‘Cardiopulmonary Exercise Testing - Is it worth the sweat? ’
Dr Jonathan Wilson, York
The meeting was opened by Dr Peter Davies, President of the LMI, who welcomed everybody to the meeting and handed over to Dr John Chambers. Dr Chambers firstly announced the sad news of the death of Professor Cecil Gray, a past president of the society and a highly influential member of the anaesthetic community. Dr David Gray said a few words about his father and a minute’s silence was observed in the lecture theatre.
Dr Chambers then introduced the speaker, Dr Jonathan Wilson, a consultant anaesthetist from York. Dr Wilson started his talk by looking at mortality following elective surgery for AAA repair, GI and colorectal surgery and compared this data for similar patients in the US which showed that there was roughly a three times greater mortality in UK patients.
Dr Wilson went on to describe his experience of Cardiopulmonary Exercise testing in York. Having started in 2001 with vascular patients, the service had expanded in 2004 to include all GI and major urology patients over 60 years and he now had experience with over a thousand patients. The method was described and the scientific rationale behind the test was explained. Major surgery causes physiological stress and patients who do badly have a stronger pro-inflammatory response or indices of impaired tissue perfusion and oxygen transport. Exercise is a physiological stress and so can be used to identify susceptible patients, primarily through a reduced oxygen consumption at the anaerobic threshold.
Dr Wilson then looked at one of the first papers comparing the results of this test with mortality after major surgery by Paul Older et al (Chest 1993, 104:701-4). They investigated 187 patients undergoing major intra-abdominal surgery. Of the 55 patients with an AT<11mls/min/kg, mortality was 18%. If there was additional myocardial ischaemia, this rose to 42%. Of those with an AT of >11mlsmin/kg with ischaemia, the mortality was 4% indicating that ischaemia in the absence of cardiac failure is not a potent cause of peri-operative mortality.
Dr Wilson described the reasons for CPX testing. Firstly the test will give a more objective idea of peri-operative mortality. Secondly it identifies patients that may be improved by pre-operative treatment such as beta blockade and finally it will give a more objective indication of the level of peri-operative care that patients need, although, he thought, that this can be the most difficult to show. In York, CPX testing was part of the pre-assessment process and identified patients with limited cardiac reserve, abnormal function, the presence of ischaemic heart disease and the effectiveness of pre-operative treatment. The anaerobic threshold is the point at which the limit of aerobic capacity is reached and lactate production starts. It is a sub-maximal test (60%) and reproducible. During aerobic exercise, the ratio between oxygen consumption and carbon dioxide production is constant. When CO2 production overtakes O2 consumption, the anaerobic threshold has been reached. This was demonstrated in graphical form.
Dr Wilson then described the relationship between age and anaerobic threshold. In patients in their early 60s, the average AT was 11.4 and this fell with age and by the early 80s, the AT was on average 8.6. This meant that most patients over 75 years will have an AT<11. He then described some, as yet unpublished, data on a large series of patients tested in his unit of which 86% had then gone on to have surgery. The overall survival rate was significantly better than UK average rates. There was a significantly increased mortality in patients with an AT<11. The main mortality in patients with an AT >11 was surgical, usually anastomotic leak/breakdown. The AT was a highly significant predictor of operative mortality. The length of stay (LOS) data also correlated with AT with a significantly lower LOS in patients with an AT>11.
Dr Wilson talked about patient management, firstly in the high risk patient (AT<11) who had a pre-op arterial line, haemodynamic optimisation with starch, oesophageal Doppler monitoring (ODM) with or without dopexamine followed by post-operative care on HDU. In contrast low risk patients (AT>11) were optimised with the ODM using starch but managed on the ward post-operatively. He also described the algorithm for the management of abdominal aortic aneurysm repair.
A paper in the European Heart Journal (2003 24(14):1304-1313) was discussed to show the better results achieved by the addition of gas exchange analysis to improve the diagnostic accuracy of standard ECG stress testing in identifying exercise induced myocardial ischaemia by using oxygen pulse flattening. A case study was also discussed which showed that a small dose of bisoprolol significantly improved cardiac function in a 71 year old with an AT of 5.7. This improved to 8.5 by an increase in stroke volume and oxygen delivery shown by a reduction in oxygen pulse flattening.
Dr Wilson looked at patient self evaluation of fitness from a paper presented at the ASA in October 2007. This looked at the Duke Activity Status Index to estimate AT and then patients were measured. This showed that patients over-estimated their level of fitness. He then briefly looked at the patients with low ATs who had not undergone surgery. They were predominantly over 75 years and generally over time had a poorer outcome than those following surgery. Survival at 18 months in the operative and non–operative AAA patients was similar but then the non-operative survival rates dropped away.
In conclusion, Dr Wilson stated that from the CEPOD report, 60-70% of patients that die after surgery, have significant cardio-respiratory disease. Cardiopulmonary exercise testing evaluates cardiac reserve, identifies cardiac abnormalities, helps evaluate pre-op treatments and more objectively evaluates the level of peri-operative care required. Finally it can help the anaesthetist to say no.
There were 5 minutes for questions before Dr Santokh Singh gave the vote of thanks. The meeting finished at 20:15.