Temperature Management

Thermoregulation & Post-Op Impact - Body's Thermostat

• Hypothalamus: Central "thermostat" regulating core body temperature (normal: 36.5-37.5°C).
• Mechanisms: Vasoconstriction/shivering (↑ heat production/conservation), vasodilation/sweating (↑ heat loss).
• Anesthesia's disruption:
  • Impairs central hypothalamic regulation.
  • Causes peripheral vasodilation, promoting heat loss.
  • Decreases metabolic heat production.
• Surgical factors: Environmental exposure, cold IV fluids, open body cavities exacerbate heat loss.
• Consequence: High risk of Inadvertent Perioperative Hypothermia (IPH).

⭐ General anesthesia significantly widens the interthreshold range (core temperatures triggering autonomic responses like shivering/sweating) from ~0.2°C to as much as 4°C.

Postoperative Hypothermia - The Big Chill

• Core body temperature < 36°C (96.8°F).
• Causes: Cold OR, anaesthesia (vasodilation, ↓thermoregulation), cold IV fluids, open cavities.
• Phases:
  • Redistribution (core → periphery): Rapid initial drop.
  • Linear decline: Heat loss > production.
  • Plateau: Vasoconstriction, shivering (if unblocked).
• Consequences:
  • Cardiovascular: Arrhythmias, ischemia, ↑BP.
  • Coagulation: ↑Bleeding (platelet/enzyme dysfunction).
  • Wound: ↑Infection risk, impaired healing.
  • Drug metabolism: Prolonged effects (e.g., relaxants).
  • Shivering: ↑O2 consumption (~300-500%), ↑cardiac work, discomfort.
• Prevention & Management:
  • Pre-warming, OR temp > 21°C.
  • Active warming: Forced-air (most effective), warm IV fluids.
  • Treat shivering: Meperidine (12.5-25mg IV), clonidine.

⭐ Mild hypothermia (34-36°C) significantly increases surgical site infection rates and adverse cardiac outcomes.

![Image of forced-air warming device applied to a postoperative patient]

Postoperative Hyperthermia/Fever - Feeling Hot Hot Hot

• Core temperature > 38°C (100.4°F) post-surgery.
• Causes (The 5 Ws) 📌:
  • Wind (POD 1-2): Atelectasis, pneumonia.
  • Water (POD 3-5): UTI.
  • Wound (POD 5-7): Surgical Site Infection (SSI).
  • Walking (POD 5+): DVT/PE.
  • Wonder Drugs: Drug fever, transfusion reactions, Malignant Hyperthermia (MH).
• Malignant Hyperthermia: Rare; suspect with high fever, rigidity, ↑ETCO₂. Dantrolene.
• Non-infectious: Surgical stress (common <48h, <38.5°C), pancreatitis.
• Workup: Guided by timing/signs. CBC, cultures, CXR.
• Management: Treat cause; antipyretics.

⭐ Most early fevers (<48h post-op) are non-infectious, due to surgical stress (cytokine release).

Temperature Monitoring Techniques - Keeping Tabs

• Core Sites (Reflect true body core temp):
  • Gold Standard: Pulmonary artery.
  • Reliable: Distal esophagus, nasopharynx, tympanic (brain temp).
  • Slower response: Bladder, rectal.
  • 📌 PENTBR: Pulmonary Artery, Esophagus, Nasopharynx, Tympanic, Bladder, Rectal.
• Peripheral Sites (Screening, less accurate):
  • Skin, axillary.

⭐ Tympanic membrane temperature closely reflects brain temperature due to shared blood supply from carotid artery.

High-Yield Points - ⚡ Biggest Takeaways

• Postoperative hypothermia (<36°C) ↑ risks of SSIs, cardiac events, and impaired wound healing.
• Shivering dramatically ↑ O2 consumption (up to 500%) and myocardial stress.
• Core temperature monitoring (e.g., esophageal, tympanic) is crucial, not peripheral.
• Forced-air warming is the most effective active rewarming technique.
• Malignant hyperthermia can present postoperatively; treat urgently with dantrolene.
• Postoperative fever often indicates infection; investigate promptly.
• Treat postoperative shivering with meperidine, clonidine, or tramadol.