Katrina Hynes, BAS, RRT, CPFT
Special Pulmonary Evaluation Laboratory
Rochester, MN 55905
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
Fax: (608) 263-7002
|Notes from the Editor||Jeffrey M. Haynes, RRT, RPFT|
|Cardiopulmonary Exercise Testing||Holly Wilson, RPFT|
|Pediatric Metabolic Testing||Elizabeth Koch, BHS, RRT, RPFT|
|Industry News: Pharmaxis Ends Aridol Sales in the U.S.||Jeffrey Haynes, RRT, RPFT|
|Quarterly Case Report: A Small Leak Will Sink a Great Ship — Ben Franklin||Jeffrey M. Haynes, RRT, RPFT|
This issue of the Bulletin features more great contributions from the Diagnostics Section membership. I’m really appreciative of all the contributions I’ve received. Thanks to members who volunteered to share their expertise, this issue features some interesting articles on exercise and metabolic testing.
Diagnostics Section members will find an abundance of continuing education programs at AARC Congress 2014, which is being held in Las Vegas, Dec. 9–12. World-renowned clinicians such as Susan Blonshine, Jack Wanger, and Carl Mottram headline an impressive array of speakers who will focus on pulmonary function testing.
Budgets are tight these days, but if you are able, I strongly encourage you to attend. There really is something for everybody. After I attended my first AARC Congress I kicked myself for never having attended before. We’ll also be hosting our section membership meeting at the Congress, which is a great opportunity to meet and network with your colleagues. Hope to see everyone there!
How many times has this happened in your lab? A patient presents with dyspnea on exertion sometimes accompanied by intermittent cough and/or chest pain with exertion. The physician orders PFTs, an echocardiogram, and maybe even a methacholine challenge test, all of which are normal or inconclusive. Now what do you do?
Two obvious choices are an exercise challenge test or a cardiopulmonary exercise test (CPET). An order for an “exercise test” is rather non-specific. The technologist may ask the ordering physician, “What question are you trying to answer?” Is it deconditioning, ventilatory limitation, exercise-induced bronchoconstriction (EIB), cardiovascular disease, or fixed airflow limitation? Good news! We can answer most of these questions with just one exercise test, the CPET. This article describes how we combine a constant workload test to assess EIB with a maximal exercise test in our facility.
Mode of exercise
In our lab we use the MGC Ultima CPX Exercise Testing system and a Case GE Exercise ECG system with a treadmill or cycle ergometer. Our pre-test assessment of the patient includes past medical history, medications, informed consent, and any limitations he may have to exercise.
If the patient is athletic we may choose to use a treadmill. However, if weight bearing exercise or balance is difficult for the patient, the cycle ergometer may be better to allow the patient to complete the test. When using the cycle ergometer the maximal VO2 is 5-10% lower than on the treadmill, which may have an impact on the reported data. Because we are combining constant workload and maximal effort (at the end of the test), the data trends do not show the typical increases seen with a standard incremental or ramp protocol. It is recommended that a physician be present in the exercise lab along with credentialed technologists to assure safety and provide interpretation.
After determining the mode of exercise we obtain a baseline 12 lead ECG (supine limbs/torso, and standing), and a standing blood pressure. We perform baseline spirometry, maximal voluntary ventilation, and slow vital capacity. We choose the appropriate protocol, which will enable us to compare pre- and post-exercise spirometry and exercise flow volume loops as they occur. For exercise tests we use forehead sensors to avoid motion artifact or reduced digit perfusion associated with finger probes. If hypoxia during exercise is a concern, collecting arterial blood gases may be appropriate, either by inserting an arterial catheter or single puncture at rest and exercise. (Measurement of arterial blood gases adds another layer of complexity, which is beyond the scope of this article.)
Next, we begin collecting exhaled gas, at rest, while the patient is standing (treadmill) or seated (bike). At this pre-exercise period we perform our first exercise FVL by asking the patient to inhale from FRC to TLC quickly, measuring IC. This allows us to plot a tidal breath against the baseline flow volume loop obtained during spirometry. These exercise FVLs will help to determine airflow limitation. Then with all the pre-testing procedures completed, we’re off to the races!
Ready, set, go
After a brief one-minute warm up, the goal is to have the patient reach a moderately high level of exertion and maintain it for at least 4-6 minutes. This “target zone” is defined by two parameters, 80-90% of target heart rate and 40-60% of target ventilation (35 * FEV1).
