Micro-Analyzing the six minute walk

Current standards for performing the Six minute walk test (6mwt) include not walking with the patient, so that they will walk at their own pace rather than attempt to keep pace with the tester. While this may allow a better result, careful observation of  the patient before, during, and after the 6mwt, and handoff of the data, will help set expectations and the initial exercise prescription.

Many clinics that perform the 6mwt use a long hallway that is marked off every 10 feet. However, the patient has to get to the starting point first, so as to measure the distance walked.  The distance from the waiting area to the start point can often cause a patient to desaturate and become noticeably short of breath. This is good information that is often absent on the reporting form.

And prior to arriving at a waiting area for the appointment, patients often have to walk from a parking area to a check- in area, and from a check- in area to the RT department where the test will be performed. Many patients must make several stops along the way just to get to the 6mwt appointment, leaving them in less than optimal shape to do the test.

Some patients are so severely impaired, just getting up to standing from being seated causes them to desaturate, become severely short of breath, or both. Making notations such as these on the forms or in the EMR will help the Pulmonary Rehab staff accurately set a starting point for the exercise prescription.

There is a question of oxygen use during a 6mwt. Some physicians want all oxywalks done on room air. If a patient is on 2L/min of oxygen, for example, why would we walk them on room air? If a physician wants to see if the patient still needs oxygen, medicare and most insurances require annual testing and qualification anyway.

If the patient is on 2L routinely, test on 2L. If they use a conserver device, test using the conserver. It will usually show that the patient may be fine while sitting, but with an increased minute volume demand with exercise, the conserver will not keep up with them and they will desaturate.

And what if the patient desaturates below 88% during the walk? Some clinicians continue the full 6 minutes, as the patient will naturally stop themselves at some point. This practice can severely compromise the heart, as eager patients try and ‘pass’ the test and push themselves to saturations in the low 80’s or even into the 70’s. Other clinicians stop the clock and put the patient on oxygen, then have the patient continue. This allows the patient to somewhat recover, and do the remainder of the walk without the true benefit of oxyhemoglobin saturation and gives a false sense of distance and speed capability.

In my opinion, it is better to get an idea of what the patient will be able to do fully saturated with oxygen. Physiology dictates that oxygen takes 20 minutes to fully saturate the red blood cells. This is why we wait 20 minutes to get an ABG on a ventilator patient after we make changes.  Therefore, if a patient desaturates halfway through the walk, I will stop the walk, get them on 2 or 3 liters of oxygen, wait at least 10 minutes, and start over again. As much as patients don’t like to wear oxygen, they are often thrilled to find they can walk 6 minutes continuously if they build up enough reserve.

Here is a classic 6mwt result:

Sat%   Heart Rate             Comment

Resting                  93        88

1 minute                90       93

2 minutes              89       96

3 minutes              88       99                             Rest x 30 seconds

4 minutes             88        99                             Rest x 10 seconds

5 minutes             88        100                           Rest x 30 seconds

6 minutes             87        105                            Total distance 600 feet

Recovery              92        99                              One minute

 

Often, the only numbers that get looked at are the starting and ending Sat% and Heart rate, and distance walked. The fact that this patient rested for more than one minute of the 6mwt is often missed. Also missing is the reason the patient stopped to rest. Shortness of breath, pain, or fatigue will all stop a patient. When asked why they stopped, many patients will state they are ‘tired’ .  Pulmonary Rehab will help the patient differentiate between short breathing, fatigue, and overexertion. I would also question the clinician as to why they only measured recovery Sat% and HR at one minute. The starting heart rate was 88, and although the sat% returned to an acceptable level, the patient had only recovered to a heart rate of 99. Waiting another minute (or two) to re-check sat% and heart rate would give us more information. A patient who requires more than 3 minutes to return to a baseline heart rate after only 6 minutes of exercise may need further consultation.

Success in a Pulmonary Rehab program requires the patient and clinician to work together to progress the patient slowly with exercise. A patient will not be able to progress if they cannot even start. A safe and logical start point is only determined by how much a patient can do, not just in 6 minutes but on an average day. Complete assessment is vital to their success, and although the 6mwt is merely a snapshot, an observant clinician performing the test can garner quite a bit of useful information to pass on to the Pulmonary Rehab staff.