Spring 2015 Diagnostics Section Bulletin

Spring 2015 Diagnostics Section Bulletin

Editor
Jeffrey M. Haynes, RRT, RPFT

Pulmonary Function Laboratory
St. Joseph Hospital
Nashua, NH
Work Email: jhaynes@sjhnh.org
Home Email: jhaynes3@comcast.net

Chair:
Katrina Hynes, BAS, RRT, CPFT
Assistant Supervisor
Special Pulmonary Evaluation Laboratory
Mayo Clinic
Rochester, MN 55905
(507) 284-4545
Hynes.Katrina@mayo.edu

Former Chair
Matthew J O’Brien, RRT, RPFT
Pulmonary Diagnostic Lab
University of Wisconsin Hospital and Clinics
600 Highland Ave Room E5/520
Madison, WI 53792-5772
(608) 263-7001
Fax: (608) 263-7002
mobrien@uwhealth.org


Technologist’s Comments: Should Patients Be Instructed To Withhold Respiratory Medication Before PFTs? Not Always!

Jeffrey M. Haynes, RRT, RPFT

Editor’s Note: The Bulletin usually starts with “Notes from the Editor.” The “notes” typically highlight the Bulletin’s content and add some additional topical information. To be quite frank, I find this as boring and unimaginative to write as you all probably find to read. I have therefore decided to retire “Notes from the Editor” and introduce “Technologist’s Comments” as avenue to offer insight, observations, and opinions regarding pulmonary diagnostics. Technologist’s Comments is not just for the editor. If you’d like to sound off on a particular topic, please email me a concise and provocative submission. Stand proud on your soapbox!

Patients are often instructed to withhold all of their respiratory medications prior to pulmonary function testing. This is regarded as so important that I’ve heard of patients being turned away and re-scheduled because they took their inhaler on the day of testing. But does this make sense? The answer is clearly “yes” if the patient has not received a diagnosis for his symptoms. This is particularly true if the patient arrives for a bronchoprovocation test.

However, instructing patients with long-standing lung disease to withhold their maintenance medication prior to a follow-up PFT really makes no sense at all. Isn’t the whole idea of a follow-up PFT to assess how the patient has responded to intervention? If this is true, shouldn’t we instruct the patient to take all of his maintenance medications (as he usually would) before we reassess his pulmonary function?

If a patient’s follow-up, medication-withheld PFT indicates little or no improvement, the typical response is to prescribe more medication; however, we haven’t really reassessed the patient’s function on his current medication! Instructing a COPD patient to withhold his maintenance medication prior to a follow-up PFT is akin to telling a patient with ischemic cardiomyopathy to withhold all of his cardiac medications prior to a stress test—crazy, right?

For this reason we have two sets of instructions for patients coming to our lab: “Diagnostic” (basically don’t take anything) and “Follow-up” (take everything as prescribed).


Analyzing VE/VCO2 and VE-VCO2 Slopes During Cardiopulmonary Exercise Testing

Richard Johnston, CPFT, Beth Israel Deaconess Medical Center, Boston, MA

Obtaining a patient’s maximum oxygen consumption (VO2) is often considered to be the primary goal of cardiopulmonary exercise testing (CPET); however, carbon dioxide production (VCO2) is just as important, if not more so.

Below the anaerobic threshold (AT), ventilation is driven primarily by arterial PCO2, and above the AT by PaCO2 and pH. Any inefficiency in either ventilation or gas exchange will cause minute ventilation to rise relative to CO2 production. For this reason the relationship between VCO2 and minute ventilation (VE) can be very informative.

VE/VCO2 is the ratio between VE and VCO2 at any given moment and is usually reported at AT. The same ratio is plotted for VE and VO2. (See figure 1)

Johnson Figure 1

A limitation of this measurement is that it requires an accurate determination of AT. In addition, VE/VCO2 does not usually reach a nadir until sometime after AT. For this reason some investigators have been able to show that the lowest observed VE/VCO2 is probably a better measurement of ventilatory efficiency than the VE/VCO2 at AT. Normal values from Sun, et al. are listed in table 1.

