What is the cause of hypothermia and bradycardia (abnormally slow heart rate) following blood transfusion (Blood Transfusion)?

From the Guidelines

Hypothermia and bradycardia following blood transfusion are primarily caused by the infusion of cold blood products, which can reduce core body temperature and slow heart rate through vagal stimulation and direct effects on cardiac pacemaker cells. This is supported by the study published in Anaesthesia in 2010 1, which highlights the importance of warming blood components to 37 °C before transfusion, especially in adults undergoing elective or emergency surgery.

Key Points to Consider

• The use of blood warmers is crucial in preventing hypothermia and bradycardia, particularly when rapidly transfusing large volumes of blood to vulnerable patients such as neonates, children, elderly patients, and those susceptible to cardiac dysfunction 1.
• Blood components should be warmed using approved, specifically designed, and regularly maintained blood warming equipment with a visible thermometer and audible warning, and settings should be monitored regularly throughout the transfusion 1.
• Improvisational methods of warming blood, such as putting the pack in warm water, in a microwave, or on a radiator, should never be used as they can cause damage to the blood components and lead to adverse reactions 1.

Prevention and Management Strategies

• Using blood warmers for rapid transfusions (>50mL/kg/hr) can help prevent hypothermia and bradycardia.
• Pre-warming IV fluids and maintaining room temperature above 21°C can also contribute to preventing these complications.
• Monitoring core temperature during massive transfusions is essential to quickly identify and address any potential issues.
• If hypothermia and bradycardia do occur, immediate action should be taken, including stopping the transfusion, applying warming measures, and administering medications such as atropine if necessary, while also investigating for potential hemolytic transfusion reactions.

From the FDA Drug Label

Atropine-induced parasympathetic inhibition may be preceded by a transient phase of stimulation, especially on the heart where small doses first slow the rate before characteristic tachycardia develops due to paralysis of vagal control Adequate doses of atropine abolish various types of reflex vagal cardiac slowing or asystole The drug also prevents or abolishes bradycardia or asystole produced by injection of choline esters, anticholinesterase agents or other parasympathomimetic drugs, and cardiac arrest produced by stimulation of the vagus.

The cause of hypothermia and bradycardia following blood transfusion is not directly addressed in the provided drug label for atropine. However, bradycardia can be caused by vagal stimulation. Atropine can prevent or abolish bradycardia or asystole produced by vagal stimulation. But the label does not provide information on the cause of hypothermia and bradycardia in the context of blood transfusion 2.

From the Research

Causes of Hypothermia and Bradycardia Following Blood Transfusion

• Hypothermia following blood transfusion can be caused by the transfusion of cold blood products, as evidenced by a study published in 3 which found that hypothermia is a significant risk factor for poor outcome in patients requiring massive transfusion.
• Bradycardia, or abnormally slow heart rate, can be a symptom of hypothermia, as the body's metabolic processes slow down in response to cold temperatures.
• Another possible cause of hypothermia and bradycardia following blood transfusion is transfusion-related acute lung injury (TRALI), which can lead to hypoxia and subsequent cardiac complications, as reported in 4.
• Hypotensive transfusion reactions, which can be caused by bradykinin-induced vasodilation, can also lead to hypothermia and bradycardia, as described in 5.
• Hemolytic transfusion reactions, which can occur when incompatible blood is transfused, can also cause hypothermia and bradycardia, as well as other symptoms such as hemolysis and coagulopathy, as discussed in 6, 4, and 7.

Risk Factors for Hypothermia and Bradycardia

• Massive transfusion, defined as the transfusion of 10 or more units of packed red blood cells within 24 hours, is a significant risk factor for hypothermia, as found in 3.
• Low plasma to red blood cell transfusion ratio is also a risk factor for hypothermia and mortality, as reported in 3.
• Prior allo-antibody formation is a risk factor for hemolytic transfusion reactions, which can cause hypothermia and bradycardia, as discussed in 4.