Disorders of Thermoregulation

Hypothermia & Basics - Frosty Fundamentals

• Normal Thermoregulation: Hypothalamus (anterior preoptic area) maintains set point (~37°C). Heat gain (metabolism, shivering, vasoconstriction) balanced by heat loss (radiation, conduction, convection, evaporation, vasodilation).

• Hypothermia: Core temperature < 35°C (95°F).

• Causes:

  • Environmental: Cold exposure (air/water).
  • Metabolic: Hypothyroidism, hypoglycemia, adrenal insufficiency.
  • CNS dysfunction: Stroke, head trauma, hypothalamic disorders.
  • Drugs: Ethanol, sedatives, opioids.
  • Other: Sepsis, extensive burns, iatrogenic.

• Stages & Features:

  Stage	Core Temp (°C)	Key Features
  Mild	32-35°C	Shivering, tachycardia, tachypnea, confusion, ataxia.
  Moderate	28-32°C	Shivering stops, bradycardia, hypotension, arrhythmias (AF), stupor. > ⭐ Paradoxical undressing may occur.
  Severe	<28°C	Coma, VF/asystole, areflexia, pulmonary edema.

• ECG: Osborn J wave (📌 camel hump at QRS-ST junction).

• Management:

  • ABCs; remove wet clothes.
  • Rewarming:
    • Passive external (mild): Warm blankets.
    • Active external (mild-moderate): Forced warm air, heating pads.
    • Active internal (moderate-severe, unstable): Warm IV fluids ($40-42°C$), peritoneal/pleural lavage, ECMO.

Heat Illnesses - Sizzling Syndromes

Caused by ↑ environmental heat. Key is core temperature & CNS status.

• Heat Cramps: Painful muscle spasms.
  • Core Temp: Normal/Slightly ↑. Mental Status: Alert. Skin: Moist.
  • Tx: Oral/IV fluids, rest.
• Heat Exhaustion: Systemic symptoms, but no significant CNS dysfunction.
  • Core Temp: < 40°C (104°F). Mental Status: Fatigue, dizziness, headache. Skin: Cool, moist.
  • Tx: Move to cool place, oral/IV fluids, active cooling.
• Heat Stroke: MEDICAL EMERGENCY!
  • Core Temp: > 40°C (104°F) WITH CNS dysfunction (delirium, seizures, coma).
  • Types:
    • Classic (Non-exertional): Elderly, chronic illness; hot, dry skin.
    • Exertional: Young athletes; skin often sweaty.
  • Complications: Rhabdomyolysis, ARDS, DIC, AKI.
  • Mgmt: ABCs, RAPID cooling (target 39°C; evaporative, immersion). Supportive. ⚠️ Avoid antipyretics.

Start["☀️ Heat Exposure
• Presence of symptoms• Environmental risk"]

Assess["📋 Clinical Assessment
• Check core temp• Mental status exam"]

Cramps["🩺 Heat Cramps
• Normal/Slight ⬆️ temp• Hydrate and rest"]

Exhaustion["🩺 Heat Exhaustion
• Temp < 40 deg C• Cool and hydrate"]

Stroke["⚠️ Heat Stroke
• Temp > 40 deg C• Rapid cooling/ICU"]

Start --> Assess

Assess -->|"Alert/Cramps"| Cramps Assess -->|"No Major CNS"| Exhaustion Assess -->|"CNS Dysfunction"| Stroke

style Start fill:#FEF8EC, stroke:#FBECCA, stroke-width:1.5px, rx:12, ry:12, color:#854D0E style Assess fill:#FEF8EC, stroke:#FBECCA, stroke-width:1.5px, rx:12, ry:12, color:#854D0E style Cramps fill:#F7F5FD, stroke:#F0EDFA, stroke-width:1.5px, rx:12, ry:12, color:#6B21A8 style Exhaustion fill:#F7F5FD, stroke:#F0EDFA, stroke-width:1.5px, rx:12, ry:12, color:#6B21A8 style Stroke fill:#FDF4F3, stroke:#FCE6E4, stroke-width:1.5px, rx:12, ry:12, color:#B91C1C

![Cooling Techniques for Managing Heat Illness](https://ylbwdadhbcjolwylidja.supabase.co/storage/v1/object/public/notes/L1/Physiology_Thermoregulation_Disorders_of_Thermoregulation/e1c3bf6a-7405-41c4-b695-a7eff7d8bbd5.png)

> ⭐ Antipyretics (e.g., paracetamol) are ineffective and potentially harmful in heat stroke because the hypothalamic thermoregulatory set point is normal; the problem is overwhelming heat gain/impaired dissipation, not a changed set point.


## Hyperthermic Syndromes & Fever - Fiery Foes

**Malignant Hyperthermia (MH) vs. Neuroleptic Malignant Syndrome (NMS)**

| Feature             | Malignant Hyperthermia (MH)                                     | Neuroleptic Malignant Syndrome (NMS)                                       |
|---------------------|-----------------------------------------------------------------|----------------------------------------------------------------------------|
| **Cause/Trigger**   | Genetic (RYR1), succinylcholine, volatile anesthetics           | Dopamine D2 antagonists (e.g., antipsychotics)                             |
| **Pathophysiology** | Uncontrolled sarcoplasmic $Ca^{2+}## Hyperthermic Syndromes & Fever - Fiery Foes

**Malignant Hyperthermia (MH) vs. Neuroleptic Malignant Syndrome (NMS)**

 release                    | Central dopamine D2 receptor blockade                                      |
| **Key Features**    | Muscle rigidity, hyperthermia, acidosis, hyperkalemia           | 📌 FEVER: Fever, Encephalopathy, Vitals unstable, Elevated enzymes (CK), Rigidity |
| **Treatment**       | Dantrolene (**2.5 mg/kg** IV), stop trigger, supportive cooling | Stop agent, supportive, dantrolene, bromocriptine                          |![Comparison of Fever vs Hyperthermia](https://ylbwdadhbcjolwylidja.supabase.co/storage/v1/object/public/notes/L1/Physiology_Thermoregulation_Disorders_of_Thermoregulation/6c625282-6fbe-4a24-bb43-d73bc32d22e6.jpg)

*   **Fever Pathophysiology**: Pyrogens → IL-1, TNF-α, IL-6 → Hypothalamic COX-2 → ↑$PGE_2$ → ↑Hypothalamic set point.
*   **Fever vs. Hyperthermia**:
    -   Fever: Elevated set point; body actively generates heat.
    -   Hyperthermia: Normal set point; overwhelmed heat dissipation.

> ⭐ Dantrolene, for Malignant Hyperthermia, blocks $Ca^{2+}$ release from sarcoplasmic reticulum.


##  High‑Yield Points - ⚡ Biggest Takeaways

> *   **Heat Stroke**: Core temp >**40°C** with **CNS dysfunction**; **exertional** type risks rhabdomyolysis.
> *   **Heat Exhaustion**: Symptoms without **CNS dysfunction**; core temp <**40°C**.
> *   **Malignant Hyperthermia**: **Autosomal dominant**; triggered by **succinylcholine/anesthetics**; treat with **dantrolene**.
> *   **NMS**: Caused by **antipsychotics**; presents with fever, **\"lead-pipe\" rigidity**, autonomic instability.
> *   **Hypothermia**: Core temp <**35°C**; look for **J waves (Osborn waves)** on ECG.
> *   **Fever**: Elevated **hypothalamic set point** by **pyrogens** (IL-1, IL-6, TNF-α).