Month: September 2019

When performing a Cardiopulmonary Exercise Test (CPET), the most important thing is making sure that the results are reliable for them to be accurately interpreted later on. A mistake made during the test can dramatically affect the interpretation and therefore, the prognosis. For this reason, we wanted to highlight some of the most common mistakes we see people make and the problems they can cause when coming to interpret the data.

 

Mask Fitting

It is vital when performing a cardiopulmonary exercise test (CPET) test that there are no leaks in the breathing circuit. In general, machine leaks will be detected during the calibration and validation processes. However, a common cause of leaking can be the seal between the patient and the flow device.

For a long time, CPET testing was performed using a mouthpiece and nose clip. On the surface, this method provides a good seal and historically with the heavyweight of flow valves. Headgear was used to support the apparatus, so the mouthpiece worked, albeit giving a rather messy result at the end of the test due to the build-up of saliva.

More recently, the mask has become the favoured method of connection to the system. The patient is able to breathe through both the nose and mouth and can swallow. Therefore, much less saliva is built up, and there is less mess.

It is critical, however, to ensure that the mask is providing a leak-free seal around the patient’s nose and mouth. First ensure you pick the correct size of mask, test fit where necessary to make sure the fit looks good. After securing the mask with the correct headgear, you need to check for a leak. Simply occlude the breathing port at the front of the mask briefly and ask the subject to inhale, making sure pressure isn’t applied to the mask. It should be sucked onto the patient’s face if no leaks are present. Reverse the process asking the subject to exhale, at which point there should be an overpressure leak once the mask is filled.

A mask leak during the test is one of the biggest problems for interpretation. It’s therefore essential to check the VO2 and VCO2 values before and during the test. The Love Medical CPET system uses the Blue Cherry software, which allows a period just before commencing the test where data can be seen to check for leaks or hyperventilation. This data is deleted as the test is started to prevent these issues from causing a problem during interpretation. Check with your CPET system provider to see if this feature is available on your software.

This short test, prior to performing the main test, will prevent wasted results and test time later.

 

Exercise Protocol

Choosing the exercise protocol can be a difficult concept when first starting to perform a cardiopulmonary exercise test (CPET) test. How many watts per minute for the ramp seems like an arbitrary calculation, is the person fitter than expected? Do they have a more sedentary lifestyle?
There is a recognised equation for calculating the work rate increment, commonly known as the Wasserman equation from the book Principles of Exercise Testing and Interpretation.

 

The Wasserman equation:

1. Determine the expected VO2 max for the patient in ml.min-1

2. Calculate and subtract the unloaded oxygen requirement:
VO2unloaded = (5.8 x BW) + 151

3. Where VO2 is expressed in ml.min-1 and BW is body weight in Kg

4. Divide the remainder by 103. This divisor represents the product of the expected oxygen cost of leg cycling (10.3 ml.min-1.W-1) and the optimal test duration (10 min).

5. The resulting quotient represents the desired work rate increment per minute:
Work rate = (Predicted VO2max – VO2unloaded)/103

 

If you find this too difficult to calculate, there is a possible shortcut. Many systems will calculate the maximum workload for a given patient data. The Love Medical ECG system, for example, has a choice of several equations to calculate this max load. Simply take this max load value and divide by 10, giving you an approximation of the required workload ramp.

A CPET test should last between 8 and 12 minutes. Should the patient not be quite fit enough for the ramp, they should still be able to reach 8 minutes. If the calculation has underestimated their fitness level, then the test should still be finished within 12 minutes. In either case, they both fall within the test time recommendations.

 

Cables and tubes

Poor management of cables and tubes during an exercise test causes mistakes, not least damage to the device or injury to the patient. To a trained eye, these problems are easy to prevent. In fact, to the layperson, cable routing can often look precarious. It’s all too easy for newcomers to cardiopulmonary exercise test (CPET) testing to miss problems, having so much to think about while setting up the test.

Always ensure flow tubes and ECG cables are routed up and away from the cycle pedals, as getting a tube caught at 60 RPM will likely cause damage. Ensure cables are routed to allow the patient to dismount without becoming tangled, again it’s easy to damage a cable with a patient desperate to get off the bike.

When routing the sample tube, in particular, the gas sample tube, ensure it comes up from the flow sensor. This will reduce the risk of moisture ingress from saliva during the test. It’s often easy to secure the sample tube using the headgear from the mask.

Always ensure connecting cables such as power leads and ergometer control leads are routed to avoid trailing across the floor. This reduces trip hazards and prevents injury or damage.

Finally, it is a good idea to remove as many cables as possible. Newer systems are designed to make use of things such as Bluetooth control for ergometers, pulse oximeters, and even ECG. This means no wires are crossing the field of the test. The Love Medical System now makes use of Bluetooth technology. This leaves only the flow tube and the gas sample line. It can be secured in the patient’s headgear, so it’s up high and away from danger for the period of the test.

