10. Infectious Disease

According to the American College of Critical Care and the Infectious Diseases Society of America (IDSA), fever in the ICU can be defined as a temperature >38.3°C (≥101°F)

A lower threshold should be considered in the immunocompromised host

Epidemiology

Fever in the ICU is a common phenomenon

Thirty percent of medical ICU patients become febrile during their hospital stay and about two thirds of patients with severe sepsis become febrile

Common Causes to Remember

Infectious: most common causes of fever in the ICU are due to infection, although not every infectious process results in fever

The most common ICU acquired infections causing fever include

VAP (occurs in approx 25% of mechanically ventilated pt)

Sinusitis (up to 75% of pt after 1 week of mechanical ventilation)

Catheter-associated bloodstream infections (5.3 per 1,000 catheter days)

Primary gram-negative septicemia

Clostridium difficile-related diarrhea

Abdominal sepsis

Complicated wound infection

Candida infection

Noninfectious: noninfectious causes in the ICU often do not exceed a body temperature of >38.9 (exceptions are drug fever and fever 2/2 blood transfusions)

They are plentiful and include the following:

Alcohol withdrawal

Postoperative fever

Post-transfusion fever

Drug fever

Cerebral infarction or SAH

Adrenal insufficiency

Myocardial infarction

Pancreatitis

Acalculous cholecystitis

Ischemic bowel

Aspiration pneumonitis

ARDS

Fat emboli

Transplant rejection

DVT/PE

Gout and pseudogout

Hematoma

Cirrhosis

Gastrointestinal bleed

Phlebitis

IV contrast reaction

Neoplastic fever

Decubitus ulcers

Key Pathophysiology

A stimulus (such as an infection, injury or drugs) elicits the release of endogenous pyrogens (interleukin [IL]-1, tumor necrosis factor, IL6, and interferons)

These interact with different cells that produce prostaglandins, which diffuse into the brain

This leads to up-regulation of the thermostatic set point

The regions responsible for coordinating the fever response are the hypothalamus and the brain stem

Through spinal and supraspinal motor systems and the sympathetic system, the body generates heat and reduces heat loss, which increases the body core temperature

Management and Treatment

Before initiating empiric antibiotic therapy, a thorough history and physical examination should be performed

Imaging should be reviewed and noninfectious causes should be excluded

Blood cultures and possibly other specimens should be collected

Interestingly, the ideal time to draw blood cultures is 1–2 hours before the onset of fever, as the concentration of bacteria in the blood peaks before the onset of fever

Thus, drawing blood cultures at the time of fever spike might not have the highest yield, and collection of blood cultures at different time points might be helpful in detecting microorganisms by randomly coinciding collection and bacteremia

Even if there is no obvious source of infection, empiric treatment should be initiated promptly after obtaining cultures if the patient’s condition is deteriorating or in immunocompromised patients

It should consist of broad-spectrum antibiotic coverage

Fever itself can be treated either with antipyretic agents (such as acetaminophen) or with external cooling methods (such as hypothermia blankets)

The benefit of routinely treating fever in the ICU continues to be debated

Fever is considered a defense mechanism and has been shown to optimize the immune response and to inhibit bacterial and viral growth

Moreover, the use of cooling blankets is known to be associated with hypermetabolism leading to increased oxygen consumption and elevated levels of catecholamines

It is, however, generally recommended to control fever >40°C (104°F), in the following patients:

Those with limited cardiorespiratory reserve

Hypoxia

Acute brain injury

Selected Infections (Not Covered Elsewhere)

Central Line Infections

Introduction

Central line–associated bloodstream infections (CLABSIs) are an important cause of morbidity and mortality

Infection localized to catheter site or catheter-associated bloodstream infections

Epidemiology

Infections associated with central lines are one of the leading causes of healthcare-related infections and have been estimated to be the eighth leading cause of death in the United States

In 2009, the estimated number of ICU CLABSIs in the United States was 18,000

These infections increase hospital stay by up to 21 days

Of note, arterial line infections are generally not considered to be a relevant source of infection; however, one study suggests the incidence to be 1.4% in a surgical ICU population

Key Pathophysiology

CLABSIs within 7 to 10 days of placement occur most commonly from extraluminal bacteria. This is from migration of bacteria from the skin to the blood through the catheter site. Central line infections >10 days occur most commonly from contamination of a hub used to access the catheter

Common organisms: gram-positive cocci (coagulase-negative staphylococcus, Staphylococcus aureus, and enterococcus species)

Predisposing host factors include chronic illness, BMT, immune deficiency, malnutrition, TPN administration, previous BSI, extremes of age and loss of skin integrity (e.g., burns), prolonged hospitalization before insertion of catheter, catheter type, catheter location (increased infection rate of internal jugular (IJ) vs subclavian catheter), conditions of insertion, catheter-site care, skill of the catheter inserter

Clinical Manifestations

Fever is the most common presenting sign

Signs of infection include erythema, induration, tenderness, or purulent discharge

Diagnosis

IDSA definition: Isolation of the same organism from a quantitative blood cx drawn through the CVC and from a peripheral vein with the single bacterial colony count at least threefold higher in the CVC as compared to the peripheral culture

A shorter time to positivity (>2 hours earlier) in the CVC culture as compared to the peripheral culture has also been shown to be sensitive as well as specific for diagnosis

CDC Definition: “recovery of a pathogen from a blood culture (a single blood culture for organisms not commonly present on the skin and two or more blood cultures for organisms commonly present on the skin) in a patient who had a central line at the time of infection or within the 48-hour period before development of infection. The infection cannot be related to any other infection the patient might have and must not have been present or incubating when the patient was admitted to the facility.”

Management and Treatment

If CLABSI is suspected, empiric therapy should be based on the most likely organism and take into consideration host factors and the overall clinical picture

For short-term catheters, removal/replacement is recommended if the infection is caused by S. aureus, Enterococcus spp., gram-negative bacteria, fungi and mycobacteria

Salvage of the catheter with antibiotic lock therapy can be attempted if the organism colonizing the central line is coagulase-negative staphylococcus

For long-term CVC catheter salvage can only be attempted in a few circumstances:

Uncomplicated CLABSI caused by organisms other than S. aureus, Pseudomonas aeruginosa, Bacillus spp., Micrococcus species, propionibacteria, fungi, or mycobacteria)

Restricted to patients with limited vascular access or those who need central access for survival

Salvage therapy should include antibiotic lock as well as systemic therapy

Prevention guidelines during insertion include:

Selection of site —subclavian vein catheters are thought to have the lowest risk of infection

Recent evidence reveals no difference in the infection rate based on catheter site except in patients with BMI > 40

No difference in infection rate in all three sites (subclavian, IJ, and femoral) if the following is instituted:

Aseptic technique

Hand hygiene

Maximal sterile barrier precautions including full body drape

Use of 2% chlorhexidine skin prep

Ultrasound for placement

Use of a checklist

Prevention guidelines during maintenance include:

Disinfecting catheter hubs, injection ports, and connectors before accessing the catheter

Replacement of administration sets other than sets used for lipids or blood products every 96 hours

Daily reassessment of need for the central line

Outcome

The mortality of CLA BSI has been reported to be as high as 12% to 25%

Necrotizing Soft Tissue Infections

Introduction

Necrotizing soft tissue infections (NSTI) (“flesh eating bacteria syndrome”) is a rare but life threatening infection of the soft tissues that is associated with a high mortality rate

It is characterized by subtle onset and rapid spread leading to necrosis spreading from fascia through muscles and subcutaneous fat tissue causing necrosis of the adjacent skin