Lateral Decubitus Position/Closed Chest

Perfusion (Q) of the nonoperative lung is greater than the operative lung because of the effects of gravity on the pulmonary circulation. The converse applies for the distribution of ventilation (V) between the lungs during invasive positive pressure ventilation. The resultant changes in ventilation and perfusion cause V/Q mismatch and shunt. The operative lung is well ventilated and poorly perfused, causing V/Q mismatch. Subsequently, the nonoperative lung is poorly ventilated and well perfused, leading to shunt. Additional challenges and further V/Q mismatch present when the operative lung is collapsed intraoperatively.

Lateral Decubitus Position/Open Chest

When the chest wall is open, compliance of the operative lung increases because it is less restricted by the chest wall. The increased compliance leads to further increases in the amount of ventilation directed to the operative lung and away from the nonoperative lung, which can lead to worsening V/Q mismatch. Under normal circumstances, the distribution of perfusion is not greatly affected by the opening of the chest. If there is a large increase in the compliance and subsequent decrease in airway pressure of the operative lung, however, perfusion to the operative lung may increase, improving shunt.

One Lung Ventilation

When ventilation to the operative lung ceases, an obligatory shunt of 20% to 30% is created, because perfusion to the operative lung persists. This leads to a reduction in Pa o ₂ . The major determinants of blood flow to the operative lung include gravity, underlying lung disease, surgical interference including clamping of the pulmonary artery, and hypoxic pulmonary vasoconstriction (HPV).

In the nonoperative lung, blood flow is determined by gravity, underlying lung disease, ventilation strategies, and HPV. The mode of ventilation is an important consideration; a reduction in tidal volume during 1 lung ventilation can result in atelectasis and increased shunt. Hyperventilation of the nonoperative lung may inhibit HPV, resulting in blood diversion to poorly oxygenated areas. Excessively high airway pressures result in an increase in pulmonary vascular resistance of the ventilated lung, leading to diversion of blood to the nonventilated lung.

Hypoxic Pulmonary Vasoconstriction

HPV maintains arterial oxygenation by diverting blood flow away from poorly ventilated areas of lung. Typically, this occurs in areas of atelectasis or low V/Q ratio. HPV may be inhibited by vasodilatory medications, such as nitroprusside, nitroglycerine, calcium channel blockers, and ß ₂ -agonists. The HPV response is maximal at normal pulmonary artery pressures and decreases at both high and low pulmonary artery pressures. Both high and low Pv o ₂ conditions inhibit HPV. A low Pv o ₂ causes HPV to occur in normoxic alveoli, diverting flow away from those alveoli. This is why a reduction in cardiac output during 1 lung ventilation may result in severe hypoxemia. HPV also is inhibited by hypocapnia and enhanced by hypercapnia.

Age

There is no upper age limit when considering lung resection surgery. Physiologic age is a better predictor of outcomes than chronologic age. Operative mortality rates related to surgical intervention in patients aged 80 years to 90 years are approximately 1.4% and long-term outcomes appear satisfactory; however, patient comorbidities and mediastinal lymph node dissection have been identified as factors that increase the risk of postoperative complications in this population.

Cough

Cough can be suggestive of pulmonary or cardiac disease. Elevated pulmonary artery pressures leading to interstitial and alveolar edema indicate cardiac etiology. Cough with expectoration for months and years commonly occurs in chronic obstructive pulmonary disease (COPD) or bronchitis. Initial assessment must be tailored to recognize triggers, such as medications, environmental factors, smoking, and COPD. Infectious etiology must be considered.

Dyspnea

Dyspnea also is a common symptom of lung and cardiac disease. When dyspnea is combined with cough or sputum, it most often is due to pulmonary disease. Inspiratory dyspnea suggests obstruction of the upper airway whereas expiratory dyspnea is more indicative of lower airway obstruction. Paroxysmal nocturnal dyspnea develops due to interstitial and interalveolar edema. If a cough develops before paroxysmal nocturnal dyspnea, it most likely is related to chronic pulmonary disease; however, if cough develops after symptoms of dyspnea, it likely is due to left ventricular failure.

