Clinical Information – Oral Version of TAT Thermometers

Normal Body Temperature (BT)

Normal BT is not a single temperature, but a range of temperatures influenced by age, time of day, and measurement site.

General Rule of Thumb

Rectal temperature is ≈2°F (1°C) higher than axillary and ≈1° F (0.5°C) higher than oral temperature.¹

Expect the Differences

Arterial temperature measurement (PA Catheter, TA Thermometry) leads all other methods in identifying fever or defervescence, and is unaffected by activities of daily living. Accordingly, it will sometimes be different from your present methods — but accurate.

Guidelines for Patient Temperature Assessment

1. Normal TA Temperature: On a stable resting patient, TAT is ≈0.8°F (≈0.4°C) higher than an optimum oral temperature, and is about the same as a rectal temperature. However, during febrile episodes, the difference can be much higher, mainly because of the artifacts of oral and rectal sites.

2. Fever Definition: Clinically, fever is defined as a BT ≥1.8°F (1°C) above the mean standard deviation at the site of recording.²

A single oral temperature of ≥101°F (38.3°C) in the absence of obvious environmental causes is usually considered fever. An oral temperature of ≥100.4°F (38.0°C) over at least 1 hour indicates a fever state.³

A single arterial temperature >101.8°F (38.8°C) in the absence of obvious environmental causes is usually considered fever. An arterial temperature >101.2°F (38.4°C) over at least 1 hour indicates a fever state. While the above are recommended guidelines, not all fevers require laboratory tests, and clinical assessment in concert with standard hospital protocol for fever workups should always prevail.

3. Oral Temperature Risks: Oral temperature can be clinically misleading, and many febrile patients can have a “normal” temperature.⁴ Mouth breathing, tachypnea, heated gases, and hot or cold fluids can distort the reading, as can intubation or inability of the patient to cooperate. Accordingly, comparisons with TA may not be reliable.

4. Rectal Temperature Risks: Rectal temperature should only be considered as a good approximation of core temperature when the patient’s thermal balance is stable, but is not suitable during and after surgery,⁵ and may be misleading after antipyretics, physical exercise, or other intervention that may change temperature quickly.

5. Axillary Temperature Risks: Based on strong evidence cited by the NIH, “axillary temperature is contraindicated in critically ill adults, and its use in the general patient population should be discouraged due to its unreliable correlation with core temperature and its poor reproducibility.”⁶

Normal Body Temperature Ranges at Various Measurement Sites:​​​​​​​

References:

1. Kuzucu EY. Measurement of temperature. Int Anesthesiol Clin, 3(3):435-49, May, 1965

2. El-Radhi AS, Carroll JE. Fever in Paediatric Practice, Ch 2, pp 15-49, Oxford Blackwell Scientific Publications, 1994

3. Hughes WT et al. 1997 Guidelines for the use of antimicrobial agents in neutropenic patients with unexplained fever. Infectious Diseases Society of America (IDSA)

4. Tandberg D et al. Effect of tachypnea on the estimation of body temperature by an oral thermometer. NE J Med, 308, 945-46,1983

5. O’Grady NP, Barie PS, Bartlett JG, et al. Practice guidelines for evaluating new fever in critically ill adult patients. Task Force of the Society of Critical Care Medicine and the Infectious Diseases Society of America. Clin Infect Dis 1998 May: 26(5):1042-59

6. Houdas Y, et al. Human body temperature. Ch 5, p89, Plenum Press, 1982, USA, UK

Fever Guidelines and Adjustment for Temporal Artery

​​​​​​​ * Fever Definition in Neutropenic Patients with Unexplained Fever

 ** Evaluation and treatment of fever in the non-neutropenic child with cancer

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