Pneumonia in the intensive care unit setting

Roentgenographic mimics of pneumonia in the critical care unit

Clinicians are confronted with a complex challenge when a patient is admitted to a critical care unit (CCU) with a significant chest roentgenography (CXR) abnormality. The etiology of a new infiltrate seen on CXR in a patient already in the CCU is more difficult to establish, but is of equal concern.

Organ-specific support in multiple organ failure: pulmonary support

The catastrophic pulmonary failure that complicates management of patients with multiple trauma or sepsis syndrome with shock is recognizable to nearly all experienced surgeons. However, the spectrum of injury is broad, the distribution of lung injury may be heterogeneous within a single patient, and many patients will not develop acute respiratory distress syndrome (ARDS) even after a major predisposing insult. The lung responds stereotypically to many disparate insults, so a better conceptual construct of ARDS may be to consider it as one component of the multiple organ dysfunction syndrome. Support of oxygen transport with positive pressure ventilation and high levels of positive end-expiratory pressure, long the mainstay of pulmonary support, has been criticized for its predilection to cause barotrauma. Newer modes of ventilation, such as pressure-controlled, inverse-ratio ventilation and permissive hypercapnia, are under investigation but have not yet been reported with scientific rigor. However, pulmonary support extends beyond the support of gas exchange. Fluid management requires close attention so that the circulation is supported but lung water accumulation is minimized. Nosocomial pneumonia greatly increases the mortality rate in ARDS, but is difficult to diagnose and must be sought aggressively. Until recently, pharmacologic therapy has held little promise, but inhalation of very low concentrations of nitric oxide appear to decrease pulmonary vascular pressures and intrapulmonary shunt. It remains unknown whether nitric oxide is effective therapy for the underlying injury, or is simply treatment for certain manifestations.

The pathogenesis of ventilator-associated pneumonia: I. Mechanisms of bacterial transcolonization and airway inoculation

Ventilator-associated pneumonia (VAP) is an infection of the lung parenchyma developing in patients on mechanical ventilation for more than 48 h. VAP is associated with a remarkably constant spectrum of pathogenic bacteria, most of which are aerobic Gram-negative bacilli (AGNB) and, to a lesser extent Staphyloccus aureus. Most authorities agree that VAP develops as a result of aspiration of secretions contaminated with pathogenic organisms, which appear to be endogenously acquired. These pathogens gain access to the distal airways by mechanical reflux and aspiration of contaminated gastric contents and also by repetitive inoculation of contaminated upper airway secretions into the distal tracheobronchial tree. Persistence of these organisms in the upper airways involves their successful colonization of available surfaces. Although exogenous acquisition can occur from the environment, the rapidity at which critically ill patients acquire AGNB in the upper airways in conjunction with the low rate of AGNB colonization of health-care workers exposed to the same environment favors the presence of endogenous proximate sources of AGNB and altered upper airway surfaces that are rendered receptive. Proximate sources of AGNB remain unclear, but potential sites harboring AGNB prior to illness include the upper gastrointestinal tract, subgingival dental plaque, and the periodontal spaces. Following illness or antibiotic therapy, competitive pressures within the oropharynx favor AGNB adherence to epithelial cells, which lead to oropharyngeal colonization. Similar dynamic changes in contiguous structures (oropharynx, trachea, sinuses, and the upper gastrointestinal tract) lead to the transcolonization of these structures with pathogenic bacteria. Following local colonization or infection, these structures serve as reservoirs of AGNB capable of inoculating the lower airways. As the oropharynx becomes colonized with AGNB, contaminated oropharyngeal secretions reach the trachea, endotracheal tube, and ventilator circuit. Contaminated secretions pooled above the endotracheal tube cuff gain access to the trachea and inner lumen of the endotracheal tube by traversing endotracheal tube cuff folds. Amorphic particulate deposits containing AGNB form along the endotracheal tube and are capable of being propelled into the distal airways by ventilator-generated airflow or by tubing manipulation. Bacteria embedded within this type of amorphous matrix are particularly difficult for the host to clear. If host defenses fail to clear the inoculum, then bacterial proliferation occurs, and the host inflammatory response progresses to bronchopneumonia.(ABSTRACT TRUNCATED AT 400 WORDS)

Treatment of severe pneumonia in hospitalized patients: results of a multicenter, randomized, double-blind trial comparing intravenous ciprofloxacin with imipenem-cilastatin. The Severe Pneumonia Study Group

