Clinical Skills · General Survey, Anthropometric Measurement, and Vital Signs

Temperature

8 min read

On this page 9 sections

In 30 seconds
Why this matters
The college version
Eli explains
Worked example
Key takeaway
Check yourself
Study tools
Sources & references

In 30 seconds

Body temperature is the balance between heat produced and heat lost. Heat is produced mainly by metabolism and muscle activity (including shivering) and lost through radiation, conduction, convection, and evaporation. The hypothalamus acts as the body's thermostat, keeping in a narrow range.

Temperature is one of the four classic vital signs and usually the first clue to infection, inflammation, or a thermoregulation problem. This topic covers why temperature matters, the measurement routes, fever versus , and what changes readings. Route documentation matters — the same body reads differently by route.

Why this matters

Fever is a common reason people seek care and a key infection/inflammation indicator.
Temperature extremes matter. Dangerously low () and high (hyperthermia) body temperatures can be emergencies.
Route and accuracy drive care decisions. Oral, rectal, axillary, tympanic, and temporal readings are not interchangeable — documenting the route prevents misinterpretation, and trustworthy readings determine whether the team is notified, comfort measures offered, or antipyretics given (per order). Vulnerable patients. Infants and older adults regulate temperature less effectively — in some commonly taught situations infants may show a low temperature rather than a fever during infection (verify current evidence; report any abnormal reading).
Scope note. Measuring temperature is often delegated to assistive personnel; interpreting the value and deciding the response is a nursing responsibility. Institutional policy governs route selection, thresholds, and escalation.

The college version

Core Concepts

Core Versus Surface Temperature

Core temperature — the deep tissues (brain, thorax, abdomen) — is what matters physiologically; surface temperature — the skin — varies with blood flow and the environment. No clinical route measures true core directly; every site approximates it differently. The rectal route comes closest; oral, tympanic, and temporal routes approximate well with correct technique; the axillary route is farthest from core and most environment-sensitive.

Measurement Routes

Oral: common for cooperative adults and older children; the thermometer sits in the sublingual pocket, with a commonly taught waiting period after hot or cold drinks, smoking, or chewing gum (follow facility policy). It may be unsuitable for patients who cannot follow instructions or have had recent oral surgery.
Rectal: the closest practical approximation of core; used when oral is not possible, such as in many infants and some critically ill patients. More invasive, requires privacy and care. Facilities commonly avoid it after rectal surgery or with rectal lesions, and in patients with low white blood cell counts (infection risk) — confirm your facility's policy.
Axillary: safe and noninvasive, commonly used in infants; the least accurate route and most affected by environment and clothing.
Tympanic (ear): an infrared probe measures the ear canal; fast, but affected by cerumen (earwax), probe placement, and ear canal shape. Many facilities avoid the ear on the side of an infection or recent surgery — follow facility policy.
Temporal artery: an infrared scanner drawn across the forehead. Noninvasive and fast, but technique matters; sweating, head coverings, or poor contact can affect readings.

Key rule: the number is only meaningful with the route — a rectal reading and an axillary reading on the same patient at the same moment will not be the same number, and neither is "wrong"; they are different approximations of core temperature.

How the Body Regulates Temperature

The hypothalamus compares blood temperature with its — the target it maintains. If blood temperature is low, the body gains heat: skin vessels constrict, muscles shiver, the person seeks warmth. If it is high, the body loses heat: vessels dilate, sweating begins, the person removes layers.

occurs when the set point is raised, usually by pyrogens — substances released during infection or inflammation. The body now treats its temperature as "too cold," so the patient feels cold and shivers (the chill phase) while climbing to the new set point. When the cause resolves, the set point falls and the patient sweats — defervescence.

Hyperthermia is different: heat gain exceeds heat loss with no change in set point — for example, with prolonged heat exposure or extreme exertion; the body's cooling mechanisms are overwhelmed rather than reset. The distinction matters because the mechanisms — and therefore the management — differ, and management is provider-directed; the nurse's role is assessment, measurement, comfort, and reporting.

Hypothermia is the opposite: heat loss exceeds production and core temperature falls below normal — a risk with cold exposure, in older adults, and perioperatively.

Factors That Affect Temperature

Circadian rhythm and age: lowest in the early morning, highest in the late afternoon; infants thermoregulate poorly and older adults have blunted responses.
Exercise, stress, emotion, hormones, medications, and environment shift readings — antipyretics, given per order, lower a fever without treating its cause.
Measurement errors: hot or cold drinks, recent exercise, poor probe placement, sweating, and cerumen cause false readings.

Measuring Temperature Accurately

Choose the route based on the patient's age, condition, and facility policy. Use calibrated equipment with a clean probe cover and follow the device's placement and hold time. Document the value with route and time, noting anything that could affect the reading. If a reading does not fit the patient, repeat it before acting — a single value is a snapshot, not a story.

