1. Does Anaerobic Threshold predict risk of peri-operative adverse events following Abdominal Aortic Aneurysm surgery? Dr Sian Davies SpR Anaesthetics James Cook University Hospital, Middlesbrough

2. Anaerobic Threshold Represents the oxygen consumption at which anaerobic metabolism begins to supplement aerobic pathways to generate energy.

3. Background Cardio-Pulmonary exercise testing (CPET) used to define anaerobic threshold (AT) levels to risk stratify patients Older (1999) – AT > 11 Low risk AT < 11 High risk Carlisle, Swart (2007) –mid-term survival correlated most closely with Ve/VCO 2 and AT to a lesser degree (open AAA repair).

4. Aim To investigate if AT values derived from our patient population undergoing AAA surgery (open or EVAR) define risk of adverse outcome.

5. Methods Patients who had undergone pre-op CPET and subsequent AAA repair were identified Surgical intervention, post-op morbidity + mortality, and length of stay (LOS) data were collected AT values established for all patients by a single blinded observer (V slope method) Statistical analysis – simple descriptive statistics and ROC analysis

6. CPET testing

7. Adverse event Cardiac –acute coronary syndrome, arrhythmia, LV dysfunction Respiratory – failure, infection Metabolic / Renal –need for dialysis or CVVH Surgical complications NOT included in analysis

8. Results 115 patients – 62 open repair 53 EVAR 30 day mortality: 2.6% (3/115) Mean AT = 10.3mlsO 2 /kg/min (sd 3.3)

9. Open AAA repair 62 patients no morbidity with morbidity 30 32 30 day mortality 3 patients 30 patients 29 patients Mean AT (SD) 11.7 (3.2) 9.4 (3.5) Median LOS (range) 11.0 (7 – 31) 13.5 (8 – 39)

10. EVAR 53 patients No morbidity With morbidity 42 patients 11 patients Mean AT (SD) 11.2 (3.3)10.5 (1.8) Median LOS (range) 4.0 (3 – 10)11.0 (5 – 21)

11. ROC analysis for open AAA AT cut off at 11.1mls/O 2 /kg/min Sensitivity 71% (low AT & morbidity) Specificity 62% (high AT &no morbidity)

12. Open AAA AT ≥ 11.1AT < 11.1 Number patients 24*26* Incidence morbidity 7/24 = 29.1% 17/26 = 65.4% LOS (median) 10 days13 days * = AT not achieved, unreadable or data missing for some patients, therefore not included in analysis.

13. EVAR AT ≥ 11.1 AT < 11.1 Number patients20* 26* Incidence morbidity 4/20 = 20% 6/26 = 23% LOS (median) 4 days5 days * = AT not achieved, unreadable or data missing for some patients, therefore not included in analysis.

15. Discussion Adverse outcome after both types of aneurysm repair was associated with lower mean AT and increased LOS

16. Discussion – open AAA Cut off for stratification between low and high risk is AT of 11.1mlsO 2 /kg/min in our patient population Consistent with previous work Reinforces AT values currently used to assess risk utilising CPET for open AAA patients

17. Discussion - EVAR Incidence of post-operative morbidity was low after EVAR Patients with low AT seemed to do well Further work based on larger patient numbers is needed to define the risk stratification of EVAR patients.

18. References Older P, Hall A, Hader R. Cardiopulmonary exercise testing as a screening test for perioperative management of major surgery in the elderly. Chest 1999. 116: 355 – 363 Carlisle J, Swart M. Mid-term survival after abdominal aortic aneurysm surgery predicted by cardiopulmonary exercise testing. British Journal of Surgery 2007. 94/8: 966 - 999

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