During this last week I was contacted by two different individuals who were asking for help in understanding their PFT results. In both cases they had a markedly elevated TLC and the interpretation included the notation that they had gas trapping and hyperinflation. Even though the amount of information they provided was minimal I am extremely skeptical that the TLC measurements were correct.
Gas trapping usually only occurs with severe airway obstruction. Hyperinflation, which at minimum consists of a chronically elevated FRC and RV, usually only occurs after prolonged gas trapping. An elevated TLC usually occurs only with prolonged hyperinflation and given the improvements in the care and treatment of COPD I’ve seen over the last several decades, has become relatively uncommon.
But one individual had perfectly normal spirometry:
And the other only had mild airway obstruction:
The individuals did not say what method was used to measure their lung volumes and since they contacted me anonymously I am not able to find this out. In a sense it doesn’t matter however, since no matter what technique was used (helium dilution, N2 washout or plethysmography) the most common testing errors lead to an overestimation of RV, FRC and TLC.
I also don’t know whether the tests were performed at a hospital-based PFT lab or one that was based in a physician’s office. Office-based PFT labs used to be rare but particularly in group pulmonology practices they have become more commonplace. A number of readers have complained that they’ve seen Medical Assistants being trained to perform spirometry, lung volumes and DLCO’s in group practice PFT labs, even in states that have legislation or regulations that require a CRT, RRT, CPFT or RPFT to perform pulmonary function testing. Although this practice is likely unethical both in the sense that it is skirting the law and more so since it is using poorly educated and trained staff to perform complex testing, it usually goes unnoticed because there is no regulatory body overseeing testing in private offices.
I would hope that trained and licensed staff would have some qualms about reporting elevated TLC’s, particularly when spirometry was normal or almost normal, but to be honest I see too many technicians who believe that whatever the computer tells them must be so and fail to look at the big picture.
Regardless of who is performing the tests, the real problem (and the responsibility) lies with the interpreting physician. Gas trapping and hyperinflation with essentially normal spirometry? Really? The kindest thing I can say about this is that the interpreting physician was asleep at the wheel. If I was feeling less kind I’d have to say they’re either woefully ignorant about testing issues, or worse, they are willfully ignoring poor quality tests.
Having said that, testing errors are rarely front and center when PFT interpretation is being taught, and I’ve seen this even with the pulmonary physicians and fellows I’ve worked with. I understand that it is important to teach the basic algorithms for interpretation when starting out and that it does take time to get these down pat. At some point though, there also needs to be a firm understanding of testing errors and what they look like, and this seems to be the part that is most often neglected.
When I started working in a pulmonary function lab in the early 1970’s pulmonary fellows were expected to spend a couple weeks actually performing tests and calculating the results from the traces on kymograph paper. That stopped after I’d been in the lab only a couple of years and was never re-started. I believe the main reason for this is that since that time pulmonary medicine has expanded into the intensive care unit and sleep medicine and pulmonary fellows don’t have the time to “waste” on pulmonary function testing. Of course I think this is shortsighted and wrong but then again I don’t have any say about what’s in the pulmonary fellowship program.
In these two instances the interpretation of gas trapping and hyperinflation is most likely wrong. For the patients this probably means extra tests, doctor visits and maybe even medications that they don’t need and I have to wonder how long, if ever, it will take for this misapprehension to be corrected. The problem likely started with the inadequate training of whoever performed the tests in the first place, and I say this whether they were technicians or MA’s, but the final nail was placed by the interpreting physician and for that reason this is where the primary responsibility for the error lies.
GIGO. Quis custodiet ipsos custodes?
PFT Blog by Richard Johnston is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License