Pipeline sources are not trouble-free: Consider contamination (particles, bacteria, viral, moisture), inadequate pressure, excessive pressures, and accidental crossover (switch between oxygen and some other gas such as nitrous oxide or nitrogen). The two more frequent problems related to pipeline supply are crossover and inadequate pressure.
This rare situation has been almost reduced to zero since the introduction of the DISS in every operating room in United States. Switching the oxygen pipeline to air or nitrous oxide will trigger the low oxygen pressure alarm (detects oxygen supply failure at the common gas outlet) as well as the hypoxic guard (minimum O2/N2O ratio controller device) in the anesthesia machine.
For a crossover, one must:
- Turn on backup oxygen cylinder, and
- Disconnect pipeline supply hose from the wall.
Gas will flow from whichever source is at a higher pressure — the pipeline (at 50 psi, containing, for example, nitrous oxide) or the emergency tank supply of oxygen (supplied to the machine at 45 psi). So you must disconnect the pipeline supply. After you are sure that the patient is receiving adequate oxygen, try to identify where the crossover happened. It is also recommended to ventilate manually when pipeline oxygen is unavailable in machines which use oxygen in whole or part as the driving gas that compresses the ventilator bellows. Maintaining mechanical ventilation in the absence of pipeline oxygen can use an entire E cylinder of oxygen (approximately 600 L) in an hour or less. This admonition applies to almost all gas machines; the exceptions are piston ventilators, which do not use driving gas or bellows at all.
The loss of oxygen pressure results in alarms, audible and visible, at 30 psi pipeline pressure. Most machines will shut off the flow of other gases when O2 pressure falls below 20 psi. Similar to a crossover, first you must open the backup oxygen cylinder fully. Once the failure of the oxygen pipeline is recognized, oxygen should be introduced into the anesthesia machine via the reserve oxygen tanks. This will repressurize the anesthesia machine’s intermediate pressure system. If the condition of the patient remains stable, a search for the oxygen pipeline supply failure should be initiated. To determine if the problem is transient or permanent, the emergency oxygen tanks may be turned off momentarily. If the patient’s condition becomes unstable, then resuscitation of the patient obviously takes precedence. Ventilation must be ensured. Changing to bag ventilation (see above) and tightening down the pop-off valve may provide enough oxygen for several minutes of ventilation. Often a supply of emergency oxygen is not immediately available for use with it. This could force the anesthesiologist to use room air as the supply gas. We recommend that a source of emergency oxygen for use with the equipment be available in each operating room. Depending on the type of anesthesia machine in use, a leak in the intermediate pressure system may mimic a failure of the oxygen pipeline supply. This is especially true of anesthesia machines without oxygen pipeline pressure gauges or where the gauges are downstream of the pressure inlet check valve. If turning on the reserve oxygen cylinder does not repressurize the anesthesia machine, then it follows that the intermediate pressure supplied to the patient has a leak. On most anesthesia machines the intermediate pressure system is relatively inaccessible, making manipulation of this system during anesthesia difficult. It may be easier and wiser to replace the broken machine, supporting the patient, in the interim, with emergency ventilation equipment. The following algorithm has been developed by the Department of Anesthesia at Stanford University School of Medicine when an “O2 SUPPLY FAILURE ALARM” occurs.