1. George A. Rose1, Richard Davies2, Ian Appadurai2, Damian M. Bailey1
Manual versus automated methods of anaerobic threshold detection; implications for clinical outcomes?
George A. Rose1, Richard Davies2, Ian Appadurai2, Damian M. Bailey1
1 Neurovascular Research Laboratory, University of South Wales, Pontypridd, United Kingdom.
2 Department of Anaesthetics, University Hospital of Wales, Cardiff, United Kingdom.
Background
Results
Cardiopulmonary exercise testing (CPX) is used to determine cardiorespiratory fitness in patients prior to major surgery given its association with post-operative survival. Typically an anaerobic threshold (AT) value of <11.0 ml O2.kg-1.min-1 (Older et al., 1999) has been employed as an objective biomarker of increased perioperative risk. In this study, we compared to what extent differences between automated versus manual (gold-standard) methods of AT detection have the theoretical potential to influence surgical risk stratification.
Automated detection of the AT overestimated V̇O2 by 13%. Fifty two false negatives (whereby a CPX pass was reported instead of a fail) occurred indicating a high rate of type II errors, with sensitivity of 55% and specificity of 91%.
* denotes significance at p < 0.05
Figure 3. Mean±SD O2 uptake comparison between AT detection methods
Figure 1. Cardiopulmonary exercise testing
Methods
A randomised sample of 213 patients scheduled for elective colorectal surgery who underwent CPX testing were retrospectively examined. Manual AT results were calculated using the gold standard ‘V-slope’ method (Beaver et al., 1986) and confirmed by two independent clinicians. Automated AT results were compiled using default settings in BreezeSuiteTM software (Medical Graphics, St Paul, MN, USA). Following confirmation of distribution normality (Shapiro W Wilks tests), data were analysed using paired samples t - tests and Chi-Squared tests. Data are expressed as mean ±SD and significance established at P < 0.05.
Figure 4. Number of CPX tests passed (AT ≥11.0 ml O2.kg-1.min-1) and failed (AT <11.0 ml O2.kg-1.min-1)
Conclusions
Automated AT detection methods allow patients to transcend risk stratification boundaries thus leading to incorrect decision making and inappropriate surgical risk stratification. Clinicians should use the manual and gold standard V-slope method for a more accurate assessment of patient cardiorespiratory fitness.
Carbon dioxide production (ml.min-1) and Respiratory Exchange Ratio
Ventilatory equivalent for carbon dioxide and end tidal oxygen tension (mmHg)
References
Beaver et al. (1986). J Appl Physiol 60(6),
Older et al. (1999). Chest 116,
Acknowledgements
Oxygen uptake (ml.min-1)
The authors would like to acknowledge The Physiological Society for a travel grant to attend this meeting.
Figure 2. Automated detection of the AT using BreezeSuiteTM software