Calcium plays an essential role in myocardial contractility, excitation-contraction coupling, and vascular tone. In cardiothoracic surgery, calcium supplementation is frequently administered during weaning from cardiopulmonary bypass (CPB) and in the early postoperative period to support haemodynamics. Despite its widespread use, the evidence base underpinning this practice remains limited and inconsistent. This narrative review explores the physiological rationale for calcium supplementation in the cardiothoracic surgical population, synthesises existing experimental and clinical data, and considers potential benefits and risks relevant to contemporary intensive care practice.

Animal models suggest that calcium desensitisation contributes to myocardial dysfunction following hypothermic circulatory arrest, with supplementation theoretically improving contractility. In human studies, calcium administration during CPB weaning or in the immediate post-CPB period has been associated with transient increases in mean arterial pressure, systemic vascular resistance and left ventricular stroke work index. However, these effects are short-lived and data beyond the early postoperative phase remains limited.

Potential risks of calcium supplementation include exacerbation of ischaemia-reperfusion injury, arrhythmogenesis, graft vasospasm, and tissue injury related to extravasation. The absence of specific guideline recommendations, in contrast to established consensus for vasopressor therapy, likely contributes to international variability in practice. Most studies are small, dated, or proof-of-concept and no high-quality randomised controlled trials have examined patient-centred outcomes such as vasopressor duration, organ dysfunction, or length of stay. Further multicentre observational and target-trial emulation studies are warranted to clarify the role of ionised calcium use in contemporary perioperative and intensive care practice.