Tobacco Use

Smoking status is a risk factor for developing several postoperative complications, including respiratory failure, intensive care unit admission, pneumonia, and wound infection, among others. Abstinence from cigarette smoking can improve perioperative outcomes and decrease the risk of cardiovascular and respiratory complications, although the necessary duration of abstinence to achieve this risk reduction is debated. Smoking cessation 12 hours to 48 hours prior to surgery reduces carboxyhemoglobin levels in the blood and shifts the oxyhemoglobin dissociation curve to increase oxygen-carrying capacity. Smoking cessation for approximately 2 weeks improves ciliary function and reduces bronchial secretions. Cessation for 4 weeks to 8 weeks before surgery decreases postoperative pulmonary complications considerably. The benefits of nicotine replacement therapies in abstaining smokers seem to outweigh the risks of continued smoking.

Chronic Obstructive Pulmonary Disease

COPD is the most common comorbid condition in patients presenting for thoracic surgery. It is characterized by a reduction in airflow that is not fully reversible. The severity of COPD is classified based on spirometry findings and correlates with an increasing risk of postoperative pulmonary complications as airflow limitation increases. Patients with severe COPD often have concomitant right ventricular dysfunction and cor pulmonale. These patients pose unique challenges during intraoperative management, particularly during 1 lung ventilation for both surgeons and anesthesiologists.

Lung Cancer

Lung cancer is the leading cause of cancer death for both men and women in the United States. Resectability of the cancer refers to whether or not a tumor can be resected completely based on anatomic location. Operability takes into account the functional status of the patient and characterizes a patient’s ability to tolerate the procedure.

Hypertension

Systemic hypertension is a known risk factor for postoperative cardiovascular complications. Preoperative evaluation should aim to rule out secondary causes for hypertension, such as renal artery stenosis and pheochromocytoma. It should evaluate the severity of the disease, which requires multiple blood pressure readings on separate occasions. It also should identify evidence of target organ involvement. Examples of target organ involvement may include coronary disease, cerebrovascular disease, impaired renal function, and signs of left ventricular hypertrophy or heart failure. Patients who have severe hypertension or moderate hypertension with target organ involvement should have their blood pressure controlled before surgery. Surgery should not be deferred, however, on the basis of a single elevated blood pressure reading in the preoperative period, except for grade 3 hypertension. A patient’s antihypertensive medications should be continued during the perioperative period, with the exception of angiotensin-converting enzyme inhibitors and angiotensin receptor blockers, which can cause profound and prolonged systemic hypotension during general anesthesia. ^,

Diabetes Mellitus

Diabetes mellitus has an impact on multiple organ systems. The disease presents increased risks for perioperative complications including myocardial infarction, stroke, limb ischemia, pressure sores, wound infection, and more. Preoperative evaluation should assess compliance with medications and symptoms of autonomic dysfunction. Blood glucose levels should be within normal limits before surgery. It is typical to discontinue long-acting oral hypoglycemic agents on the day of surgery yet continue insulin regimens the evening before. Type 1 diabetics mellitus should have basal insulin pumps continued to prevent diabetic ketoacidosis.

Airway Assessment

Airway assessment is an essential part of the preoperative evaluation of any surgical patient. The aim is to predict potential difficulties with mask ventilation and endotracheal intubation based on a patient’s physical features and to develop a management plan accordingly. This is important especially for placement of double-lumen endotracheal tubes, which technically can be more challenging than single-lumen tubes. Anatomic features with airway implications include Mallampati score, ability to open the mouth, thyromental distance, neck mobility, and neck circumference.

Lung Examination

Respiratory rate, regularity, and depth and effort of breathing should be observed. Restrictive lung disease is characterized by rapid shallow respirations, whereas obstructive disease features slow deep respirations. Asymmetric chest movement can occur due to phrenic nerve pathology, pneumothorax, or pleural effusion. On percussion, hyperresonance is indicative of emphysema or pneumothorax. Dullness suggests pleural effusion, atelectasis, or pneumonia. On auscultation of the lungs, prolonged expiration, expiratory wheezes, and rhonchi are indicative of obstructive lung disease. Absent breath sounds may indicate pleural effusion or atelectasis. Bronchial breath sounds are suggestive of pneumonia.

Complete Blood Cell Count and Metabolic Studies

Complete blood cell count may reveal polycythemia caused by chronic tobacco use. Liver function tests may be abnormal due to metastatic lung cancer. Elevations in calcium may be due to bone metastasis or a paraneoplastic syndrome associated with tumor. Syndrome of inappropriate antidiuretic hormone may occur in squamous cell lung cancer and may cause hyponatremia. Elevated alkaline phosphatase may be a result of liver or bone metastasis.

