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Chapter: Clinical Anesthesiology: Anesthetic Management: Anesthesia for Patients with Respiratory Disease

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Anesthesia : Chronic Intrinsic Pulmonary Disorders

Chronic intrinsic pulmonary disorders are also often referred to as interstitial lung diseases.

CHRONIC INTRINSIC PULMONARY DISORDERS

Chronic intrinsic pulmonary disorders are also often referred to as interstitial lung diseases. Regardless of etiology, the disease process is generally character-ized by an insidious onset, chronic inflammation of alveolar walls and perialveolar tissue, and progres-sive pulmonary fibrosis. The latter can eventually interfere with gas exchange and ventilatory func-tion. The inflammatory process may be primarily confined to the lungs or may be part of a generalized multiorgan process. Causes include hypersensitivity pneumonitis from occupational and environmentalpollutants, drug toxicity (bleomycin and nitrofu-rantoin), radiation pneumonitis, idiopathic pulmo-nary fibrosis, autoimmune diseases, and sarcoidosis. Chronic pulmonary aspiration, oxygen toxicity, and severe ARDS can also produce chronic fibrosis.

Preoperative Considerations

Patients typically present with dyspnea on exertion and sometimes a nonproductive cough. Symptoms of cor pulmonale are present only with advanced disease. Physical examination may reveal fine (dry) crackles over the lung bases, and, in late stages, evi-dence of right ventricular failure. The chest radio-graph progresses from a “ground-glass” appearance to prominent reticulonodular markings, and, finally, to a “honeycomb” appearance. Arterial blood gases usually show mild hypoxemia with normocarbia. PFTs are typical of a restrictive ventilatory defect (see above), and carbon monoxide diffusing capac-ity is reduced.

Treatment is directed at abating the disease process and preventing further exposure to the causative agent (if known). Glucocorticoid and immunosuppressive therapy may be used for idio-pathic pulmonary fibrosis, autoimmune disorders, and sarcoidosis. If the patient has chronic hypox-emia, oxygen therapy may be started to prevent, or attenuate, right ventricular failure.

Anesthetic Considerations

A. Preoperative Management

Preoperative evaluation should focus on determin-ing the degree of pulmonary impairment as well as the underlying disease process. The latter is impor-tant in determining the potential involvement of other organs. A history of dyspnea on exertion (or at rest) should be evaluated further with PFTs and arte-rial blood gas analysis. A vital capacity of less than 15 mL/kg is indicative of severe dysfunction (nor-mal is >70 mL/kg). A chest radiograph is helpful in assessing disease severity.

B. Intraoperative Management

The management of these patients is complicated by a predisposition to hypoxemia and the need to con-trol ventilation to ensure optimum gas exchange; anesthetic drug selection is generally not critical. The reduction in FRC (and oxygen stores) predis-poses these patients to rapid hypoxemia following induction of anesthesia. Because these patients may be more susceptible to oxygen-induced toxicity, particularly patients who have received bleomy-cin, the inspired fractional concentration of oxygen should be kept to the minimum concentration com-patible with acceptable oxygenation (Spo2 of >88% to 92%). High peak inspiratory pressures during mechanical ventilation increase the risk of pneumo-thorax and should prompt adjustment of the venti-latory parameters. In patients with severe restrictive disease, using an I:E ratio of 1:1 (or even an inverse ratio ventilation) and dividing the minute ventila-tion to a higher respiratory rate (10–15 breaths/ minute) may help to maximize the inspiratory time per tidal volume and minimize the peak and plateau ventilatory pressures.

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