Overview
Definition:
Perioperative temperature management refers to the strategies and interventions employed to maintain normothermia (a normal body temperature) in patients before, during, and after surgical procedures
Intraoperative hypothermia, defined as a core body temperature below 36°C, is a common complication associated with anesthesia and surgical stress, leading to adverse outcomes including impaired wound healing, increased infection risk, and importantly, coagulopathy.
Epidemiology:
Intraoperative hypothermia affects 20-70% of surgical patients, depending on the type and duration of surgery
The incidence of coagulopathy secondary to hypothermia varies but is significant, contributing to increased blood loss and transfusion requirements.
Clinical Significance:
Maintaining normothermia is critical in surgery to optimize physiological function and prevent complications
Hypothermia directly impairs platelet function and enzyme activity in the coagulation cascade, leading to a dilutional and functional coagulopathy
This exacerbates surgical bleeding, increases the need for blood products, prolongs operating times, and elevates patient morbidity and mortality
Effective perioperative temperature management is thus a cornerstone of surgical patient safety and optimal outcomes.
Pathophysiology
Mechanism Of Hypothermia:
Anesthesia-induced vasodilation leads to peripheral heat loss
Reduced metabolic rate decreases endogenous heat production
Large surgical wounds expose warm tissues to cooler operating room environments
Intravenous fluid administration at room temperature also contributes to heat loss.
Effect On Platelets:
Platelet aggregation and adhesion are significantly reduced at lower temperatures
Studies show that platelet function is impaired by 10% for every 1°C drop in temperature below normal
This leads to a qualitative platelet defect.
Effect On Coagulation Cascade:
Enzymatic reactions within the coagulation cascade are temperature-dependent
Factors V, VIII, IX, and XI are particularly sensitive to hypothermia, leading to decreased thrombin generation and fibrin clot stability
This results in a quantitative and qualitative impairment of the clotting process.
Fibrinolysis And Temperature:
Hypothermia can also impair the breakdown of fibrin clots by inhibiting fibrinolytic enzymes, though this effect is generally less pronounced than its impact on platelet and coagulation factor function
However, in the context of surgical bleeding, the net effect is a pro-hemorrhagic state.
Clinical Presentation
Signs Of Hypothermia:
Initial peripheral vasoconstriction leading to cool skin
Shivering is an attempt to generate heat, but may be suppressed by anesthetic agents
As hypothermia progresses, skin becomes mottled, and mental status may decline
Core temperature measurement is the definitive diagnostic criterion.
Signs Of Coagulopathy:
Increased surgical bleeding from incision sites, drains, and surgical field
Oozing from raw surfaces
Prolonged bleeding after clamp release
Petechiae or ecchymoses may be present but are less common in acute perioperative hypothermia-induced coagulopathy
Need for increased blood product transfusion.
Diagnostic Approach
Temperature Monitoring:
Continuous core body temperature monitoring is essential
Preferred sites include esophageal probes (mid-esophagus), pulmonary artery catheters, or urinary bladder probes
Tympanic and axillary temperatures are less reliable indicators of core temperature
Rectal temperature is also an acceptable alternative if core access is not feasible.
Coagulation Assessment:
Baseline coagulation profile (PT, aPTT, INR, platelet count) should be obtained preoperatively
During surgery, if excessive bleeding is noted, repeat coagulation tests are crucial
Viscoelastic assays like thromboelastography (TEG) or rotational thromboelastometry (ROTEM) can provide rapid, comprehensive assessment of coagulation status, including platelet function, and are valuable in managing surgical bleeding
Rapid platelet count and fibrinogen levels are also useful.
Management
Prewarming:
Initiate active warming of the patient for at least 15-30 minutes before induction of anesthesia
This helps to saturate subcutaneous heat reserves and reduce the core-to-peripheral temperature gradient
Use forced-air warming blankets.
Intraoperative Warming Strategies:
Maintain operating room temperature at 21-23°C and humidity at 50%
Use forced-air warming blankets over the entire body, except for the surgical site
Administer warmed intravenous fluids and blood products (using fluid warmers)
Humidify anesthetic gases
Use heated breathing circuits.
Management Of Hypothermia:
If hypothermia occurs (core temp < 36°C), implement aggressive rewarming strategies
This includes increasing the use of forced-air warming, using heated irrigation solutions, and considering active rewarming devices like warming blankets or pads
For severe or refractory hypothermia, cardiopulmonary bypass can be used for rapid rewarming.
Management Of Coagulopathy:
Address the underlying cause: rewarm the patient
Transfuse blood products judiciously based on laboratory results and clinical bleeding
Platelet transfusions are indicated for platelet counts < 50,000/µL (or < 100,000/µL in neurosurgery or spine surgery) or impaired platelet function
Fresh frozen plasma (FFP) is indicated for prolonged PT/aPTT
Cryoprecipitate is used to correct fibrinogen deficiency (fibrinogen < 1.5 g/L)
Consider procoagulant medications like tranexamic acid or desmopressin (DDAVP) judiciously
Viscoelastic assays guide targeted therapy.
Prevention Strategies
Preoperative Assessment:
Identify patients at high risk for hypothermia and coagulopathy, including those undergoing long procedures, major vascular or orthopedic surgery, or those with existing coagulopathies.
Standardized Warming Protocols:
Implement standardized perioperative warming protocols across all surgical departments
Ensure availability and proper use of warming devices and techniques.
Intraoperative Monitoring:
Continuous monitoring of core body temperature and vigilant observation for excessive bleeding are crucial
Prompt intervention upon detecting hypothermia or coagulopathy is key.
Education And Awareness:
Educate surgical and anesthesia teams on the importance of normothermia and the impact of hypothermia on coagulation
Regular training and reinforcement of best practices are essential for DNB and NEET SS preparation.
Key Points
Exam Focus:
Hypothermia impairs platelet aggregation and coagulation factor function, leading to surgical coagulopathy
Core body temperature monitoring is essential
Forced-air warming and warmed fluids/blood are key interventions
Viscoelastic assays (TEG/ROTEM) are important tools.
Clinical Pearls:
A 1°C drop in core temperature impairs platelet function by approximately 10%
Even mild hypothermia (34-36°C) can significantly affect coagulation
Always check the temperature on the warming blanket settings
Remember that shivering is a sign of heat production and can be suppressed by anesthesia, so it is not a reliable indicator of normothermia during surgery.
Common Mistakes:
Underestimating the incidence and impact of intraoperative hypothermia
Inadequate warming measures
Relying solely on peripheral temperature monitoring
Delaying intervention for hypothermia or coagulopathy
Injudicious use of blood products without considering underlying causes and specific deficiencies.