Chest Radiography

A baseline chest radiograph often is included in the assessment of patients presenting for thoracic surgery. Important radiographic findings with perioperative implications include tracheal deviation or obstruction, pleural effusion implying diminished vital capacity and functional residual capacity, bullous lung disease at risk of rupture from positive pressure ventilation, cavitation with air fluid levels suggesting infectious process, and alveolar or interstitial infiltrates that contribute to V/Q mismatch and shunt.

Chest Computed Tomography

It is routine for lung cancer patients to have a computed tomography (CT) scan of the chest to determine anatomy of the tumor, nodal involvement, and metastatic spread. Thus, CT scan has a role in evaluation and staging of lung cancer, helping to decide on management strategy and operative approach. The limitation of CT scan is the reduced precision for recognizing mediastinal lymph node metastasis compared with PET-CT scan.

Electrocardiogram

The simplicity of electrocardiogram and its capability to provide details of the electrical functions of the heart makes it important in assessment of patients with cardiothoracic pathology. New-onset arrhythmias, such as atrial fibrillation or left bundle branch block, should be investigated further prior to surgery. Evidence of left ventricular hypertrophy in a patient with systemic hypertension may indicate target organ involvement and necessitate preoperative blood pressure optimization.

Arterial Blood Gas

Arterial blood gas analysis can be performed on patients who are considered for lung resection, although this test is not required preoperatively. Baseline oxygenation and ventilation values can aid in intraoperative ventilator management and postoperative care of the thoracic surgery patient; however, arterial P o ₂ and P co ₂ have not been shown to predict postoperative complication rates accurately.

Spirometry

Measured forced expiratory volume in 1 second (FEV ₁ ) is an essential assessment tool when evaluating a patient for thoracic surgery. FEV ₁ predicts the degree of respiratory impairment in patients with COPD. Patients with a preoperative FEV ₁ greater than 80% predicted often can tolerate pneumonectomy and with greater than 70% predicted can tolerate lobectomy. A preoperative FEV ₁ less than 60% predicted is a strong indicator of postoperative respiratory complications and 30-day mortality.

Diffusing capacity of carbon monoxide (DLCO) can determine the presence of emphysematous changes in lung tissue. Preoperative DLCO has been shown to significantly predict mortality and postoperative pulmonary complications after lung resection. DLCO values less than 60% are considered inappropriate for major lung resections whereas DLCO greater than 70% is associated with decreased postoperative complication rates.

Predicted Postoperative Lung Function

Predicted postoperative (PPO) lung function studies determine the contribution of the segment of the lung to be resected to a patient’s overall lung function, thereby allowing for a prediction of the patient’s postoperative pulmonary function status. These studies were first described in the 1970s and are used routinely today. Quantitative radionuclide perfusion lung scanning is recommended to determine PPO FEV ₁ and PPO DLCO for patients requiring pneumonectomy. In patients undergoing lobectomy, however, the anatomic method of segmental counting can be used.

PPO FEV ₁ and PPO DLCO should be calculated in all patients whose baseline FEV ₁ and DLCO are less than 80% predicted. PPO FEV ₁ and PPO DLCO values greater than 60% indicate low risk of postoperative morbidity after major anatomic lung resection. PPO FEV ₁ and PPO DLCO values between 30% and 60% warrant a low-technology exercise test, such as stair climbing or 6-minute walk tests. The stair climbing test has been shown an adequate predictor of postoperative pulmonary and cardiac complications and is both safe and economical; however, standardizing the test has been challenging.

Cardiopulmonary Exercise Testing

Cardiopulmonary exercise testing (CPET) is used to evaluate for abnormalities in oxygen transport that may be masked at rest. CPET calculates maximal oxygen consumption (V o _2max ), an indicator of cardiorespiratory fitness, which can be used to predict a patient’s ability to tolerate certain thoracic surgical procedures. CPET is indicated when either the calculated PPO FEV ₁ or PPO DLCO is less than 30% predicted. A V o _2max greater than 20 mL/kg/min is preferred for patients undergoing pneumonectomy whereas V o ₂ max greater than 15 mL/kg/min may be acceptable for lobectomy. V o _2max less than 10 mL/kg/min indicates a high risk of mortality after major anatomic lung resection and necessitates the calculation of PPO V o _2max .