the downstream position. C and D, The safest configuration exists when oxygen is located in the downstream position. (Adapted from Eger El II, Hylton RR, Irwin RH, et al: Anesthetic flow meter sequence—A cause for hypoxia. Anesthesiology 24:396, 1963.)