Unmasking Hypoxia in COVID-19 – Six Minute Walk Test
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Pulmonary manifestation of COVID-19 can be easily picked up by a simple user friendly 6 minute walk test which can detect desaturation to pick up silent hypoxia which has been often referred to as “happy hypoxia”.

Another observation in COVID 19 patients is at rest they appear comfortable and saturation are maintained above 94%, however mild exertion like using washroom often makes them hypoxic and/or short of breath. Thus, in this group of patients, it is important to identify hypoxia early, stratify the risk and plan treatment.

A simple 6 minutes’ walk test (6MWT)2 is a reliable tool to assess cardiorespiratory effort tolerance in chronic lung and chronic heart failure patients. Traditionally the test involves measuring the heart rate and blood pressure along with oxygen saturation using a finger pulse oximeter probe. Researchers have proposed a stopping criterion for the test based on drop in the measured oxygen saturation (SpO2) by finger probe. The test provides a global assessment of the cardio-pulmonary reserves. A simple effort of walking at a steady pace in patients with compromised cardio respiratory reserves may precipitate a drop in oxygen saturation.

There are many physiological variables which may be attributed to drop in saturation, however the most important been hearts inability to improve cardiac output and second, decrease in lung diffusion capacity which can be due to lung infiltration due to COVID 19 pneumonia and/or due to alveolar capillary micro thrombi in the pulmonary circulation.

The 6-minute walk test can also predict the anaerobic threshold in patients. Anaerobic threshold is a reflection of combine efficiency of heart, lung and circulation and marks the onset of anaerobic metabolism due to oxygen deficit secondary to inadequate oxygen delivery.

The principle of 6-minute walk test in COVID 19 is to identify patients who are not hypoxic at rest, but become hypoxic (silent Hypoxia) on 6-minute walk test. The 6MWT will ascertain evidence of hypoxia identified by SpO2 less than 94% or an absolute drop in SpO2 by more than 3% from base line during or at end of the test. Patients over 60 years of age may have a shorter- 3-minute walk test (3MWT) if they are unable to perform a 6-minute test.

The test is indicated in all COVID-19 positive patients who are not hypoxic or short of breath at rest. The test is contraindicated if patient is hypoxic at rest SpO2 less than 94 %, Short of breath at rest, not able to walk unassisted, Eisenmenger’s syndrome, severe anaemia, known patient of unstable angina or valvular heart disease.

Source: https://www.japi.org/x2647464/unmasking-hypoxia-in-covid-19-six-minute-walk-test-
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