In a patient with an acute asthma attack, a normal or high Paco2
indicates that the patient can no longer maintain the work of breathing and is often a sign of impending respiratory failure. A pulsus paradoxus and electrocardiographic signs of right ventricular strain (ST-segment changes, right axis deviation, and right bundle branch block) are also indicative of severe airway obstruction.
Asthmatic patients with active bronchospasm presenting for emergency surgery should be treated aggressively. Supplemental oxygen, aerosolized β2
-agonists, and intravenous glucocorticoids can dramatically improve lung function in a few hours.
Intraoperative bronchospasm is usually manifested as wheezing, increasing peak airway pressures (plateau pressure may remain unchanged), decreasing exhaled tidal volumes, or a slowly rising waveform on the capnograph.
Other causes, such as obstruction of the tracheal tube from kinking, secretions, or an overinflated balloon; bronchial intubation; active expiratory efforts (straining); pulmonary edema or embolism; and pneumothorax, can simulate bronchospasm.
Chronic obstructive pulmonary disease (COPD) is currently defined as a disease state characterized by airflow limitation that is not fully reversible. The chronic airflow limitation of this disease is due to a mixture of small and large airway disease (chronic bronchitis/bronchiolitis) and parenchymal destruction (emphysema), with the representation of these two components varying from patient to patient.
Cessation of smoking is the long-term intervention that has been shown to reduce the rate of decline in lung function.
Preoperative interventions in patients with COPD aimed at correcting hypoxemia, relieving bronchospasm, mobilizing and reducing secretions, and treating infections may decrease the incidence of postoperative pulmonary complications. Patients at greatest risk of complications are those with preoperative pulmonary function measurements less than 50% of predicted.
Restrictive pulmonary diseases are characterized by decreased lung compliance. Lung volumes are typically reduced, with preservation of normal expiratory flow rates. Thus, both forced expiratory volume in 1 sec (FEV1
) and forced vital capacity (FVC) are reduced, but the FEV1
/FVC ratio is normal.
Intraoperative pulmonary embolism usually presents as unexplained cardiovascular collapse, hypoxemia, or bronchospasm. A decrease in end-tidal CO2
concentration is also suggestive of pulmonary embolism, but is not specific.
The impact of preexisting pulmonary disease on respiratory function during anesthesia and in the postoperative period is predictable: Greater degrees of preoperative pulmonary impairment are associated with more marked intraoperative alterations in respiratory function and higher rates of postoperative pulmonary complications. Failure to recognize patients who are at increased risk is a frequent contributory factor leading to complications, as patients may not receive appropriate preoperative and intraoperative care. This chapter examines pulmonary risk in general and then reviews the anesthetic approach in patients with the most common types of respiratory disease.
Certain risk factors (Table 24-1) may predispose patients to postoperative pulmonary complications. The incidence of atelectasis, ...