What is the best way to assess functional capacity before major surgery?

Assessment of functional capacity before major non-cardiac surgery: an international, prospective cohort study. Duminda N Wijeysundera et al. Lancet 2018

Unless you’re good at guessing, it’s not much use being a detective – Agatha Christie

Introduction

  • This study sought to compare the accuracy of pre-operative subjective assessment (METS) with cardiopulmonary exercise testing (CPET, the Duke Activity Index Score (DASI) questionnaire and pre-operative NT pro-BNP levels.
  • The prognostic accuracy of these values for predicting post-operative morbidity and mortality was also assessed.

Methods

  • An International, multi-centre, prospective cohort study conducted in 25 hospitals (Canada, UK, Australia and New Zealand).
  • Primary outcome = Death or myocardial infarction within 30 days after surgery
  • Secondary outcome = Death within one year after surgery
  • Other outcomes:
    • Death or myocardial injury within 30 days
    • Moderate or severe post-operative complications defined by the Clavien-Dindo classification
  • Inclusion criteria were patients >40 years of age undergoing elective non-cardiac surgery (with an anticipated overnight stay or longer) with at least one risk factor for cardiac complications.
  • Exclusion criteria included; planned endovascular approach, pregnancy, cardiac conditions or absolute contraindications to CPET.
  • All patients recruited underwent pre-operative subjective functional assessment (by an anaesthetist), DASI questionnaire, CPET and NT Pro-BNP measured. Anaesthetist s blinded to these results (except whereby adverse events during CPET warranted unmasking eg. arrhythmia).
  • Patients were assessed with daily ECG and Troponin until day 3 post-operatively. Further follow up was conducted at 30 days and 1 year.

Results

  • 6548 met inclusion criteria with 1741 consenting to participate.
  • 1401 underwent both surgery and CPET and were included in analysis.
  • Subjective assessment of functional capacity had a sensitivity of 19.2% for identifying peak oxygen consumption of less than 14 mL/kg per min and a specificity was 94·7%.
  • Peak oxygen consumption was positively correlated with DASI scores (p<00001), and negatively correlated with NT pro­BNP concentrations (p<0·0001).
  • Subjectively assessed preoperative functional capacity had no significant adjusted association with the four main study outcomes.
  • DASI scores were associated with the primary outcome (OR 0.91 CI 0.83-0.99) and 30-day death or myocardial injury (OR 0.96 CI 0.92-0.99)
  • NT Pro-BNP was associated with 30-day death or myocardial injury (OR 1.78 CI 1.21-2.62) and 1-year death (OR 2.91 CI 1.54-5.49).
  • Peak oxygen consumption was associated with in-hospital moderate or severe complications (OR 0.86 CI 0.78-0.97).

Discussion 

  • Only 27% of patients approached consented to the study. Those that did consent may be a skewed cohort of patients ie. those willing to undergo pre-operative CPET for the purpose of the study.
  • Study did not adequately explain what happened to patients who were deemed unfit for surgery based on subjective assessment.
  • The sample size was based on a 5% primary outcome event rate. The actual event rate only 2% meaning the study was underpowered for this.
  • No adjustments were made for multiple testing.
  • Subjective assessment may influence complication rates in terms of minimising post-operative risks through augmentation of anaesthetic conduct. An effect that cannot be measured.
  • The author’s state that functional assessment should not be used for peri-operative risk evaluation. However, CPET failed also failed to predict MI, myocardial injury or death.
  • CPET did predict moderate to severe post-operative complications based on the Clavien-Dindo classification.
  • DASI scores proved a useful predictor of cardiac complications and are easily implemented.

Change to clinical practice?

  • Greater use of the DASI for pre-operative risk prediction should be considered.
  • Additionally pre-operative NT Pro-BNP should be considered for prediction of post-operative cardiac complications.

Summary by Dr Sam Curtis

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