One key function in vaporizer maintenance is calibration. Following repair, refitting, and lubrication, the unit is assembled and tested. Adjustments made during assembly are refined in test. Measurements are recorded on specialized forms, which become a part of Primary Medical's permanent record of the vaporizer. When Primary Medical Products ships the unit, it has been calibrated and documented.
The calibration, process in most fields is conducted against a set of formal specifications. It may be surprising to users of anesthesia vaporizers that the manufacturers' specifications for flow and other key parameters are so sparse that merely satisfying them would be inadequate for Primary Medical. In particular, the manufacturer specifies only one value in a formal manner; resistance to carrier gas flow under nominal conditions (16% tolerance). All other documented values are best regarded as nominal, not specific. For example, one may find numerous plots of the flow of various agents as functions of temperature and dial setting. The only indication of the accuracy of those diagrams is that another source of error in delivery of agent (carrier gas composition) is regarded as "negligible," since it is... normally less than 10% of setting.
Regarding 10% error as negligible should hardly be surprising either to the anesthesiologist or to the biotech engineer. The engineer knows that the vaporizer is a fully mechanical device which contains a corrosive environment; over the range of variables it must handle, the vaporizer is doing well to maintain monotonicity in flow vs. dial setting, let alone precision. The anesthesiologist perceives the issue of precision from another perspective: the effect on the patient. If only because of individual variation in sensitivity to the agent, the anesthesiologist relies on patient monitoring, not on dial setting, to establish the proper flow. In administering anesthetic, the key properties of the vaporizer are that it does not leak when shut off; promptly increases/decreases flow with increasing/ decreasing dial setting; and even under adverse conditions or probable failure, will not permit catastrophic flow of agent to the patient.
Primary Medical regards no avoidable error as "negligible" but concurs with engineers, anesthesiologists and vaporizer manufacturers that there are limits beyond which calibration cannot go. In practice, there are no hard flow specifications to satisfy; there are, however, indicators in the profile of a unit's calibration over years of maintenance which are more significant than measurements at any one time. Of course, Primary Medical verifies that the unit satisfies both the manufacturer's specifications and the anesthesiologist's requirements before shipping, and warrants that performance for one year. More significantly, we track the quality of calibration over repeated maintenance sessions to anticipate some forms of incipient failure.
A final note is in order on the causes of failure of a vaporizer which Primary Medical has maintained. In our experience, the most common error is encountered at installation (notably misalignment in the bracket, which may cause leakage of agent). Primarily in older units, lacking keyed-fillers, use of the wrong agent may both cause error in administration of the agent to that patient and fouling of the vaporizer itself, requiring immediate maintenance. Mishandling can also cause major degradation of calibration or even failure; shipping damage is all but eliminated using Primary Medicals special boxing method, but applying vertical force on the dial (e.g., lifting the unit by the dial) can be as effective as applying a sledge hammer. By handling a calibrated vaporizer with care and following the manufacturer's and Primary Medical's rules, it can be relied on to satisfy of your requirements and all applicable specifications.