Underutilized spirometry, missed opportunities

A friend is taking her father to a PFT lab (2500 miles away from where I am the moment so I couldn’t go along with them) because he has been short of breath for a couple of years, but oddly enough, only when lying on his side. I expect that despite these rather specific symptoms he will only get routine spirometry. I don’t necessarily fault the PFT Lab he’s going to for this, partly because physician orders often don’t include specifics, partly because they may not have the facilities to perform supine or lateral spirometry, and partly because its not clear lateral spirometry would show anything.

I don’t think that my lab is necessarily any better. We have only one room with an exam table that allows us to perform positional spirometry and that is largely because of the ALS patients we regularly see. Even so, unless we received specific orders to perform supine or lateral spirometry it’s unlikely that one of our technicians would think it was necessary and then take it on themselves to perform it. That itself is part of the problem not only for my lab but for the field of Pulmonary Function testing in general (but that’s another story).

The real problem however, is that the way in which spirometry is performed around the world is focused almost exclusively on detecting expiratory airway obstruction. It may be true that airway obstruction is primarily expiratory, but this ignores that fraction of individuals who have some degree of inspiratory obstruction. It also overlooks those individuals whose FVC is underestimated and FEV1/FVC ratio overestimated due to some degree of gas trapping. It also overlooks individuals that have positional airway obstruction that is not evident in the upright position.

We’ve fallen into the trap of thinking that there’s only one way to perform spirometry, and this is a mistake.

Spirometry is usually taken as being synonymous with the Forced Vital Capacity maneuver. That may be the way the word spirometry has come to be used but it really isn’t correct. Spirometry refers to any test that can be performed with a spirometer and (among other tests) includes the Slow Vital Capacity (SVC) and the Forced Inspiratory Vital Capacity (FIVC). This also means that there is much more that can be done with a spirometer than what it’s ordinarily used for.

A patient visit to a pulmonary clinic may appear simple but actually depends on the convergence of numerous high-value resources. Patient, physician, technician and clerical time. Waiting room, exam room, lab and office space. Spirometers, computers, an institution’s clinical database and the software that binds them together. I would like to suggest that the way in which spirometry is usually performed provides information that, although not necessarily incorrect, may instead be misleading for some fraction of patients. This fraction may or may not be small and there is no way to estimate this correctly since it will vary largely based on the patient population. Regardless, in order to maximize resource utilization, I think that the amount of information that can be obtained from spirometry needs to maximized as well.

For this reason I would like to suggest that a patient’s initial spirometry session should include Forced Expiratory Vital Capacity (FEVC) maneuvers, Forced Inspiratory Vital Capacity (FIVC) maneuvers, Slow Vital Capacity (SVC) maneuvers and when appropriate, positional FEVC maneuvers.

Why?

One reason is to obtain a patient’s largest Vital Capacity (VC) for the FEV1/VC ratio. The FEVC, FIVC and SVC maneuvers are performed differently and a patient may reach a higher VC with a FIVC or SVC than they would with an FEVC. My experience is that perhaps as many as 20% of patients that perform a SVC reach a higher VC than they did during the FEVC maneuver. For at least a quarter of these patients, this increased VC reduces the FEV1/VC ratio enough that it is then consistent with airway obstruction when it wasn’t previously.

Another reason is to rule out inspiratory airway obstruction. The number of patients with inspiratory obstruction is probably small, but since the baseline assumption is that obstruction is primarily expiratory, this has not been studied to any degree. So the number may (or may not) be small but some fraction of patients have inspiratory obstruction and these individuals need to be identified. To some extent this would be satisfied by ending the FEVC maneuver with an FIVC maneuver (and this is part of the ATS/ERS spirometry guidelines) but those researchers who have studied inspiratory flow rates recommend performing the FIVC as a separate maneuver (which also maximizes the possibility of obtaining a larger FIVC than FEVC).

Another reason is to obtain the Inspiratory Capacity (IC) and the Expiratory Reserve Volume (ERV). A reduced IC, when seen along with moderate or severe expiratory airway obstruction, is an indication of gas trapping. In addition more than one researcher has shown that the ERV/IC ratio is the best indication of the affects of obesity on lung function.