Intravenously administered ciprofloxacin was compared with imipenem for the treatment of severe pneumonia. In this prospective, randomized, double-blind, multicenter trial, which included an intent-to-treat analysis, a total of 405 patients with severe pneumonia were enrolled. The mean APACHE II score was 17.6, 79% of the patients required mechanical ventilation, and 78% had nosocomial pneumonia. A subgroup of 205 patients (98 ciprofloxacin-treated patients and 107 imipenem-treated patients) were evaluable for the major efficacy endpoints. Patients were randomized to receive intravenous treatment with either ciprofloxacin (400 mg every 8 h) or imipenem (1,000 mg every 8 h), and doses were adjusted for renal function. The primary and secondary efficacy endpoints were bacteriological and clinical responses at 3 to 7 days after completion of therapy. Ciprofloxacin-treated patients had a higher bacteriological eradication rate than did imipenem-treated patients (69 versus 59%; 95% confidence interval of -0.6%, 26.2%; P = 0.069) and also a significantly higher clinical response rate (69 versus 56%; 95% confidence interval of 3.5%, 28.5%; P = 0.021). The greatest difference between ciprofloxacin and imipenem was in eradication of members of the family Enterobacteriaceae (93 versus 65%; P = 0.009). Stepwise logistic regression analysis demonstrated the following factors to be associated with bacteriological eradication: absence of Pseudomonas aeruginosa (P < 0.01), higher weight (P < 0.01), a low APACHE II score (P = 0.03), and treatment with ciprofloxacin (P = 0.04). When P. aeruginosa was recovered from initial respiratory tract cultures, failure to achieve bacteriological eradication and development of resistance during therapy were common in both treatment groups (67 and 33% for ciprofloxacin and 59 and 53% for imipenem, respectively). Seizures were observed more frequently with imipenem than with ciprofloxacin (6 versus 1%; P = 0.028). These results demonstrate that in patients with severe pneumonia, monotherapy with ciprofloxacin is at least equivalent to monotherapy with imipenem in terms of bacteriological eradication and clinical response. For both treatment groups, the presence of P. aeruginosa had a negative impact on treatment success. Seizures were more common with imipenem than with ciprofloxacin. Monotherapy for severe pneumonia is a safe and effective initial strategy but may need to be modified if P. aeruginosa is suspected or recovered from patients.

Pseudomonas aeruginosa-induced lung and pleural injury in sheep. Differential protective effect of circulating versus alveolar immunoglobulin G antibody

The overall objective of these studies was to determine whether IgG antibody to Pseudomonas aeruginosa would modify the acute lung and pleural injury that developed over 24 h after the instillation of 10(10) live P. aeruginosa into the distal airspaces of one lung in unanesthetized sheep. Using a quantitative experimental model to measure protein permeability across the alveolar epithelial, lung endothelial, and pleural mesothelial barriers, the effect of IgG antibody to P. aeruginosa was examined under four different experimental conditions. First, the effect of IgG antibody to P. aeruginosa in the circulation was examined by instilling 10(10) live P. aeruginosa in 5% ovine albumin in sheep that had been vaccinated. Under these conditions, the presence of circulating IgG antibody to P. aeruginosa reduced lung endothelial injury but did not modify the lung epithelial or pleural injury caused by intraalveolar P. aeruginosa. Therefore, the second experimental protocol determined the effect of instilling immune serum from a sheep that had been vaccinated so that IgG antibody to P. aeruginosa was present in both the circulation and in the airspaces along with instillation of live bacteria. Under these conditions, injury to the lung endothelium, alveolar epithelium, and pleural space was completely prevented. Therefore, the third protocol examined the protective effect of instillation of IgG antibody to P. aeruginosa in the airspaces concurrent with the live bacteria. Interestingly, intraalveolar IgG antibody to P. aeruginosa prevented all evidence of lung epithelial and pleural injury, and this effect was associated with a marked decrease in the number of viable bacteria in the lung after 24 h. Therefore, the fourth protocol examined the prophylactic effect of instillation of the specific IgG antibody to P. aeruginosa 24 h before instillation of the bacteria. With this prophylactic regimen, epithelial, endothelial, and pleural injury were prevented, and there was a significant decrease in the number of bacteria recovered from the lung. Thus, delivery of IgG antibody to P. aeruginosa the distal airspaces of the lung alone may provide a novel therapeutic approach to preventing acute pulmonary infection caused by P. aeruginosa.