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
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).