Monitoring Parameters for 6-Minute Walk Test in Rickets Patients
In patients with rickets, the 6-minute walk test should be performed yearly (starting at age 5-6 years) to quantify functional consequences on bone and muscle, with specific monitoring of distance walked, oxygen saturation, heart rate, dyspnea/fatigue scores, and continuous observation for gait abnormalities or signs of distress. 1
Pre-Test Baseline Assessment
Before starting the test, obtain the following measurements after the patient has rested for at least 10 minutes 1, 2:
- Pulse rate and blood pressure 1, 2
- Baseline oxygen saturation (SpO2) and heart rate 1, 2
- Dyspnea and fatigue levels using the Borg scale (0-10) 1, 2
Ensure the patient is wearing comfortable clothing and appropriate walking shoes, and allow them to use their usual walking aids (cane, walker) if needed 1.
Primary Outcome: Distance Walked
The total distance walked in meters is the primary outcome measure and should be carefully tracked using a mechanical lap counter, marking each 60-meter lap completed 1, 2. This distance measurement is particularly important in rickets patients as it reflects the functional impact of bone deformities and muscle weakness on mobility 1.
Continuous Monitoring During the Test
Critical Safety Observations
Watch the patient continuously throughout the 6 minutes for signs requiring immediate test termination 2:
- Chest pain
- Intolerable dyspnea
- Leg cramps or staggering
- Diaphoresis (excessive sweating)
- Pale or ashen appearance
Gait and Musculoskeletal Assessment
In rickets patients specifically, observe for 1:
- Limb deformities affecting gait (valgus or varus deformities)
- Joint alignment issues during walking
- Signs of bone or joint pain that may limit performance
- Muscle weakness manifesting as difficulty maintaining pace
Oxygen Saturation Monitoring
Continuous SpO2 monitoring is strongly recommended, particularly to identify exercise-induced desaturation (defined as a drop of ≥4% to <90%) 2. If using pulse oximetry, ensure it is lightweight (less than 2 pounds), battery-powered, and secured so the patient doesn't need to hold it 1.
Standardized Encouragement Protocol
Use only standardized phrases at specific time intervals to avoid artificially inflating the distance walked 1, 2:
- At 1 minute: "You are doing well. You have 5 minutes to go"
- At 2 minutes remaining: "Keep up the good work. You have only 2 minutes left"
- At 3 minutes remaining: "You are doing well. You are halfway done"
- At 4 minutes remaining: "Keep up the good work. You have 4 minutes to go"
- At 5 minutes: "You are doing well. You have only 1 minute to go"
Do not walk with the patient or use other words of encouragement, as this can alter results by up to 30% 3.
Post-Test Measurements
Immediately after the 6-minute test ends 1, 2:
- Record final Borg dyspnea and fatigue scores (remind patient of their pre-test scores)
- Document SpO2 and pulse rate from the oximeter
- Note any reasons for stopping prematurely if the test was not completed
- Mark the exact stopping point to calculate the final partial lap distance
Rickets-Specific Considerations
Correlation with Disease Severity
The 6-minute walk distance in rickets patients correlates with 1:
- Severity of limb deformities (intercondylar/intermalleolar distance)
- Degree of bone pain and joint disability
- Overall functional capacity affected by osteomalacia
Longitudinal Monitoring
Perform the test yearly at approximately the same time of day to track functional improvement or deterioration 1. With appropriate treatment (phosphate supplementation and active vitamin D), you should expect improvement in walking distance as rickets heals and limb deformities reduce 1.
Integration with Other Assessments
The 6MWT results should be interpreted alongside 1:
- Clinical measurement of intercondylar/intermalleolar distance
- Radiographic assessment of limb alignment
- Serum alkaline phosphatase levels (biomarker of rickets activity)
- Orthopedic evaluation of limb deformities
Safety Requirements
Emergency equipment must be immediately available 2:
- Oxygen source
- Sublingual nitroglycerin
- Aspirin
- Albuterol
- Telephone access
- Automated electronic defibrillator
The technician must be certified in Basic Life Support cardiopulmonary resuscitation 2.
Common Pitfalls to Avoid
Do not use a treadmill for the 6-minute walk test, as patients cannot pace themselves and results are not interchangeable with corridor tests (patients walk 14% less distance on average) 1.
Do not provide a warm-up period before the test, as this is not part of the standardized protocol 1.
Do not allow the patient to walk with other patients or have the technician walk alongside them, as this affects performance 3.