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Basics ⬇

Basics

Definition

  • Bacteremia-the presence of viable bacterial organisms in the bloodstream.
  • Sepsis-systemic inflammatory response to bacterial infection (e.g., fever, hypotension).
  • Terms are not synonymous, although often used interchangeably.

Pathophysiology

  • Shedding of bacterial organisms into the bloodstream-may occur transiently, intermittently, or continually.
  • The most critical host response for elimination of bacteremia-provided by mononuclear phagocyte system of the spleen and liver; activation leads to release of numerous cellular mediators (cytokines), some of which are beneficial and others detrimental; may lead to death of the host.
  • Neutrophils-relatively more important for defense against extravascular infection.
  • Bacteremia-may occur as a transient, subclinical event or escalate to overt sepsis when the immune system is overwhelmed; generally of more pathologic significance when the bloodstream is invaded from venous or lymphatic drainage sites.

Systems Affected

Cardiovascular

  • With peracute development of septicemia-increased or decreased cardiac output, decreased systemic vascular resistance, and increased vascular permeability; ultimately, refractory hypotension develops, leading to multiorgan failure and death.
  • Endocarditis-may develop; presence of bacteremia alone is not sufficient for induction; multiple factors involving both the host and the bacterial organism must be favorable for bacterial adherence to heart valves.

Hemic/Lymphatic/Immune

  • Coagulation disorders and thromboembolism.
  • Kidney and myocardium especially prone to septic embolization.
  • With chronic bacteremia-antigenic stimulation of the immune system may lead to immune-complex deposition.

Endocrine

A syndrome of relative adrenal insufficiency has been reported in dogs with sepsis.

Other

  • Respiratory
  • Gastrointestinal
  • Hepatobiliary

Signalment

Species

  • Dog and cat.
  • No age, sex, or breed predispositions reported.
  • Large-breed male dogs-predisposed to bacterial endocarditis and discospondylitis.

Signs

General Comments

  • Development may be acute or may occur in a vague or episodic fashion.
  • Variable and may involve multiple organ systems.
  • May be confused with those of immune-mediated disease.
  • Clinical-more severe when gram-negative organisms are involved.
  • Dogs-the earliest signs are usually referable to the gastrointestinal tract.
  • Cats-respiratory system more commonly involved.

Historical Findings

A thorough history is essential; historical findings highly variable depending upon underlying cause.

Physical Examination Findings

  • Intermittent or persistent fever; hypothermia more common than fever in cats in one study.
  • Lameness.
  • Depression.
  • Tachycardia; bradycardia more common than tachycardia in cats in one study.
  • Heart murmur.
  • Weakness.

Causes

  • Dogs-gram-negative organisms (especially E. coli) most common; Gram-positive cocci and obligate anaerobes also important; polymicrobial infection reported in about 20% of dogs with positive blood cultures.
  • Cats-bloodstream pathogens usually Gram-negative bacteria from the Enterobacteriaceae family or obligate anaerobes; E. coli and Salmonella most common Gram-negative organisms cultured.
  • Pseudomonas aeruginosa-uncommon isolate from animal blood cultures.

Risk Factors

  • Peracute-pyometra and disruption of the gastrointestinal tract most often associated.
  • More protracted onset-infections of the skin, upper urinary tract, oral cavity, and prostate.
  • Hyperadrenocorticism, diabetes mellitus, liver or renal failure, splenectomy, malignancy, and burns-predisposing factors.
  • Immunodeficient state-chemotherapy, FIV, splenectomy; particular risk.
  • Glucocorticoids-considered an important risk factor for bacteremia; allows greater multiplication of bacteria in extravascular tissues.
  • Intravenous catheter-provides rapid venous access for bacteria.
  • Indwelling urinary catheters-may be a predisposing factor.
  • Rectal exam.

Diagnosis ⬆ ⬇

Diagnosis

Differential Diagnosis

  • Consider other causes of fever, heart murmur, joint or back pain, or hypotension.
  • Clinical signs of more chronic bacteremia may be confused with immune-mediated disease.

CBC/Biochemistry/Urinalysis

  • Neutrophilic leukocytosis with a left shift and an associated monocytosis-most common hematologic abnormalities.
  • Neutropenia-may develop.
  • Hypoalbuminemia and a high ALP (up to two times upper limit of normal)-up to 50% of affected dogs.
  • Hypoglycemia-about 25% of affected dogs; hyperglycemia more common than hypoglycemia in cats in one study but another report found most cats with hypoglycemia.

Other Laboratory Tests

  • With suspected catheter-induced sepsis-submit catheter tip for culture.
  • Urine culture-may be useful; positive culture does not determine if urinary tract is primary or secondary source of infection.
  • Coagulation parameters should be monitored in most cases.

Imaging

May identify source of bacteremia (e.g., pyometra, prostate) or secondarily infected organs (e.g., discospondylitis).

Diagnostic Procedures

Blood Culture Indications

  • Any patient that develops fever (or hypothermia), leukocytosis (especially with a left shift), neutropenia, shifting leg lameness, recent onset or changing heart murmur, or any sign of sepsis that cannot be explained.
  • Essential for confirming suspected bacteremia and for optimizing management of the patient; one study of critically ill animals reported approximately 75% of cats and 50% of dogs had positive blood cultures.
  • Clinical findings-not reliable for discriminating between particular types of bacteria.

