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Surgery can influence the patient’s pulmonary function. Pul-monary complications of surgery are common, costly, and increase morbidity and mortality in both the near term and the long term. The preoperative assessment of lung function and optimization of the management of preexisting lung conditions can improve outcomes. This chapter discusses surgery-related changes in pulmonary physiology, the impact of common post-operative pulmonary complications, risk factors for these com-plications, and recommendations for preoperative pulmonary assessment and management, including those related to the evaluation of the lung resection candidate.

PULMONARY PHYSIOLOGY

During and after surgery, ventilation, ventilation-perfusion matching, and airway clearance are altered by many mecha-nisms. The mechanisms responsible and the degree of impair-ment are influenced by the type of surgery and the patient’s underlying health. The following is a general description of potential physiologic changes related to surgery.

Ventilation The supine position leads to decreases in all lung volumes, except tidal volume, because of the loss of the mechanical advantage provided by gravity. General anesthesia can worsen the restrictive defect in part through respiratory muscle relaxation and a shift of the balancing recoil forces of the lung and chest wall. Lung and chest wall mechanics are altered by surgery, particularly sternotomy, thoracotomy, and upper abdominal procedures. Diaphragm dysfunction and basal atelectasis may persist long after surgery. The residual effects of anesthesia can impair ventilatory drive in the immediate postoperative period. Shallow breathing related to pain and the effects of opiate use also contribute. In combination, functional residual capacity (FRC) can fall up to 50% for as long as 1 week in high-risk patients undergoing high-risk procedures.

Ventilation-Perfusion Matching The reduction in FRC can be significant enough to result in atelectatic areas of the lung. Decreases in mucociliary clearance and the cough reflex secondary to anesthetic and opiate use and shallow breathing as a result of pain further contribute to the development of atelectasis. In atelectatic areas of the lung, ideal ventilation-perfusion matching shifts toward shunting where blood flow continues but ventilation is reduced or absent. This effect can be magnified by volatile anesthetic agents that influence hypoxic vasoconstriction. The end result of these changes is postoperative hypoxemia. Anemia and increased oxygen consumption may also contribute to observed oxygenation problems.

Airway Clearance Many of these mechanisms impair the postoperative patient’s ability to clear their airways of mucus. Respiratory muscle dysfunction, atelectasis, pain, and medica-tion use, resulting in a decreased cough reflex or decreased mucociliary clearance, are contributing factors.

POSTOPERATIVE PULMONARY COMPLICATIONS

The frequency of postoperative pulmonary complications (PPCs) varies with type of surgery, the patient’s health, and the definition of the complication. Pulmonary complications of surgery are at least as common as cardiac complications and may result in prolonged hospital stays, increased morbidity and mortality, and increased costs (Table 73-1).

RISK FACTORS

The many risk factors for PPCs can be classified as patient or surgery related and assigned a simple rating based on the amount and quality of evidence available for support as a risk factor (Table 73-2).

Patient-Related FactorsIn several studies, chronic obstructive pulmonary disease (COPD) has been found to double the risk of PPCs. The degree of risk is directly related to the severity of obstruction. One study of patients after upper abdominal surgery found that those with decreased breath sounds or other adventitious sounds (e.g., wheezing, rales) had a sixfold increased rate of PPCs.

In contrast, well-controlled asthma has not been found to be a risk factor for PPCs. A large retrospective analysis found that rates of bronchospasm, laryngospasm, and respiratory failure in patients with well-controlled asthma were compa-rable to healthy individuals. Those with poorly controlled asthma (e.g., more frequent albuterol use, recent emergency department visit for asthma) do have an increased risk for PPCs.

Pulmonary hypertension (PH), primary and secondary, may be associated with increased rates of PPCs and in-hospital mortality. In one study, 21% of patients with PH developed respiratory failure versus 3% in matched controls after noncar-diac surgery.

A patient’s general health may be assessed by using the American Society of Anesthesiologists (ASA) classification system (Table 73-3). Studies have shown a direct correlation between a higher ASA class and increased pulmonary compli-cations. Patients with an ASA Class III or higher have a twofold to threefold increase in PPCs compared with those with ASA Class II or lower. Difficulty or inability to perform activities of daily living has also been linked to increased complications.

Chapter 73

Preoperative Pulmonary EvaluationHilary Petersen l Peter Mazzone

Section 14THORACIC SURGERY