Flashcards in Ventilator-Associated Pneumonia (VAP) article Deck (27)
What is ventilator-associated pneumonia (VAP)?
- a type of hospital-acquired (or nosocomial) pneumonia that develops after more
than 48 hours of mechanical ventilation.
(Its incidence is estimated to be 9 to 27 percent, with a mortality of 25 to 50 percent)
Ventilator-associated pneumonia (VAP) is
usually suspected when a patient receiving mechanical ventilation develops what 3 signs?
- a new or progressive pulmonary infiltrate with fever
- purulent tracheobronchial secretions
(one or all of these may arouse suspicion)
Additional signs of possible VAP include:
- increased respiratory rate
- increased minute ventilation
- decreased tidal volume
- decreased oxygenation
- need for more ventilatory support or inspired oxygen
What are some differential diagnoses of VAP? (there are 10 from the article, give it a whirl)
• Aspiration pneumonitis (ie, chemical aspiration without infection)
• Pulmonary embolism
• Acute respiratory distress syndrome
• Pulmonary hemorrhage
• Lung contusion
• Infiltrative tumor
• Radiation pneumonitis
• Drug reaction
• Cryptogenic organizing pneumonia
Why are diagnostic tests required whenever VAP is suspected?
- because the clinical findings alone are nonspecific
What is the purpose of diagnostic testing in regards to VAP?
to confirm VAP and identify the likely pathogen
What diagnostic testing is done to confirm VAP?
- radiographic imaging
- analysis of lower respiratory tract secretions, including Gram stain and culture
(a lung biopsy can be diagnostic, but is seldom performed because of its invasiveness)
The diagnosis of VAP requires an abnormal chest radiograph. Why?
- because a normal chest xray means they don't have VAP (although ventilator-associated tracheobronchitis may exist)
- an abnormal chest xray is nonspecific ;(
Bronchoscopic sampling of the lower respiratory tract is performed using what two methods?
- bronchoalveolar lavage (BAL)
- protected specimen brush (PSB)
(BAL - the infusion and aspiration of sterile saline through a flexible fiberoptic bronchoscope that is wedged in a bronchial segmental orifice.
PSB - a brush is contained within a protective sheath, designed to minimize the likelihood that the brush will be contaminated during bronchoscopy)
What are two non-bronchoscopic sampling techniques?
- tracheobronchial aspiration
(Tracheobronchial aspiration is performed by advancing a catheter through the endotracheal tube until resistance is met and then applying suction.
Mini-BAL is performed by advancing a catheter through the endotracheal tube until resistance is met, infusing sterile saline through the catheter, and then aspirating)
Does bronchoscopic sampling (as opposed to non-bronchoscopic sampling) improve mortality, length of hospital stay, duration of mechanical ventilation, or length of ICU stay?
(but it may lead to a narrower antimicrobial regimen and/or more rapid de-escalation of antimicrobial therapy)
The most common microscopic analysis is the Gram stain of a lower respiratory specimen. What is it used to characterize?
- the morphology of bacteria and other types of cells present
What is a quantitative culture?
- it is a count of pulmonary pathogens
(reported as a number in colony forming units (cfu) / mL)
In general, do quantitative cultures derived from non-bronchoscopic specimens tend to have a higher or lower specificity than quantitative cultures derived from bronchoscopic specimens?
a lower specificity
(However, this is balanced by a higher sensitivity, resulting in comparable diagnostic accuracy)
How are semiquantitative culture reported?
- typically as heavy, moderate, light, or no growth
Which would be more likely to distinguish between patients whose airways are colonized versus those who actually have VAP: quantitative cultures or semiquantitative cultures?
- quantitative cultures
(with semiquantitative cultures, false-positive results are more likely, which can lead to inappropriate therapy)
Lower respiratory tract specimens should be c ollected ________ initiating antibiotic therapy?
(because antibiotic therapy reduces the sensitivity of both microscopic analysis and culture)
(Similarly, specimens should be collected prior to changing the antibiotic regimen of patients suspected of developing VAP while receiving antibiotics)
Will antibiotic therapy influence the type of pathogens that cause VAP?
(In a prospective cohort study of 135 patients, prior antibiotic use was independently associated with VAP due to an antibiotic-resistant pathogen, especially if the antibiotic regimen included a third generation cephalosporin, fluoroquinolone, or imipenem)
Which biologic marker is one of the most promising to try to distinguish between bacterial and non-bacterial causes of pneumonia?
(Procalcitonin is the peptide precursor of calcitonin. It is released by parenchymal cells in response to bacterial toxins, leading to elevated serum levels in patients with bacterial infections)
Serum procalcitonin levels are not recommended to guide the decision of whether to initiate antibiotics in patients with suspected VAP. However, in what two situations would procalcitonin levels be useful in patients with confirmed VAP?
- in deciding whether to discontinue antibiotic therapy
- as a prognostic marker (since progressive increases in procalcitonin have been associated with septic shock and mortality)
If sampling of the lower respiratory tract is delayed, should antibiotic therapy be delayed?
- no, it should not delay the initiation of necessary antibiotic therapy
(i know it's the opposite of one of the previous answers, but i think this is a delay of several days, not hours)
(empiric, broad-spectrum antimicrobial therapy should be initiated)
Empiric antimicrobial therapy can be withheld if the clinical suspicion for VAP is ____ and microscopic analysis of lower respiratory tract samples is ________.
How many days after lower respiratory tract sampling and the initiation of empiric antimicrobial therapy should the culture results should be checked and the patient's response to antimicrobial therapy assessed?
- 2 to 3 days
Patients with negative cultures who have not improved may or may not have VAP?
- they may not have VAP
(other diagnoses or sites of infection should be sought)
Patients with negative cultures who have improved may or may not have VAP?
- they may not have VAP
(antimicrobial therapy should be discontinued, unless it is indicated for an infection other than VAP)
Patients with positive cultures who have not improved probably have or do not have VAP?
- they probably have VAP
(However, they may be receiving inappropriate antimicrobial therapy, have a complication of the VAP, have a second source of infection, or have a second diagnosis. The antimicrobial regimen should be adjusted and then complications, other sites of infection, and other pathogens should be sought)