FEVER & HYPERTHERMIA

ESSENTIAL INQUIRIES

Age.
Localizing symptoms.
Weight loss.
Joint pain.
Injection substance use.

Immunosuppression or neutropenia.
History of cancer.
Medications.
Travel.

General Considerations

The average normal oral body temperature taken in mid-morning is 36.7°C (range 36–37.4°C). This spectrum includes a mean and 2 standard deviations, thus encompassing 95% of a normal population, measured in mid-morning (normal diurnal temperature variation is 0.5–1°C). The normal rectal or vaginal temperature is 0.5°C higher than the oral temperature, and the axillary temperature is correspondingly lower. Rectal temperature is more reliable than oral temperature, particularly in patients who breathe through their mouth or in tachypneic states.

Fever is a regulated rise to a new “set point” of body temperature. When stimuli act on monocyte-macrophages, these cells elaborate pyrogenic cytokines, causing elevation of the set point through effects in the hypothalamus. These cytokines include interleukin-1 (IL-1), tumor necrosis factor (TNF), interferon-gamma, and interleukin-6 (IL-6). The elevation in temperature results from either increased heat production (eg, shivering) or decreased loss (eg, peripheral vasoconstriction). Body temperature in cytokine-induced fever seldom exceeds 41.1°C unless there is structural damage to hypothalamic regulatory centers. 

1. Fever

Fever as a symptom provides important information about the presence of illness—particularly infections—and about changes in the clinical status of the patient. The fever pattern, however, is of marginal value for most specific diagnoses except for the relapsing fever of malaria, borreliosis, and occasional cases of lymphoma, especially Hodgkin disease. Furthermore, the degree of temperature elevation does not necessarily correspond to the severity of the illness. In general, the febrile response tends to be greater in children than in adults. In older persons, neonates, and in persons receiving certain medications (eg, NSAIDs or corticosteroids), a normal temperature or even hypothermia may be observed. Markedly elevated body temperature may result in profound metabolic disturbances. High temperature during the first trimester of pregnancy may cause birth defects, such as anencephaly. Fever increases insulin requirements and alters the metabolism and disposition of drugs used for the treatment of the diverse diseases associated with fever.

2. Hyperthermia

Hyperthermia—not mediated by cytokines—occurs when body metabolic heat production or environmental heat load exceeds normal heat loss capacity or when there is impaired heat loss; heat stroke is an example. Body temperature may rise to levels (> 41.1°C) capable of producing irreversible protein denaturation and resultant brain damage; no diurnal variation is observed.

Neuroleptic malignant syndrome is a rare and potentially lethal idiosyncratic reaction to major tranquilizers, particularly haloperidol and fluphenazine; however, it has also been reported with the atypical neuroleptics (such as olanzapine or risperidone). Serotonin syndrome resembles neuroleptic malignant syndrome but occurs within hours of ingestion of agents that increase levels of serotonin in the central nervous system, including serotonin reuptake inhibitors, monoamine oxidase inhibitors, tricyclic antidepressants, meperidine, dextromethorphan, bromocriptine, tramadol, lithium, and psychostimulants (such as cocaine, methamphetamine, and MDMA). Clonus and hyperreflexia are more common in serotonin syndrome whereas “lead pipe” rigidity is more common in neuroleptic malignant syndrome. Neuroleptic malignant and serotonin syndromes share common clinical and pathophysiologic features to malignant hyperthermia of anesthesia (see Chapters 25 and 38).

3. Fever of Undetermined Origin

(See Fever of Unknown Origin, Chapter 30)

Most febrile illnesses are due to common infections, are short-lived, and are relatively easy to diagnose. In certain instances, however, the origin of the fever may remain obscure (“fever of undetermined origin,” FUO) even after protracted diagnostic examination. In upper respiratory tract infections, fever typically lasts no more than 3–5 days, beyond which additional evaluation should be considered. he term “FUO” has traditionally been reserved for unexplained cases of fever exceeding 38.3°C on several occasions for at least 3 weeks in patients without neutropenia or immunosuppression (see Chapter 30). Some authors have advocated for changing the definition of FUO in frail elderly nursing home patients to a persistent oral or tympanic membrane temperature of 37.2°C (99°F) or greater, or persistent rectal temperature of 37.5°C (99.5°F) or greater.

Differential Diagnosis

See Table 2–7. The causes of FUO among elderly patients differ from those in younger patients, and a definitive diagnosis can be achieved in a larger proportion of elderly patients (up to 70%). Although the general diagnostic approach and distribution of infectious and noninfectious causes are roughly similar between age groups, tuberculosis and temporal arteritis are particularly more common causes of FUO in the elderly.

Treatment

Most fever is well tolerated. When the temperature is > 40°C, symptomatic treatment may be required. A temperature > 41°C is likely to be hyperthermia and thus not cytokine mediated, and emergent management is indicated. (See Heat Stroke, Chapter 37.)

A. General Measures for Removal of Heat

Regardless of the cause of the fever, alcohol sponges, cold sponges, ice bags, ice-water enemas, and ice baths will lower body temperature. They are more useful in hyperthermia, since patients with cytokine-related fever will attempt to override these therapies.

B. Pharmacologic Treatment of Fever

1. Antipyretic drugs—Antipyretic therapy is not needed except for patients with marginal hemodynamic status. Aspirin or acetaminophen, 325–650 mg every 4 hours, is effective in reducing fever. These drugs are best administered continuously rather than as needed, since “prn” dosing results in periodic chills and sweats due to fluctuations in temperature caused by varying levels of drug.

2. Antimicrobial therapy—In most febrile patients, empiric antibiotic therapy should be deferred pending further evaluation. However, empiric antibiotic therapy is sometimes warranted. Prompt broad-spectrum antimicrobials are indicated for febrile patients who are clinically unstable, even before infection can be documented. These include patients with hemodynamic instability, those with neutropenia (neutrophils < 500/mcL), others who are asplenic (surgically or secondary to sickle cell disease) or immunosuppressed (including individuals taking systemic corticosteroids, azathioprine, cyclosporine, or other immunosuppressive medications) (Tables 30–4 and 30–5), and those who are HIV infected (see Chapter 31). For treatment of fever during neutropenia following chemotherapy, outpatient parenteral antimicrobial therapy with an agent such as ceftriaxone can be provided effectively and safely. If a fungal infection is suspected in patients with prolonged fever and neutropenia, fluconazole is an equally effective but less toxic alternative to amphotericin B.

C. Treatment of Hyperthermia

Discontinuation of the offending agent is mandatory. Treatment of neuroleptic malignant syndrome includes dantrolene in combination with bromocriptine or levodopa (see Chapter 25). Treatment of serotonin syndrome includes administration of a central serotonin receptor antagonist cyproheptadine or chlorpromazine alone or in combination with a benzodiazepine (see Chapter 25). In patients for whom it is difficult to distinguish which syndrome is present, treatment with a benzodiazepine may be the safest therapeutic option.

When to Refer

Once the diagnosis of FUO is made, referral to infectious disease specialist or rheumatologist may be appropriate to guide specific additional tests.

When to Admit

• Malignant hyperthermia.
• Heat stroke.
• For measures to control temperature when it is > 41°C or when associated with seizure or other mental status changes.