Cold Sepsis: Why Hypothermia in Infection Should Terrify You

Cold Sepsis: Why Hypothermia in Infection Should Terrify You

Dispatch sends you for a “generally unwell” patient. You walk in and find a 74-year-old man in his recliner. He is confused but arousable. Skin is cool and dry. Heart rate 108. Blood pressure 96/58. You check a temperature: 35.4 degrees C.

No fever. Cool skin. No obvious source. This does not look like sepsis.

Except it is. And it is worse than the version with the fever.

The Fever You Expected Is a Good Sign

Fever is the immune system working. When pyrogens trigger the hypothalamic set point to rise, it means the body has detected the threat and is mounting a coordinated response — increasing metabolic rate, enhancing immune cell function, and creating a less hospitable environment for pathogens.

Hypothermia in the setting of infection means that response has failed.

The Sepsis-3 criteria include temperature below 36 degrees C as a defining criterion alongside fever for good reason. A core temperature under 36 degrees C in a patient with suspected infection is not a mild finding. It is a red flag that the immune system is losing the fight before it started (Singer et al., JAMA 2016).

The Numbers Are Ugly

Multiple studies have shown that hypothermic sepsis carries significantly higher mortality than febrile sepsis:

• A large retrospective analysis found that septic patients presenting with hypothermia (below 36 degrees C) had mortality roughly 1.7 times higher than febrile septic patients (Rumbus et al., Front Med 2017).
• Hypothermic patients are more likely to have bacteremia, more likely to develop shock, and more likely to die within 28 days (Kushimoto et al., Crit Care Med 2005).
• The Surviving Sepsis Campaign guidelines specifically call out hypothermia as a marker of severity that should not be overlooked (Evans et al., Intensive Care Med 2021).

Here is what makes this dangerous in the field: hypothermic sepsis does not look dramatic. No rigors, no flushing, no “obviously febrile” presentation. The patient is often quietly altered, cool, and dry — which can easily be attributed to dehydration, a medication effect, or just being old.

Why Does Hypothermia Happen in Sepsis?

The exact mechanisms are still being studied, but the leading explanations include:

• Immune exhaustion — The body cannot mount the metabolic response needed to generate fever. This is sometimes associated with persistent lymphopenia, a marker of immune collapse.
• Overwhelming pathogen load — The infection is so severe that the normal inflammatory cascade is suppressed rather than amplified.
• Extremes of age — Elderly patients and neonates are particularly prone to hypothermic sepsis because their thermoregulatory responses are already blunted.
• Peripheral vasodilation — In distributive shock, heat loss through dilated capillary beds can drop core temperature below normal.

How to Catch It

The fix is simple, but it requires you to actually do it: take a temperature on every patient where sepsis is on your differential. Not “looks warm,” not “skin feels normal.” An actual number.

Then apply the same suspicion you would give to a 39-degree fever. A patient with a suspected infection and a temperature of 35.2 degrees C should worry you more, not less.

Pair the temperature with these findings and your index of suspicion should go through the roof:

• New confusion or altered mental status
• Tachycardia without another explanation
• Respiratory rate over 22
• Mottled or cool extremities
• Hypotension or a blood pressure well below their baseline

The Prehospital Piece

You cannot give antibiotics in most systems. But you can do three things that matter:

1. Recognize it. Call it what it is in your handover: “I am concerned about sepsis with hypothermia — temp is 35.4, altered from baseline, heart rate 108.” That sentence changes the receiving team’s triage speed.
2. Support perfusion. IV access, fluid bolus per protocol, trend vitals. These patients can decompensate fast.
3. Keep them warm. This sounds basic, but hypothermic sepsis patients are already losing a battle they cannot afford to lose. Blankets, warm cabin, minimize exposure during assessment. You are not treating hypothermia — you are stopping it from getting worse while the immune system is already on its knees.

The Pearl

A cold septic patient is sicker than a hot one. Hypothermia in infection is not a mild finding — it signals immune failure, carries nearly double the mortality, and often presents quietly enough to be missed. Take the temperature. Trust the number. Say it in your handover.

---

References

• Singer M, et al. The Third International Consensus Definitions for Sepsis and Septic Shock (Sepsis-3). JAMA. 2016;315(8):801-810. PubMed
• Rumbus Z, et al. Fever Is Associated with Reduced, Hypothermia with Increased Mortality in Septic Patients: A Meta-Analysis of Clinical Trials. PLoS One. 2017;12(1):e0170152. PubMed
• Kushimoto S, et al. Body temperature abnormalities in non-neurological critically ill patients: a review of the literature. J Intensive Care. 2014;2:14. PubMed
• Evans L, et al. Surviving Sepsis Campaign: International Guidelines for Management of Sepsis and Septic Shock 2021. Intensive Care Med. 2021;47:1181-1247. PubMed

This clinical pearl is for educational discussion only. Always follow your local protocols and medical direction. Your protocols exist for good reasons — this content is meant to enhance your clinical thinking, not replace your guidelines.