c556c467_egal__Cleaning___Sterilization_Pre_Anesthesia_Checklist_2008_Rationale
[Step] Verify auxiliary oxygen cylinder and self-inflating manual ventilation device are available & functioning [Rationale] 
Failure to be able to ventilate is a major cause of morbidity and mortality related to anesthesia care. Because equipment failure with resulting inability to ventilate the patient can occur at any time, a self-inflating manual ventilation device (eg. AMBU bag) should be present at every anesthetizing location for every case and should be checked for proper function. In addition, a source of oxygen separate from the anesthesia machine and pipeline supply, specifically an oxygen cylinder with regulator and a means to open the cylinder valve, should be immediately available and checked. After checking the cylinder pressure, it is recommended that the main cylinder valve be closed to avoid inadvertent emptying of the cylinder through a leaky or open regulator.
Anesthesia Gas Machine- Machine checklist, Medicolegal, Cleaning & Sterilization
Rationale