Open heart surgery remains an essential therapeutic approach for a wide range of cardiovascular diseases, including coronary artery disease, valvular heart disease, congenital cardiac defects, and diseases of the thoracic aorta. Despite continuous improvements in surgical techniques, cardiopulmonary bypass (CPB), anaesthesia, perioperative monitoring, and blood conservation strategies, postoperative bleeding continues to be an important complication of cardiac surgery. Bleeding following cardiac surgery varies considerably in severity, ranging from manageable chest-drain losses to severe haemorrhage requiring massive transfusion or emergency surgical re-exploration. To improve consistency in clinical assessment and research, the Universal Definition of Perioperative Bleeding was developed to classify bleeding according to parameters such as postoperative chest tube drainage, transfusion requirements, delayed sternal closure, and surgical re-exploration [1]. Re-exploration for bleeding is one of the most serious consequences of postoperative haemorrhage. Previous studies have reported that approximately 2–6% of patients undergoing cardiac surgery may require surgical re-exploration because of excessive bleeding or cardiac tamponade [2]. Although the frequency varies according to the type and complexity of surgery, institutional practices, patient characteristics, and thresholds for reopening, re-exploration is consistently associated with less favourable postoperative outcomes. The requirement for reopening the chest may expose an already critically ill patient to additional anaesthesia, surgical trauma, hypothermia, haemodynamic instability, infection risk, and further disturbances of haemostasis. Postoperative bleeding after open heart surgery is multifactorial. Surgical causes include bleeding from vascular anastomoses, grafts, cannulation sites, the sternum, internal thoracic artery harvest sites, and other operative tissues. A meta-analysis evaluating sources of bleeding in patients requiring re-exploration demonstrated that identifiable surgical bleeding sites are common, confirming that technical causes contribute substantially to this complication [3]. At the same time, nonsurgical or microvascular bleeding may result from coagulation abnormalities produced by CPB, platelet dysfunction, haemodilution, hypothermia, fibrinolysis, residual heparin effect, and consumption of coagulation factors. The haemostatic changes occurring during major cardiac procedures may therefore make differentiation between surgically correctable bleeding and generalized coagulopathy particularly challenging [4]. Several preoperative, intraoperative, and postoperative characteristics have been investigated as potential predictors of re-exploration. Patient-related factors reported in previous studies include advanced age, renal dysfunction, elevated operative risk, obesity, low preoperative platelet count, anaemia, and exposure to antiplatelet or anticoagulant medications. Operative factors include urgent or emergency surgery, complex procedures, redo operations, prolonged CPB duration, extended aortic cross-clamp time, and procedures other than isolated coronary artery bypass grafting. In an early large study of more than 6,000 cardiac surgical patients, increased age, preoperative renal insufficiency, operations other than coronary artery bypass surgery, and prolonged bypass time were identified as independent predictors of re-exploration [5]. More recent studies have similarly identified factors such as elevated serum creatinine, urgent or emergency operative status, higher operative risk scores, increased body mass index, and reduced platelet count as being associated with re-exploration for postoperative bleeding [6]. The clinical importance of identifying these predictors is considerable because re-exploration is associated with substantial postoperative morbidity. Patients undergoing re-exploration frequently require greater quantities of red blood cells, fresh frozen plasma, platelets, and other haemostatic products. Both blood transfusion and reoperation for bleeding have independently been associated with adverse outcomes after cardiac surgery, suggesting that postoperative haemorrhage may contribute to complications through several interacting mechanisms [7]. Re-exploration has also been associated with renal dysfunction, respiratory complications, prolonged mechanical ventilation, neurological events, longer intensive care unit and hospital stays, and increased mortality. Large observational studies and systematic reviews have therefore regarded bleeding requiring re-exploration as an important marker of adverse outcome following cardiac surgery. The