Functional Capacity
Rationale
Evaluation of functional capacity is integral to preoperative risk assessment and a fundamental prerequisite for safe perioperative care. This can inform decisions regarding patient optimisation, or the need for an ICU bed post-operatively.
Objective functional capacity assessments are required to support preoperative risk stratification, as subjective assessments have been shown to be less accurate at identifying those with poor cardiopulmonary fitness or predicting postoperative complications1.
Methods of assessing functional capcity
There are many ways this can be done. Some give detailed physiological detail, some can be based on patient history. Methods include:
- Duke Activity Status Index (DASI)2
- 6-minute walk test (6MWT)
- Exercise ECG and pharmacological stress testing
- Perioperative cardiac biomarker screening
- Cardiopulmonary Exercise Testing (CPET)
Of these tests, only the first (the DASI) is suitable for routine use in the Pre-Operative Assessment Clinic (POAC). It can be conducted through questioning a patient, and shows correlation with biophysical measures such as the 6MWT.
The Duke Activity Status Index (DASI)
This consists of a series of questions that are asked about progressively more intense forms of physical activity. The key is determining if the activities can be performed without being limited by breathlessness or chest discomfort (i.e. joint pain is not a ‘valid’ limiting factor). This scale has significant correlation with peak oxygen uptake by the patient, and therefore acts as a valid surrogate for more invasive tests.
In the POAC setting, it’s use is in screening a patient to determine
- if they need more testing of the cardiorespiratory system
- if they need undergo a more detailed review by a consultant anaesthesiologist
- if a postoperative stay in the ICU may be required
The result of this is a measure of the patients maximum sustained exercise tolerance through the use of metabolic equivalents of task (METs). 1 MET is the resting O2 consumption of 3.5mL/kg/min for a 40-year-old man. It has been shown that if a person cannot achieve maximum METS > 4 they have poor functional capacity3, and are at greater risk for cardiac complications or death in the post-operative period4.
It is these patients (with METs < 4 or whose METs have inexplicably declined) that should be considered for further testing or enhanced post-operative care.
Online resources
The simplest way to ensure that the result has been correctly processed is to use a calculator, such as found at MDCalc.