Achieving these parameters will require operating in a manual mode, changing the workload accordingly. The patient should reach his target zone within the first four minutes of exercise. Prolonged warm up should be avoided. Continue to monitor the patient, measuring an FVL and blood pressure every two minutes. After six minutes of target zone exercise, ask the patient if he can do more. If he is able to do this safely, increase the workload until the patient reaches maximal exercise limitation. Repeat maximal spirometry efforts at 5, 10, 15, and 20 minutes post-exercise, or until a fall in FEV1 of 10-15% or more is observed. If the FEV1 falls by >10-15% administer albuterol and repeat spirometry after ten minutes.
One of the challenges associated with exercise testing is the inability to create the exact environmental factors that induce the patient’s symptoms. For instance, while vacationing in Morocco last year, I experienced an uncontrollable, dry cough after running up a giant sand dune in the Sahara desert. The cough dissipated after approximately 30 minutes. I’m convinced I was having asthma-like symptoms due to hyperventilation of dry air. Those same conditions would be difficult to recreate in the exercise lab, and a eucapnic voluntary hyperventilation test may be more appropriate.
Figure 1 shows CPET data from a healthy 31-year-old male with suspected exercise-induced asthma.
He exercised at a high level (both HR and minute VE) for seven minutes and then continued for another minute at a slightly higher workload. His post-exercise spirometry showed a 19% fall in FEV1 at 15 minutes, consistent with EIB. Figure 2 shows that he also appears to have had airflow limitation during exercise.
Perhaps we can’t answer all questions with one test, but we are able to present a complete picture through the broad spectrum of data collected by the CPET.
Whether a patient is spontaneously breathing or being mechanically ventilated, there are many challenges when obtaining metabolic measurements, especially in the pediatric population.
In the tenth edition of Ruppel’s Manual of Pulmonary Function Testing, metabolic measurements are defined as “any of several precise caloric need and nutritional status assessment tools.” Metabolic measurements are commonly referred to as indirect calorimetry (IC), the resting energy expenditure (REE) test, or metabolic cart testing. Sometimes metabolic testing is also called “oxygen consumption testing,” though this term is more commonly used in cardiopulmonary exercise testing as it refers to the measurement of the volume of oxygen used by the tissues.
Indirect calorimetry is the process that measures the oxygen consumed (V̇O2) and the carbon dioxide produced (V̇CO2) to determine the caloric needs for the body. IC provides the respiratory quotient (RQ), which is the ratio of V̇CO2 to V̇O2, and the REE, which is the estimated caloric needs of the body expressed by kilocalories over a 24 hour period. Obtaining metabolic measurements via IC can provide more reliable data than predicted equations for assessment and management of nutritional support.
Known nutritional deficits, difficulty weaning from mechanical ventilation, increased ventilatory demand, and abnormal weight gain/loss are indications for obtaining metabolic measurements by IC. Typically, IC is requested by dietitians/nutritionists as it provides caloric information and nutritional status. As pulmonary function technologists, we may not understand all the nutritional ins and outs, but we need to understand ventilation, V̇O2, V̇CO2, and the PFT systems that commonly obtain the measurements. The process of collecting exhaled gases and understanding the quality of the collection will provide the most valuable data to providers managing the nutritional support of the patients. Physicians and nutritionists are interested in obtaining the values for REEs and RQ and often do not understand the difficulty in collecting that data.
Obstacles are many
The goal during IC measurements is to reach a “steady state” of consistent and reliable data over a set time period (usually five minutes). To achieve steady state there must be less than 5-10% variation in V̇O2, V̇CO2, FiO2, and RQ. The inability to reach steady state occurs frequently and diminishes the reliability of the measurements. Documentation of whether or not steady state was achieved is crucial, as this will inform the provider of the strength of the measurement. The RQ value obtained should be in the range of 0.67-1.3. If the RQ value is outside of this range, the measurements should be deemed invalid due to error in collection of data (e.g. leak, incomplete capture of exhaled volume/gas, or analyzer error).
There are many obstacles that we face when performing IC, whether on a spontaneously breathing patient by the canopy method or on a mechanically ventilated patient through the ventilator. These obstacles are often more difficult to overcome in the pediatric population. One of the first considerations when performing IC with a PFT system on mechanically ventilated patients is the type of ventilator. An exhalation port is necessary to connect to the metabolic cart for the collection of the exhaled gases. Single limb circuits and external PEEP valves make connection to certain metabolic carts impossible.
