Failure of the Oxygen Gauge to Accurately Reflect the Pressure in the Oxygen Tank
An E-cylinder oxygen tank was connected to a DRE VSO2 anesthesia machine with the use of a Western Medica regulator and a standard pressure gauge in an office-based surgical setting. This E-cylinder served as the primary source of oxygen. Another E-cylinder was also connected to the anesthesia machine with a separate pressure gauge for backup. A standard anesthesia checkout was performed at the start of the day. Visual and audible low-oxygen pressure alarms were checked as well as the pressure of oxygen in both E-cylinders, which showed both tanks to be full (2000 psi) and line pressure >40 psi. During the day, the oxygen tank was checked before each case to confirm that the primary oxygen tank was at least half full. Over the course of the day, and with repeated use, the pressure in the primary tank did not fall below 1000 psi, as reflected by the oxygen gauge, and this was recorded before the start of each case.
During the anesthetic care of a patient, the visual and audible oxygen alarms sounded, and oxygen flow pressure decreased to 0 psi. However, inspection of the pressure gauge on the primary E-cylinder showed that there was still 1000 psi of oxygen remaining in the tank. The backup oxygen source was immediately opened, with repressurization of the system to >40 psi and oxygen flow increased. A new anesthesia machine (with a new primary and secondary source of oxygen) was brought in, and the case was completed without incident.
Upon evaluation of the oxygen gauge, we noticed that the dial was stuck at 1000 psi. To find out why this occurred, we removed the lens cover of the gauge. The lens cover was easily removed, and the gauge immediately went down to zero. Further inspection of the perimeter of the gauge showed a break at the rim in the bottom corner. This break caused the glass covering to sit at an angled position, placing pressure on the dial. The dial was held in place at the 1000 psi mark because the glass covering of the gauge was pushing against it and keeping it from falling down any further. This scenario may happen on any pressure gauge, but would be especially dangerous if it occurs on oxygen tanks which are located on code carts or resuscitation carts.
As a result of our experience, and to avoid similar situations from happening, we recommend that the following steps be followed. (1) A routine preanesthesia checkout typically includes checking the audible and visual oxygen alarms on depleting the system of oxygen, and checking the pressure gauge only on repressurizing the system. However, in addition, we recommend that the pressure gauges be checked routinely when the system has been depleted of oxygen to make sure they go all the way down to zero. This may be done simultaneously with checking the audible and visual oxygen alarms. (2) The regulator and the pressure gauge should be physically inspected for any crack, breakage, or other damage, especially around the perimeter. (3) Pressure gauges on oxygen tanks on code carts and resuscitation carts should routinely be checked to make sure the pressure gauge goes all the way down to zero. This also emphasizes the importance of both an oxygen pressure gauge and a low-oxygen alarm on respiratory equipment in other clinical settings such as code carts, even when the standards do not require it.