Johnson Table 1

Values above the 95% confidence level should be considered abnormal.

The VE-VCO2 slope, on the other hand, is obtained by linear regression of VE versus VCO2 and is calculated from numerous data points. For this reason, it may be a more reliable measurement than VE/VCO2. There is a different VE-VCO2 slope before and after AT due to lactic acidosis. (See figure 2) Accordingly, the VE-VCO2 slope is usually reported as either the slope from the start of exercise to AT (VE-VCO2AT) or from the start to peak exercise (VE-VCO2Peak).

Johnson Figure 2

When CPETs are performed as part of a pre-surgical risk assessment a low maximum VO2 is usually associated with a poor prognosis. Maximum VO2, however, can be reduced not just because of cardiac or pulmonary disease but because of musculoskeletal limitations, patient safety issues (blood pressure or ECG changes), or poor patient motivation. A significant advantage of the VE-VCO2AT slope is that it is relatively linear and accurate values can be obtained during a shortened or submaximal test. Numerous investigators have shown that the VE-VCO2AT slope correlates better with post-surgical mortality than does the maximum VO2 and that values above 34 likely indicate an increased hazard level. The practice at my lab is to report both the maximum VO2 and the VE-VCO2AT slope when a CPET is being performed as part of a pre-op assessment.

Although the VE-VCO2Peak is dependent on how far an individual is able to exercise beyond his AT, many investigators have shown that it has even greater prognostic power than VE-VCO2AT. The current American Heart Association (AHA) guidelines on cardiopulmonary exercise testing recommend measuring and reporting VE-VCO2Peak, and a value >40 should be considered abnormal.

Arena, et al. performed a risk assessment in conjunction with the VE-VCO2Peak slope and have proposed a classification system for patients with cardiac disease. This has been adopted in the most recent European Association for Cardiovascular Prevention/AHA statement on cardiopulmonary exercise testing. (See table 2)

<<ATTENTION LAYOUT: INSERT JOHNSTON TABLE 2 HERE>>
Johnson Table 2

Because the ventilatory equivalent for CO2 is dependent both on ventilatory and gas exchange efficiency there are a variety of potential causes for elevated values. These include:

  • Ventilation-perfusion mismatching
  • Pulmonary vascular disease
  • Elevated VD/VT

Some investigators believe elevated VE-VCO2 slopes are due to a low PaCO2 set point that is secondary to chronic hypoxia, chronic respiratory alkalosis, or chronic metabolic acidosis, and some research validates this point. Other studies have shown normal PaCO2 patterns in cardiac patients during exercise, so the relevance of this factor is unclear.

VE-VCO2 is usually elevated in patients with:

  • Congestive heart failure
  • Pulmonary hypertension
  • Idiopathic pulmonary fibrosis

Interestingly, patients with mild COPD can have a normal VE-VCO2AT but the slope tends to increase as the severity of COPD increases, except when hypercapnia is present.

Patients with known pulmonary and cardiac disease often undergo CPET to determine the primary etiology of their limited exercise capacity. My lab’s current practice is to consider an elevated VE-VCO2 slope as reflective of a primary limitation only if accompanied by a significant decrease in SpO2. One exception to this is when a patient achieves a pulmonary mechanical limitation (maximum minute ventilation greater than 85% of the predicted maximum) in the absence of obstructive or restrictive lung disease. In these cases an elevated VE-VCO2 slope indicates that inefficient ventilation is likely the factor driving the patient’s elevated minute ventilation.

Most studies on VE-VCO2 slope have used breath-by-breath measurement systems. Some researchers have criticized mixing chambers for causing a delay in the apparent VCO2 and an underestimation of the VE-VCO2 slope, but there has been no systematic study of this hypothesis. The averaging of breath-by-breath VE and VCO2 data over periods of 10, 30, and 60 seconds has shown no significant difference in the calculated VE-VCO2 slope. Studies have shown that both VE/VCO2 and VE-VCO2 slope measurements are repeatable in healthy individuals.

