What is the purpose of a walk test for patients on home oxygen therapy?

Purpose of Walk Tests for Home Oxygen Therapy

The primary purpose of a walk test for patients on home oxygen therapy is to determine if they experience exercise-induced oxygen desaturation and to establish the appropriate oxygen flow rate needed to maintain oxygen saturation ≥90% during physical activity.

Assessment of Exercise-Induced Desaturation

• Walk tests evaluate whether patients desaturate during exercise, defined as a drop in SpO2 of ≥4% to <90%, which is the key criterion for ambulatory oxygen therapy eligibility 1.
• The 6-Minute Walk Test (6MWT) is the most commonly used field walking test as it evaluates the integrated response of all body systems involved during exercise, including pulmonary, cardiovascular, and muscular systems 1.
• Oxygen desaturation during the 6MWT may reflect oxygen desaturation during patients' activities of daily living, making it clinically relevant for determining home oxygen needs 1.

Titration of Appropriate Oxygen Flow Rate

• The walk test allows healthcare providers to determine the most appropriate oxygen flow rate and device to correct exercise desaturation 1.
• During the assessment, oxygen flow rates are adjusted until the patient maintains SpO2 ≥90% throughout the exercise, typically starting with baseline measurement on room air followed by titration with supplemental oxygen 1.
• The British Thoracic Society guidelines recommend a structured approach where flow rates are increased after 20-minute rest periods between walk tests until adequate oxygenation is achieved 1.

Demonstration of Clinical Benefit

• A positive response to ambulatory oxygen during a walk test requires meeting at least 2 of 3 criteria: SpO2 ≥90% throughout the test, ≥10% increase in walking distance from baseline, and improvement in Borg dyspnea scale of at least 1 point 1.
• The walk test helps quantify the improvement in exercise capacity with supplemental oxygen compared to room air, which is critical for justifying the prescription of ambulatory oxygen therapy 1.

Protocol Elements

• Standard walk test protocols include:
  • Baseline assessment of SpO2, heart rate, and dyspnea using the Borg scale 1
  • A standardized walking course (typically 30m for 6MWT) 1
  • Continuous or interval monitoring of oxygen saturation during exercise 1
  • Assessment of walking distance, symptoms, and physiological parameters 1
• The test should be performed with the patient carrying or wheeling the oxygen device as they would use it in everyday life, as carrying the device can negate the effect of oxygen therapy 1.

Common Pitfalls and Considerations

• Treadmill tests are not recommended as substitutes for corridor walk tests because patients walk shorter distances on treadmills (14% less on average), making results not interchangeable 1.
• A practice walk test should be performed before the actual assessment, as improvement in walking distance may be overestimated without one 1.
• The 6MWT may overestimate oxygen needs during typical daily activities for some patients, as it often represents a higher level of exertion than routine activities 2.
• Different oxygen devices vary in weight and functionality, so patients should be tested with the specific device they will use at home 1.

Follow-up Assessment

• Patients prescribed ambulatory oxygen should have follow-up assessment at 8 weeks to check compliance and troubleshoot any device issues 1.
• Annual reassessment is recommended to adjust flow rates and devices as the patient's condition changes 1.
• Patients initiated on long-term oxygen therapy (LTOT) who are active outdoors should receive ambulatory oxygen assessment to determine if their flow rate needs increasing during exercise 1.

By using standardized walk tests to assess oxygen needs during activity, healthcare providers can optimize ambulatory oxygen therapy to improve patients' exercise capacity, reduce symptoms, and potentially enhance quality of life.