timing of re-exploration is another important consideration. Prolonged conservative management despite ongoing haemorrhage may expose the patient to persistent hypovolaemia, repeated blood transfusion, coagulation factor depletion, hypothermia, tissue hypoperfusion, and eventual cardiac tamponade. Haneya et al. reported substantially higher mortality among patients re-explored more than 12 hours after cardiac surgery compared with those undergoing earlier re-exploration [8]. More recently, Shou et al. demonstrated a progressive increase in morbidity and mortality with increasing delay to re-exploration and suggested that early intervention, particularly within the first few hours when clinically indicated, may result in better outcomes [9]. These findings emphasise the importance not only of preventing severe bleeding but also of rapidly recognizing patients who are likely to require surgical intervention. Considering its association with transfusion requirements, postoperative complications, resource utilization, and both short- and long-term mortality, re-exploration for bleeding remains an important quality and safety concern in open heart surgery. Contemporary evidence has also demonstrated poorer long-term survival among patients requiring re-exploration compared with those who do not [10]. Identification of reliable predictors could facilitate preoperative risk stratification, correction of modifiable coagulation abnormalities, appropriate management of antithrombotic medications, meticulous intraoperative haemostasis, closer postoperative surveillance, and timely decisions regarding surgical reopening. Therefore, evaluation of the predictors of re-exploration for bleeding following open heart surgery is clinically relevant and may contribute to improved perioperative management and postoperative outcomes.

Study Design and Setting This was a single-centre, retrospective observational cohort study conducted at the Laxmipat Singhania (LPS) Institute of Cardiology & Cardiac Surgery, Kanpur, Uttar Pradesh, India. The study evaluated clinical and perioperative factors associated with the need for surgical re-exploration due to postoperative bleeding following open heart surgery. Medical records of patients who underwent open heart surgery between January 2018 and December 2020 were reviewed. A total of 150 patients fulfilling the predefined eligibility criteria were included in the final analysis. The study was designed and reported in accordance with the principles of the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement. Study Population Adult patients undergoing major open heart surgical procedures during the study period constituted the study population. Procedures included coronary artery bypass grafting (CABG), valve replacement or repair, combined CABG and valve surgery, and other major cardiac procedures requiring surgical opening of the chest and cardiopulmonary bypass (CPB), where applicable. Patients were subsequently classified according to whether or not they required surgical re-exploration for postoperative bleeding. Inclusion Criteria Patients were eligible for inclusion if they: 1. Were aged 18 years or older. 2. Underwent open heart surgery during the study period from January 2018 to December 2020. 3. Had complete perioperative records sufficient to determine the occurrence or absence of postoperative re-exploration for bleeding. 4. Had available preoperative, intraoperative, and relevant postoperative clinical and laboratory information required for predictor analysis. Exclusion Criteria Patients were excluded if they: 1. Were younger than 18 years. 2. Underwent procedures not involving open cardiac surgery. 3. Required re-exploration for indications unrelated to bleeding or cardiac tamponade. 4. Had incomplete medical records in which the primary study outcome could not be established. 5. Died intraoperatively before completion of the primary surgical procedure. 6. Underwent surgery for major traumatic cardiac injury. Sample Size and Sampling Technique The final study sample consisted of 150 eligible patients. As this was a retrospective study of an existing institutional cohort, eligible patient records available during the predefined study period were screened consecutively. Patients satisfying the eligibility criteria and having adequate clinical information were included until the final study cohort was established. No patient was selected according to postoperative outcome, thereby preserving the cohort nature of the study. Primary Outcome The primary outcome was re-exploration for postoperative bleeding. Re-exploration was defined as an unplanned return to the operating room with reopening of the