FRCA Notes

Measure of Functional Capacity

The curriculum asks us to list 'methods of assessment of functional cardiorespiratory capacity'.

Resources

Objective methods for preoperative assessment of functional capacity (BJA Education, 2022)
Subjective methods for preoperative assessment of functional capacity (BJA Education, 2022)
Physiological relationship between cardiorespiratory fitness and fitness for surgery: a narrative review (BJA, 2022)
A simplified (modified) Duke Activity Status Index (M-DASI) to characterise functional capacity: a secondary analysis of the Measurement of Exercise Tolerance before Surgery (METS) study (BJA, 2020)
Risk assessment for major adverse cardiovascular events after noncardiac surgery using self-reported functional capacity: international prospective cohort study

Most subjective measures of functional capacity are poorly sensitive, so objective measurements should be used to aid quantify perioperative risk
Chief among these is cardiopulmonary exercise testing, which has its own dedicated page
Others include:

The Duke Activity Status Index (DASI)
The incremental shuttle walk test
The six minute walk test
The step test

The DASI is a questionnaire that requires the patient to indicate whether they can perform specific tasks

Score and Metabolic equivalents (METs)

The patient's answers to the DASI questionnaire provide information as to their functional capacity, measured in metabolic equivalents
The maximum score is 58.2 METs

1 MET = basal metabolic rate
1 MET approximates to a VO₂ of 3.5ml/kg/min

1 MET = eating, washing
3 METs = walking 100m (110yds) on flat ground at 2.5mph
4 METs = walking up one/two flight of stairs
8 METs = jogging
10 METs = strenuous sporting activities

The sum of the METs can be used to estimate an individuals peak oxygen uptake
Estimated VO₂ = 0.43 x (DASI + 9.6)
A total DASI score >34 ≈ VO₂ peak of 10ml/kg/min

DASI Score correlates well with peri-operative outcome
<4 METs is associated with an increased incidence of post-operative complications

The DASI is liable to bias if the completion of the questionnaire is inaccurate

A patient walks back and forth between two markers, 10m apart
The pace required is to the sound of a tone
The initial pace is 30m/min, which increases by 10m/min each minute thereafter
Patient continues until they are exhausted or unable to complete the 10m distance within the time

The outcome measured is total distance walked
There is a linear relationship between systemic VO₂ and walking distance
Peak VO₂ can be accurately predicted from the ISWT distance
A distance >400m correlates with a VO₂ peak of >15ml O₂/kg/min

Patient walks up-and-down a flat, 30m-length corridor for six minutes
Distance walked correlates with cardiac output and VO₂ peak
Median distance in healthy individuals is 500-600m
Mean survival better if can walk >332m
Overall a poor predictor of adverse post-operative outcomes

Patient step up and down on a 20cm step for 3 mins