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Myths and methodologies: Assessment of dynamic cerebral autoregulation by the mean flow index
Markus Harboe Olsen1, Christian Gunge Riberholt1,2, Ronan M G Berg3,4,5,6
1Department of Neuroanaesthesiology, The Neuroscience Centre, Copenhagen University Hospital - Rigshospitalet, Copenhagen, Denmark.
Abstract:
The mean flow index-usually referred to as Mx-has been used for assessing dynamic cerebral autoregulation (dCA) for almost 30 years. However, concerns have arisen regarding methodological consistency, construct and criterion validity, and test-retest reliability. Methodological nuances, such as choice of input (cerebral perfusion pressure, invasive or non-invasive arterial pressure), pre-processing approach and artefact handling, significantly influence mean flow index values, and previous studies correlating mean flow index with other established dCA metrics are confounded by inherent methodological flaws like heteroscedasticity, while the mean flow index also fails to discriminate individuals with presumed intact versus impaired dCA (discriminatory validity), and its prognostic performance (predictive validity) across various conditions remains inconsistent. The test-retest reliability, both within and between days, is generally poor. At present, no single approach for data collection or pre-processing has proven superior for obtaining the mean flow index, and caution is advised in the further use of mean flow index-based measures for assessing dCA, as current evidence does not support their clinical application.
Insights
The mean flow index (Mx) for assessing dynamic cerebral autoregulation (dCA) has methodological issues. Current evidence does not support its clinical application due to validity and reliability concerns.
Area of Science:
- Neuroscience
- Physiology
- Medical Technology
Background:
- The mean flow index (Mx) has been a standard for dynamic cerebral autoregulation (dCA) assessment for nearly 30 years.
- Concerns exist regarding the methodological consistency, validity, and reliability of Mx in dCA evaluation.
Purpose of the Study:
- To critically evaluate the methodological consistency, construct validity, criterion validity, and test-retest reliability of the mean flow index (Mx) for dCA assessment.
- To determine if current evidence supports the clinical application of Mx-based measures for dCA.
Main Methods:
- Review of existing literature on mean flow index (Mx) calculations for dCA.
- Analysis of methodological factors influencing Mx values, including input data, pre-processing, and artifact handling.
- Examination of studies correlating Mx with other dCA metrics, assessing discriminatory and predictive validity, and test-retest reliability.
Main Results:
- Methodological choices significantly impact Mx values, with no single approach proving superior.
- Previous correlations with other dCA metrics are flawed by issues like heteroscedasticity.
- Mx demonstrates poor discriminatory validity and inconsistent prognostic performance, with generally poor test-retest reliability.
Conclusions:
- Significant methodological inconsistencies and validity limitations challenge the use of mean flow index (Mx) for dCA assessment.
- Current evidence does not support the clinical application of Mx-based measures for evaluating dynamic cerebral autoregulation.
- Caution is advised regarding the continued use of Mx for dCA evaluation until methodological concerns are resolved.
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