 

Blood Pressure cuff

Fitting the blood pressure cuff should be a simple procedure. However, like so many of the operations surrounding the cardiopulmonary exercise test (CPET), it is complicated due to the number  of tasks involved in preparing a subject for testing.

Some people still choose to perform a manual blood pressure using a sphygmomanometer and a stethoscope, but as technology moves forward, it is becoming increasingly popular to automate the process. This allows better focus on the patient by the tester rather than a rush to collect BP results.

When using an automatic Blood Pressure device, it’s important to ensure that the BP cuff is the correct size. If it’s too small, you can hurt the patient, too big, and you may not get any values from the BP machine. Once this is done, ensure that the microphone covers the brachial artery as the cuff is positioned on the arm. This will ensure the correct signal required by the device. Take a little time over this step to ensure it’s working well; it’s much harder to correct during the test.

Perform a test measurement at rest and ensure the results are what is expected, and the system should be ready to test.

 

Saddle height

Setting the saddle height of the ergometer is simple enough, as lots of ergometers have a manual adjustment. This consists of adjusting the saddle height without the subject in position and then getting the subject onto the ergometer to check it. When pedalling, the subject’s leg on the downstroke of the pedal should not be fully extended. This should provide optimum comfort during the test.

However, manual adjustments mean that there’s room for human error. If the initial adjustment attempt is not correct, the subject has to stand on the pedals before the test to make the final adjustments. This can be both uncomfortable and dangerous for the subject.

Many systems now employ a fully electronic saddle height adjustment, allowing the saddle height to be fully adjusted with the subject sat in place. This method also gives a value to the actual height, making it much easier to reset to the correct height for any future test. Furthermore, the electronic adjustment on the Love Medical Ergometers allows the saddle to be adjusted with the patient in situ, making the whole operation much safer.

Let us know if you agree with our list or if you think there’s something we missed!

 

Want to learn more?

We run a number of CPET Interpretation training courses each year which suit all levels and areas of speciality. If you are keen to learn more about performing and interpreting CPET, why not drop us an email to education@lovemedical.com to find out when our next course is.

Cardiopulmonary Exercise Testing (CPET) is a diagnostic test which looks at the heart and lungs of an individual during exercise. The human body is designed with vast reserves, and many illnesses or problems cannot be detected at the rest state. By putting the body under stress during exercise, we can recognise some of these conditions.

The CPET test is one of the most powerful non-invasive diagnostic tests available in modern medicine. CPET has been utilised for many years within respiratory medicine as a differential diagnosis for shortness of breath, allowing the physician to determine if it is of Cardiac or respiratory cause. Recently the importance of the test as a Cardiac screening tool has become more prevalent and is used in Heart Failure patients as well as diagnosis of coronary heart disease (CHD).

The biggest growth in CPET testing has been seen in the Peri-operative sector where diagnostic CPET is used to assess the fitness level of prospective surgical patients, in an effort to better manage their post-operative care and thus improve surgical outcomes.

The test is known by various other names, including the Exercise Test and the Stress Test. However, they are, in essence, the same thing, measuring four main components. Including Heart Rate, which is done via a full 12 lead ECG, Oxygen Uptake, Carbon Dioxide output and Breathing rate, usually measured using a combined gas and flow analyser. Finally, the body will require some form of an exercise device. This may be any device, but in a hospital situation, it is usually a cycle ergometer, or possibly a treadmill.

 

Who might need a CPET test?

For many years, Cardiopulmonary Exercise Testing (CPET) has been used in two main areas. In hospitals it is predominantly used as a differential diagnosis tool, enabling the physician to determine the underlying cause of shortness of breath. Shortness of breath or Dyspnea can have many causes, some being respiratory such as COPD or Lung Cancer whilst other causes may be Cardiac such as Congestive Heart Failure, it is also possible for shortness of breath to be caused by a circulatory problem.

CPET also found favour in the sports and fitness arena, in particular as a tool to determine fitness by assessing the volume of Oxygen Output of a person under exercise (VO2).

More recently, obtaining a diagnosis from a body under exercise has been adopted by more and more specialists within the hospital environment. In areas such as cardiology, the CPET test has been shown to be a more useful diagnostic tool than the standard ECG stress test.

The use of CPET in the perioperative setting utilises the measurement to assess an individual’s fitness prior to surgery. This assessment is better allowing the surgical and anaesthetics teams to determine the person’s post-operative level of care. Dependant on the results of the test, an individual may not need to be referred directly to an ICU bed, but instead downgraded to an HDU bed or even directly back to the ward.

High-quality evidence shows that the fitter a person is prior to surgery, the shorter their stay, and the fewer complications are incurred throughout and postsurgery.

