Why should the axilla be patted dry before measuring a client’s axillary temperature?

Why Pat Dry Before Axillary Temperature Measurement

Moisture in the axilla causes evaporative cooling that artificially lowers the measured temperature, leading to inaccurate readings that can miss fever or hypothermia.

The Core Problem: Evaporative Cooling Effect

• Moisture on the skin surface creates an evaporative cooling effect that reduces the measured axillary temperature below the true body temperature 1
• Axillary temperature measurements are already inherently less accurate than core temperature methods, consistently reading 1.5-1.9°C below tympanic temperatures even under ideal conditions 1
• Any additional cooling from moisture compounds this existing measurement gap, making an already imprecise method even more unreliable 1

Clinical Significance of Accurate Measurement

Impact on Critical Decisions

• In hypothermia management, accurate temperature monitoring is essential because treatment protocols differ significantly based on specific temperature thresholds (mild <36°C, moderate 32-34°C, severe <28°C) 1
• Missing fever detection due to falsely low readings can delay critical interventions in sepsis, heat stroke, or post-cardiac arrest care 1
• Axillary measurements can vary by up to 1°C due to external factors including moisture, local blood flow, and incorrect placement 1

The Measurement Gap

• Research demonstrates that axillary temperatures underestimate core temperature by approximately 1.0°F (0.5-0.6°C) on average, and this gap widens with moisture present 2, 3
• In one study, the mean difference between rectal and axillary temperatures was 1.04°C (SD 0.45°C), requiring adjustment by adding 1°C to approximate core temperature 3
• Bladder probes and axillary measurements show variability up to almost 1°C even without moisture interference 1

Proper Technique for Axillary Measurement

Step-by-Step Protocol

1. Pat the axilla completely dry with a soft cloth or towel before thermometer placement 1
2. Apply emollient to the thermometer (not the skin) to reduce friction during insertion and removal, particularly in vulnerable populations like neonates 1
3. Place the sensor over the axillary artery with the arm adducted firmly to the side 1
4. Hold the thermometer in place for the full measurement cycle (typically 30-60 seconds for digital devices) 4
5. Consider using the left axilla preferentially, as studies show better correlation with core temperature (r = 0.786) 5

When Axillary Measurement Is Appropriate

Clinical Context Matters

• Axillary temperature is recommended as a first-line method in neonates and young children who cannot cooperate with oral measurement, but only when proper technique including drying is followed 1, 4, 5
• For critical care situations requiring precise core temperature monitoring (therapeutic hypothermia, heat stroke, post-cardiac arrest), esophageal, bladder (in non-anuric patients), or pulmonary artery catheter measurements are superior to axillary readings 1
• Axillary and oral temperatures are inadequate for measurement during active temperature manipulation for therapeutic hypothermia 1

Common Pitfalls to Avoid

Critical Errors in Practice

• Never rely on axillary temperature alone in emergency situations without considering the inherent 1-1.5°C underestimation 1, 3
• Do not use axillary measurement as the sole method for detecting hypothermia in trauma or post-operative patients, as it consistently underestimates core temperature 1
• Avoid placing the thermometer over wet skin, as approximately 20% of febrile patients can be misdiagnosed as afebrile due to measurement error 6
• In heat stroke emergencies requiring rapid cooling, rectal temperature monitoring is essential (not axillary) because core temperature >40°C (104°F) is the diagnostic threshold 1

Special Populations

• In neonates with epidermolysis bullosa or fragile skin, use emollient on the thermometer to reduce friction, but still ensure the axilla is dry before measurement 1
• For patients undergoing temperature management during cesarean delivery or other surgery, skin temperature monitoring (including axillary) reads 2.0-4.0°C less than core temperature 1

The Bottom Line for Practice

Patting the axilla dry eliminates the evaporative cooling artifact that would otherwise cause falsely low temperature readings, which is critical because axillary measurements already underestimate core temperature by 1-1.5°C 1, 2, 3. This simple step prevents compounding an inherent measurement limitation with an avoidable technical error that could lead to missed diagnoses of fever or hypothermia.