Most patients with depressed consciousness may experience pharyngeal aspiration, which, in the presence of underlying diseases that impair host defense mechanisms and alterations in oropharyngeal flora, may manifest as aspiration pneumonia. Patients having undergone cardiac surgery may have residual effects from sedation or may be receiving opioids that may depress protective reflexes. Additionally, cardiac surgical patients may sustain a neurologic injury that could also predispose them to an aspiration event. Concomitantly, patients with diabetes or morbid obesity are prone to delayed gastric emptying, thereby also increasing the risk for aspiration of gastric contents. K. pneumoniae is frequently implicated in aspiration pneumonia.

Clinical manifestations of pulmonary aspiration depend in large part on the nature and volume of aspirated material. Aspiration of large volumes of acidic gastric fluid (Mendelson’s syndrome) produces fulminating pneumonia and arterial hypoxemia. Aspiration of particulate material may result in airway obstruction, and smaller particles may produce atelectasis. Radiographically, infiltrates are most common in dependent areas of the patient’s lungs. Penicillin-sensitive anaerobes are the most likely cause of aspiration pneumonia. Clindamycin is an alternative to penicillin and may be superior for treating necrotizing aspiration pneumonia and lung abscess. Hospitalization or antibiotic therapy alters the usual oropharyngeal flora such that aspiration pneumonia in hospitalized patients often involves pathogens that are uncommon in community-acquired pneumonias. There are limited data to suggest that treatment of aspiration pneumonia with antibiotics improves outcome.

Lung abscess may develop after bacterial pneumonia. Alcohol abuse and poor dental hygiene are important risk factors. Septic pulmonary embolization, which is most common in intravenous drug abusers, may also result in formation of a lung abscess. A finding of an air–fluid level on the chest radiograph signifies rupture of the abscess into the bronchial tree, and foul-smelling sputum is characteristic. Antibiotics are the mainstay of treatment of a lung abscess. Surgery is indicated only when complications such as empyema occur. Thoracentesis is necessary to establish the diagnosis of empyema, and treatment requires chest tube drainage and antibiotics. Surgical drainage is necessary to treat chronic empyema.

Postoperative pneumonia occurs in approximately 20 % of patients undergoing major thoracic, esophageal, or major upper abdominal surgery but is rare in other procedures in previously fit patients. Chronic respiratory disease increases the incidence of postoperative pneumonia threefold. Other risk factors include obesity, age older than 70 years, and operations lasting more than 2 h.

Ventilator-associated pneumonia (VAP) is the most common nosocomial infection in the ICU and makes up one third of the total nosocomial infections. VAP is defined as pneumonia developing more than 48 h after patients have been intubated and mechanically ventilated. Ten percent to 20 % of patients with tracheal tubes and mechanical ventilation for more than 48 h acquire VAP, with mortality rates between 5 and 50 %. Anesthesiologists and intensive care physicians play critical roles in the prevention, diagnosis, and treatment of VAP. Several simple interventions may decrease the occurrence of VAP, including meticulous hand hygiene, oral care, limiting patient sedation, positioning patients semi-upright, repeated aspiration of subglottic secretions, limiting intubation time, and considering the appropriateness of noninvasive ventilation support.

VAP is difficult to differentiate from other common causes of respiratory failure, such as acute respiratory distress syndrome and pulmonary edema. VAP is usually suspected when a patient develops a new or progressive infiltrate on chest radiograph, leukocytosis, and purulent tracheobronchial secretions. A tracheal tube or a tracheostomy tube provides a foreign surface that rapidly becomes colonized with upper airway flora. The mere presence of potentially pathogenic organisms in tracheal secretions is not diagnostic of VAP. A standardized diagnostic algorithm for VAP employing clinical and microbiologic data is used in the National Nosocomial Infections Surveillance System and the clinical pulmonary infection score to promote diagnostic consistency among clinicians and investigators. A clinical pulmonary infection score greater than 6 is consistent with a diagnosis of VAP (see Table 8.2).

In approximately half the patients suspected on clinical grounds of having VAP, the diagnosis is doubtful, and distal airway cultures do not grow organisms. Arbitrary thresholds that have been proposed to suggest a diagnosis of VAP are 10³ colony-forming units/mL (cfu/mL) of organisms grown from protected specimen brush, 10⁴ cfu/mL of organisms grown from bronchoalveolar lavage, or 10⁵ to 10⁶ cfu/mL of organisms grown from tracheal aspirates. Therefore, the accurate diagnosis of VAP is difficult and elusive at best.

The treatment of VAP includes supportive care for respiratory failure plus therapy for the organisms most likely to be implicated. Principles to apply when choosing appropriate therapy for VAP include knowledge of organisms likely to be present, local resistance patterns within the ICU, a rational antibiotic regimen, and a rationale for antibiotic de-escalation or stoppage. The most common pathogens are P. aeruginosa and S. aureus. Prognosis is improved if treatment is initiated early. Therefore, despite the high rate of false-positive diagnoses, broad-spectrum therapy should be initiated to cover resistant organisms such as methicillin-resistant S. aureus and P. aeruginosa. If known multidrug-resistant organisms, such as A. baumannii and extended-spectrum β-lactamase-producing organisms, a carbapenem antibiotic may be appropriate pending culture results. Treatment should be narrowed to target specific organisms according to cultures and sensitivities and should be stopped at 48 h if cultures are negative. Eight days of therapy are usually sufficient, except for non-lactose-fermenting gram-negative organisms, for which a 14-day course is recommended.

One of the major goals for the critical care health team is to ensure that patients with VAP do not experience a setback following surgery. Because patients with respiratory failure may be PEEP dependent, a PEEP valve should be used to decrease the likelihood of “de-recruitment” of alveoli when they are transported to the operating room. In the operating room, protective mechanical ventilation should be used, with tidal volumes of 6–8 mL/kg of lean body mass. Ideally, the same ventilator settings that were used in the ICU should be used, including mode of ventilation and PEEP. The lowest inspired oxygen should be administered to achieve adequate oxygen saturation (e.g., >95 %). If the ventilator in the operating room is limited in its capabilities, consideration should be given to bringing an ICU ventilator into the operating room. If pneumonia is suspected and body fluids (e.g., pleural effusion, empyema, bronchial washing) are drained or suctioned, specimens should be sent to the laboratory for culture and identification of pathogens. Important findings regarding VAP are listed in Box 8.1.