Temperature Monitoring 

1. PHYSIOLOGY OF BODY TEMPERATURE

  • Normal core temperature: 36.5–37.5°C
  • Controlled by: Hypothalamus (preoptic anterior area)
  • Balance between:
    • Heat production
      • Basal metabolism
      • Shivering (↑ 2–5× heat)
      • Non-shivering thermogenesis (brown fat)
    • Heat loss
      • Radiation (60%)
      • Convection
      • Conduction
      • Evaporation

Core vs Peripheral Temperature

  • Core temperature: Brain, heart, lungs → tightly regulated
  • Peripheral temperature: Skin → variable

 Normal gradient: 0.5–1°C
 Increased gradient = shock / vasoconstriction

Axillary temperature is typically 0.5–1°C lower than oral temperature


 2. DEFINITIONS 

Condition

Definition

Fever

≥ 38°C (regulated rise, cytokine-mediated)

Hyperthermia

Uncontrolled rise (no set-point change)

Hypothermia

< 35°C

Pyrexia of unknown origin

≥38.3°C for >3 weeks

3. SITES OF TEMPERATURE MEASUREMENT

Site

Accuracy

Use in ICU

Notes

Pulmonary artery

 Gold standard

Rare (PAC)

True core temp

Esophageal

++++

Intubated patients

Best intra-op/ICU

Bladder

++++

Foley present

Good if urine flow adequate

Rectal

+++

ICU fallback

Lagging, contamination risk

Tympanic

+++

Quick screening

Affected by technique

Oral

++

Limited ICU use

Affected by O2, intubation

Axillary

+

Least reliable

Screening only

 4. ICU-SPECIFIC CONSIDERATIONS

A. Accuracy Hierarchy 

Pulmonary artery > Esophageal > Bladder > Rectal > Tympanic > Axillary

B. Continuous vs Intermittent

Type

Use

Continuous

ICU, OR, unstable patients

Intermittent

Ward, OPD


Recommended ICU ambient temperature is 20–24°C with 30–60% humidity and ≥12 air changes/hour.”


5. CLINICAL APPLICATIONS IN CCM

 Hypothermia

Classification

Stage

Temp

Mild

32–35°C

Moderate

28–32°C

Severe

<28°C


 Targeted Temperature Management (TTM)

  • Post-cardiac arrest: 32–36°C (guidelines)
  • Prevent fever in:
    • Stroke
    • Traumatic brain injury

Neuro ICU Importance

  • Fever ↑ ICP, ↑ cerebral metabolism
  • Strict normothermia required

 6. SOURCES OF ERROR 

Factor

Effect

Poor probe placement

False readings

Low urine output (bladder)

Inaccurate

Stool in rectum

High reading

Earwax (tympanic)

Low reading

Vasoconstriction

Skin temp unreliable

Rapid temp change

Lag (rectal)