This note explores the concept of vaporizer maintenance. By examining the reasons for needing different kinds of maintenance, we hope to help you determine when to submit a vaporizer to us for service.
Vaporizer maintenance may be considered either preventative or corrective. Corrective maintenance is undertaken when performance of the unit is noted to be faulty; it is impossible to defer corrective maintenance, so it is impossible to schedule or to avoid. Preventive maintenance may be either routine or triggered. Triggered preventive maintenance is initiated when an external event makes continued use of the unit questionable. While the event cannot be predicted, a unit requiring triggered preventive maintenance may continue in use for a period of time without penalty - except for the risk that damage will. accumulate, and corrective maintenance might become necessary. Routine preventive maintenance can be scheduled and may be deferred as required by conditions. In general, routine preventive maintenance is least disruptive of operations and least costly since major repairs are seldom required. Triggered preventive maintenance is slightly more likely to incur extra expense and is somewhat disruptive of routine schedules. Corrective maintenance is likely to be costly (due to accumulated damage), to require extra service time, and to disrupt normal operations most severely. It is fair to say that a major reason for doing preventive maintenance is to minimize the risk of needing corrective maintenance
Representative Causes
Figure 1 (above) shows a typical failure point of a Tec 3, Tec 4, Tec 5, Tec 6, Drawover and Acoma vaporizers. It is a seal of synthetic rubber mounted on the shaft of the control valve. (This seal is similar to an o-ring whose cross-section is a truncated triangle.) In normal operation, it is subjected to compression and shaft rotation in the presence of small amounts of anesthetic agent. Over time and use, the seal swells and weakens. Because of the way it is confined, the seal swells along the shaft, increasing the arc of contact but degrading its quality. Eventually, the material becomes stiff as well as distorted and may develop cracks through which agent leaks. With normal usage, the seal shows significant swelling and slight stiffening after a year of service. Primary Medical always replaces it whenever it services a unit. Thus, routine preventive maintenance includes replacing the seal to reduce the risk that it will degrade with time and cause leakage of agent.
Many different events could initiate damage to the seal, triggering preventive maintenance if recognized, or eventually initiating corrective maintenance. One of the more common occurrences is exposing the seal to liquid agent. That occurs when anesthesia system pressure increases; simultaneously raising the pressure within the vaporizer chamber and forcing fluid against the seal. We suspect that almost all degradation of the seal in practice arises from exposure to liquid agent; concentration of the agent in the gas is so low that it is unlikely to degrade the synthetic rubber.
Once the seal begins to deform and harden, it becomes susceptible to cracking. While cracks which can cause leakage could occur without a triggering event, our experience point often to mishandling, such as lifting the vaporizer by the control valve or hitting the unit with a hard object. Once the seal leaks, it spills agent into the air and reduces the flow to the patient
Effects of Damage
We have seem that increased external pressure on the reservoir bag can trigger accelerated degradation of the seal and that mishandling can trigger leakage. Effects of swelling and hardening of the seal can include not only leakage due to cracking, but also sticking of the control valve, leading to difficult rotation or even inability to set a desired flow rate. Leakage may be consistent throughout dial rotation or variable as a function of position of the valve; if variable, leakage may also make it difficult or impossible to set a desired flow rate. The anesthesiologist may detect the problem as inconsistent changes in flow when the dial is rotated, as mechanical difficult in rotating the dial in some regions, and/or as unexpected response of the patient to changes in dial setting. Clearly, if any of those problems occurs, corrective maintenance is needed immediately.
The indications that a triggering event has occurred may be quite subtle until damage increases to the stage where corrective maintenance is needed. For example, gradual increase in stiffness of the dial which may indicate degradation of the seal may be unnoticed when a single anesthesiologist uses a single vaporizer most of the time. If the triggering event or events should go unnoticed, the result may be that the first time the anesthesiologist finds a need for maintenance comes when immediate, corrective action is required - with maximum disruption and likely increased cost.
Periodic Maintenance
Many of Primary Medical's customers find that periodic maintenance is the best way to avoid the disruption of corrective maintenance and is a cost effective solution. Consistent with the recommendation of many vaporizer manufacturers, they schedule routine preventive maintenance of each unit annually. Others may monitor vaporizer performance more closely, attempting to detect subtle changes suggesting the need for triggered preventive maintenance. Some wait for the overt effects of accumulated damage, and accept the need for disruptive and costly corrective maintenance, and the potential patient risk associated with waiting for corrective maintenance.
The choice is yours.