Validity of the 6 min walk test as a surrogate for the anaerobic threshold in the preoperative assessment clinic

Rhona Sinclair, V. Goodridge, Alan Batterham, Gerard Danjoux

    Research output: Contribution to conferencePaper

    Abstract

    Functional assessment of exercise capacity is now widely recognized as a major determinant of preoperative risk prediction
    before major surgery. Two different techniques are principally used in the UK: cardiopulmonary exercise testing (CPET) and
    subjective patient-reported assessment of metabolic equivalents (METs). The identification of anaerobic threshold (AT), from CPET, presently represents the UK gold standard; however, reported METs form a cornerstone of the American Heart Association preoperative guidelines. Unpublished data from our institution have demonstrated a poor correlation between patient-reported METs and oxygen consumption (VO2) at AT (r¼0.31). The sensitivity and predictive value of METs to identify objective, CPET-derived exercise capacity was also low (sensitivity 24%). With this in mind, our group felt that where CPET is unavailable, a more robust test of exercise capacity is required to accurately assess the operative risk. We propose that the 6 min
    walk test (6MWT) may fulfil this requirement. The aim of this study was to examine the validity of the 6MWT against a criterion measure derived from CPET: AT.
    Fifteen participants, undergoing major non-cardiac surgery, were recruited from our preoperative assessment clinics. CPET
    was conducted according to our standardized ramped protocol with participants exercising until they attained their AT. AT was
    derived from the data recorded using the V-slope method. After a short rest period, participants completed two separate 6MWT; the
    furthest distance walked was recorded. Statistical analysis used an ordinary least-squares linear regression method to derive the validity coefficient (r) and the standard error of the estimate (SEE),
    providing the typical prediction error associated with the prediction of AT from the results of a 6MWT in an individual patient. All participants completed three tests. Mean age was 69.5 (SD 7.0) yr (12 males and three females). Data from 13 participants were suitable for statistical analysis (two exclusions: one unreadable
    CPET and one invalid 6MWT from knee injury). The group achieved a mean AT of 10.1 (SD 3.5) ml O2 kg21 min21 and a mean 6MWT distance of 548.1 (SD 74.1) m. The distances
    walked during two 6MWT demonstrated a mean improvement of 19 m; the 6MWT was a highly reliable test, with an intraclass
    correlation (3.1) of 0.94. We found a validity coefficient of r¼0.76, with a standard error of prediction of AT from distance walked during 6MWT of +2.4 ml O2 kg21 min21. The 6MWT demonstrates a strong correlation with AT in this pilot study, with good repeatability between tests. It may provide a robust, cheap, accurate alternative for measuring exercise capacity where CPET is unavailable. On the basis of this encouraging exploratory phase correlation, we now plan to undertake
    a definitive concurrent validity study.
    Original languageEnglish
    Publication statusPublished - 2009
    Event2008 Meeting of the Anaesthetic Research Society, Royal College of Anaesthetists - London, United Kingdom
    Duration: 20 Nov 200821 Nov 2008

    Conference

    Conference2008 Meeting of the Anaesthetic Research Society, Royal College of Anaesthetists
    CountryUnited Kingdom
    CityLondon
    Period20/11/0821/11/08

    Bibliographical note

    Functional assessment of exercise capacity is now widely recognized as a major determinant of preoperative risk prediction before major surgery. Two different techniques are principally used in the UK: cardiopulmonary exercise testing (CPET) and subjective patient-reported assessment of metabolic equivalents (METs). The identification of anaerobic threshold (AT), from CPET, presently represents the UK gold standard; however, reported METs form a cornerstone of the American Heart Association preoperative guidelines. Unpublished data from our institution have demonstrated a poor correlation between patient-reported METs and oxygen consumption (VO2) at AT (r¼0.31). The sensitivity and predictive value of METs to identify objective, CPET-derived exercise capacity was also low (sensitivity 24%). With this in mind, our group felt that where CPET is unavailable, a more robust test of exercise capacity is required to accurately assess the operative risk. We propose that the 6 min walk test (6MWT) may fulfil this requirement. The aim of this study was to examine the validity of the 6MWT against a criterion measure derived from CPET: AT. Fifteen participants, undergoing major non-cardiac surgery, were recruited from our preoperative assessment clinics. CPET was conducted according to our standardized ramped protocol with participants exercising until they attained their AT. AT was derived from the data recorded using the V-slope method. After a short rest period, participants completed two separate 6MWT; the furthest distance walked was recorded. Statistical analysis used an ordinary least-squares linear regression method to derive the validity coefficient (r) and the standard error of the estimate (SEE), providing the typical prediction error associated with the prediction of AT from the results of a 6MWT in an individual patient. All participants completed three tests. Mean age was 69.5 (SD 7.0) yr (12 males and three females). Data from 13 participants were suitable for statistical analysis (two exclusions: one unreadable CPET and one invalid 6MWT from knee injury). The group achieved a mean AT of 10.1 (SD 3.5) ml O2 kg21 min21 and a mean 6MWT distance of 548.1 (SD 74.1) m. The distances walked during two 6MWT demonstrated a mean improvement of 19 m; the 6MWT was a highly reliable test, with an intraclass correlation (3.1) of 0.94. We found a validity coefficient of r¼0.76, with a standard error of prediction of AT from distance walked during 6MWT of +2.4 ml O2 kg21 min21. The 6MWT demonstrates a strong correlation with AT in this pilot study, with good repeatability between tests. It may provide a robust, cheap, accurate alternative for measuring exercise capacity where CPET is unavailable. On the basis of this encouraging exploratory phase correlation, we now plan to undertake a definitive concurrent validity study.

    Fingerprint Dive into the research topics of 'Validity of the 6 min walk test as a surrogate for the anaerobic threshold in the preoperative assessment clinic'. Together they form a unique fingerprint.

  • Cite this

    Sinclair, R., Goodridge, V., Batterham, A., & Danjoux, G. (2009). Validity of the 6 min walk test as a surrogate for the anaerobic threshold in the preoperative assessment clinic. Paper presented at 2008 Meeting of the Anaesthetic Research Society, Royal College of Anaesthetists, London, United Kingdom.