Introduction
An essential aspect in the management of pulmonary hypertension is an ongoing functional assessment of the patient. Because dyspnea on exertion is the most common symptom of pulmonary hypertension, a simple test was developed to help evaluate the patient’s activity tolerance. This test is simply the distance a patient can walk unassisted in 6 minutes over a prescribed, flat course and is known as the 6-minute walk test.
The 6MWT does not evaluate specific organ systems or any mechanisms which might limit the exercise capacity of the patient. It has been a central methodology in numerous studies of pulmonary arterial hypertension (PAH) and has become one of the primary ways that patients with PAH are assessed over time.
6MWT Safety
The 6MWT should be performed under circumstances where there are rapid and appropriate response measures available, should an emergency arise during the test. Supplemental supplies that should be on-hand include oxygen, sublingual nitroglycerin, aspirin, and albuterol. The technician should be certified in CPR with a minimum of Basic Life Support (AHA-approved course); ACLS certification is desirable. If a patient is on chronic oxygen therapy, oxygen should be given at the standard rate for that patient or as directed by the physician or study protocol.
Reasons for immediate discontinuation of the 6MWT include:
- Chest pain
- Intolerable dyspnea
- Leg cramps
- Staggering
- Diaphoresis
- Pale or ashen appearance
It is important that technicians be trained to recognize these problems and the appropriate clinical responses. If a test is stopped for any reason, the patient should be placed in a sitting or supine position, as appropriate, based on physician or technician assessment of event severity.
In the case of an event-based stoppage, the technician should obtain:
- Blood pressure
- Pulse rate
- O2 saturation
- Physician evaluation
- Oxygen should be given, as necessary
Performing the 6MWT
The 6MWT should be performed in a long, straight, enclosed corridor with a hard, seldom traveled surface. The walking course must be 30 meters in length (~100 foot hallway required; a shorter corridor requires patients to change direction more frequently, possibly reducing the 6MWD). The length of the corridor should be marked every 3 meters, and turnaround points should be each marked with a traffic cone. The end of each 60-meter lap should be marked on the floor with bright tape.
Equipment Required
- Countdown timer or stopwatch
- Mechanical lap counter
- 2 small cones to mark the turnaround points
- Chair that can be easily moved along the course (in case patient must sit)
- Worksheets
- Source of oxygen
- Sphygmomanometer
- Telephone
- Automated electronic defibrillator
Patient Preparation for the 6MWT
- Patient should wear comfortable clothing.
- Walking shoes
- Patients should use any usual walking aids (cane, walker, etc.).
- Patients should continue any usual medical regimens.
- A light meal is acceptable before early morning or early afternoon testing.
- Patients should not have exercised vigorously within 2 hours of beginning the test.
6MWT Measurement Criteria
- Any repeat testing should be performed at the same time of day.
- Warm-up periods are not allowed.
- Patient should sit at rest in a chair near the starting position for at least 10 minutes prior to the test. This time can be used to measure pulse and BP, and to check for test contraindications.
- Pulse oximetry is optional (see guidelines for further details).
- Prior to starting the test, the patient should rate their baseline dyspnea and overall fatigue using the Borg Scale (Figure 1).
6MWT Instructions for the Patient
(See the American Thoracic Society Guidelines for complete details)
- Patient is to walk as far as possible in 6 minutes, back and forth in the designated hallway.
- Patient will probably become out of breath, so it is acceptable to slow down, stop, and/or rest as needed; patient can lean against the wall if necessary but resume walking as soon as they are able.
- Patient should pivot briskly around the cones and continue without hesitation.
- Jogging or running is not allowed.
- The patient is positioned at the starting line and timing commences when the patient begins to walk.
- Standardized phrases of encouragement are allowed at specified intervals.
Deviation from this protocol lessens the validity and comparability of the test results.
After 6MWT Completion
- Technician marks the spot on the floor where the patient stops at 6 minutes.
- Record the post-walk Borg dyspnea and fatigue score; patient can be queried as to what prevented them from walking further.
- If pulse oximetry is used, the SpO2 and pulse should be recorded and the sensor removed.
- The number of laps is recorded and is added to the additional distance (in meters) for the final partial lap. Total distance is rounded up to the nearest meter.
Sources of Test Variability
There are many sources of test variability with the 6MWT. These are detailed in Figure 2.
Interpretation of the 6MWT
6MWT’s are usually performed before and after an intervention for PAH at 3 month intervals. The primary question addressed by these tests is as follows: “Has the patient experienced a clinically significant improvement in 6MWD as a result of the intervention?”
Assuming good quality assurance in the protocol, change in 6MWD is expressed as either an absolute distance (in meters) or as a percentage of the baseline test(s). It is important to note that a statistically significant improvement in 6MWD in a study may not actually reflect an important clinical improvement.
References
1. ATS Committee on Proficiency Standards for Clinical Pulmonary Function Laboratories. ATS statement; guidelines for the six-minute walk test. Am J Respir Crit Care Med 2002;166(1):111-117.
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