Figure 9-31 Inappropriate use of the oxygen flush valve to check the low-pressure circuit of an Ohmeda machine equipped with a check valve. The area within the rectangle (dotted line) is not checked by the inappropriate use of the oxygen flush valve, and the components located within this area are precisely the ones most subject to breakage and leaks. Positive pressure within the patient's circuit closes the check valve, and the value on the airway pressure gauge does not decline despite leaks in the low-pressure circuit. (Adapted from Andrews JJ, Brockwell RC: Delivery systems for inhaled anesthetics. In Barash PG, Cullen BF, Stoelting RK [eds]: Clinical Anesthesia, 4th ed. New York, Lippincott-Raven, 2000, pp 567–594.)