Guidelines

  • Current antimicrobial therapy-does not preclude collection of blood cultures; advise laboratory that patient is receiving antibiotics; steps can be taken to inactivate certain medications.
  • Anaerobic cultures-special bottles may not be necessary.
  • Sets (pairs) of samples-inform laboratory that for each submitted pair of bottles, one is for aerobic culture and the other for anaerobic.
  • Collect at least two (and preferably three) sets of samples-improves chance of obtaining a positive culture and facilitates interpretation of results.
  • Volume-the greater the volume of collected blood, the better the chances of obtaining positive cultures; often only a few organisms present per milliliter of blood; 10 mL of blood per culture recommended; may not be possible for cats and small dogs; have an assortment of culture bottles available (including 25, 50, and 100 mL); small bottles useful for small patients for maintaining appropriate blood-to-culture broth ratio.
  • Timing-for most patients, sufficient to take three cultures over a 24-hour period; for critically ill patients, take three cultures over a 2-hour period.

Collection

  • Bottles-warm to room temperature; apply alcohol or iodine to the rubber stopper.
  • Patient-clip hair; thoroughly disinfect skin before venipuncture to avoid contamination; wipe with 70% alcohol, then apply an iodine-based disinfectant; allow a minimum of 1 minute of contact time with the skin.
  • Withdrawing blood-wearing a sterile glove, palpate the vein; draw blood into a sterile syringe; evacuate all air from the syringe; attach a new needle before inoculating blood into the bottles.
  • Samples-maintain culture bottles at room temperature for transport to the laboratory.

Media

  • Commercial multipurpose nutrient broth media-recommended.
  • A medium that supports growth of both aerobes and anaerobes-ideal.
  • Often the laboratory that processes the culture will supply culture bottles.

Interpretation of Results

  • Single positive culture-not possible to distinguish true bacteremia from sample contamination.
  • Two or more positive cultures identified as the same organism desired.
  • Coagulase-negative staphylococci, -hemolytic streptococci, and Acinetobacter-probably contamination.
  • Enterobacteriaceae, Bacteroidaceae, Pseudomonas aeruginosa, Staphylococcus aureus, Staphylococcus intermedius, -hemolytic streptococci, and yeasts-nearly always clinically significant bacteremia.
  • Negative results from two or three successive cultures-generally eliminates bacteremia owing to common pathogens; some less common bacteria may take several weeks to grow.

Pathologic Findings

Varies with the underlying cause.

Treatment ⬆ ⬇

Treatment

Appropriate Health Care

  • Success-requires early identification of the problem and aggressive intervention; careful monitoring essential, because the status of patient may change rapidly.
  • Hypotension-intravenous fluids; isotonic fluids (e.g., lactated Ringer's) at a rate up to 90 mL/kg/h in dogs and 55 mL/kg/h in cats; use caution when hypoalbuminemia or increased vascular permeability is a concern.
  • Volume expanders (e.g., hydroxyethyl starch)-may help maintain oncotic pressure.
  • With hypoglycemia-may add dextrose to intravenous fluids.
  • Electrolytes and acid-base balance-correct abnormalities.
  • External sources of infection-give appropriate attention to wound care and bandage changes.
  • Internal sources of infection (e.g., pyometra or disruption of the bowel)-surgical intervention essential.

Nursing Care

As appropriate for each patient's situation.

Diet

Nutritional support-provide by assisted feeding or placement of a feeding tube.

Client Education

Prognosis should be discussed with client.

Surgical Considerations

Any identifiable focus of infection such as an abscess should be located and removed where possible.

Medications ⬆ ⬇

Medications

Drug(s) Of Choice

  • Antibiotics-usually selected before culture and sensitivity results available; empiric therapy acceptable while waiting for results; do not delay treatment.
  • Antimicrobials-give intravenously; direct therapy to cover all possible bacterial organisms (gram-positive and -negative; aerobic and anaerobic).
  • If patient not in shock-a good choice is a first-generation cephalosporin; dogs and cats: administer cefazolin at 40 mg/kg IV as a loading dose; then 20–30 mg/kg IV q6–8h (dogs and cats).
  • Aminoglycosides-add to protocol if more aggressive therapy is warranted; administer gentamicin at 2–4 mg/kg IV q8h (dogs and cats).

Contraindications

Glucocorticoids and NSAIDs-value in treating septic shock; do not improve survival unless given within the first few hours of the onset; may complicate the clinical picture in potentially ischemic organs (e.g., gastrointestinal tract and kidneys).

Precautions

Aminoglycosides-use with caution with renal impairment.

Follow-Up ⬆ ⬇

Follow-Up

Patient Monitoring

  • Aminoglycoside therapy-monitor renal function.
  • Blood pressure and ECG.

Possible Complications

Multiple organ failure

Expected Course and Prognosis

Bacteremia is associated with a high rate of mortality; death owing to hypotension, electrolyte, and acid-base disturbances, and endotoxemic shock.

Miscellaneous ⬆

Miscellaneous

Associated Conditions

  • Suspected discospondylitis (dogs)-may need to screen for Brucella canis.
  • See “Risk Factors” for possible underlying diseases.

Synonyms

  • Septic shock
  • Septicemia

Abbreviations

  • ALP = alkaline phosphatase
  • ECG = electrocardiogram
  • FIV = feline immunodeficiency virus
  • NSAID = nonsteroidal anti-inflammatory drug

Author Sharon Fooshee Grace

Consulting Editor Stephen C. Barr

Client Education Handout Available Online

Suggested Reading

Bellhorn TL, Macintire DK. Bacterial translocation: Clinical implications and prevention. Compend Contin Educ Pract Vet 2002, 32:1165–1178.

Burkitt JM, Haskins SC, Nelson RW, et al. Relative adrenal insufficiency in dogs with sepsis. J Vet Intern Med 2007, 21:226–231.

Morresey PR. Synthesis of proinflammatory mediators in endotoxemia. Compend Contin Educ Pract Vet 2001, 23:829–836.