Describe the anesthetic evaluation before lung resection.
Preoperative evaluations begin with basic information required before all anesthetics. A determination is then made as to whether the patient is in optimal condition for the planned procedure or whether further preoperative preparation is indicated. Finally, an assessment is formu-lated to predict lung function following resection. The specific pulmonary evaluation will include history of cough, sputum production, chest pain (possibly pleuritic), dyspnea, wheezing, arm pain (resulting from Pancoast tumor involving the brachial plexus), weakness (resulting from myasthenic syndrome), other endocrine syndromes (caused by tumors secreting hormones), and weight loss (hypoproteinemia). Physical examination includes auscul-tation for wheezing, rales, and rhonchi. Wheezing may require treatment with bronchodilators, and infected sputum indicates antibiotic treatment. Chest radiograph, tomography, computed tomography (CT), and magnetic resonance imaging (MRI) provide further information on the tumor site, structures involved, and possible airway compromise.
Lung function tests are indicated to predict the risk of respiratory failure, right heart failure (cor pulmonale), or atelectasis, as well as to guide bronchodilator therapy. Spirometry is a noninvasive test that provides data on lung volumes and gas flow rates. Flows are tested without, and then following bronchodilator therapy, such as albuterol by inhaler, to determine reversible obstructive airway disease. Improved flows following bronchodilator therapy indicate preoperative adjustments in the bronchodilator regimen.
Pulmonary function tests that may correlate with out-come include forced expiratory volume in 1 second (FEV1), forced vital capacity (FVC), maximum voluntary ventila-tion (MVV), and ratio of residual volume to total lung capacity (RV/TLC). Based on how much lung tissue is to be resected, a predicted postoperative (PPO) function can be calculated. A PPO FEV1 greater than 40% predicted has been correlated with improved outcome. An FVC less than 50% predicted, or RV/TLC greater than 50% predicted may indicate higher risk.
Whereas spirometry reflects respiratory mechanics, gas exchange correlates with diffusing capacity for carbon monoxide (DLCO). A PPO DLCO less than 40% predicted indicates reduced lung parenchymal function, and corre-lates with increased risk.
Cardiopulmonary reserve can be evaluated by measuring the maximal oxygen consumption (VO2max). A VO2max less than 10 mL/kg/min indicates very high risk, and a VO2max greater than 20 mL/kg/min indicates reduced risk. Other tests of cardiopulmonary reserve include exercise oximetry, and a fall in oxygen saturation by pulse oximetry (SpO2) of 4% during exercise may indicate increased risk.
If lung function results are poor, split lung function testing (ventilation–perfusion radiospirometric studies) and even unilateral pulmonary artery occlusion studies (to temporarily exclude blood flow to the ipsilateral lung) may be indicated. Ultimately, the operative decision to perform pneumonectomy versus lobectomy versus wedge resection is a clinical one in which the patient’s overall condition is considered.