Systemic Infections

The literature on bacteremia and sepsis is filled with jargon, and so the terms used in this entry are defined first. Bacteremia is the presence of viable bacteria in the blood, whereasinfection is the inflammatory response to invasion of sterile tissues by microorganisms. Thesystemic inflammatory response syndrome (SIRS) is a physiological response to inflammation and/or infection along with two or more of the following conditions: temperature > 38 degrees Celcius or < 36 degrees Celcius; heart rate > 90 beats per minute; respiratory rate > 20 per minute; partial pressure of carbon dioxide (Pa CO2) < 32 millimeters of mercury (mm Hg); and white blood cells (WBC) > 12,000 cells per millimeter cubed (mm3), < 4,000 cells/mm3, or > 10% band forms. Sepsis is defined as SIRS plus microbiologically confirmed infection—usually a positive blood culture.

Risk factors for severe infection in elderly patients include dementia, delirium, excess injury, aspiration, decreased gag and cough reflex, endocrine deficiency, poor nutrition, immunosenescence of T- and B-cells, immobility, and skin breakdown. The risk factors for severe sepsis and mortality include those factors plus concomitant medical illness, diminished cardiopulmonary reserve, and age-related decrease in organ function, particularly renal function.

The genitourinary tract is the most common source of bacteremia in elderly patients, with gram-negative bacteria being the most commonly isolated causative agents. Escherichia coli is the leading isolate, accounting for the majority of urinary tract infections, followed byKlebsiella, Providencia, andProteus. Other frequent sources of bacteremia include the respiratory tract, the gastrointestinal tract, and endovascular devices. Among the gram-positive organisms causing sepsis, Staphylococcus aureus is the most common, followed byEnterococcus spp. and viridans group streptococci.

Diagnosing sepsis in elderly patients can be challenging. Fever may be blunted or absent in many elderly patients, and others may be hypothermic—a poor prognostic sign. Presenting symptoms in elderly patients may include delirium, weakness, anorexia, malaise, urinary incontinence, and falls. Awareness of these manifestations may increase the recognition of sepsis in older patients.

Prompt source control and early administration of antibiotics are the keys to successful management of sepsis. Broad-spectrum antibiotic therapy should be initiated as soon as possible and no later than 1 hour after the recognition of sepsis. Blood cultures and other cultures from suspected sites should be collected before antibiotic administration (if possible). Aggressive initial resuscitation with fluid is almost always required, and vasopressors (agents that increase blood pressure) may be needed to maintain adequate tissue perfusion. Treatment with recombinant human-activated protein C should be considered in patients with a high risk of death due to severe sepsis unless there is the presence of active bleeding or platelet counts of less than 30,000/mm3, and older adults have been shown to benefit as much as younger adults. Steroids are reserved for patients [Page 554]with documented relative adrenal insufficiency. Packed red blood cell transfusions should be considered in patients with hemoglobin less than 7 milligrams per deciliter (mg/dl), except for older patients with histories of coronary artery disease, in whom the hemoglobin level should be kept above 10 mg/dl.

Physicians taking care of elderly patients with severe sepsis must be prepared to discuss end of life issues early in the patients' illness. Prolonging life may be futile in some cases, and withholding or withdrawing care may be in the best interest of the patients. Advanced directives, if available, should always be followed.

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