Poststernotomy mediastinitis is a rare but severe complication of cardiac surgery with high mortality; the outcome largely depends on the timeliness of diagnosis and initiation of etiotropic therapy.

Description of the observation. A 60-year-old patient who had undergone coronary artery bypass grafting with the use of the left internal thoracic artery developed postoperative wound soaking on the third day after surgery, without overt signs of sternal instability or pronounced purulent discharge. However, a rapid increase in C-reactive protein levels and leukocyte formula shift were observed, accompanied by significant changes in additional biomarkers (ESId, presepsin, and HLA-DR expression on monocytes). These findings served as a basis for early chest CT imaging, which confirmed the diagnosis of sternomediastinitis, leading to the activation of surgical management (staged mediastinal debridement, vacuum-assisted therapy, and subsequent sternal reconstruction using metallic implants).

Conclusion. This case demonstrates that an extended monitoring protocol of inflammatory biomarkers and immune status enables early suspicion of mediastinitis before the development of classical local manifestations and allows timely adjustment of treatment strategy.