Approach to a fever: Clinical sciences

Chapters:

Watch video only

Introduction0:00–0:43

Fever is generally defined as a temperature of 100.4 degrees Fahrenheit or 38 Celsius, or higher. It occurs when chemical triggers, called pyrogens, stimulate the thermoregulatory center in the hypothalamus, which in turn elevates the body temperature.
Pyrogens can be either endogenous, like cytokines from various inflammatory processes or tumors; or exogenous, like antigens from various pathogens.
Now, some important causes of fever to keep in mind include infection, venous thromboembolism, malignancy, autoimmune disease, and certain medications, as well as fever of unknown origin.

Unstable Patient0:43–1:16

Now, if your patient presents with a fever, you should first perform an ABCDE assessment to determine if your patient is unstable or stable.
If unstable, stabilize their airway, breathing, and circulation. Next, obtain IV access and start fluid resuscitation as well as broad-spectrum intravenous antibiotics.
Place your patient on continuous vital sign monitoring, including blood pressure, heart rate, and oxygen saturation. Finally, if needed, provide supplemental oxygen!Okay, let’s jump right back to the ABCDE assessment and take a look at stable patients.

Stable Patient1:16–1:48

In this case, start by obtaining a focused history and physical examination. A body temperature of 100.4 degrees Fahrenheit or 38 degrees Celsius or higher confirms a fever, which could be accompanied by tachycardia.
Once you confirm the presence of fever, your next step is to determine the underlying cause by taking a deeper look at history and physical examination for additional clues.
Okay, the first cause of fever to consider is infection! Your patient’s history may include close contact with a sick individual, recent travel, IV substance use, or high-risk sexual activity.

Infection1:48–3:14

They may report symptoms like cough, malaise, chills, muscle or joint pain, painful urination, or decreased appetite, as well as additional symptoms based on the organ system involved.
Additionally, physical exam findings might reveal tachycardia, tachypnea, lymphadenopathy, abnormal breath sounds, a lesion on the genitalia, or a rash, depending on the underlying cause.
At this point, consider infection as a cause of fever, with your next step being to order labs, including a CBC, as well as inflammatory markers like ESR, CRP, and procalcitonin.
Keep in mind that lab work-up might be extensive depending on which infection is suspected. For example, if you suspect a bacterial infection, you may need to obtain blood or urine cultures; or if you suspect a viral infection, you might need to obtain a viral serology.
Additionally, in some cases, you may consider imaging, like a chest X-ray, CT, or MRI. If confirmatory testing identifies infection, or if you can make a clinical diagnosis based on your findings, diagnose infection as a cause of fever.Next up is venous thromboembolism.

Venous thromboembolism3:14–5:04

In this case, your patient may have risk factors like age over 65, recent surgery, prolonged immobilization, or active malignancy.
Other important risk factors include obesity, smoking, pregnancy, and oral contraceptive use, as well as certain genetic conditions that promote thrombosis.
Additionally, your patient may report extremity pain with swelling and warmth in the affected area, suggesting a DVT; or even trouble breathing, sharp chest pain, or hemoptysis that suggests a PE.
In the case of a DVT, your physical exam may reveal an edematous limb with erythema, warmth, and tenderness to palpation.
It may also show a palpable thrombotic vein, or a positive Homan sign, characterized by pain in the calf muscles during ankle dorsiflexion.
On the flip side, a PE will likely show exam findings such as tachycardia, tachypnea, or wheezing. With these findings, consider venous thromboembolism as a cause of fever, and obtain a Doppler ultrasound of the affected extremity to evaluate for a DVT; or consider a chest computed tomography angiography to evaluate for a PE.
If either reveals a thrombus, diagnose venous thromboembolism as the source of fever!Here’s a clinical pearl! Recurrent infections and thrombosis can present as complications of malignancy.
So, if a patient presents with an infection, or has unexplained thrombosis with other risk factors, be sure to investigate the possibility of malignancy.Next, assess for signs and symptoms of malignancy.

Malignancy5:04–5:57

These are usually nonspecific and include symptoms such as malaise, night sweats, and weight loss; and the physical exam may reveal lymphadenopathy, cachexia, or even a palpable mass.
If your patient presents with these findings, consider malignancy as a cause of fever! To confirm the diagnosis, obtain additional diagnostic tests, which will vary based on the suspected malignancy.
These can include imaging, like an MRI or CT scan; or procedures, such as a colonoscopy, to help locate the malignancy. If you suspect a hematologic malignancy, order a bone marrow biopsy; or, if you suspect a solid cancer, obtain a tissue biopsy!
If testing reveals a tumor or malignant cells, diagnose malignancy as the source of fever.You should also think of autoimmune conditions.

Autoimmune conditions5:57–7:27

These patients may present with symptoms like fatigue, skin rash, and joint pain or swelling, as well as other symptoms depending on the involved tissues.
Additional findings on physical exam may include lymphadenopathy, hepatosplenomegaly, muscle weakness, or joint deformities.
With these findings, consider an autoimmune disease as a cause of fever. Next, based on your suspicion, check for autoantibodies, like antinuclear antibodies, rheumatoid factor, or antineutrophil cytoplasmic antibodies.
Additionally, you might need to check complement levels, such as C3 and C4, or consider an ACE or lysozyme level. Finally, based on the patient’s clinical picture, consider ordering imaging studies, or even a bone marrow or tissue biopsy.The lab results might reveal positive autoantibodies and low C3 and C4, as well as elevated ACE and lysozyme; while imaging could show disease-related abnormalities, such as joint space narrowing or erosions on joint X-ray, or ground glass opacities or hilar adenopathy on chest X-ray.
Additionally, a bone marrow biopsy or tissue biopsy might reveal signs of an inflammatory process, such as inflammatory infiltrate or granulomatous disease.
If this is the case, diagnose an autoimmune disease as the cause of the fever.Another cause to consider is medication-induced fever.

Medication-induced fever7:27–7:53

Medication-induced fever typically occurs with exposure to certain medications, such as beta-lactams, sulfa-containing medications, diuretics, or antiepileptics.
If you identify a causative medication, diagnose medication-induced fever, and stop the medication if possible!Finally, if you cannot identify a source for the fever, consider a fever of unknown origin.

Fever of unknown origin7:53–8:35

Your patient will report a daily fever more than 100.9 degrees Fahrenheit or 38.3 degrees Celsius for more than 3 weeks without a known diagnosis despite getting appropriate evaluation.
They will also likely have nonspecific findings on physical examination, like lymphadenopathy. Lab work and imaging, such as chest X-ray, CT, or MRI, will also be nonspecific.
If your patient meets these criteria, they have a fever of unknown origin, so be sure to continue investigating for the cause!

Review8:35–9:07

Alright, as a quick recap… Fever is typically defined as a temperature of 100.4 degrees Fahrenheit or 38 Celsius or greater.
If your patient presents with a fever, start by performing an ABCDE assessment, and if they’re unstable, stabilize them accordingly.
If your patient is stable, assess for the underlying source of fever, including infection, venous thromboembolism, malignancy, autoimmune disease, and medication-induced fever.
If you can’t identify a source for the fever,
Approach to a fever: Video, Steps, and Uses | Osmosis