Definition
A.Therapeutic hypothermia, also called targeted temperature management (TTM), consists of intervention(s) for the management of fever and includes the use of antipyretic medications, surface cooling, and intravascular devices to reduce temperature.
B.Fever is defined by at least one core temperature measurement of ≥38.3°C on two consecutive days.
C.High fever is defined by one or more measurement of core temperature of ≥39.5°C.
D.Fevers of acute brain injury (either traumatic or vascular in nature) are independently associated with worse outcomes, which are associated with temperatures greater than 37.3°C in a number of studies.
1.Fever control is important because it contributes to cerebral ischemia and possible worsening of cerebral edema, leads to increased intracranial pressures, and results in decreased levels of consciousness.
Incidence
A.The incidence of fever with traumatic brain injury (TBI) is difficult to quantify because targeted therapies are often initiated within hours of onset. However, it is estimated that there are approximately 1.4 million cases of TBI in the United States annually.
B.Patients with subarachnoid hemorrhage (SAH) have been shown to have a high incidence of fever development; SAH occurs in as many as 72% of patients diagnosed with SAH.
C.Patients with intracranial hemorrhage (ICH) have up to a 53% risk of fever development in some studies, and this risk increases to as much as 83% with patients who also have intraventricular hemorrhage (IVH).
Pathogenesis
A.Noninfectious, or central, fever is the physiological loss of ability to autoregulate body temperature. In ICUs, fever with a noninfectious source has been shown to have an earlier onset (within 72 hours of admission) than fever with an infectious source.
B.Infectious fevers occur in response to infection. Fever is associated with sepsis in up to 74% of hospitalized patients and as many as 90% of those with severe sepsis.
C.Heat shock proteins are induced by fever. These are critical for anti-inflammatory effects and cellular survival during stress.
D.Patients with neurological injury are at risk for both infectious and noninfectious fevers.
Predisposing Factors
A.Infectious processes.
1.Bacterial.
a.Urinary tract infection.
b.Upper respiratory infection.
i.Pneumonia.
ii.Bronchitis.
iii.Sinusitis.
c.Central line infection.
d.Bloodstream infection.
e.Cerebrospinal fluid (CSF) infection.
i.Ventriculitis.
ii.Meningitis.
f.Cellulitis.
g.Clostridium difficile enteritis.
2.Fungal.
3.Viral.
a.Influenza.
b.Meningitis.
c.Shingles.
d.HIV/AIDS.
e.Mumps/measles/rubella.
f.Infectious mononucleosis.
g.Herpes.
B.Surgical incisions, which should be monitored for signs and symptoms of infection.
C.Invasive lines and devices, which may predispose patients to infection.
1.Foley catheters.
2.Endotracheal tubes/tracheostomies.
3.External ventricular drains/ventriculoperitoneal shunts/lumbar drains.
4.Gastrostomy tubes.
5.Central lines, arterial lines, pulmonary artery catheters, peripherally inserted central catheters, intravenous lines.
D.Some medications.
1.Steroids.
2.Antibiotics.
3.Serotonergic drugs, which may lead to serotonin syndromes.
4.Anesthetics, specifically volatile anesthetic agents, which are associated with malignant hyperthermia.
5.Anticholinergic agents.
6.Sympathomimetic agents.
E.Deep vein thrombosis (DVT).
F.Blood transfusion reactions.
G.Mechanical ventilation, which puts patients at increased risk for developing ventilator-associated infections.
H.Chronic medical illnesses, which may result in compromised immune systems and/or autoimmune disorders.
Subjective Data
A.Common complaints/symptoms.
Patients with brain injuries may not be alert enough to reliably provide subjective
complaints. Spinal cord injured patients may not be able to describe pain in detail due to sensory or thermoregulatory loss.
1.Warm or overheated feeling.
2.Chills.
3.Generalized body aches.
4.Sweating.
5.Palpitations or fluttering of heart.
6.Headache.
B.Other signs and symptoms.
1.Decreased level of consciousness or altered mental status.
2.Tachycardia.
3.Tachypnea.
4.Hypotension or hypertension.
5.Increased intracranial pressure.
6.Vasospasm in patients with SAH as evidenced by trending transcranial Doppler velocities and/or digital subtraction angiography (DSA), computed tomography angiogram (CTA), or magnetic resonance angiography (MRA) imaging.
7.Positive cultures: Blood, CSF, pleural fluid, urine.
8.Abnormal lab results: Elevated white blood cell (WBC) count, erythrocyte sedimentation rate (ESR), C-reactive protein (CRP).
C.Review of systems.
1.Assess patient for fever or symptoms suggesting fever prior to hospital admission.
2.Inquire about any recent or current known infections, cold/influenza symptoms, or abnormal rashes/skin lesions.
3.Evaluate for any chills, shivering, or other symptoms suggestive of fever.
4.Assess for loss of appetite, weight loss, dehydration, or nausea or vomiting or other gastrointestinal (GI) upset.
Physical Examination
A.Check blood pressure, pulse, respirations, and temperature.
1.Temperature monitoring methods are essential in order to obtain accurate and reliable measurements. Continuous monitoring is ideal, but if this is not possible, patients’ temperatures should be checked on an hourly basis using core methods.
a.The most accurate source of core temperature monitoring is using a pulmonary artery catheter.
b.Other core methods of temperature monitoring include intravesicular (bladder), esophageal, and rectal.
c.Peripheral methods of temperature monitoring include tympanic membrane, axillary, and oral.
B.Look for any lines or drains that may be a nidus for infection.
