Test of the Circle System

The circle system test (see Appendix 1 , steps 11 and 12) evaluates the integrity of the circle breathing system, which spans from the common gas outlet to the Y-piece (see Fig. 9-22 ). It has two parts: the leak test and the flow test. To thoroughly check the circle system for leaks, valve integrity, and obstruction, both tests must be performed preoperatively. The leak test is performed by closing the pop-off valve, occluding the Y-piece, and pressurizing the circuit to 30 cm H₂ O using the oxygen flush valve. The value on the pressure gauge does not decline if the circle system is free of leaks, but this does not ensure valve integrity. The value on the gauge is 30 cm H₂ O if the unidirectional valves are stuck shut or if the valves are incompetent.

The flow test checks the integrity of the unidirectional valves, and it detects obstruction in the circle system. It can be performed by removing the Y-piece from the circle system and breathing through the two corrugated hoses individually. The valves should be present, and they should move appropriately. The operator should be able to inhale but not exhale through the inspiratory limb. The operator should be able to exhale but not inhale through the expiratory limb. The flow test can also be performed by using the ventilator and a breathing bag attached to the Y-piece as described in the 1993 FDA Anesthesia Apparatus Checkout Recommendations (see Appendix 1 , step 12).^[163]