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J.L., a 28-year-old man, was admitted with a severe traumatic brain injury following a motor vehicle crash. He required intubation and mechanical ventilation upon arrival at the hospital. He had no significant past medical or social history. His admission height and weight were 72 inches and 85 kg, respectively.

The patient progressed without complication until the morning of hospital day 6. During rounds it is identified that J.L. has an increasing white blood cell count (from 11.4 to 15.1 cells/mm3), was febrile overnight (39°C), and has macroscopically purulent sputum on examination. His morning chest radiograph shows that he has a new right-sided infiltrate. Arterial blood gases (ABGs) on an inspiratory oxygen concentration of 40% are as follows: Pao2 76 mm Hg, Paco2 36 mm Hg, HCO3 20 mEq/L, and pH 7.31. Blood pressure (BP) is 130/80 mm Hg and heart rate (HR) is 90 bpm. The team suspects late-onset ventilator-associated pneumonia and conducts a bronchoscopic bronchoalveolar lavage (BAL), along with blood and urine cultures. Following the sample collection empiric antibiotics are to be started.

What steps are involved prior to the initiation of antimicrobial therapies in this patient?

The clinical and radiographic presentation is consistent with late-onset ventilator-associated pneumonia. The goals of therapy include eradication of the causative organism and symptom resolution. Initiation of appropriate antibiotic therapy is essential in achieving these goals for all infections including ventilator-associated pneumonia. Prior to antibiotic initiation, samples for culture should be drawn from any suspected sources. It is important to obtain cultures prior to antibiotic therapy, as failure to do so has been shown to decrease the yield of the causative organism.1 Current guidelines by the Infectious Diseases Society of America recommend that at least two sets of blood cultures and a lower respiratory tract sample be obtained to aid in the diagnosis of pneumonia.2 Cultures are critical in helping to identify the causative organism(s), which will dictate the choice of antibiotics as well as the duration of therapy. Culture data also help to determine the duration of therapy as certain bacterial species have been shown to respond better to shorter durations of antibiotics than have other species.3 Negative lower respiratory tract samples at 72 hours in the absence of antibiotic changes can be used to discontinue antibiotic therapy, limiting unnecessary drug exposure.2 If the samples are positive, they help in the identification of the causative organism and its in vitro susceptibility profile. This information is essential for antibiotic de-escalation and tailoring of antibiotic therapy to ensure appropriate treatment while minimizing the risk for the development of resistance.

While culture data are extremely important in the delivery of an optimal antibiotic regimen, it is imperative that the collection of cultures not delay the initiation of the empiric antibiotic regimen. If cultures cannot be obtained in a timely manner, then antibiotics should ...

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