sternotomy after completion of the initial cardiac operation because of persistent or excessive postoperative bleeding and/or suspected cardiac tamponade attributable to postoperative haemorrhage. Reoperations performed exclusively for indications unrelated to bleeding, such as graft dysfunction, valvular dysfunction, mediastinal infection, or other non-haemorrhagic surgical complications, were not considered primary outcome events. Data Collection Data were retrospectively extracted from operation theatre records, anaesthesia records, intensive care unit charts, laboratory reports, transfusion records, and hospital medical records using a standardized data collection form. The collected variables were divided into preoperative, intraoperative, and early postoperative variables. Preoperative Variables The following baseline variables were recorded: • Age • Sex • Body mass index, where available • Hypertension • Diabetes mellitus • Smoking status • Chronic kidney disease or renal dysfunction • Previous cardiac surgery • Preoperative left ventricular ejection fraction • Type of cardiac disease • Preoperative haemoglobin concentration • Platelet count • Serum creatinine • International normalized ratio (INR) • Activated partial thromboplastin time, where available • Use of antiplatelet agents • Use of oral anticoagulants • Urgency of surgery, classified as elective or urgent/emergency Particular attention was given to preoperative antithrombotic therapy because recent exposure to antiplatelet or anticoagulant drugs could potentially influence perioperative haemostasis. Intraoperative Variables Operative and anaesthetic variables evaluated as potential predictors included: • Type of cardiac surgical procedure • Isolated versus combined procedure • Primary versus redo cardiac surgery • Cardiopulmonary bypass duration • Aortic cross-clamp duration • Intraoperative blood loss • Lowest intraoperative temperature, where documented • Intraoperative packed red blood cell transfusion • Fresh frozen plasma transfusion • Platelet transfusion • Requirement for additional haemostatic products • Duration of surgery For patients undergoing cardiopulmonary bypass, systemic anticoagulation was achieved according to the institutional heparinization protocol, followed by protamine administration after termination of CPB. Surgical haemostasis was assessed before final sternal closure according to routine institutional practice. Postoperative Assessment Following surgery, patients were transferred to the cardiac intensive care unit and managed according to the institutional postoperative cardiac surgical protocol. Haemodynamic status and mediastinal/chest drain output were monitored closely. Postoperative variables collected included chest-drain output during the early postoperative period, postoperative haemoglobin level, platelet count, coagulation profile, blood-product requirements, haemodynamic instability, need for inotropic or vasopressor support, and time from completion of primary surgery to re-exploration. The decision to undertake re-exploration was based on the treating cardiac surgical team's assessment of the overall clinical condition, including the magnitude and persistence of chest-drain bleeding, haemodynamic status, transfusion requirements, coagulation status, and clinical or echocardiographic suspicion of cardiac tamponade. Identification of Potential Predictors Potential predictors of re-exploration were selected on the basis of their clinical relevance and availability in the medical records. To maintain appropriate temporal relationships, the primary predictor model focused principally on variables known before completion of the index cardiac operation, including preoperative patient characteristics, laboratory parameters, comorbidities, type and urgency of surgery, CPB duration, aortic cross-clamp duration, and intraoperative transfusion requirements. Early postoperative measurements, such as chest-drain output and postoperative coagulation parameters, were analysed separately as indicators associated with impending re-exploration rather than being automatically included in the baseline prediction model. This approach was used to minimize incorporation of variables that may represent manifestations of the bleeding event itself. Secondary Outcomes Secondary postoperative outcomes included: • Requirement for packed red blood cell transfusion • Fresh frozen plasma and platelet transfusion • Duration of mechanical ventilation • Intensive care unit length of stay • Total postoperative hospital stay • Acute kidney injury, where documented • Postoperative neurological complications • Surgical-site or mediastinal infection • In-hospital mortality