 

What does CPET involve?

Modern Cardiopulmonary Exercise Testing (CPET) is performed on a cycle ergometer, it is usually designed around a work protocol that ramps a subject to their maximum exercise tolerance, and the protocol will increase the effort required to pedal at a continuous rate, at a 5, 10, 15 watts per minute increase, or more for fitter individuals. The optimum workload ramp is between 8 and 12 minutes, so most protocols are designed to reach an individual’s max workload in 10 minutes.

The maximum workload for an individual can be calculated from their age, height and weight, but there’s also need to consider their current level of physical activity to determine their level of fitness. Creating a ramp that is too short may give too little data for interpretation, and a ramp that is too long can alter the result. A test should start with a 3-minute rest phase, followed by a 3-minute freewheel phase, and finally finish with 5 minutes of recovery, to ensure heart rate and breathing values normalise to the rest state.

Data for the test is recorded through a number of sensors. Usually, respiratory data is collected through a flow sensor connected to a facemask. It is also possible to use a mouthpiece, although this can be a little messier with saliva build-up at the end of the test. As mentioned before, Heart Rate is usually recorded via a 12 lead ECG, requiring 12 ECG electrodes placed around the subject’s chest. Other measurements that may be taken include Blood pressure, via an arm cuff and Pulse Oximetry via an ear sensor.

A good education for the subject is vital before a test, as patients can often misunderstand the results, thinking that a poor test proves that surgery is required. This is quite the opposite; the better the test results from a CPET test, the more likely the team will be happy to move a patient forward to surgery. This is because there is much less risk associated with carrying out surgery on fitter individuals.

 

Are there any risks?

Risks from Cardiopulmonary Exercise Testing (CPET) is minimal. The level of risk is comparable to carrying out mild to moderate exercise. However, the CPET test is performed in a controlled and managed environment, with trained staff on hand in the event of any problems. Less than one in a thousand patients experience some adverse reaction similar to that of a cardiology exercise test. During a CPET test, additional observations can be made including breathing patterns, Blood Pressure and Pulse Oximetry, alongside the full 12 lead ECG. If a patient exhibits any adverse symptoms, the test will be stopped immediately, and in the event of a problem, the Cycle Ergometer offers the safest option for the patient.

 

What information will be analysed?

All of the test data will be analysed by the clinical team to build a complete picture of the subjects overall health and fitness level. The analysis does not focus solely on the maximum level of exercise, although this is considered. It is also essential for the team to calculate the Anaerobic or Lactate Threshold, sometimes called the AT, at the point at which aerobic energy production is supplemented by anaerobic mechanisms, causing a sustained increase in lactate and metabolic acidosis. The AT is an excellent determinant of an individual’s fitness level, which can be improved with training.

It could be the case that someone with poor results is required to complete a safe exercise regime before surgery to reduce the risk and shorten the recovery time. Although more research is needed, many teams have been led to look at the advantages of ‘Prehabilitation’ or training prior to any surgical intervention, of which the current evidence suggests is largely beneficial to the patient’s wellbeing, during and after surgery. For more information about exercising prior to surgery, particularly heart surgery, click here. Around 8 million surgical procedures are performed in the UK each year with a low 2% complication rate. However, it’s possible that exercise regimes prior to surgical intervention performed more widely could lower the complication rate even further.

 

What to wear for the test

Simply consider Cardiopulmonary Exercise Testing (CPET) to be exercise, wear comfortable, loose-fitting clothes, training clothes if they are available and suitable footwear such as trainers, allowing the subject to perform the test to the best of their ability.

 

Before the test

Before visiting the hospital for a CPET test, some simple rules that should be followed, to avoid a poor result:

• Don’t Eat – Subjects should be advised to avoid eating a minimum of 2 hours before the test.
• No Alcohol – Subjects should be advised to avoid alcohol for a minimum of 4 hours before the test.
• Avoid Exercise – Subjects should be advised not to perform any intense exercise before the test.
• No Smoking – Subjects should be advised to avoid smoking a minimum of 1 hour before the test

Any and all medications should be discussed with the physician beforehand to determine if it can be used normally before the CPET test.

 

If the patient has experienced any of the following, they should contact the team performing the test.

• Chest Pain on or just before the day of the test
• Chest Infection on or up to 3 weeks before the test
• Heart Attack or Stroke within 4 weeks
• Recent surgery in particular Eye, stomach or chest
• Attendance at A&E for any other reason within last week

 

Want to learn more?

We run a number of Cardiopulmonary Exercise Testing (CPET) Interpretation training courses each year which suit all levels and areas of speciality. So if you are keen to learn more about performing and interpreting CPET, why not drop us an email to education@lovemedical.com to find out when our next course is.