How It Works / Step-by-Step Process

Select the route per patient age, condition, and facility policy; gather the device with a clean probe cover.
Prepare the patient: explain; check for hot/cold drinks, exercise, or smoking (oral route); ensure privacy.
Place the device per its instructions (sublingual pocket for oral; slide-scan across the forehead for temporal).
Hold and read per the device; discard the probe cover.
Document value with route and time; compare with baseline; repeat if it does not fit; report and escalate per policy.

Common Confusions

Do Not Confuse	With	The Difference
Fever	Hyperthermia	Fever is a raised set point; hyperthermia is overwhelming heat gain with no set-point change.
A value from one route	A value from another route	Routes approximate core differently — rectal reads higher than axillary on the same patient.
"98.6 °F is normal for everyone"	An average with normal variation	It is a commonly cited average; normal ranges and circadian swings vary.

Eli explains

The same idea, in plain words

Explain it like I’m 10

Your body is like a house with a thermostat in your brain. When you get sick, the thermostat can be turned up, so your body works to get warmer — that is why you shiver and feel cold even while your temperature is going up. Nurses measure temperature with a thermometer in the mouth, ear, armpit, or across the forehead to see what the thermostat is doing, and they write down which spot was used because the same body reads a little differently at each spot.

Worked example

The parent with a warm toddler. A parent brings a 3-year-old who "feels warm." The nurse chooses the axillary route (common for young children per policy) and reads 37.9 °C — within the range commonly considered normal for axillary readings, which typically run lower than oral. The nurse documents "37.9 °C axillary," not just "37.9," and since the child is playful and drinking, rechecks per policy and teaches the parent what to watch for.

A different evening, the parent reports the child shivering and "freezing cold" despite feeling hot to the touch. The nurse understands the chill phase: the hypothalamus has raised its set point, and shivering is the body generating heat to reach it — expected physiology, not a cold room. The nurse measures, documents the trend, and reports per facility criteria. Knowing why the body behaves this way turns "shivering but feverish" into a predictable pattern — and tells the nurse what to watch for next (the sweating phase as the fever breaks).

Key takeaways

Temperature reflects the balance between heat production and heat loss, regulated by the hypothalamus.
Routes (oral, rectal, axillary, tympanic, temporal) give different numbers — document the route.
Rectal is closest to core; axillary is least accurate and most environment-sensitive.
Fever = raised set point (pyrogens); hyperthermia = heat gain without a set-point change; hypothermia = excess heat loss.
Chills during fever mean the body is climbing to a higher set point; sweating during defervescence means it is returning to normal.
Infants and older adults thermoregulate less effectively.
Antipyretics lower fever but do not treat the cause; they are given per order.

Check yourself

6 review questions from the chapter. Try each one, then open the answer.

Which route comes closest to core, and which is the least accurate?
Show answer
Rectal comes closest to core; axillary is the least accurate and most affected by the environment.
Explain the difference between fever and hyperthermia.
Show answer
Fever is a raised set point (pyrogens) with the body working to reach a higher temperature; hyperthermia is heat gain exceeding heat loss with no set-point change (for example, heat exposure).
Why might a patient shiver while their temperature is rising?
Show answer
Because the hypothalamus has raised its set point — shivering generates heat to reach the new target, so the patient feels cold even as the temperature rises.
Why must the route be documented with every temperature reading?
Show answer
Because each route approximates core differently — the same body produces different numbers by route, so the number is only interpretable with its route.
List three factors that can make a reading inaccurate.
Show answer
Examples: hot/cold drinks before an oral reading, recent exercise, poor probe placement, sweating, cerumen, room temperature.
Why do infants and older adults need extra attention when it comes to temperature?
Show answer
Infants thermoregulate poorly and older adults have blunted responses — both can be sick without the expected fever pattern, so any abnormal reading warrants attention and reporting.

Keep learning

Ready to build on this? Continue to the next lesson.

Study tools & related lessonsKey vocabulary · Related

Key vocabulary

Core temperature: Temperature of the deep tissues (brain, thorax, abdomen).
Set point: The target temperature the hypothalamus maintains.
Pyrogen: A substance (often from infection or inflammation) that raises the set point.
Fever (pyrexia): A raised set point with the body working to reach a higher temperature.
Hyperthermia: Heat gain exceeding heat loss with no set-point change.
Hypothermia: Core temperature below normal because heat loss exceeds production.
Antipyretic: A medication that lowers fever (given per order).

Sources & references

openstax.org — Clinical Nursing Skills

This lesson was adapted from the open educational references above; their licenses and attributions are preserved. See Copyright & Licensing.

Educational content only. It is not medical, legal or professional advice. Found an error? Tell us.