These outcomes were compared between patients who underwent re-exploration and those who did not. Statistical Analysis Data were analysed using IBM SPSS Statistics. Continuous variables were assessed for distribution using graphical methods and the Shapiro–Wilk test. Normally distributed continuous variables were expressed as mean ± standard deviation, whereas non-normally distributed variables were presented as median with interquartile range. Categorical variables were expressed as frequency and percentage. Comparisons between patients requiring re-exploration and those not requiring re-exploration were performed using the independent-samples Student's t-test for normally distributed continuous variables and the Mann–Whitney U test for non-normally distributed continuous variables. Categorical variables were compared using the Chi-square test or Fisher's exact test, as appropriate.

Table 1. Baseline demographic and clinical characteristics according to re-exploration status Variable Re-exploration (n=15) No re-exploration (n=135) P value Age, years, mean ± SD 61.8 ± 10.2 58.4 ± 9.5 0.194 Male sex, n (%) 11 (73.3) 96 (71.1) 1.000 BMI, kg/m², mean ± SD 25.1 ± 3.6 25.8 ± 3.8 0.493 Hypertension, n (%) 10 (66.7) 83 (61.5) 0.785 Diabetes mellitus, n (%) 8 (53.3) 54 (40.0) 0.409 Chronic kidney disease, n (%) 4 (26.7) 9 (6.7) 0.027 Previous cardiac surgery, n (%) 3 (20.0) 5 (3.7) 0.034 LVEF <40%, n (%) 5 (33.3) 22 (16.3) 0.149 Current/former smoker, n (%) 6 (40.0) 46 (34.1) 0.775 Patients who required re-exploration had numerically higher age and greater prevalence of several comorbidities. Chronic kidney disease and previous cardiac surgery were significantly more frequent in the re-exploration group. No significant differences were observed for age, sex, BMI, hypertension, diabetes mellitus, smoking status, or reduced left ventricular ejection fraction. Table 2. Preoperative laboratory and antithrombotic characteristics Variable Re-exploration (n=15) No re-exploration (n=135) P value Haemoglobin, g/dL, mean ± SD 11.2 ± 1.5 12.4 ± 1.6 0.006 Platelet count, ×10⁹/L, mean ± SD 154 ± 46 204 ± 52 <0.001 Serum creatinine, mg/dL, median (IQR) 1.42 (1.08–1.86) 1.08 (0.88–1.31) 0.003 INR, median (IQR) 1.18 (1.09–1.28) 1.09 (1.02–1.18) 0.041 Recent antiplatelet therapy, n (%) 9 (60.0) 67 (49.6) 0.588 Oral anticoagulant use, n (%) 4 (26.7) 12 (8.9) 0.058 Preoperative haemoglobin and platelet counts were significantly lower among patients requiring re-exploration. Serum creatinine and INR were also significantly higher in the re-exploration group. Oral anticoagulant use showed a trend toward increased re-exploration but did not reach conventional statistical significance. Table 3. Operative characteristics according to re-exploration status Operative variable Re-exploration (n=15) No re-exploration (n=135) P value Elective surgery, n (%) 9 (60.0) 122 (90.4) — Urgent/emergency surgery, n (%) 6 (40.0) 13 (9.6) 0.005 Isolated CABG, n (%) 6 (40.0) 76 (56.3) 0.278 Isolated valve surgery, n (%) 3 (20.0) 37 (27.4) 0.757 Combined/complex procedure, n (%) 6 (40.0) 22 (16.3) 0.039 Redo cardiac surgery, n (%) 3 (20.0) 5 (3.7) 0.034 CPB duration, min, mean ± SD 151 ± 36 112 ± 29 <0.001 Aortic cross-clamp duration, min, mean ± SD 92 ± 27 71 ± 23 0.002 Intraoperative PRBC, units, median (IQR) 3 (2–4) 1 (0–2) <0.001 Intraoperative FFP, units, median (IQR) 2 (0–4) 0 (0–2) 0.002 Intraoperative platelet transfusion, n (%) 8 (53.3) 24 (17.8) 0.004 Patients subsequently requiring re-exploration were significantly more likely to have undergone urgent/emergency, redo, or combined/complex cardiac procedures. The mean cardiopulmonary bypass duration was approximately 39 minutes longer in the re-exploration group. Similarly, aortic cross-clamp duration and intraoperative blood-product requirements were significantly greater among these patients. Table 4. Early postoperative characteristics and clinical outcomes Postoperative outcome Re-exploration (n=15) No re-exploration (n=135) P value Chest-drain output during first 6 h, mL, median (IQR) 960 (780–1230) 390 (280–520) <0.001 24-h chest-drain output, mL, median (IQR) 1660 (1380–2120) 700 (510–920) <0.001 Postoperative PRBC, units, median (IQR) 4 (3–6) 1 (0–2) <0.001 Postoperative FFP, units, median (IQR) 4 (2–6) 1 (0–2) <0.001 Mechanical ventilation, h, median (IQR) 18 (12–31) 8 (6–13) <0.001 ICU stay, days, median (IQR) 5 (4–8) 3 (2–4) <0.001 Postoperative hospital stay, days, median (IQR) 12 (9–17) 8 (7–11) 0.002 Acute kidney injury, n (%) 5 (33.3) 10 (7.4) 0.008 Neurological complication, n (%) 2 (13.3) 3 (2.2) 0.078 Surgical-site/mediastinal infection, n (%) 3 (20.0) 4 (3.0) 0.022 In-hospital mortality, n (%) 3 (20.0) 4 (3.0) 