Pre-Operative Assessment for Thoracic Surgery

The curriculum asks for knowledge of 'preoperative functional investigations of respiratory and cardio-respiratory performance' in thoracic surgery.

There hasn't been a SAQ/CRQ purely on this motif, but it is likely to form part of CRQs on thoracic surgery, or feature as stand-alone SBAs or SOE questions.

Resources

All thoracic surgery constitutes high risk surgery for the purposes of risk stratification

Lung cancer surgery is associated with greater impact on QoL than surgery for other disease states or cancers
Pneumonectomy is associated with poorer post-operative QoL than lobectomy

Appropriate pre-operative assessment is required to mitigate this risk where possible and inform shared decision making
There is, however, no one test capable of determining a patient's suitability for thoracic surgery and in general an MDT approach is required

Pre-operative risk assessment for pneumonectomy comprises of:

Estimating operative mortality
Assessing risk of perioperative cardiac events (see: Perioperative Cardiac Risk Assessment)
Assessing risk of post-operative dyspnoea

The Thoracoscore can be used to estimate post-operative mortality for patients undergoing thoracic surgery
However, it may have poor discriminative and predictive ability for mortality and post-operative pulmonary complications following elective lung resection
As such, assessment should be focussed more on patient's physiological reserve, including functional capacity

Evaluation of lung function establishes the impact of lung resection on quality of life with respect to post-resection dyspnoea

Dynamic lung volumes i.e. respiratory mechanics

In general;

Lobectomy requires a pre-operative FEV₁ >1.5L
Pneumonectomy requires a pre-operative FEV₁ >2L

The most valid test for post-thoracotomy respiratory complications is the predicted post-operative forced expiratory volume in 1 second (ppo-FEV₁)
It is calculated as:

ppo-FEV₁ = Pre-operative FEV₁ x % remaining lung

The percentrage of remaining lung is calculated as: (19 - number of bronchopulmonary segments to be resected)/19
A ppo-FEV₁ of <0.8L is generally considered high risk, although the ppo-FEV₁ described as a percentage is generally used instead:

% ppo-FEV₁ = ppo-FEV₁ x predicted FEV₁ for age|gender|height

Risk category	ppo-FEV₁
Low risk	>40%
Moderate risk	30-40%
High risk	<30%

One needs to establish the aetiology of abnormal preoperative values, as these may improve (e.g. resect a tumour obstructing a bronchial lumen) or not (COPD) after surgery

Quantitative ventilation/perfusion scintigraphy can also be used, to:

Establish how much each lobe is functionally active, as some to do not contribute greatly to pre-operative FEV₁
Help predict post-operative lung function in those with a % ppo-FEV₁ <40%

Other tests could include quantitative CT or dynamic perfusion MRI

Transfer factor (TL_CO) i.e. lung parenchymal function

Transfer factor (a.k.a diffusing capacity for carbon monoxide (DL_CO)) is a measure of the effectiveness of gas transfer at the alveoli

It is measured in mmol/kPa/min and expressed as percentage of predicted value
Its value correlates with the total functional surface area of the alveolar-capillary membrane
Transfer coefficient (K_CO) is transfer factor indexed to lung volume i.e. measured in mmol/kPa/min/litre

TL_CO is an important predictor for post-operative morbidity
The ppo-TL_CO can be calculated in a similar way to ppo-FEV₁, and patients risk stratified as either:

Risk category	ppo-TL_CO
Low risk	>40%
Moderate risk	30-40%
High risk	<30%

A reduced ppo-TL_CO is a predictor for post-operative morbidity, even if ppo-FEV₁ and other spirometry is normal

If either, or both, ppo-FEV₁ and ppo-TL_CO are <30%, it indicates a high risk of post-operative dyspnoea and need for long-term oxygen therapy

Cardiopulmonary fitness

Pulmonary function assessment alone is a poor predictor of patients' perceptions of physical disruptions to ADL's post-op
QoL after surgery may be more related to cardiopulmonary fitness

Exercise testing can be performed using CPET or other tests such as shuttle walk testing

A VO_{2 peak} <15ml O₂/kg/min is associated with increased post-operative complications
A VO_{2 peak} <10ml O₂/kg/min is generally regarded as a contraindication to pneumonectomy as it is associated with increased post-operative morbidity and mortality

Age

Although age alone is not a good indicator of fitness for surgery, an age >80yrs is associated with:

A 2x increased risk of respiratory complications (40%)
A 3x increased risk of cardiac complications inc. arrhythmias (40%)
Excessive mortality in those >70yrs (22%)

Respiratory

COPD

Patients with ppo-FEV₁ <40% should have a TTE to assess right heart function
Cor pulmonale will occur in 40% of those with an FEV₁ <1L and 70% of those with an FEV₁ <0.6L

Smoking; discontinue for 6 - 8 weeks prior to surgery

Pre-operative hypoxaemia e.g.

SpO₂ <90% at rest
SpO₂ decreasing >4% with exercise

Other

Cardiovascular comorbidities
Pre-existing renal impairment ± diuretic therapy
Weight loss >10% and/or low BMI
Low serum albumin

Low risk

Both ppo-FEV₁ and ppo-TL_CO are ≥40%

Moderate risk

Either ppo-FEV₁ and/or ppo-TL_CO are ≤40%
Good performance on functional capacity testing

→ risk of mild-moderate post-operative dyspnoea

High risk

Either ppo-FEV₁ and/or ppo-TL_CO are ≤40%
Moderate or poor performance on functional capacity testing

→ risk of severe post-operative dyspnoea and need for long-term oxygen therapy