1.Urinary Foley catheter.
2.Central venous catheters, arterial lines.
3.Lumbar drain, ventricular drain.
4.Any other surgical lines or drains.
5.Lines for mechanical ventilation.
C.Examine skin thoroughly.
1.Check for cellulitis.
2.Recent surgical wounds.
3.Any skin breakdown.
D.Auscultate heart and lungs.
1.Listen for murmurs or consolidation.
E.Perform a neurological exam as appropriate for the patient’s diagnosis.
Diagnostic Tests
A.All tests and imaging should be directed at ruling out infectious causes of fever as well as venous thromboembolism, transfusion reaction, drug fever, adrenal insufficiency, thyroid storm, and any other noninfectious, noncentral etiologies. Tests should be ordered with discretion and with the individual patient in mind.
B.Laboratory tests.
1.Complete blood count with differential.
a.Acute neurological injury can cause a rise in inflammatory markers, similar to an infectious response. The percentage of neutrophils, however, is likely higher in patients with infectious fever.
2.Basic metabolic panel.
3.Liver function tests and bilirubin.
4.Amylase and lipase.
5.ESR/CRP.
6.Cortisol.
7.Thyroid-stimulating hormone (TSH), triiodothyronine (T3), and thyroxine (T4).
8.Procalcitonin.
C.Microbiology.
1.HIV antibody.
2.Heterophile antibody.
3.Hepatitis serologies.
4.Urine culture.
5.Blood culture.
6.CSF culture.
7.Tuberculin skin test.
D.Imaging.
1.Chest radiograph.
2.CT of chest and abdomen.
3.Ultrasonography.
Evaluation and Management Plan
A.If the fever is caused by an infectious source, source control is the priority, which involves removing any related lines or drains as well as choosing an effective antimicrobial agent.
B.If the fever is caused by a noninfectious, noncentral condition, it will need to be addressedaccordingly. Possible causes are:
3.Drug fever.
4.Adrenal insufficiency.
5.Thyroid storm.
C.If other etiologies of fever have been ruled out and the most likely cause of a patient’s fever is central and due to neurological injury, the following treatments can be used.
1.Pharmacologic methods.
a.Antipyretic agents: Acetaminophen, aspirin, or nonsteroidal anti-inflammatory drugs (NSAIDs).
i.These agents are likely to be ineffective in brain-injured patients with impaired temperature regulatory mechanisms.
ii.Acetaminophen is the preferred agent because aspirin and NSAIDs have undesirable side effects such as platelet dysfunction and GI upset.
b.Steroids: Not used because of multiple side effects.
2.External cooling.
a.Evaporation.
i.Water or alcohol sponge baths.
b.Conduction.
i.Ice packs.
ii.Immersion in cold water.
iii.Water-circulating cooling blankets or pads. Improved accuracy with newer technology provides constant monitoring of temperature and adjustment of circulating water to maintain desired body temperature.
c.Convection.
i.Fans.
ii.Ambient air temperature control.
iii.Air-circulating cooling blankets.
d.Radiation.
i.Skin exposure.
3.Invasive cooling.
a.Cold saline boluses.
b.Intravascular catheters.
D.Complications.
Many serious complications arise from induction of hypothermia as opposed to normothermia in a patient. Most of these adverse effects are not problematic until core body temperatures are 35°C or lower. However, a number of complications may occur when attempting maintenance of normal temperatures.
1.Hepatic and renal toxicity.
2.Catheter-related thrombosis and infection.
3.Skin breakdown.
a.Surface cooling may predispose to skin lesions due to its intrinsic mechanism of action via contact with skin.
b.This risk may be low depending on the type of material used, the temperature of the material, and the length of time of intense cooling.
c.Skin should be monitored for blistering, bruising, or sign of breakdown from prolonged cold exposure.
d.Circulating water temperature should be monitored continuously, and prolonged periods of cold circulating water should be avoided.
4.Subsequent infections.
5.Shivering.
a.The metabolic effects of shivering can be considerable, resulting from increased energy expenditure.
b.Shivering can produce heat, which is counterproductive.
c.The implications and management of shivering are extensive (see the following section Shivering During Targeted Temperature Management
).
Follow-Up
A.There are no special follow-up needs for central fevers, because they are generally related to the initial neurological insult.
B.Follow-up and postdischarge monitoring is related to the patient’s admission diagnosis as well as new issues that may have occurred during hospitalization.
Consultation/Referral
A.Inpatient consults are relevant to the diagnosis of each patient.
B.Examples of consults for noncentral fevers.
1.Infectious disease.
2.Wound/ostomy.
3.Hematology.
4.Endocrinology.
5.Pharmacy.
6.Others related to fever etiology.
C.Pastoral care.
Special/Geriatric Considerations
A.Geriatric individuals often have unique presentations and require special considerations when gathering a history and physical.
B.Treatment methods may also vary slightly due to multiple comorbidities and less reserve.
1.The elderly are more prone to ICU delirium and mental status changes while hospitalized, making history and physical examination challenging at times.
2.Skin breakdown is a regular concern in geriatric patients, because mobility and skin caliber are lower in these individuals, particularly with external cooling methods.
3.Geriatric patients may not always mount a febrile response to infection. They can become hypothermic in an infected state.
4.The effectiveness of different cooling methods increase with advanced age secondary to
slower counterregulatory response to small temperature changes, decreased metabolism, decreased vascular response (and as a result, vasoconstriction), and often a lower body mass index (BMI).
5.Medications may need to be adjusted more frequently in the elderly, whether because of hepatic/renal function or low BMI.
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