Ventilator associated pneumonia

Ventilator associated pneumonia is the most frequent presentation of hospital acquired infection of the lower respiratory tract, and the leading nosocomial infection worldwide.

Definition by the CDC: 2 or more serial chest x-rays with at least 1 of the following-new or progressive and persistent infiltrate, consolidation, or cavitation; clinical signs with at least 1 of the following: fever >38°C, leukopenia or leucocytosis, altered mental status for adults over the age of 70 years; plus at least 2 of the following-new onset of purulent sputum, change of the character of the sputum, or increased respiratory secretions, or increased requirement in suctioning, new onset of worsening cough, or dyspnea, or tachypnea, rales or bronchial breath sounds, worsening gas exchange, increased oxygen requirement, or increased ventilation demand; and microbiological criteria of at least 1 of the following-positive blood culture not related to another source, positive pleural fluid culture, positive bronchoalveolar lavage, five percent or more cells with intracellular bacteria on direct exam of Gram stained bronchoalveolar lavage fluid or histopathological evidence of pneumonia.

Most common and fatal nosocomial infection in ICU’s

Occurs in 9% to 24% of patients intubated longer than 48 hours.

Prolonged endotracheal intubation associated with airway tissue injury, infection, patient discomfort and need for sedation

Probably related to colonization of the aerodigestive tract with pathogenic bacteria and to aspiration of contaminated secretions.

Microaspirations around the tracheal tube cuff and formation of a biofilm lead to progressive bacterial spread in the tracheal bronchial tree,  ultimately leading to pneumonia.

Doubles the risk of dying compared with similar patients without ventilator associated pneumonia.

VAP attributable mortality of up to 13%.

VAP contributes to increase systemic antibiotic consumption, duration of mechanical ventilation, and ICU length of stay, and costs.

More than 30% of patients develop at least one episode of pneumonia within 3 weeks of mechanical ventilation.

Is the most common hospital-acquired infection among patients with acute respiratory failure.

Peak incidence occurs after seven days of ventilation.

Accounts for 50% of all antibiotics used in the ICU setting.

Early onset pneumonia, occurring within 96 hours of the onset of ventilatory support is usually attributed to antibiotic-sensitive bacteria.

Late onset of pneumonia, occurring after 96 hours after the start of mechanical ventilation is usually caused by antibiotic-resistant bacteria.

Associated with a significant increase in mortality of about 25%.

Prolongs duration of ventilation, length of stay in the ICU, total hospital length of stay and cost of hospitalization.

Inappropriate antibiotics associated with a 5.8 fold increased risk of death.

Elevating the head of the bed 45 degrees reduces risk significantly.

Mortality and morbidity reductions associated with the use of low tidal volume ventilation, use of tight glucose control, introduction of sedation and weaning protocols, and use of altered patient positioning to prevent ventilator assisted pneumonia.In

A randomized trial of diagnostic studies of bronchoalveolar lavage with quantitative culture of bronchoalveolar lavage fluid and endotracheal aspiration with nonquantitative culture of the aspirate are associated with similar outcomes and overall use of antibiotics.

Diagnosis difficult since many conditions among critically ill patients have similar clinical signs including acute respiratory distress syndrome, sepsis, congestive heart failure, alveolar hemorrhage, pulmonary emboli and atelectasis.

Poor correlation between clinical diagnosis and true underlying ventilator associated pneumonia, with more than 50% of patients with the diagnosis not having the disease, and up to one third os patients with the process not diagnosed appropriately.

Interobserver agreement in the diagnosis is poor.

North American Silver Coated Endotracheal Tube (NASCENT) study examined the potential benefit of such a tube in preventing VAP in the ICU in patients expected to require mechanical ventilation for 24 hours or longer: able to lower the VAP frequency from 7.5% for the control group to 4.8% for the group receiving silver-coated endotracheal tubes, a relative risk reduction of 33.9%and an absolute reduction of 2.7%, suggesting 37 patients would have to be treated with the silver coated endotracheal tube to prevent 1 case of VAP (Kollef).

NASCENT study indicated that the use of endotracheal tubes coated with silver ions micro dispersed in a polymer to prevent biofilm formation at its surface and impairing respiratory tract bacterial colonization and VAP did not reduce duration of intubation, duration of hospitalization in the ICU, decrease length of stay frequency or severity of adverse effects or mortality rates (Kollef).

Tracheotomy performed earlier than 3 weeks may be associated with quicker weaning from mechanical ventilation, but this has not been the experience in randomized controlled trials.

Tracheotomy within 2 days of hospital admission decreases mortality rate, incidence of pneumonia, and length of ICU stay compared with the procedure after 14-16 days of endotracheal intubation (Rumbak MJ).

In a study comparing tracheotomy within 4 days following intubation compared to waiting at least 14 days: no difference was noted in mortality, duration of mechanical ventilation, length of ICU stay and incidence of infections (Blot F).

In a randomized trial comparing early tracheotomy, after 6-8 days of intubation, compared to late tracheotomy, days 13-15, in 600 patients without pneumonia: no statistical improvement was noted in incidence of ventilator associated pneumonia (Terragni PP).

No studies have established that residual gastric volume monitoring decreases the risk of ventilation associated pneumonia.

No specific relationship has been demonstrated between increased gastric volume, regurgitation, gastric content aspiration and ventilator associated pneumonia.

Among adult patients requiring mechanical ventilation and receiving enteral nutrition, the absence of gastric volume monitoring was not inferior to routine residual gastric volume monitoring in terms of the development of ventilated associated pneumonia (Reignier J et al).

In the above study there was no significant differences between the groups in ICU acquired infections, mechanical ventilation duration, ICU stay lengths or mortality rates.

A two day course of antibiotics therapy with amoxicillin-Clavulanate in patients receiving 32-34°C at targeted temperature management strategy after out of hospital cardiac arrest resulted in a lower incidence of early ventilator associated pneumonia than placebo (Francois B).