0.022 Re-exploration was associated with substantially increased postoperative bleeding and blood-product utilization. Patients undergoing re-exploration also experienced longer mechanical ventilation, ICU stay, and hospital stay. Acute kidney injury, surgical-site/mediastinal infection, and in-hospital mortality were significantly more frequent among re-explored patients. Table 5. Univariable analysis of predictors of re-exploration for bleeding Predictor Odds ratio (OR) 95% CI P value Age, per 10-year increase 1.39 0.85–2.28 0.191 Diabetes mellitus 1.71 0.59–5.00 0.323 Chronic kidney disease 5.09 1.35–19.23 0.017 Previous cardiac surgery 6.50 1.38–30.59 0.018 LVEF <40% 2.57 0.80–8.25 0.111 Haemoglobin, per 1-g/dL decrease 1.55 1.10–2.19 0.013 Platelet count, per 10×10⁹/L decrease 1.21 1.09–1.34 <0.001 Serum creatinine, per 0.5-mg/dL increase 1.74 1.13–2.69 0.012 Oral anticoagulant use 3.73 1.03–13.52 0.045 Urgent/emergency surgery 6.26 1.92–20.38 0.002 Combined/complex surgery 3.42 1.11–10.57 0.033 Redo cardiac surgery 6.50 1.38–30.59 0.018 CPB duration, per 10-min increase 1.31 1.16–1.48 <0.001 Cross-clamp duration, per 10-min increase 1.28 1.08–1.51 0.004 Intraoperative PRBC, per additional unit 1.67 1.25–2.23 <0.001 On univariable analysis, chronic kidney disease, previous cardiac surgery, low haemoglobin, reduced platelet count, elevated serum creatinine, anticoagulant use, urgent/emergency surgery, complex surgery, redo surgery, prolonged CPB and cross-clamp durations, and greater intraoperative red-cell transfusion were associated with an increased likelihood of re-exploration. Table 6. Multivariable analysis of independent predictors of re-exploration for bleeding Predictor Adjusted OR 95% CI P value Platelet count, per 10×10⁹/L decrease 1.18 1.05–1.34 0.006 CPB duration, per 10-min increase 1.22 1.07–1.40 0.003 Urgent/emergency surgery 3.71 1.12–12.31 0.032 Preoperative creatinine, per 0.5-mg/dL increase 1.51 0.98–2.34 0.063 Because only 15 re-exploration events occurred, the number of variables in the final model was restricted to reduce overfitting. In the adjusted analysis, lower preoperative platelet count, prolonged cardiopulmonary bypass duration, and urgent/emergency surgery emerged as independent predictors of re-exploration for bleeding. Elevated preoperative serum creatinine showed a clinically relevant association but did not retain conventional statistical significance after adjustment. The model demonstrated good discriminatory ability, with an area under the receiver operating characteristic curve of 0.86 (95% CI: 0.77–0.95). Figure 1 illustrates the incidence of surgical re-exploration for postoperative bleeding among 150 patients who underwent open heart surgery. Of the total study population, 15 patients (10.0%) required surgical re-exploration, whereas 135 patients (90.0%) did not require re-exploration. Thus, the overall incidence of re-exploration for postoperative bleeding in the present study was 10.0%. Figure 2 compares the mean cardiopulmonary bypass duration between patients who required surgical re-exploration and those who did not. The mean CPB duration was significantly longer in the re-exploration group (151 ± 36 minutes) compared with the non-re-exploration group (112 ± 29 minutes). This difference was statistically significant (P < 0.001), indicating that prolonged cardiopulmonary bypass duration was associated with an increased likelihood of re-exploration for postoperative bleeding. Figure 3 presents the receiver operating characteristic (ROC) curve of the multivariable model used to predict re-exploration following open heart surgery. The model demonstrated good discriminatory ability, with an area under the curve (AUC) of 0.86 and a 95% confidence interval of 0.77–0.95. This indicates that the prediction model had a strong ability to distinguish between patients who required re-exploration for postoperative bleeding and those who did not. The ROC curve lies well above the reference line, reflecting good overall predictive performance.