Leaks are probably the most frequent problem with collecting data. Leaks can occur within the ventilator circuit, around the tracheal tube cuff or uncuffed tubes, or in the metabolic cart itself. External procedures, like hemodialysis, peritoneal dialysis, and even left ventricular assist devices can affect measurements. Instability of FiO2 can also affect measurements; for example, an FiO2 greater than 0.6 is too high for stable readings. Insufficient volume of exhaled gas or the inability to distinguish between inspired and expired gas due to bias flow or asynchrony can affect data collection. Increased water vapor in the circuit and the presence of other ventilation gases (NO, He, or anesthetics) may result in sensor malfunction.
Ventilated infants and children
Metabolic measurements are often requested on difficult-to-wean, critical, or long-term vent patients. There are many considerations when trying to obtain a metabolic cart test on a ventilated pediatric/infant patient. Most are on pressure ventilation, volume variable (small volumes), and have uncuffed tubes or are dependent on a high FiO2.
To attempt to lessen many of the issues that cause inaccurate measurements, pre-planning for the metabolic cart test is a must. Communication between the ICU staff and the PFT lab is essential for success. Deciding on a time when the patient can be the least disturbed, having the RN or RT suction 30-60 minutes prior to testing, and determining whether or not feeds are to be held and for how long are all important considerations.
If a patient has an uncuffed tube, it is often necessary to change to a cuffed tube (well in advance of the metabolic cart being attempted). The ventilator settings must be reviewed and confirmation made that they will support data collection. We do not attempt testing on a patient with an FiO2 > 0.6, or patients being ventilated with heliox or nitric oxide. If sedation is needed, it should be given prior to the study and documented.
During the data collection, the room should be quiet, lights should be dimmed, and no interruptions should occur. It may be beneficial to use a new, dry ventilator circuit to lessen the water vapor and limit the breaks in the circuit for any type of leak. The analyzers and the flow sensor of the metabolic cart should be calibrated prior to the set-up, and the metabolic cart should be set for appropriately if there is bias flow on the ventilator.
Spontaneously breathing infants and children
There are also obstacles in obtaining IC on spontaneously breathing pediatric patients, although in our experience, we seem to be able to obtain reliable measurements more often in this population compared to patients on mechanical ventilation. Measurements are obtained with the use of a canopy or hood system. The Carefusion VMax Encore system is used in our institution, which recommends room air, patient weight of at least 10 kg (weight can be lower if utilizing the low-flow option), NPO for 2-4 hours, and avoidance of medications that alter metabolism. In addition, the patient should be awake but relaxed for the study. The pump fan speed should be adjusted to keep the fraction of exhaled carbon dioxide (FECO2) at the desired range of 0.7-1.0 (ideally 0.75–0.85).
Children three years or older are ideal because the child is typically >10 kg, can go without eating/feeds for more than four hours, and will follow instructions to lay still (while watching a movie if needed) under the hood/canopy. However, several concerns arise if there is a need to do IC in children less than three years. Firstly, the manufacturer’s hood/canopy is an adult size (large), and to my knowledge there are no longer any commercially available small hoods designed for metabolic testing. (Please contact me if you know otherwise). When using the large hood on the smaller patients, it is difficult to keep the FECO2 in range even with the low-flow option at the lowest speed.
We had the pleasure of collaborating with a research dietitian who was attempting a study on very small infants and we adapted an infant oxygen hood for these smaller patients. This seemed to work very well at the lower pump fan speed to keep the FECO2 within the desired range and captured more realistic volumes and metabolic data. Having an infant stay awake but quiet is next to impossible. This study was performed by the dietitian while infants were asleep and compared sleep metabolic rate (SMR) to the basal metabolic rate (BMR).
Collaboration is key
Although there are many issues in obtaining valid IC measurements, I feel that metabolic measurements are underutilized and would assist in the management of nutritional support in critical and non-critical patients. Unfortunately, ensuring accuracy of the data collection is often difficult and can be a source of frustration for the entire team. Optimizing data collection requires collaboration and communication among the nurses, respiratory therapists, pulmonary function technologists, dietitians, and physicians on the case.
