الفهرس 
PATHOPHYSIOLOGY AND RISK FACTORSOnly 14 pages are availabe for public view
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Abstract
VAP is the most common and fatal nosocomial ICU infection among mechanically ventilated patients. Each episode of VAP results in extended ICU and hospital stay and increased cost of treatment per patient. VAP is not particularly selective, and any patient mechanically ventilated for >48 hours is at risk of developing an episode.
Pathophysiology of VAP involves two main processes: colonization of the respiratory and digestive tracts and microaspiration of secretions of the upper and lower parts of the airway.
Endotracheal tubes cause an abnormal interruption between the upper airway and the trachea, bypassing the structures in the upper airway and providing bacteria a direct route into the lower airway.
Risk factors for development of VAP in ICU include Endotracheal intubation, Increased duration of mechanical ventilation, Prolonged hospital stay ,Presence of invasive devices, Prior use of antimicrobial, Red cell transfusions, Supine position, Surgery, Advanced age, Co-morbid disease, Colonisation of the oropharyngeal cavity with hospital-acquired pathogens, Sinus colonisation or sinusitis, Immune suppression, Malnutrition, Sepsis, Acute respiratory distress syndrome, Organ failure, Neurological/neuromuscular disease , Burns and trauma.
Diagnosing VAP remains difficult and controversial. The objective of making a correct diagnosis of VAP is to be able to determine whether the patient has pneumonia, identify the causative pathogen, and target therapy accordingly to achieve a better outcome for the patient.
Ventilator-associated pneumonia is usually suspected when the individual develops Symptoms of fever (>38.3C), leukocytosis (> 10,000), leukopenia (<5,000), purulent secretions and new or changing infiltrates seen on chest films. Because of the poor specificity of the clinical diagnosis of VAP and of qualitative evaluation of ETA, a composite clinical score, called the clinical pulmonary infection score (CPIS) was developed based on six variables: fever, leukocyte count, quantity and purulence of tracheal secretions, oxygenation, type of radiographic abnormality, and results of tracheal aspirate culture and Gram stain.
Diagnostic testing is required whenever ventilator-associated pneumonia (VAP) is suspected because the clinical findings alone are nonspecific. The purpose of diagnostic testing is to confirm VAP and identify the likely pathogen. Diagnostic testing involves radiographic imaging and analysis of lower respiratory tract secretions, including Gram stain and culture. Lung biopsy can be diagnostic, but is seldom performed because of its invasiveness.
There are a variety of methods for sampling material from the airways and alveoli, including bronchoscopic and nonbronchoscopic techniques.
Bronchoscopic sampling of the lower respiratory tract includes Bronchoalveolar lavage (BAL) and Protected specimen brush (PSB).
Nonbronchoscopic sampling of the lower respiratory tract includes Endo Tracheal Aspirate (ETA), Mini- bronchoalveolar lavage (mini-BAL)and Blind Protected specimen brush (BPSB).
The evaluation of biomarkers such as measuring C-reactive protein (CRP) ,procalcitonin (PCT) and soluble triggering receptor expressed on myeloid cells (sTREM) appear to be promising in improving the process of diagnosing VAP.
The most important factor influencing the mortality of ventilator-associated pneumonia is prompt and adequate empiric treatment. Multiple studies have demonstrated that delays in appropriate antimicrobial therapy or inappropriate initial antimicrobial therapy has been demonstrated to be a risk factor for increasing mortality. Since initial empiric antibiotic treatment is a major influence on mortality, the assessment of risk factors for multidrug resistant organisms is a key point in therapy.
The measures aimed at prevention of VAP provide a great advantage in comparison with treatment. Many trials have assessed several measures of VAP prevention that may be grouped into pharmacological and nonpharmacological measures.
Nonpharmacological measures include many ways in prevention which are:
- Appropriate staffing levels in the intensive care unit with an inverse relationship between the adequacy of staffing levels and duration of stay and subsequent development of VAP
- Nasotracheal intubation or feeding tube has been identified as a risk factor promoting the development of VAP and sinusitis. Available investigations and experience suggest that the preferred route of tracheal and gastric intubation is via the oropharynx and not the nasopharynx.
- The pressure of the endotracheal tube cuff should be sufficiently high to avoid the loss of gas from the lower respiratory tract and the leakage of bacterial pathogens around the cuff into the lower respiratory tract.
- Several international medical societies recommend semirecumbent position as one of the most effective and simple strategies to prevent VAP.
- Using strategies to shorten the duration of mechanical ventilation such protocols aimed at limiting the administration of sedation and accelerated weaning from mechanical ventilation using either weaning protocols or early attempts at spontaneous breathing.
- Continuous aspiration of subglottic secretions, avoiding re-intubation and early tracheostomy are more greatly associated with a lower incidence of VAP. Pharmacological measures include many ways in prevention which are :
- Stress ulcer prophylaxis are often used to protectively reduce peptic acidity. Sucralfate has been advocated as an alternative, but potentially less active, Consequently, if stress ulcer prophylaxis is indicated, the risk and benefits of each therapeutic strategy should be carefully considered.
- Prophylactic parenteral antimicrobial may play a role in the prevention of VAP among specific high-risk populations including patients with head trauma or coma .
- selective decontamination of the digestive tract (SDD) is one strategy to prevent colonization of oral cavity, throat, stomach, and intestines of ICU patients although the evidence supporting the use of SDD in ICU is high SDD is not widely used in clinical practice.
- Prophylaxis to reduce DVT is aspect of the VAP prevention. DVT prophylaxis has been considered standard practices in ICU for many years.
- Decontamination of the oropharynx with oral application of antimicrobial or antiseptics or with standard oral care alone