A Nosocomial Infection

Ventilator-Associated Pneumonia is a common nosocomial infection in the ICU accounting for 13% to 18% of all nosocomial infections. Critically ill patients supported by mechanical ventilation are especially vulnerable to ventilator-associated pneumonia, leading to increased mortality and morbidity and prolonged hospital stay. VAP is often caused by Pseudomonas aeruginosa,Klebsiella pneumoniae, Serratia marcescens, Enterobacter, Citrobacter,Acinetobacter and Stenotrophomonas species.

Mechanical Ventilation and Pneumonia

The endotracheal tube serves as a route for inoculation of the bacteria such as P. aeruginosa. The symptoms include fever, hypoxia and purulent sputum. Because of intubations, bacteria have direct access to the lower airways and the endotracheal tube bypasses normal filtration mechanisms and the epiglottis.

Intubation affects and alters the natural host mechanisms by reducing the cough effort, interfering the mucociliary clearance, and damaging the epithelial layer exposing the basement membrane allowing bacterial colonization. Intubation also results in increased mucus production to trap bacteria, which results in accumulation of mucus in the respiratory tract.

Infection may be even due to improper hand washing, not changing the gloves from patient to patient, and contamination of respiratory devices like nebulizers, spirometers, oxygen sensors, bag-valve mask devices, and suction catheters (Shelby Hixson, 1998).

An inception cohort study to identify factors associated with the development of ventilator-associated pneumonia (VAP) and to examine the incidence of VAP in different intensive care unit (ICU) populations has identified four factors that influence the occurrence of VAP namely, an organ system failure, patient age, antibiotic administration and supine head positioning during the first 24 hours of mechanical ventilation (Kollef, 1993).

Epidemiology

A retrospective case-control analysis using quantitative bronchoscopic cultures collected from 62 intubated patients has shown Streptococci and Hemophilus as common pathogens. Gram-negative rods have also been isolated more frequently after lengthier intubation (Bert et.al, 1996).

AAVentilator-associated pneumonia (VAP) caused by Pseudomonas aeruginosa has been found to be associated with higher case fatality rates than VAP caused by other bacterial etiologies (Crouch et.al, 1996). Dore et.al (1996), have investigated the role of anaerobic bacteria in ventilator-associated pneumonia (VAP) in patients with a first episode of bacteriologically documented VAP using protected specimen brushes (PSB). Prevotella melaninogenica, Fusobacterium nucleatum and Veillonella parvula were the major anaerobic strains isolated. The study has shown that VAP due to anaerobes occurred more often in orotracheally-intubated patients than in nasotracheally-intubated patients.

Diagnosis

An increase in WBC count, chest radiograph infiltrates and purulent secretions serve as presumptive evidences of the disease. A study to assess the accuracy of clinical parameters for the diagnosis of ventilator-associated (VA) pneumonia and the diagnostic value of several invasive techniques has shown that the presence of fever, purulent secretions and chest radiograph infiltrates do not effectively always indicate presence or absence of pneumonia (Torres et.al, 1994). Hence, Clinical diagnosis is based on laboratory diagnosis by bacterial culture methods.

A prospective postmortem study to assess the diagnostic accuracy of bronchoscopic techniques and nonbronchoscopic techniques like Bronchoalveolar lavage [BAL] , Protected specimen brush [PSB],Blind bronchial sampling [BBS] and mini-BAL in the diagnosis of ventilator-associated pneumonia (VAP) has shown that the sensitivity of BBS was significantly higher than that of PSB (Papazian et.al.1995).

Conclusions

Initial empiric therapy is done with broad-spectrum antibiotics. An antibiotic sensitivity test gives the right drug. Proper hand washing, use of fresh gloves when suctioning patients orally or through the endotracheal tube helps in reducing infections. Nasal care and proper cleansing of the nasopharynx reduces bacterial infection.

For patients who have an nasogastric or nasoenteric tube, the endotracheal tube is placed nasally. Since the tubes remain for prolonged periods, secretions accumulate and crust in the nares. Thus, routine cleansing of the nose and suctioning nasopharyngeal secretions should be done and evaluated. Stagnated mucus in the lower airways serves as an excellent medium for bacterial growth, when the pathogens reach the lower airways. Periodic turning and positioning of the patient assists in disintegration of these secretions.

Use of beds that provide vibration or rotation to prevent VAP is also recommended. Suction of patients is done only during auscultation of adventitious lung sounds or other assessments. This suction mandate reduces trauma to the airways.

Stagnant mucus aided by a lack of a cough reflex aids infection and hence suctioning and interventions that facilitate effective coughing are to be done periodically.

References

American Thoracic Society and the Infectious Diseases Society of America. (2005). "ATS/IDSA Guidelines: Guidelines for the management of adults with HAP, VAP, and HCAP". Am J Respir Crit Care Med 171: 388.

Bert F, Lambert Zechovsky N. (1996) Sinusitis in mechanically ventilated patients and its role in the pathogenesis of nosocomial pneumonia.. Eur J Clin Microbiol Infect Dis.15: 533-544.

L Papazian, P Thomas, L Garbe, I Guignon, X Thirion, J Charrel, C Bollet, P Fuentes and F Gouin (1995).

M. H. Kollef (1993). Ventilator-associated pneumonia. A multivariate analysis. JAMA 270 (16).

P Dore, R Robert, G Grollier, J Rouffineau, H Lanquetot, JM Charriere and JL Fauchere (1996). Incidence of anaerobes in ventilator-associated pneumonia with use of a protected specimen brush. Am. J. Respir. Crit. Care Med., 153, (4), 04 1996, 1292-1298.

S Crouch Brewer, RG Wunderink, CB Jones and KV Leeper Jr (1996). Ventilator-associated pneumonia due to Pseudomonas aeruginosa. Chest 109; 1019-1029.

Shelby Hixson and Tracey King (1998), Nursing Strategies to Prevent Ventilator-Associated Pneumonia, Advanced Practice in Acute and Critical Care (9).

Torres, M el-Ebiary, L Padro, J Gonzalez, JP de la Bellacasa, J Ramirez, A Xaubet, M Ferrer and R Rodriguez-Roisin (1994). Validation of different techniques for the diagnosis of ventilator- associated pneumonia. Comparison with immediate postmortem pulmonary biopsy. Am. J. Respir. Crit. Care Med., 149(2), 02; 324-331.

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