Does Anaerobic Threshold predict risk of peri-operative adverse events following Abdominal Aortic Aneurysm surgery?

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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

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Anaerobic Threshold

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

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Background

• Cardio-Pulmonary exercise testing (CPET) used to
  define anaerobic threshold (AT) levels to risk
  stratify patients
• Older (1999) AT gt 11 Low risk
• AT lt 11 High risk
• Carlisle, Swart (2007) mid-term survival
  correlated most closely with Ve/VCO2 and AT to a
  lesser degree (open AAA repair).

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Aim

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

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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

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CPET testing
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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

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Results

• 115 patients 62 open repair
• 53 EVAR
• 30 day mortality 2.6 (3/115)
• Mean AT 10.3mlsO2/kg/min (sd 3.3)

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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)

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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)

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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)

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Open AAA

• AT 11.1 AT lt 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.

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EVAR

• AT 11.1 AT lt 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.

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Discussion

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

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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

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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.

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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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Any questions?