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/VCO2 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 = 10.3mlsO2/kg/min (sd 3.3)

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)

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)

ROC analysis for open AAA

AT cut off at 11.1mls/O2/kg/min

Sensitivity 71% (low AT & morbidity)

Specificity 62% (high AT &no morbidity)

Open AAA

AT ≥ 11.1 AT < 11.1

Number patients 24* 26*

Incidence morbidity 7/24 = 29.1% 17/26 = 65.4%

LOS (median) 10 days 13 days

* = AT not achieved, unreadable or data missing for some patients, therefore not included in analysis.

EVAR

AT ≥ 11.1 AT < 11.1

Number patients 20* 26*

Incidence morbidity 4/20 = 20% 6/26 = 23%

LOS (median) 4 days 5 days

* = AT not achieved, unreadable or data missing for some patients, therefore not included in analysis.

AT and post-operative adverse events

0

10

20

30

40

50

60

70

AT <11.1 AT >11.1 AT <11.1 AT >11.1

open AAA EVAR

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 11.1mlsO2/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?