Postoperative bleeding requiring surgical re-exploration remains one of the most clinically important complications following open heart surgery. In the present study, 15 of 150 patients (10.0%) required re-exploration for bleeding or cardiac tamponade. The observed rate is somewhat higher than that reported in several large cardiac surgical cohorts. Karthik et al. reported re-exploration in 3.1% of 2,898 patients undergoing coronary artery bypass grafting (CABG), while Mehta et al., using data from more than 528,000 CABG procedures, reported a reoperation rate of 2.4% [11,12]. Kristensen et al. reported a comparatively higher incidence of 7.0% among unselected cardiac surgical patients undergoing extracorporeal circulation [13]. Differences between studies may reflect variation in the complexity and urgency of surgical procedures, institutional thresholds for re-exploration, patient risk profiles, perioperative anticoagulant exposure, and methods used to define excessive postoperative bleeding. One of the most important findings of the present study was the association between lower preoperative platelet count and re-exploration. Patients requiring re-exploration had a mean platelet count of 154 ×10⁹/L compared with 204 ×10⁹/L among patients who did not require re-exploration. After adjustment, each 10 ×10⁹/L decrease in platelet count was associated with an approximately 18% increase in the odds of re-exploration. This observation is supported by Lopes et al., who demonstrated that lower preoperative platelet counts were significantly associated with bleeding-related re-exploration following cardiac surgery [14]. Their prospective cohort also highlighted the importance of blood-product requirements and haemostatic abnormalities in patients who subsequently required surgical revision. The present findings therefore reinforce the value of careful preoperative assessment of both platelet quantity and function, particularly among high-risk patients. The importance of platelets in this setting is biologically plausible because cardiac surgery, particularly when cardiopulmonary bypass (CPB) is used, can produce both quantitative and qualitative platelet abnormalities. Platelets may undergo activation, consumption, haemodilution, and functional impairment during extracorporeal circulation. Consequently, even a platelet count that is not severely reduced before surgery may confer greater bleeding risk when combined with CPB-related platelet dysfunction. In the present study, intraoperative platelet transfusion was also more frequent among patients subsequently requiring re-exploration, probably reflecting greater haemostatic disturbance rather than being a direct causal factor. A second major independent predictor identified in the present study was prolonged CPB duration. Mean CPB duration was 151 ± 36 minutes in patients undergoing re-exploration compared with 112 ± 29 minutes in those without re-exploration. Multivariable analysis showed that every additional 10 minutes of CPB increased the adjusted odds of re-exploration by approximately 22%. Similar findings have been reported by Kristensen et al., who identified prolonged extracorporeal circulation as a significant risk factor for reoperation due to postoperative bleeding [13]. Ruel et al., in a cohort of 16,793 cardiac surgical patients, also identified CPB duration as a predictor of re-exploration [15]. Longer CPB exposure may increase bleeding risk through haemodilution, platelet dysfunction, activation and consumption of coagulation factors, inflammatory responses, and fibrinolytic activity. Prolonged CPB duration may also represent a surrogate marker of technically difficult or more complex surgery. In the present study, combined or complex procedures were significantly more common among patients requiring re-exploration, supporting the possibility that both the biological effects of prolonged extracorporeal circulation and greater procedural complexity contribute to postoperative haemorrhage. Urgent or emergency surgery emerged as another independent predictor of re-exploration. Forty percent of patients in the re-exploration group underwent urgent or emergency surgery compared with only 9.6% in the non-re-exploration group. After adjustment, urgent or emergency surgery was associated with a 3.71-fold increase in the odds of re-exploration. These results are consistent with previous studies. Ruel et al. identified emergency operative status as an important correlate of re-exploration, while large registry analyses have similarly demonstrated an increased risk of bleeding-related reoperation in higher-risk and non-elective cardiac surgical patients [12,15]. There are several possible explanations for the increased bleeding risk associated with emergency surgery. Patients requiring urgent intervention may have less opportunity for correction of anaemia, thrombocytopenia, renal dysfunction, or coagulation abnormalities before surgery. In addition, discontinuation intervals for antiplatelet or anticoagulant drugs may be inadequate. Englberger et al. demonstrated that exposure to clopidogrel within three days before CABG was associated with greater postoperative drainage, increased transfusion requirements, and a significantly higher incidence of re-exploration [16]. In the present study, oral anticoagulant exposure showed an association with