VE/VCO2 at AT and the lowest observed VE/VCO2 are affected by increased equipment deadspace and become elevated when deadspace increases. Interestingly, the VE-VCO2 slope is not affected, and when VE is corrected by subtracting the deadspace contribution, VE/VCO2 values are essentially unchanged with increasing deadspace.

Most studies on the VE/VCO2 and VE-VCO2 slope have been performed using a cycle ergometer. The ATS/ACCP statement on exercise testing indicates that cycle ergometry is the preferable testing mode but acknowledges that treadmills remain in common use and that individuals generally attain a higher maximum VO2 with them. One study on a relatively small group of healthy individuals has shown that the VE-VCO2 slope and lowest observed VE/VCO2 are slightly higher in women when testing is performed with a treadmill than with an ergometer, but no significant differences were seen in men.

Most CPET test systems report VE/VCO2 throughout exercise and at AT. VE-VCO2 slope is less commonly available and it may be up to the individual lab to calculate these values manually. The simplest approach is to enter the averaged VE and VCO2 values obtained during exercise (data obtained at rest should be excluded) into spreadsheet. A least-squares linear regression can then be performed on the data up to AT and separately up to peak exercise and then included in the CPET report.

VE/VCO2 and VE-VCO2 slope are values obtained during a CPET that have a superior prognostic power for surgical risk and general mortality risk assessment than the maximum VO2. Importantly, some of these values can be obtained from submaximal tests. Elevated values are useful in detecting inefficient ventilation and assessing its causes. For all these reasons, analysis of the VE/VCO2 and VE-VCO2 slopes should be included in CPET interpretations.

Resources

  • Arena R, et al. Peak VO2 and VE/VCO2 slope in patients with heart failure: a prognostic comparison. Am Heart J 2004;147:354-360.
  • ATS/ACCP Statement on Cardiopulmonary Exercise testing. Am J Resp Crit Care Med 2003;167:211-277.
  • Balady, et al. Clinician’s guide to cardiopulmonary exercise testing: A scientific statement from the American Heart Association. Circ 2010;122:191-225.
  • Corra U, et al. Ventilatory response to exercise improves risk stratification in patients with chronic heart failure and intermediate functional capacity. Am Heart J 2002;143(2):416-426.
  • Davis JA, et al. Exercise test mode dependency for ventilatory efficiency in women but not men. Clin Physiol Func Imaging 2006;26:72-78.
  • Davis JA, et al. Test-retest reliability for two indices of ventilatory efficiency measured during cardiopulmonary exercise testing in healthy men and women. Clin Physiol Fun Imaging 2006;26:191-196.
  • Guazzi, et al. EACPR/AHA Joint Scientific Statement. Clinical recommendations for cardiopulmonary exercise testing data assessment in specific patient populations. Eur Heart J 2012;33:2917-2927.
  • Koike A, et al. Prognostic power of ventilatory responses during submaximal exercise in patients with chronic heart disease Chest 2002;121:1581-1588.
  • Ponikowski P, et al. Enhanced ventilatory response in patients with chronic heart failure and preserved exercise tolerance. Circulation 2001;103:967-972.
  • Sun XG, et al. Ventilatory efficiency during exercise in healthy subjects. Am J Resp Crit Care 2002;166:1443-1448.
  • Teopompi E, et al. Ventilatory response to carbon dioxide output in subjects with congestive heart failure and in patients with COPD with comparable exercise capacity. Respir Care 2014;59(7):1034-1041.

