CME INDIA Presentation by Dr N K Singh.
Why it matters?
- The majority of COVID-19 patients (81%) have uncomplicated or mild illness: nonpneumonia or mild pneumonia.
- About 14% develop severe illness with blood oxygen saturation (Spo2) falling below 93% and requiring oxygen therapy.
- Approximately 5% develop critical illness with respiratory failure, septic shock, and multiple organ dysfunction requiring intensive care unit (ICU) treatment
Is it a pointer to window of opportunity?
- Patients with mild disease can quickly deteriorate to severe or critical cases.
- The median time from symptom onset to the development of pneumonia is approximately 5 days and that from symptom onset to severe hypoxemia and ICU admission is typically between 7 and 12 days.
- Therefore, there is a window of opportunity, albeit for a short period of a few days, before the onset of severe symptoms to allow for risk stratification.
- The rationale is to identify those among mild cases that are likely to progress to severe illness and transfer them to a higher level of care. If the logistics relevant to a local area preclude testing all the mild cases, then one could consider targeting high-risk groups such as higher age and those with comorbid conditions.
What is the validity of this test?
- The 6-minute walk test (6MWT) is a validated clinical test to assess the cardiopulmonary reserve and fundamentally designed for use in adults with chronic respiratory disease and therefore may be an appropriate test to triage COVID-19 patient
- Prediction of the trajectory of illness from symptom onset is difficult, 6 min walking test has emerged as a very valuable test to fill the gap in prognostication of covid patient.
What are test procedures?
- The test involves having the patient walk as far as possible on a straight track ideally 100 feet in length, for example, corridor or hallway. The total distance walked is the primary objective of the test and is compared with reference standards for interpretation.
- It has been proposed to perform the modified 6MWT test on the fourth or fifth day of clinical illness based on the viral load patterns in mild cases compared to severe cases.The consistent recommendation that symptomatic patients in health care settings should wear a mask cannot be ignored for this test
- In terms of metabolic equivalents (METs), walking 1400 feet in 6 minutes will be equivalent to 3 METs
- Here’s how it is to be done:
- The patient must wear a simple cloth or surgical mask
- The pretest baseline Oxygen Saturation should be > 94%, the individual must not short of breath, be at rest and should be able to walk unsupported
- The individual must walk in the confinement of his/ her room for 6mins non-stop, without any oxygen support
- After the walk is complete, use a Pulse Oximeter to measure if the oxygen saturation of the individual has dropped below 93%, or if there is an absolute drop of more than 3%
What are very important considerations?
- It is important to note if the person is feeling unwell i.e. light headed or short of breath while performing the test, these significant findings need to be noted. This is called ‘unmasking hypoxia’, these patients may progress to be Hypoxic and hence early intervention in the form of admission to a hospital, or shifting to ICU with Oxygen support +/- steroids as per the admitting doctor.
- Oxygen concentration in the blood should stay between 94%-100%, a drop below 90% should be considered as an emergency and the patient must immediately be hospitalized.
- It is important to note that the 6min walk test may be cut short for 3mins in patients above 60yrs of age. At many busy hospitals, 3 min walk test is being done.
Is it mandatory to do it Post discharge?
Dr N.K. Singh: The 6-minute walking test is a potential tool in discharge assessment.
Dr Arvind Ojha, Kolkata: If you do a 6-minute walk test & detect hypoxia, will it be advisable to discharge the patient immediately after. We have a state guideline to follow, which says to be discharged if no oxygen requirement in last 3 days if the patient is otherwise stable. Off course no fever for same duration.
Dr A. K. Virmani, Jamshedpur: 6 MWT is not mandatory at discharge.
What are Relative contraindications?
- Resting heart rate of more than 120
- A systolic blood pressure of more than 180 mm Hg, and a diastolic blood
- pressure of more than 100 mm Hg
- Reasons for immediately stopping a 6MWT include the follow – (1) Chest pain, (2) Intolerable dyspnea, (3) Leg cramps, (4) Staggering, (5) Diaphoresis, and (6) Pale or ashen appearance
Dr Vijay Datar, Tarapur, Maharashtra: If a patient becomes hypoxic after 6MWT, Spo2 goes down from 97 to 90,after how many minutes of resting, we should expect spo2 to come back to 97?
Dr N.K. Singh: A practice test is not needed in most clinical settings but should be considered. If a practice test is done, wait for at least .1 hour before the second test and report the highest 6MWD as the patient’s 6MWD baseline. Can not be repeated if pulse rate and BP is not settled and patient does not feel comfortable. Repeat testing should occur at the same time of the day to reduce intraday variability.
Dr Atri gangopadhaya, Pulmonologist, Ranchi: It depends on etiology of desaturation. Average 15minutes.Earliest return in cardiogenic cause for desaturation, then severe obstructive airway disease, longest return in interstitial lung disease.
Sources of variability
Factors reducing the 6MWD
- Shorter height
- Older age
- Higher body weight
- Female sex
- Impaired cognition
- A shorter corridor (more turns)
- Pulmonary disease (COPD, asthma, cystic fibrosis, interstitial lung disease)
- Cardiovascular disease (angina, MI, CHF, stroke, TIA, PVD, AAI)
- Musculoskeletal disorders (arthritis, ankle, knee, or hip injuries, muscle wasting, etc.)
Factors increasing the 6MWD
- Taller height (longer legs)
- Male sex
- High motivation
- A patient who has previously performed the test
- Medication for a disabling disease taken just before the test
- Oxygen supplementation in patients with exercise-induced hypoxemia
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I do advise this, even in non hospitalized cases,in domicilliary stages, to assess their functional capabilities, certainly with the comorbidity in consideration, viz, cardiac or pulmonary background.
I follow with a video call in some patients also.
It is a very good input thanks sir but I want to know the distance traveled in 6 minut in different situations and how it will be interpreted for severity
In different situations it varies.For example in PAH distance travelled less than 300 meter is adverse prognostic factor.In CRT improvement from 5 to 74 meter is correlated with improvement.In HFrEF improvement from 55 to 107 meter found better predictor.In fact minimally clinically important difference(MCID) concept is being validated. In general 30 meter improvement from baseline of 250 meter is more relevant from baseline 460 meter.
Thank you so much for this valuable information in the present scenario
Excellent information
Information is very very useful for day to day practice