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. 2013 Feb 21;2(1):2.
doi: 10.1186/2047-0525-2-2.

Anaerobic Threshold, Is It a Magic Number to Determine Fitness for Surgery?

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Anaerobic Threshold, Is It a Magic Number to Determine Fitness for Surgery?

Paul Older. Perioper Med (Lond). .
Free PMC article

Abstract

The use of cardiopulmonary exercise testing (CPET) to evaluate cardiac and respiratory function was pioneered as part of preoperative assessment in the mid 1990s. Surgical procedures have changed since then. The patient population may have aged; however, the physiology has remained the same. The use of an accurate physiological evaluation remains as germane today as it was then. Certainly no 'magic' is involved. The author recognizes that not everyone accepts the classical theories of the anaerobic threshold (AT) and that there is some discussion around lactate and exercise. The article looks at aerobic capacity as an important predictor of perioperative mortality and also looks at some aspects of CPET relative to surgical risk evaluation.

Figures

Figure 1
Figure 1
Plot of base excess, lactate,V˙CO2andV˙CO2. Simultaneous plot of lactate, base excess and gas exchange. This was obtained from a man exercising on a cycle ergometer. Samples at one minute intervals. Note that the base excess falls very much as the reciprocal of the lactate rise. Data from author’s laboratory.
Figure 2
Figure 2
Traditional nine-panel plot. This format emanates from Wasserman and colleagues. This is one of several formats currently used but is by far the most common. There is a new format published recently from UCLA (Figure 3) and another one devised by Professor Whipp. The 9-panel format allows 15 variables to be plotted on 9 graphs. Note in Panel 7, the lines indicating vital capacity, inspiratory capacity and maximum ventilatory volume. This is useful in assessing respiratory function. Ve, minute volume, VO2 = oxygen uptake, HR = heart rate, VCO2 = carbon dioxide output, Vt, tidal volume, RER = respiratory exchange ratio, PETO2 = partial pressure end-tidal oxygen, PETCO2 = partial pressure end-tidal carbon dioxide. Data from author’s laboratory.
Figure 3
Figure 3
New nine-panel plot. This is the same test as Figure 2. The panel numbers refer to their original position in Figure 2. This new format was first announced in [16]. Ve = minute volume, VO2 = oxygen uptake, HR = heart rate, VCO2 = carbon dioxide output, Vt = tidal volume, RER = respiratory exchange ratio, PETO2 = partial pressure end-tidal oxygen, PETCO2 = partial pressure end-tidal carbon dioxide. Data from author’s laboratory.
Figure 4
Figure 4
Relationship of AT measured as ml.min−1.kg−1 to AT ml.min−1.m2. The metabolic cart is usually programmed to index V˙O2 as ml.min−1.kg-1 whereas the pulmonary artery catheter is programmed to index as ml.min-1.m2. Note that ml.min−1.m2 indirectly uses height in indexing. Indexing as ml.min−1.kg−1 does not use height. This graph allows direct comparison. Data from author’s laboratory.
Figure 5
Figure 5
Triage according to AT. Patients with either no cardiac failure or mild to moderate cardiac failure are triaged to the ward. Only patients with moderate to severe or severe cardiac failure are triaged to ICU. Data modified from [42].
Figure 6
Figure 6
Colour graphics interpretation of AT and V˙O2/WR slope. This graphic shows the gradual change from high risk (red) to low risk (green) via an area of caution (yellow). It plots the AT and the V˙VO2 /WR slope. This minimizes the assumption that an AT of 10.9 ml.min−1.kg−1 is very different from an AT of 11.1 ml.min−1.kg−1 (see text). Reproduced with permission from Cortex Biophysik GmbH.
Figure 7
Figure 7
Oxygen pulse under two different conditions. (a,b) Panel 2 on the traditional Wasserman et al. 9-panel plot. In both cases, the patients are taking beta-adrenergic blocking drugs. (a) A low oxygen pulse in a woman. (b) An elevated oxygen pulse on a female patient. Note the low pulse rate and the compensating elevated oxygen pulse. The lower horizontal dotted line is the predicted value.
Figure 8
Figure 8
AT ml.min−1.kg−1 vs.V˙e/V˙O2. This graph shows how the V˙e / V˙O2 rises as the value of the AT falls. A value for V˙e / V˙O2 of greater than 35 is abnormal. Data from the author’s laboratory.
Figure 9
Figure 9
Pulmonary vascular resistance vs.V˙e/V˙O2. All patients in this study had an AT of 10 ml.min−1.kg−1 or less. The graph shows the large variation in pulmonary vascular resistance with a V˙e / V˙O2 of greater than 35. To be certain that the pulmonary vascular resistance will exceed 35 kPa.L-1.s, the Ve / V˙O2 needs to be greater than 45. Note the PVRI of those patients with a V˙e / V˙O2 of 35. Data from the author’s laboratory.

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