re-exploration in univariable analysis, although it did not remain an independent predictor in the final model. Preoperative renal dysfunction was another notable finding. Chronic kidney disease was present in 26.7% of patients requiring re-exploration compared with 6.7% of those without re-exploration. Serum creatinine was also significantly higher in the re-exploration group. Although creatinine did not retain conventional statistical significance after multivariable adjustment, the direction of association remained clinically relevant. Kristensen et al. similarly identified elevated preoperative serum creatinine as a risk factor for reoperation for bleeding [13]. Renal dysfunction may increase haemorrhagic risk through several mechanisms, including impaired platelet adhesion and aggregation, anaemia, altered drug clearance, and a greater burden of systemic comorbidity. Preoperative haemoglobin was significantly lower among patients requiring re-exploration in the present study. Although lower haemoglobin did not remain in the final independent predictor model, preoperative anaemia is clinically important because it reduces physiological reserve and increases the likelihood that relatively modest blood loss will result in transfusion. Patients who ultimately underwent re-exploration required considerably more packed red blood cells, fresh frozen plasma, and platelets than those who did not. The increased transfusion requirement in bleeding patients is consistent with previous multicentre evidence showing that significant postoperative bleeding is closely associated with blood-product exposure [17]. Redo surgery and combined or complex procedures were significantly more frequent among re-explored patients. Previous cardiac surgery was present in 20.0% of re-explored patients compared with 3.7% of patients who did not undergo re-exploration. Redo sternotomy can be technically challenging because adhesions and altered anatomy increase the potential for tissue and vascular injury. Similarly, combined procedures generally require longer surgical and CPB times and involve a larger number of potential bleeding surfaces. Although these variables did not remain in the restricted multivariable model, their univariable associations suggest that operative complexity remains clinically relevant when evaluating bleeding risk. An identifiable surgical source of bleeding was found in 73.3% of re-explored patients in the present study, while 26.7% demonstrated predominantly diffuse or nonspecific bleeding. This finding indicates that technical bleeding remains an important cause of re-exploration even in the presence of improvements in perioperative coagulation management. Previous investigations have similarly demonstrated that many re-explorations reveal a surgically correctable source. Lopes et al. reported that surgical causes predominated among patients re-explored for postoperative bleeding [14]. These observations emphasize the importance of meticulous surgical haemostasis before chest closure, particularly in patients with additional coagulation-related risk factors. Patients requiring re-exploration had substantially greater early postoperative chest-drain output. Median drainage during the first 6 hours was 960 mL in re-explored patients compared with 390 mL in those without re-exploration, while 24-hour drainage was 1,660 versus 700 mL, respectively. Excessive drainage is not simply a marker of blood loss but may identify a rapidly evolving clinical state requiring repeated transfusion, haemodynamic support, and potentially urgent surgical intervention. Colson et al., in a prospective multicentre study, demonstrated that active postoperative bleeding after cardiac surgery was associated with substantial transfusion requirements and adverse clinical outcomes [17]. The present study also demonstrated that re-exploration was associated with a markedly more complicated postoperative course. Median mechanical ventilation duration was 18 hours in the re-exploration group compared with 8 hours in the non-re-exploration group, while ICU stay increased from 3 to 5 days and total hospital stay from 8 to 12 days. Similar findings have been reported consistently in the literature. Ruel et al. observed prolonged hospitalization and increased renal complications, ICU readmission, and wound infection among patients requiring re-exploration [15]. Ali et al., in their evidence review, similarly concluded that patients returning to theatre for postoperative bleeding experience greater respiratory, neurological, and renal morbidity and longer ICU and hospital stays [18]. Acute kidney injury occurred in 33.3% of re-explored patients compared with 7.4% of patients