Core Hyperthermia Prior to Cardiac Surgery

In the operating room, a discrepancy between core temperature (e.g., rectal or bladder) and surface skin temperature may be noted prior to initiation of cardiopulmonary bypass (CPB). Core hyperthermia in this setting has several possible etiologies and important hemodynamic implications.

1. Infectious and Technical Considerations

Infection or inflammation may present with elevated core temperature before surgery.
Temperature probe malfunction (particularly with surface probes) must be excluded, as false elevation can occur.
Malignant hyperthermia, although rare, should remain in the differential when temperature rises abruptly following anesthetic induction.

2. Heart Failure and Increased Afterload

In the setting of heart failure, hyperthermia may be associated with increased systemic vascular resistance (SVR).
Elevated SVR not only augments left ventricular workload but also contributes to impaired heat dissipation.

3. Pulmonary Overcirculation

Excessive pulmonary blood flow, common in certain congenital heart lesions, traps heat in the pulmonary circuit and cardiac chambers.
Because dissipation through systemic circulation and skin is limited, core temperature rises disproportionately compared with surface measurements.

4. Systemic-to-Pulmonary Collaterals

The presence of aortopulmonary collaterals can produce a similar effect by channeling systemic blood into the pulmonary circulation.
This results in increased pulmonary flow, elevated intrathoracic heat retention, and reduced systemic thermal regulation.

Clinical Implications

In scenarios related to heart failure, pulmonary overcirculation, or systemic-pulmonary collaterals (points 2–4), systemic vascular resistance is frequently elevated.
This necessitates careful afterload management during initiation of CPB, as excessive SVR may compromise myocardial protection and systemic perfusion.