Post-bronchodilator FEVC, FIVC and SVC maneuvers would also need to be performed to fully assess an individual’s response to bronchodilator. At the present time the ATS/ERS statement on interpretation only considers increases in FEV1 and FVC to be significant. Research has shown however, that significant increases in inspiratory flow rates or increases in IC can occur without a corresponding increase in FEV1 or FVC. The number of patients with these kind of increases is again probably small, but determining which patients exhibit them will certainly have a bearing on their clinical management.

Finally, whenever there are the appropriate patient symptoms, positional (supine or lateral) FEVC (and maybe FIVC?) maneuvers should also be performed. Changes in VC in the supine position when compared to upright are an indication of diaphragmatic weakness. Changes in flow-volume loop contours that occur in supine or lateral positions can indicate the presence of bodies pressing against the larger airways as well as other airway disorders. Again, the number of patients with these specific problems is probably small, but when a patient complains of a notable increase in dyspnea in a specific position, it should be investigated.

I will not disagree that the majority of patients are well served by routine FEVC testing. I will also not disagree that the majority of patients who have FIVC and SVC testing will not have any significant findings. The point is that there is a certain number of patients whose problems are not detectable without FIVC, SVC and positional testing. The fraction of the normal patient population with problems that can only be seen by these additional spirometry tests is not known because this has never been studied. At a guess it has to be at least 5% since approximately that fraction of patients that perform an SVC in my lab have an FEV1/SVC ratio that is significantly lower than the FEV1/FVC ratio.

To some extent I am advocating that all initial patient spirometry should include FIVC and SVC testing but that is mostly because the indications for whom this would be useful are unclear. This flow diagram is my best guess for a structured approach to this kind of testing:

Spirometry_Flow_Diagram

I will acknowledge that there are a number of roadblocks towards regularly performing a full range of spirometry tests and the first of these is the software our test systems come with. At the present time I don’t know of any software that allows the FIVC to be performed and reported separately from an FEVC. At one time my lab’s software allowed us to mix-and-match the FEVC and FIVC components from different tests but this feature was lost several software upgrades ago.

Another problem is that comparing results to a baseline value is assumed to consist of only pre- and post-testing. So what happens when you perform baseline tests, post-bronchodilator tests and then positional tests? Not much since only one type of post-test can be reported unless you start a new patient visit and because in some labs billing, appointments and reporting are tied together this requires work-arounds both in reporting and billing.

What I’d like to see in a report would look something like this:

Spirometry_Table

There is also the problem of compensation. There are no CPT codes for FIVC, SVC and positional spirometry which means its not possible to bill for them. This is a fault of our more than somewhat byzantine payment system (which still has no CPT code for MIPs and MEPs despite their having been included in the ATS statement on respiratory muscle testing in 2002). For this reason my lab has performed supine spirometry on ALS patients for over 15 years while only being able to charge for routine spirometry. I feel very strongly however, that a PFT Lab is a diagnostic service whose purpose is the accurate assessment of lung function and that means doing the tests that facilitate this. To do any less is to fail our patients and physicians.

One final thought is that performing FIVC, SVC and positional testing is also an opportunity to improve patient care without additional equipment. We all need new and updated equipment but let’s also work smarter and make the best use out of what we already have.

Spirometry is more than just the FVC. The FIVC, SVC and positional testing are also part of spirometry but are significantly underutilized and the information they can provide is often overlooked. It may not be necessary to routinely perform all of these tests (although I am obviously advocating that to some extent they should) but at the very least we should be willing to recognize that there are times when they should be performed.

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2 thoughts on “Underutilized spirometry, missed opportunities

  1. I have seen referenced in lectures That an elevated IC/ERV ratio is the hallmark of pseudo-restriction but I’m having difficulty finding a good reference on this that explains why that is the case. Can you help me out here ?

    • Adamo –

      I don’t have any references for you on an elevated IC/ERV ratio and I’m also not sure what is meant by pseudo-restriction. Assuming that it means a lowered FVC in the presence of a normal TLC this would primarily imply the presence of an elevated RV but I suppose it’s possible the RV is elevated at the expense of the ERV. I will mention in passing that an elevated IC/ERV ratio is seen in obesity and FVC often declines with an increasing BMI but it usually remains WNL as does TLC and RV. Did the lecturers explain the conditions that come along with pseudo-restriction?

      Regards, Richard

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