Septic Shock Workup: Approach Considerations, Initial Laboratory ...

Blood cultures

Blood cultures should be obtained in patients with suspected sepsis (or blood infection) to facilitate isolation of a specific organism and tailoring of antibiotic therapy. These cultures are the primary means of diagnosing intravascular infections (eg, endocarditis) and infections of indwelling intravascular devices. Individuals at high risk for endocarditis are intravenous (IV) drug abusers and patients with prosthetic heart valves.

Patients at risk for bacteremia include adults who are febrile with an elevated WBC or neutrophil band count, elderly patients who are febrile, and neutropenic patients who are febrile. These populations have a 20-30% incidence of bacteremia. The incidence of bacteremia increases to at least 50% in patients with sepsis and evidence of end-organ dysfunction.

The Surviving Sepsis Campaign recommends obtaining at least 2 blood cultures before antibiotics are administered, with 1 percutaneously drawn and the other(s) obtained through each vascular access (unless the device was inserted < 48 hours beforehand). [11, 60] Again, however, it must be remembered that blood cultures are positive in fewer than 50% of cases of sepsis. [3, 4, 5]

To optimize recovery of aerobic bacteria from patients with suspected intra-abdominal infection, 1-10 mL of fluid can be directly inoculated into an aerobic blood culture; an additional 0.5 mL of fluid should be sent for Gram staining and, if indicated, fungal cultures. [2] For anaerobic bacteria, 1-10 mL of fluid can also be directly inoculated into an anaerobic blood culture bottle.

Susceptibility testing for organisms that have a high risk for resistance (eg, Pseudomonas, Proteus, Acinetobacter, Staphylococcus aureus, and predominant [moderate to heavy growth] Enterobacteriaceae) should be performed. [2] Unfortunately, in patients with community-acquired intra-abdominal infection, blood cultures are not of much clinical utility; Gram staining of the infected material also is not generally useful in such cases.

Urinalysis and urine culture

Urinalysis and urine culture are indicated for every patient who is in a septic state. Urinary tract infection (UTI) is a common source for sepsis, especially in elderly individuals. Adults who are febrile without localizing symptoms or signs have a 10-15% incidence of occult UTI. Obtaining a culture is important for isolating a specified organism and tailoring antibiotic therapy.

Gram stain and culture of secretions and tissue

The Gram stain is the only immediately available test that can document the presence of bacterial infection and guide the choice of initial antibiotic therapy. Secretions or tissue for Gram stain and culture from the sites of potential infection (eg, cerebrospinal fluid [CSF], wounds, respiratory secretions, or other body fluids) may be are obtained as they are identified, preferably before administering antibiotic therapy. [11, 60]

At least 1 mL of fluid or tissue is needed for cultures. [2] For aerobic or anaerobic cultures, 0.5 mL of fluid or 0.5 g of tissue should be transported to the laboratory in the appropriate aerobic or anaerobic transport medium. [2]

If pneumonia is suspected, a sputum specimen should be obtained for Gram stain and culture, provided that the patient has a productive cough and that a good-quality specimen can be obtained. [66] Any abscess should be drained promptly and purulent material sent to the microbiology laboratory for analysis. If meningitis is suspected, a CSF specimen should be obtained.

Routine culture and susceptibility studies should be obtained in the following cases [2] :

• Perforated appendicitis and other community-acquired intra-abdominal infections in which there is significant resistance of a common community isolate to an antimicrobial regimen in widespread use locally

• Higher-risk patients who have a greater risk of harboring resistant pathogens, such as those with previous antibiotic exposure

Although Gram staining may be helpful for identifying healthcare-related infections (eg, presence of yeast), it has not proved to be of clinical value in community-acquired intra-abdominal infections. [2] Anaerobic cultures are not necessary for community-acquired intra-abdominal infections if empiric antimicrobial therapy against common anaerobic pathogens is administered.