Observations and Consequences of a Hypoxic O2 Pipeline Condition
Itemized Discussion Points
1. N2O is supplied, instead of O2, via the O2 flow meter
2. N2O is supplied, instead of O2, when pressing the "O2 flush" valve
3. The "O2 failsafe" device is fooled and allows delivery of a hypoxic gas mixture
4. The "hypoxic guard" device (O2 proportioning device) does not prevent delivery of a hypoxic gas mixture
5. N2O is used as the drive gas, instead of O2, during mechanical ventilation
6. N2O, that is now the drive gas, is vented directly to the room in most anesthesia ventilators with gas driven bellows
7. The O2 analyzer, if present, alarms when FiO2 drops below alarm threshold
8. The pulse oximeter, if present, alarms when SpO2 drops below alarm threshold
9. Initially, end-tidal CO2 will be normal if ventilation (not oxygenation) is adequate
10. Airway pressure will be normal if ventilation is adequate
A hypoxic O2 pipeline already present at the start of a first case of the day will be detected if the clinician performs a pre-use check according to the 1993 FDA Anesthesia Apparatus Checkout Recommendations. Specifically, step 9c [Reinstall (O2) sensor in circuit and flush breathing system with O2] and step 9d [Verify that monitor now reads greater than 90%] of the 1993 FDA pre-use check recommendations will raise a warning that something is amiss and potentially help to identify the hypoxic O2 pipeline condition.
The footnote at the end of the 1993 FDA pre-use check recommendations states that "If an anesthesia provider uses the same machine in successive cases, these steps (9c and 9d included because there is an asterisk next to step 9 - authors' addition) need not be repeated or may be abbreviated after the initial checkout." Thus, if the gas in an O2 pipeline becomes hypoxic after the first case of the day, an abbreviated pre-use check per the 1993 FDA recommendations for a following case of the day may not detect the low FiO2 associated with a hypoxic O2 pipeline condition.
The 1993 FDA pre-use check also does not guard against gas in the O2 pipeline becoming hypoxic in the middle of a case. While this may appear far-fetched, we have been informed of such a case in a military hospital where the central O2 supply was actually a bank of O2 H-cylinders in the cellar. A medical orderly was tasked with monitoring the pressure gauges on the O2 cylinders and opening a new H-cylinder when the one being used was nearing exhaustion. The new "O2 cylinder" that was opened while cases were proceeding was misfilled with Argon and multiple fatalities occurred at different anesthetizing locations.
Most developed countries have guidelines for testing O2 outlets after construction or renovation and before they are used. This system too has been reported to fail. In one reported instance, the O2 outlets after the addition of 3 new ORs were correctly plumbed and passed when tested. Subsequently, the O2 outlets were repositioned and during repositioning of the outlets, the gas pipes were crossed. The O2 outlets were not tested again after the repositioning and patient fatalities occurred in different anesthetizing locations.
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