VENTILATOR-ASSOCIATED PNEUMONIA

VENTILATOR-ASSOCIATED PNEUMONIA Ventilator-associated pneumonia (VAP) is the most common nosocomial infection in the ICU and makes up one third of the total nosocomial infections. Ten percent to 20% of patients with tracheal tubes and mechanical ventilation for more than 48 hours acquire VAP, with mortality rates of 15% to 50%. Anesthesiologists and intensive care physicians have important roles to play 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 semiupright, aspiration of subglottic secretions, limiting intubation time, and considering the appropriateness of noninvasive ventilation support.
Diagnosis VAP is difficult to differentiate from other common causes of respiratory failure, such as acute respiratory distress syndrome and pulmonary edema. 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 19-4 ).Both the National Nosocomial Infections Surveillance and the clinical pulmonary infection score are relatively sensitive for VAP (>80%) but nonspecific when applied to individual patients. 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 10 colony-forming units/mL (cfu/mL) of organisms grown from protected specimen brush, 10 cfu/mL of organisms grown from bronchoalveolar lavage, or 10 to 10 cfu/mL of organisms grown from tracheal aspirates.
Treatment and Prognosis The treatment of VAP includes supportive care for respiratory failure plus therapy for the organisms most likely to be implicated. 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. baumanii 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 hours if cultures are negative. Eight days of therapy are usually sufficient, except for nonlactose fermenting gram-negative organisms, for which a 14-day course is recommended.
Management of Anesthesia Patients with VAP frequently require anesthesia for tracheostomy. Major surgery should be deferred until the pneumonia has resolved and respiratory function has improved. Tracheostomy is not an emergency procedure. It may be ill advised to proceed when patients have minimal pulmonary reserve, such as a requirement for more than 50% inspired oxygen or a positive end-expiratory pressure (PEEP) of 7.5 or higher. One of the major goals for the anesthesiologist is to ensure that patients with VAP do not experience a setback following anesthesia. Patients with respiratory failure may be PEEP dependent. When they are transported to the operating room, a PEEP valve should be used to decrease the likelihood of “derecruitment” of alveoli. In the operating room, protective mechanical ventilation should be used, with tidal volumes of 6 to 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.