The following statement was released by Pharmaxis in August 2014:
It is with deep regret that Pharmaxis is announcing the closing of its United States operation, as of August 29, 2014. Because of this very difficult decision, Pharmaxis, Inc. (US) will no longer commercialize ARIDOL® (mannitol inhalation powder) Bronchial Challenge Test Kit in the US.
Pharmaxis has diligently tried to resolve the supply issues that emerged in 2013. Unfortunately, we have been unable to ensure a continuous and sustainable product supply. The issues related to supply were not due to product safety or efficacy.
If Pharmaxis is able to identify and secure a US commercial partner who is able to re-establish the supply of ARIDOL, as a valued customer, you will be notified directly. The company is committed to this effort of re-establishing supply however, the timeline to achieve this objective cannot be determined at this time.
I inquired about the circumstances that led to this decision. A Pharmaxis representative told me that the FDA ordered an inspection of the contracted manufacturer’s facility in Australia, the same facility that is manufacturing this product for the European market. (This is what I was also told in January.) The inspection was reportedly completed in February 2014 and according to Pharmaxis no problems were identified. From that point on, a large amount of product bound for the U.S. market sat in Australia waiting for the FDA to officially give the okay for product distribution to resume.
Months came and went and Pharmaxis claims that there was no news on when the FDA would finalize the inquiry. By this summer all of the product produced for the U.S. market was set to expire in September and that’s when Pharmaxis decided to end their U.S. operation. I did peruse the FDA website looking for info but didn’t find any. I don’t know what the complete story is, but this is the story according to a Pharmaxis representative.
Reviewing technologist performance is an essential part of a PFT laboratory quality assurance program. The following is an example of how technologist oversight can be used to correct spurious test data.
A 24-year-old male experiencing dyspnea on exertion presented for a complete PFT. Spirometry was normal, with all values between the predicted and upper limit of normal (ULN). Diffusion testing was performed following spirometry:
As shown above, the DLCO and VA were much higher on effort #2 than effort #1. Because reproducibility criteria were not satisfied (10% or 3 ml/min/mm Hg), a third effort was performed and reproducibility criteria were met. Efforts #2 and #3 were averaged to produce the reported values.
As shown below, the DLCO and VA were significantly higher than the ULN, with values exceeding 1.6 times the predicted value. The other non-physiologic finding was that the VA via diffusion testing exceeded the TLC via plethysmography (TLCpleth) by 3 liters. Unfortunately the technologist failed to recognize the “ALERT!” message in the volume/time pane, which once clicked on points out that the VA significantly exceeds TLCpleth and provides troubleshooting advice.
All calibration data from the testing day were found to be within expected ranges. In addition, biologic controls and DLCO simulations performed before and after the date of testing did not show any out-of-control conditions.
The patient was contacted and asked to return for repeat testing (performed by myself). The following data were obtained:
Remarkably the TLCpleth was precisely the same and lung volume subdivisions were comparable. You may have noticed that the predicteds were slightly higher on the second test session; this is because a height of 69 inches was entered for the first test, when his measured height was actually 70 inches. The first DLCO measurement from the initial testing session (Figure 1) was very similar to both recordings made during repeat testing (Figure 5). The non-physiologic data from efforts #2 and #3 from the first test session are most likely due to contamination of the alveolar sample with air (exogenous dilution of FICO and FIHe calculate greater lung volume and gas exchange). This could occur if the patient’s lips were not sealed on the mouthpiece; however, the %max vs. time graph in Figure 1 indicates something different. The alveolar sample collection bag is measured between the green vertical lines (CO is red, helium is blue) while the inspiratory test gas is verified between the two blue vertical lines. The CO and helium tracing not returning to the 100% line on the %max axis between the blue vertical lines indicates that the inspiratory test gas bag had been contaminated with room air. Figure 5 shows confirmation of proper test gas concentrations (CO and helium return to 100% %max between the blue vertical lines). This could occur from a hole in the bag; however, one would expect all three tests to be affected and biologic testing to be out-of-control. With this system the inspiratory sample bag is automatically emptied and filled prior to the first test. However, on subsequent efforts there is an option to not empty the inspiratory bag, just add to it. This option was exercised by the testing technologist. Unfortunately a poorly seated valve allowed air contamination of the inspiratory bag during the waiting period between subsequent efforts.
Bulletin deadlines: Winter Issue: December 1; Spring Issue: March 1; Summer Issue: June 1; Fall Issue: September 1.