Figure 1
In an age of microcomputers and scanning electrophotometers, the TEC vaporizer stands out as a mechanical wonder. It is as precise as a fine watch, yet rugged and reliable. In a hostile and corrosive environment, it remains free of corrosion. Its operation is remarkably simple, yet depends on complex calibration and precise adjustment. Primary Medical is a business built to provide that calibration and adjustment to users of a variety of TEC vaporizers.
We have prepared this overview to help our customers understand and to explain to their managements what we do and why regular preventive maintenance is critical to safe use of the TEC vaporizer. Figure 1 is a cut-away view of a TEC vaporizer in operation. While each manufacturer's design differs in significant detail from every other's, their basic operation is similar.
The vaporizer contains a reservoir (1) of the anesthetic agent. In its simplest terms, the unit's only purpose is to vaporize a controlled amount of the anesthetic into the flowing carrier gas to allow delivery of a precise level to the patient. The carrier gas enters the unit through the inlet (2) and is separated into two streams. One (3) bypasses the vaporizer chamber and flows directly to the outlet port (4). In bypass mode, a plate (5) seals off the path to the wick chamber (6) so that no anesthetic enters the stream of carrier gas. In operation, the vaporizer permits a portion of the gas stream to flow into the wick chamber and through the wick (7). Passing through the wick, the gas picks up vaporized anesthetic. The stream of mixed gasses is then merged (8) with the bypass stream of carrier gas for delivery to the patient.
Figure 2
Figure 2 shows a highly schematic form of the control elements of a TEC vaporizer. The elements of control are common to all manufacturers' products, although they differ both in the design of the elements and in their placement in the stream. The components of vaporizer control are three resistance elements, or essentially, flow restrictors. A fixed resistance (1) limits the maximum flow through the wick chamber so that an acceptable minimum amount of carrier gas is always delivered to the patient. An adjustable resistance (2) is used by the anesthesiologist to set the desired level of anesthetic in the flow. However, the amount and percentage of anesthetic delivered depends not only on the setting of the control knob (3) but also on the temperature, density and pressure of the working gas. The pressure of that gas is controlled outside the vaporizer, but compensation for temperature variation is handled internally by a compensating valve (4).
The restrictors used within the vaporizer require fine channels whose dimensions are precisely controlled. When maintained, each component of the path is cleaned of any debris which may have accumulated. That debris comes from microscopic impurities in the gas stream which escape its filtration, from trace impurities in the anesthetic fluid and from other sources such as the environment of the surgery when the vaporizer inlet or outlet is disconnected. Because of the precision of the internal pathways, even the infinitesimal amounts of debris from those sources can be enough over time to disrupt its calibration. When that occurs, the amount of anesthetic delivered to the patient no longer corresponds to the value dialed in. While small errors do not directly endanger the patient's health, those which may accumulate over time will complicate the work of the anesthesiologist. Unless maintained, the vaporizer can become so contaminated that precise control is compromised. Since the degradation of performance is gradual and is not externally visible, preventive maintenance should be scheduled based on time and use of the unit.
Primary Medical Products provides independent maintenance of all brands and models of TEC vaporizers. We have been in operation for about two decades, and provide service on models which are no longer supported by their manufacturers as well as on all current units. Our single-point service can simplify your operations, and we can provide fast turn-around without compromising quality of service. Through use of specialized and automated equipment, we can also offer cost savings which make necessary maintenance economical as well as precise and effective.