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

Anaerobic Threshold

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

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).

Aim

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

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

CPET testing

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

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)

Open AAA repair

62 patients no morbidity 30 30 patients

Mean AT (SD) 11.7 (3.2) Median LOS (range) 11.0 (7 – 31)

with morbidity 32 30 day mortality 3 patients 29 patients

9.4 (3.5) 13.5 (8 – 39)

EVAR

No morbidity 53 patients With morbidity 42 patients

Mean AT (SD) Median LOS (range) 11.2 (3.3) 4.0 (3 – 10)

11 patients

10.5 (1.8) 11.0 (5 – 21)

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)

Open AAA

Number patients AT ≥ 11.1

24*

AT < 11.1

26*

Incidence morbidity

7/24 = 29.1%

LOS (median)

10 days 17/26 = 65.4% 13 days * = AT not achieved, unreadable or data missing for some patients, therefore not included in analysis.

EVAR

Number patients Incidence morbidity LOS (median)

AT ≥ 11.1

20* 4/20 = 20% 4 days

AT < 11.1

26* 6/26 = 23% 5 days * = AT not achieved, unreadable or data missing for some patients, therefore not included in analysis.

AT and post-operative adverse events

70 60 50 40 30 20 10 0 AT <11.1

AT >11.1

open AAA AT <11.1

EVAR AT >11.1

morbidity % LOS (days)

Discussion

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

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

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.



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

Any questions?