Formal guidelines for spirometry use were provided in 2005 through a collaboration between the American Thoracic Society (ATS) and European Respiratory Society (ERS). These standards are periodically reviewed, and in November of 2019, the ATS/ERS 2019 Spirometry Update Task Force published an update. Several important changes were made with the intent of creating a better patient experience and more accurate test results.
Pulmonary function tests are unique in that the patient must actively participate in most lung function testing in order for the results to be valid. When contrasted with other diagnostic testing, pulmonary function laboratories in most places in the world do not have a laboratory accreditation program that mandates practices that will help guarantee the reliability of the test results. Although standardization of testing practices has been guided by ATS/ERS for the past few decades, adoption of their recommendations has typically been heterogeneous and slow. Because of this, ERT is taking steps to spread awareness of the new, patient-centric guidelines.
In this blog we share just a few of the highlights and elaborate on how professionals can implement them.
More accurate results: Importance of starting forced exhalations from full inflation
One of the most important changes to the guidelines came from evidence that forced exhalation could be performed perfectly but still gives erroneously low results because the forced exhalation started from a lung volume below full inflation. It is easy to remember the adage, “if they don’t breathe it in, they can’t blow it out.” The new standards give detailed guidance on how to vigorously coach patients to full inflation and stress that site operators must actively observe the subject for evidence they are fully inflated.
When teaching operators how to conduct forced exhalations, very little emphasis has been placed on how to coach to full inflation (fig. 1, step 1). While most spirometers display volume-time tracings and flow-volume curves, it is better for operators to focus their attention on the patient and use feedback from observing the patient to determine when to change the coaching from maximum inflation (fig. 1, step 2)to the explosive start of the forced exhalation (fig 1, step 3). Many operators look instead at the screen for evidence that inspiratory airflow has stopped or just deliver their coaching in a practiced cadence that does not involve actively looking for feedback that the subject is fully inflated when they instruct the patient to start the forced exhalation.
The following illustration shows the four phases of the forced exhalation maneuver.
Figure 1: FIVC after EOFE
It is better to look for evidence that the subject is at full inflation by observing the patient. When at full inflation, the patient will not look comfortable. Typically, the eyebrows will raise, the eyes will widen and the head may quiver. This quivering is caused by isometric contraction of accessory muscles of inspiration which cannot increase the volume of the thorax further.
By positioning themselves so both the patient and the screen can be observed, operators can optimize the timing of the command to start the forced exhalation. When signs are present indicating the subject is at full inflation, it is important to give the command to start the forced exhalation immediately to avoid a delay that could result in loss of air prior to application of maximum expiratory effort (back extrapolated volume). Breath holding at full inflation for more than 1-2 seconds can also negatively impact the contribution of lung elastic recoil on the FEV1.
Verifying full inflation (after the effort has been completed)
The total volume that was forcefully exhaled is called the forced vital capacity (FVC). The new standards stipulate that the procedure should no longer end after the forced exhalation. Rather, immediately following a forced exhalation, the subject should be vigorously coached to rapidly inspire to full inflation again (fig 1, step 4).
The volume inhaled to full inflation after the end of the forced exhalation is called the forced inspiratory vital capacity (FIVC) and should closely match (within 5% or 0.10L, whichever is larger) the FVC for that effort. If this is demonstrated, it is very likely that the forced exhalation started from full inflation. If the FIVC is significantly larger than the reported FVC, this can be taken as evidence that the forced exhalation did not start from full inflation and the effort should not be considered acceptable, even if it meets all of the other criteria that define acceptability of the FEV1 and FVC. The operator can then focus their instruction and coaching efforts to maximize lung inflation on subsequent efforts.
The addition of this 2nd inspiration to full inflation will take time for operators to incorporate into their routine, but once it becomes second nature, it is likely that operators will find their patients doing fewer efforts in a measurement session as there will be fewer efforts that did not meet the important condition of starting from full inflation.
There are many more changes in the 2019 guidelines, including changes to the end of the forced exhalation acceptability criteria that pertain to pediatric patients and patients with interstitial lung disease. Individuals involved with testing should familiarize themselves with the new guidelines and implement the changes as soon as possible. Equipment manufacturers are incorporating the new guidelines into their testing software and many vendors either already have or are expected to release updates soon.
Kevin McCarthy, RPFT is a former manager of Pulmonary Function at the Cleveland Clinic Health System, ERT Clinical Overread Specialist and member of the ATS Proficiency Standards for Pulmonary Function Laboratories committee and the ATS/ERS 2019 Spirometry Update Task Force.