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Cardio-pulmonary exercise testing (CPEX) and major surgery

All major surgery is associated with some risk, and often the most serious risks are heart or lung based (cardiac or pulmonary). In order to try to quantify the risks associated with surgery, a number of different assessments have been tried. One of the most promising appears to be cardio-pulmonary exercise testing (CPEX).

CPEX is a type of exercise stress test that measures the function of heart and lung as a combined unit. The test is able to distinguish whether shortness of breath is caused by heart failure or lung disease. Patients undergoing CPEX testing have a number of parameters measured firstly at rest and then with exercise. The exercise test either consists of a treadmill test or a cycle ergometer test (we use the cycle test). During the exercise test an ECG measures the heart rate and rhythm, as well as checking for angina. Oxygen uptake and carbon dioxide output is measured on a breath by breath basis. The ‘anaerobic threshold’ (AT) or lactic acid threshold is the point at which the subject moves from aerobic to anaerobic metabolism. The AT threshold appears to be one of the best predictors of outcome in major surgery. The higher the AT threshold the fitter the subject is and the more likely they will do well with surgery. Some subjects will be taken to their exercise limit to assess their VO2Max. A subject’s VO2Max is the maximum amount of oxygen in millilitres, one can use in one minute per kilogram of body weight and is closely related to overall fitness.

An important paper on survival after AAA surgery was recently published in the BJS:

Mid-term survival after abdominal aortic aneurysm surgery predicted by cardiopulmonary exercise testing.
Carlisle J, Swart M.
British Journal Surgery 2007 Aug;94(8):966-9

CONCLUSION: Preoperative CPX testing, combined with simple co-morbidity scoring, identified patients unlikely to survive in the mid-term, even after successful AAA repair.

CPEX at extreme altitude
The 2007 Caudwell Xtreme Everest Expedition performed the most extensive CPEX experiment ever undertaken assessing 200 subjects at sea level (London) and at increasing altitudes to 5,300m (Everest Base Camp). Climbers underwent CPEX testing as high as the 8,000m (South Col on Everest) in attempt to investigate how the body responds to exercise in extreme hypoxia (lack of oxygen).


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South Col of Everest   Measuring VO2Max South Col of Everest

South Col of Everest

Measuring V02Max on South Col of Everest

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