How can we assess a patient’s fitness for surgery?

Surgery places a person’s body under physiological stress: the magnitude of the stress response is proportional to the severity of the surgical trauma. The surgical stress response increases an individual’s O₂ consumption (V̇O₂). Patients who are less physiologically fit will be less able to increase their O₂ delivery and may therefore be unable to match the increase in V̇O₂. Respiratory and cardiovascular co-morbidities place a major limitation on the cardiovascular response to major surgery, but physical deconditioning also plays a significant role.

When a patient is assessed for a surgical procedure, a number of factors must be considered:

• 
  

  The invasiveness and surgical difficulty of the proposed surgical procedure;

  
  
• 
  

  The patient’s co-morbidities, which may be previously known or newly diagnosed, and may be well controlled, poorly controlled or uncontrolled;

  
  
• 
  

  The patient’s physical fitness, which may be quantified using exercise testing.

Ultimately, the aim of the preoperative assessment process is to identify those individuals at significant risk of perioperative complications in order to:

• 
  

  Better inform the patient of their individual risk so as to help them with their decision-making.

  
  
• 
  

  Inform decision-making by the multidisciplinary team; for example, an alternative, less invasive surgical procedure may instead be offered to a patient (e.g. endovascular aortic aneurysm repair in place of open repair).

  
  
• 
  

  Plan post-operative care; for example, a high-dependency bed may be required.

How can you clinically assess exercise capacity?

Exercise capacity can be assessed by asking the patient a series of questions relating to their everyday activities, such as ‘How far can you walk on the flat?’ or ‘How many stairs can you climb without stopping?’ The problem is that these questions are very subjective, and patients often overestimate their exercise tolerance.

Are there any more objective methods of assessing exercise capacity?

There are a number of more objective methods available:

• 
  

  Questionnaire based, such as the Duke Activity Status Index (DASI). DASI is a 12-question self-assessment in which patients are asked about whether they can complete certain physical tasks. Each task is weighted according to its metabolic cost (in metabolic equivalents, METs). A patient who is unable to complete physical tasks of at least 4 METs is at higher risk of perioperative complications.

  
  
• 
  

  Incremental shuttle walk test, in which patients are asked to walk continuously between two cones set 9 m apart, with a progressively decreasing time permitted to reach the next cone. Patients who are unable to walk at least 250 m are at increased perioperative risk of complications. While this test is cheap and easy to carry out, there are groups of patients who may be unable to perform a walk test: lower limb amputees, those with peripheral vascular disease or those with hip or knee osteoarthritis.

  
  
• 
  

  Cardiopulmonary exercise testing (CPET), which is considered the gold-standard exercise test. During a CPET test, the patient’s expired gases are measured whilst the patient carries out a continually increasing amount of work on an electromagnetically braked cycle ergometer. Over 5000 measurements are taken during the 10‑minute test, including:

  
  
  
  
  1. 
     

     – The work rate (in Watts);

     
     
  2. 
     

     – Metabolic gas exchange measurements: V̇O₂, CO₂ production (V̇CO₂) and respiratory exchange ratio (=V̇CO₂/V̇O₂).

     
     
  3. 
     

     – Ventilatory measurements: oxygen saturations, V̇_E, V_T, respiratory rate, ventilatory equivalents for O₂ (V̇_E/V̇O₂) and CO₂ (V̇_E/V̇CO₂).

     
     
  4. 
     

     – Cardiovascular parameters: heart rate, electrocardiogram (ECG) ST-segment changes and non-invasive blood pressure.

  The data points are graphically represented in a standard format, known as the nine-panel plot. Two important values can be determined through analysis of CPET data:
  
  
  
  1. 
     

     – Anaerobic threshold (AT), the V̇O₂ above which aerobic metabolism is supplemented by anaerobic metabolism. An AT < 10.2 mL kg^–1 min^–1 is associated with a greater risk of perioperative complications.

     
     
  2. 
     

     – Peak oxygen consumption (V̇O_{2 peak}), the maximum V̇O₂ achieved by the patient in the test. ‘Normal’ V̇O_{2 peak} measurements are typically 25–40 mL kg^–1 min^–1; V̇O_{2 peak} < 15 mL kg^–1 min^–1 is associated with a higher risk of perioperative complications.

  
  

One of the advantages of CPET is that useful data can often be obtained for individuals who cannot complete other exercise testing due to diseases such as peripheral vascular disease.