Systemic hypothermia in non-aortic cardiac surgery: a narrative review.

Background and Objective: Systemic hypothermia is commonly used in most cardiac operations in order to reduce metabolic demand and augment both myocardial and other end-organ protection. With modern improvements in perfusion and protection strategies, some surgeons now routinely perform non-aortic surgery under normothermic conditions. However, there is limited evidence and conflicting reports on the "optimal" temperature conditions for cardiac surgery, resulting in a paucity of guidelines and a wide variety in practice. We aim to give a thorough review of the current evidence comparing hypothermia and normothermia in cardiac surgery. Methods: A narrative review was conducted comparing studies that involved hypothermia and/or normothermia within cardiac surgery. Search terms included: temperature cardiac surgery, temperature cardiopulmonary bypass, normothermia surgery, hypothermia surgery, normothermia cardiac, hypothermia cardiac, normothermia cardiopulmonary bypass. Applicable manuscripts and abstracts from PubMed during the timeframe of 1/1/1990 to 1/1/2025 were included, including a range of experimental, observational, prospective, and randomized studies. In addition, prior narrative reviews and meta-analyses were included. Evidence was collected and synthesized across bleeding/transfusion need, neurologic outcomes, arrhythmias, renal function, inflammation and wound healing, and anesthetic pharmacology. Key Content and Findings: Cooling effectively decreases metabolic rate and provides additional end-organ protection. Large, observational datasets have reported limited but meaningful improvements in short- and long-term survival with hypothermia. However, more modern studies across observational and randomized cohorts evaluating individual organ outcomes show limited differences between hypothermia and normothermia in cardiac surgery patients. The most meaningful difference is consistently demonstrated in greater coagulopathy in hypothermic patients. Neurologic and renal outcomes in hypothermia are conflicting between studies, with no consistent difference. There is likely a modest impact of hypothermia on worsening wound healing and higher arrhythmogenicity. Lastly, hypothermia has a known prolongation of effects and clearance of anesthetics, but in a predictable manner. Conclusions: No single temperature strategy is universally superior for non-aortic cardiac surgery. Hypothermia has benefits in myocardial and end-organ protection, but with a cost in coagulopathy. Temperature management should be individualized, balancing these two considerations with the modest impacts noted in renal function, neurologic outcomes, wound healing, and anesthetics.