ANESTHESIA FOR PATIENTS WITH OBSTRUCTIVE PULMONARY DISEASE
Certain risk factors may predispose patients to postoperative pulmonary complications. Atelectasis, pneumonia, pulmonary embolism, and respiratory failure are common following surgery, but the incidence varies widely, depending on the patient population studied and the surgical procedures performed. In the abdominal surgery population, the incidence of postoperative pulmonary complications ranges from 2% to 6%. The two strongest predictors of complications are the operative site and a history of dyspnea, the latter of which correlates with the degree of preexisting pulmonary disease.
The association between smoking and respiratory disease is well established; abnormalities in maximal midexpiratory flow (MMEF) rates are often demonstrable well before symptoms of COPD appear. Most smokers will not have pulmonary function tests (PFTs) performed preoperatively; therefore, it is best to assume that these patients have some degree of pulmonary compromise. In otherwise normal individuals, advanced age is associated with an increased prevalence of pulmonary disease and an increased closing capacity. Obesity per se does not increase the likelihood of postoperative pulmonary complications. However, obstructive sleep apnea does contribute to adverse perioperative outcomes.
Thoracic and upper abdominal surgical procedures can have marked effects on pulmonary function. Operations near the diaphragm often produce diaphragmatic dysfunction and a restrictive ventilatory defect. Upper abdominal procedures significantly (>30%) decrease functional residual capacity (FRC). This effect is maximal on the first postoperative day and usually persists for 7–10 days. Rapid shallow breathing with an ineffective cough caused by pain (splinting), a decrease in the number of sigh breaths, and impaired mucociliary clearance leads to atelectasis and loss of lung volume. Subsequent ventilation–perfusion mismatch (shunt) produces hypoxemia. Residual anesthetic effects, recumbent position, sedation from opioids, abdominal distention, and restrictive dressings are also contributory. Complete relief of pain with regional anesthesia can decrease, but usually does not completely reverse, these abnormalities. Persistent atelectasis and retention of secretions promote the development of postoperative pneumonia.
When patients with a history of dyspnea present without the benefit of a previous workup, the differential diagnosis can be quite broad and may include both primary pulmonary and cardiac pathologies.
OBSTRUCTIVE PULMONARY DISEASE
Obstructive and restrictive diseases are the two most common abnormal patterns as determined by PFTs, and the former are by far more common. Obstructive diseases include asthma, emphysema, chronic bronchitis, cystic fibrosis, bronchiectasis, and bronchiolitis. The primary characteristic of these disorders is resistance to airflow. An MMEF of less than 70% (forced expiratory flow [FEF25–75%]) is often the only abnormality early in the course of these disorders. Values for FEF25–75% in men and women are normally greater than 2.0 L/s and 1.6 L/s, respectively. As the disease progresses, both forced expiratory volume in the first second of exhalation (FEV1) and the FEV1/FVC (forced vital capacity) ratio are less than 70% of the ...