Eliminating Waste within Preventative Maintenance and BioControl Programs in a Pulmonary Physiology Lab

Ann Wilson, BS, RRT, RPFT, Wellspan Health-York Hospital, York, PA

The idea of assessing waste in my pulmonary function lab began when I attended a LEAN Leader Continuous Improvement Management Development Program meeting. The concept with LEAN is that we can have continuous improvement within an organization if we first recognize that we have problems, identify every employee as a potential problem solver, and utilize a sound approach to analysis and problem solving. LEAN has two basic tenants: total elimination of waste and respect for people. LEAN tools illuminate waste and people eliminate waste.

Our BioControl program required large amounts of staff time and potentially harbored large amounts of waste. The preventative maintenance (PM) and BioQC program in the pulmonary physiology lab was time intensive and grueling for the staff. We had three plethysmographs and a screener system. Once a month, seven hours of potential patient testing time were blocked from the schedule at the start of the day. As many as four staff members were utilized for the PM and BioQC. Staff tore down the circuits, wiped the equipment down with cleaning solution, redressed the equipment, did all calibrations, and finally ran a full spectrum of tests on themselves on each of the four pieces of equipment.

The first question we asked ourselves was, “Why do we do this?” This was an easy question to answer: preventative maintenance is recommended by the equipment manufacturer and BioQC is recommended by the American Thoracic Society (ATS).

However, I immediately identified a few concerns:

  • If we encountered problems with a circuit change we immediately created a bottleneck for patient service when we had patients scheduled to immediately follow the PM.
  • Technical support for our equipment company was located on the West Coast, and since we started at 0700 EST we often had to wait for call-backs due to the difference in time zones. This also created delays in patient care when the testing equipment was not operational.
  • We had staff doing BioQC testing on themselves who did not qualify as BioQC subjects per ATS recommendations. For example, several staff are asthmatics.
  • There was a general lack of standardization on how each staff member conducted circuit changes and BioQC.

I called four other testing facilities to find out what their PM and BioQC programs looked like, then went to the “Gemba” to observe. Gemba is the LEAN term referring to the location of the work. I actually sat with a stopwatch and wrote down every detail and time period associated with the task. I discovered some variations in the process. All staff did not utilize the same order for testing. Some staff used the flanged mouthpiece and others did not. Due to the variations I also observed that the time required to complete the task differed amongst staff members. (See table 1)

Wilson Table 1

The goal was to improve the efficiency of the PM and BioQC program by reducing wasted time, developing standard work flow, and increasing the time available for patient testing. I identified that we could standardize the order of the BioQC testing, have all staff use a flanged mouthpiece, change the time of day when the process was completed, and change the actual process-work balance. We also reduced the number of staff who did BioQC testing every month from four to two. One person did all the testing on each piece of equipment and one person assisted with the entire process. We eliminated staff who did not qualify as BioQC subjects. This didn’t mean they didn’t help with the process, they just weren’t serving as BioQC subjects. We also kept some extra essential spare parts available for the PM process in case we encountered problems. The table below shows the revised work flow process.

Wilson Table 2

As a result of our efforts, we were able to rededicate two hours of time back to patient testing, which increased revenue potential. In addition, we were able to eliminate unnecessary work for staff and definitely improve staff satisfaction with the entire process. The results of this LEAN project were well received by all.


An Introduction to DLCO Simulation QC

Jason Blonshine, RRT, CPFT, TechEd Consultants, Inc., Mason, MI

A DLCO simulator device allows laboratories to assess the accuracy and precision of their DLCO testing device. In one study up to 25% of labs were found to be running DLCO equipment considered out-of-control (>3mL/mm/Hg off target DLCO).1 The majority of these out-of-control conditions can be corrected with equipment repair and replacement of faulty parts. The ATS/ERS guidelines recommend that laboratories routinely run basic QC measures such as syringe DLCO and biologic controls. However, a DLCO simulator offers a higher level of quality control because it can identify errors that may escape detection by syringe DLCO and biologic control testing.

