Postoperative pulmonary complications are the second most common complication, following nausea and vomiting, in the postanesthesia care unit (PACU). Anesthetic, surgical, and patient factors contribute to the likelihood of pulmonary complications. Hypoxia in the PACU can be divided into two categories: hypoventilation with a low PAO2, or impaired O2 exchange with a decreased alveolar-arterial gradient.
Atelectasis due to anesthesia occurs in almost all patients. It leads to ventilation-perfusion mismatch or dead space ventilation and hypoxemia. Atelectasis occurs as a result of respiratory physiology changes caused by anesthetic medications, positioning, pain, and mechanical limitations imposed by surgery, pregnancy, or obesity. Loss of respiratory muscle coordination and tone leads to abnormal chest wall function, decreased lung volumes, and reduced capacities. Impaired gas exchange and surfactant function also lead to atelectasis. Atelectasis occurs in dependent lung fields.
Development of atelectasis can be decreased by using adequate positive-end expiratory pressure (PEEP) and by using recruitment maneuvers intraoperatively. In the PACU, use of incentive spirometry and noninvasive ventilation therapy such as continuous positive airway pressure (CPAP) limit atelectasis and hypoxemia.
Bronchospasm and increased airway resistance are likely to occur in patients with reactive airways such as asthma or chronic pulmonary disease (COPD). Pharyngeal and tracheal stimulation from secretions, aspiration, or suctioning can trigger constriction of bronchial smooth muscle. In a patient who is intubated, bronchospasm will manifest as high peak airway pressures, low tidal volumes, and high end-tidal carbon dioxide. In a spontaneously ventilating patient, a patient will exhibit labored breathing with retraction of accessory muscles. Treatment is aimed at the underlying etiology and includes inhaled albuterol, intravenous anticholinergics, and though it does not act acutely, intravenous steroids. If treatment is resistant, then IV epinephrine should be administered.
Anesthesia can decrease the lung’s defense mechanisms and lead to pneumonia. Anesthetic changes in the lung include impaired cough, forced vital capacity, mucociliary clearance, surfactant function, and alveolar macrophage activity. Bacteria enter the airways via aspiration or endotracheal tube contamination as it passes through the oral cavity. Factors that increase pneumonia risk include intubation greater than 48 hours, age over 65 years, COPD, prolonged surgery, trauma or emergency surgery, and intraoperative transfusion.
Hypoventilation can be defined as Paco2 greater than 45 mm Hg. Severe hypoventilation with respiratory acidosis causing circulatory depression occurs with Paco2 levels greater than 60 or pH less than 7.25. Conditions leading to hypoventilation include:
The most common cause of airway obstruction in the PACU is relaxation and weakness of pharyngeal muscles due to residual anesthetic, neuromuscular blockade, or opioids. Patients with obstructive sleep apnea (OSA) are more prone to obstruction and high dosages of sedating medications should be used cautiously. Maneuvers ...