Hong Kong Respiratory Medicine

Dr. Miranda Yung, Respiratory Medical Department, Kowloon Hospital, Oct 2009
Lung cancer is amongst the top leading causes of death from cancer in the world. Surgical resection remains the only curative therapy for patients with localized non-small cell lung cancer. Commonly performed operations include pneumonectomy and lobectomy. Incidence of complications varies, depending on the extent of resection, the pulmonary reserve and the presence of any comorbid conditions in the patients. The aim of preoperative pulmonary assessment is to identify patients who are at increased risk of having peri-operative complications and long-term disability from surgical resection of lung cancer using the least invasive tests available.

Initial evaluation
Before taking the patient to surgery, a detailed medical history including the presence of any coexisting disease, smoking history, and patient’s functional capacity should be sought1.

Pulmonary-specific evaluation
Spirometry
The forced expiratory volume in one second (FEV1) is regarded as being the best spirometric value for predicting complications of lung resection. Guidelines from he American College of Chest Physicians and the British Thoracic Society suggest that patients with a preoperative FEV1 greater than 2L (or >80% predicted) generally tolerate pneumonectomy. Those with a preoperative FEV1 in excess of 1.5L tolerate lobectomy2,3.

Diffusion capacity
DLCO can reflect the alveolar membrane integrity and the pulmonary capillary blood flow inside the lungs. In a retrospective study by Ferguson et al4, DLCO was found to be the most important predictor of mortality and postoperative pulmonary complications. If the patient has undue dyspnoea on exertion or interstitial lung disease, despite having an adequate FEV1, measuring DLCO is still recommended3. Patients with preoperative results for FEV1 and DLCO both >80% predicted do not need further physiological testing.
Arterial blood gas measurement
Resting arterial PO2 is probably not an important predictor of postoperative complications following lung resection. Hypercapnia (arterial PCO2 >45mmHg) is traditionally considered a significant risk factor for pulmonary resection5. However, this hypothesis has never been proven by studies, which showed no difference in postoperative complications between patients with a preoperative PCO2 less than and those higher than 45mmHg6,7. Thus, hypercapnia per se is not a contraindication to surgery.

Predicted postoperative pulmonary function
In patients with a preoperative FEV1 or DLCO <80% predicted, predicted postoperative lung function (PPO) may be calculated by estimating the amount of functioning lung tissue lost with the surgical resection. Methods include segment method, ventilation & perfusion scans and quantitative-CT scans.

Segment Method
There are altogether 19 segments in the whole lung, with 10 segments in the right and 9 segments in the left lung 8. Postoperative FEV1 = Preoperative FEV1 x
No. of pulmonary segments remaining after resection  total no. of segments in the whole lung. The anatomic method is recommended to estimate lung function after a lobectomy9. However, it tends to underestimate actual postoperative FEV1 values after pneumonectomy.
Radionuclide perfusion scan method
It is the preferred method to estimate the PPO FEV1 and DLCO after pneumonectomy10. The percentage of radioactivity contributed by each lung correlates with the contribution of function of that lung. Normally, the right lung contributes 55% and the left lung contributes 45% of lung function1.
Using the following formula from Kristersson et al11, Postoperative FEV1 = preoperative FEV1 x % of radioactivity contributed by non-operated lung. A predicted postoperative FEV1 >40% of the predicted normal value was associated with no postoperative mortality, whereas a value <40% predicted was associated with 50% mortality12. High mortality and morbidity were also associated with a predicted postoperative DLCO <40% predicted.

Exercise testing
Patients with a low predicted postoperative FEV1 are considered to be at high risk for lung resection surgery and need further workup. This can be verified by means of exercise testing. Exercise testing can be of several forms, ranging from simple stair climbing to complete cardiopulmonary exercise testing.

Stair climbing
Stair climbing test has been recently found to be a reliable predictor of postoperative complications and mortality following lung resection13,14. It was found to correlate well with lung function. A patient who was able to climb 3 flights of stairs was considered to be a suitable candidate for lobectomy. Pneumonectomy candidates were expected to climb 5 flights of stairs3. In a prospective series of 640 lobectomy and pneumonectomy candidates, patients climbing less than 12 meters were associated with increased morbidity, mortality and costs compared with those climbing to 22 meters15.

Desaturation
In addition to the altitude reached at stair climbing test, the presence of an exercise oxygen desaturation greater than 4% was a strong predictor of adverse outcome16.

Cardiopulmonary exercise testing (CPET)
Guidelines2,9 have recommended the use of CPET in preoperative risk assessment in those patients with either predicted postoperative FEV1 or DLCO <40%. The most important measurement that correlates with postoperative complications is the level of work achieved, as measured by maximum oxygen consumption (VO2max). Patients who achieve a VO2max >15ml/kg/min can undergo surgery with an acceptable rate of postoperative complications. Those with a value <10ml/kg/min indicates an increased risk for perioperative death and cardiopulmonary complications and should be managed by non-surgical modalities3.

References
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