A DLCO simulator uses two precision syringes, one to simulate inhaled volume and a second to simulate exhalation of a precision gas. The “inhaled volume” and “exhaled gas” concentration data are combined with temperature, barometric pressure, and dead space (system, anatomic, filter) to produce expected DLCO values. The expected value is compared to the measured DLCO and a % error can be calculated. Using this information you can quickly identify what, if any, equipment issues might be occurring.

DLCO Simulation Device

Blonshine Photo

Photo courtesy of James Sullivan, BA, RPFT.

The DLCO simulation can take more time than normal QC, up to 1-2 hours depending on your experience with the device. The simulator is hooked directly to the mouthpiece or filter and you perform a DLCO maneuver using the two syringes.

First the small syringe is filled with a precision gas (+/- 1%), and then the maneuver begins. Tidal volume breathing is done with the large syringe; the syringe is emptied completely, followed by a full inhalation within four seconds. During the ten second breath hold the valve is switched over to the small syringe filled with precision gas, which is then exhaled into the mouthpiece to complete the maneuver.

The software (EasyLab QC, Kansas City, MO) is used to calculate the expected DLCO and shows the percent error for each value (DLCO, VA, IVC, expired CO, expired tracer gas). This information gives you immediate insight into any malfunction. This procedure is usually completed over a range of volumes (3L, 4L, and 5L), and gas concentrations to simulate different ranges of volume and DLCO that may be encountered during patient testing.

A QC program should be an integral part of any pulmonary function lab’s operating procedures to ensure your equipment is running at the best possible level. Using a strong QC program combined with simulations, training, and good coaching helps ensure your lab is producing accurate results that can better guide patient care.

Reference

  1. Jensen R, Leyk M, Crapo R, Muchmore D, Berclaz PY. Quality control of DLCO instruments in global clinical trials. Eur Respir J 2009;33:1-7.

Quarterly Case Report: A Positive Methacholine Challenge Without a Significant Change in FEV1

Jeffrey M. Haynes, RRT, RPFT

A 30-year-old male presented to the PFT laboratory for a methacholine challenge test due to intermittent dyspnea following exercise. Baseline spirometry data are presented below:

Haynes Figure 1

Spirometry showed a symmetrical reduction in FVC and FEV1, which is often regarded as a restrictive defect; however, this pattern is also seen in asthmatic subjects. The results of methacholine challenge testing are seen in figure 2.

Haynes Figure 2

A maximum FEV1 decline of 8% following a full methacholine challenge is typically interpreted as a “negative” test. However, the patient complained of dyspnea and chest tightness. Examination of sGaw data before and after methacholine challenge testing suggested a different response to methacholine.

Baseline                       Post Methacholine                  Post Bronchodilator

FEV1               2.93                            2.70 -8%                                3.14 +7%

sGaw               .26                              0.07 -73%                             .33 +27%

Baseline Open Shutter Panting

Haynes Figure 3

Post Methacholine Open Shutter Panting

Haynes Figure 4

Khalid, et al. showed that a significant number of patients who had negative methacholine challenge tests using FEV1 criteria had positive tests when applying sGaw criteria (>50% reduction). 1 Parker, et al. examined the characteristics of patients with a –FEV1 response and +sGaw response. 2 Patients who showed an exclusive +sGaw response had a lower TLC and higher FEF25-75/FVC ratio, suggesting pulmonary dysanapsis (proportionally larger airways to parenchymal mass) as a causative factor.

Teaching points

  • Using ∆ FEV1 exclusively to determine airway hyperresponsiveness likely results in a significant number of false negative conclusions.
  • Pulmonary dysanapsis may have a causative role in the –FEV1 +sGaw phenotype.

References

  1. Khalid I, et al. Specific conductance criteria for a positive methacholine challenge test: are the American Thoracic Society guidelines rather generous? Respir Care 2009;54(9):1168-1174.
  2. Parker AL, et al. Pulmonary function characteristics in patients with different patterns of methacholine airway hyperresponsiveness. Chest 2002;121(6):1818-1823.

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