Is an oral temperature of 35.9 degrees Celsius (hypothermia) within the normal range?

Is 35.9°C Oral Temperature Normal?

No, an oral temperature of 35.9°C is not normal—it represents mild hypothermia and warrants clinical evaluation and intervention. 1

Temperature Classification

According to established trauma guidelines, 35.9°C falls within the mild hypothermia range:

• Conventional classification: Mild hypothermia is defined as 35–32°C 1
• Trauma patient classification: Mild hypothermia is defined as 36–34°C (slightly narrower range) 1
• Your patient at 35.9°C: Falls just below the normal threshold and meets criteria for mild hypothermia in both classification systems 1

Normal Temperature Standards

The normal body temperature range varies by measurement site and patient population:

• General ICU patients: Fever is defined as ≥38.3°C, with normal range implied below this threshold 1
• Elderly in long-term care: Normal oral temperature is <37.2°C on repeated measurements 1
• Important caveat: Basal body temperatures in frail elderly may be lower than the traditional mean of 37.7°C, but 35.9°C still represents hypothermia even in this population 1

Clinical Significance and Mortality Risk

Hypothermia at this level carries significant morbidity and mortality implications:

• Trauma patients: Those with core temperatures <36°C have substantially higher mortality rates compared to normothermic patients, even with similar injury severity 2, 3
• Severely injured patients: Hypothermia below 34°C is associated with 40% mortality in trauma, and your patient at 35.9°C is approaching this critical threshold 3
• Physiologic consequences: Even mild hypothermia impairs coagulation, increases bleeding risk, and compromises cardiovascular function 1, 4

Immediate Actions Required

You must actively rewarm this patient and investigate the underlying cause:

1. Remove from cold environment and eliminate sources of ongoing heat loss (wet clothing, cold surfaces) 1
2. Apply warming measures: Use warming blankets, increase environmental temperature, and consider radiant heaters 1
3. Monitor core temperature: Oral temperature is acceptable for monitoring if more invasive methods (esophageal, bladder, pulmonary artery catheter) are not in place 1
4. Investigate etiology: Look for trauma, sepsis, environmental exposure, medications (antipsychotics, benzodiazepines, beta-blockers), endocrine disorders, or debilitating illness 5, 6

Critical Pitfalls to Avoid

• Do not dismiss as "normal variation": While elderly patients may have lower baseline temperatures, 35.9°C represents pathologic hypothermia requiring intervention 1
• Avoid rapid rewarming in severe cases: If hypothermia worsens below 32°C, slow controlled rewarming is essential to prevent cardiac arrhythmias and rewarming shock 4, 6
• Monitor for complications: Watch for coagulopathy, cardiac arrhythmias, and metabolic derangements as temperature normalizes 1, 4
• Consider infection: In elderly or debilitated patients, hypothermia may indicate sepsis rather than fever 1

Temperature Measurement Considerations

Oral temperature is reliable when measured correctly:

• Must be placed in sublingual pouch next to sublingual artery 1
• Can be affected by recent hot/cold intake, smoking, or rapid breathing 1
• Electronic thermometry is superior to mercury thermometers 1
• If accuracy is critical, consider rectal, esophageal, or bladder temperature monitoring 1