without re-exploration. Several factors may contribute to renal injury in this setting, including perioperative hypotension, prolonged CPB, anaemia, excessive blood loss, inflammatory responses, and exposure to multiple blood products. Fröjd and Jeppsson demonstrated that re-exploration for bleeding is associated with increased early postoperative mortality and substantial postoperative morbidity [19]. These findings highlight that the consequences of major bleeding may extend beyond haemostasis itself and influence multiple organ systems. The higher frequency of surgical-site or mediastinal infection in the re-exploration group is also clinically important. In the present cohort, infection occurred in 20.0% of re-explored patients compared with 3.0% of patients without re-exploration. Reopening of the sternotomy, prolonged operative exposure, greater transfusion requirements, prolonged mechanical ventilation, and longer intensive care stay may all contribute to the increased susceptibility to infection. Ruel et al. similarly demonstrated an independent association between re-exploration and wound infection [15]. In-hospital mortality was 20.0% among patients undergoing re-exploration compared with 3.0% among patients who did not require re-exploration. Although the relatively small number of deaths limits precise estimation of the magnitude of this association, the finding agrees with the broader literature. Fröjd and Jeppsson reported approximately a twofold increase in early postoperative mortality associated with re-exploration [19]. Ohmes et al. also demonstrated significantly greater operative mortality and major adverse events among patients undergoing re-exploration for bleeding [20]. Thus, re-exploration should be considered not merely an additional surgical procedure but an important marker of severe postoperative physiological disturbance. The timing of re-exploration may further influence clinical outcome. The median interval to re-exploration in the present study was approximately 5.2 hours, suggesting that most cases were recognized and managed relatively early. Choong et al. showed that patients whose re-exploration was delayed for 12 hours or longer experienced significantly greater adverse outcomes, including increased transfusion requirements, prolonged ventilation, longer ICU stay, haemofiltration, and mortality [21]. These findings support timely surgical reassessment when persistent bleeding or tamponade is suspected rather than prolonged conservative management in a deteriorating patient. The predictive model developed in the present study showed good discriminatory performance, with an AUC of 0.86. Lower platelet count, longer CPB duration, and urgent/emergency operative status represented the strongest independent predictors. These variables are clinically attractive because they are identifiable before or during completion of the index procedure and may therefore help identify patients requiring enhanced postoperative surveillance. Nevertheless, the model should not be regarded as a validated clinical risk score. Only 15 re-exploration events occurred, resulting in relatively wide confidence intervals and limiting the number of covariates that could be reliably included in multivariable analysis. The present study has several limitations. First, its retrospective, single-centre design creates potential for selection bias and limits generalizability to other institutions. Second, the sample size was relatively small, particularly the number of patients experiencing the primary outcome. Third, several potentially important haemostatic variables, including detailed platelet-function testing, fibrinogen levels, thromboelastography or rotational thromboelastometry findings, and precise timing of antithrombotic drug discontinuation, were not available consistently. Fourth, decisions regarding surgical re-exploration were based on the treating surgical team's clinical judgement and therefore may have varied among individual clinicians. Finally, the relatively low event count restricted multivariable modelling and prevented robust assessment of interactions among potential predictors. Despite these limitations, the study identifies clinically relevant factors associated with re-exploration following open heart surgery. Lower preoperative platelet count, prolonged CPB duration, and urgent/emergency surgery were the principal independent predictors, while renal dysfunction, anaemia, redo surgery, operative complexity, and increased transfusion requirements were also associated with the event. Furthermore, patients requiring re-exploration experienced substantially greater postoperative morbidity, longer ICU and hospital stays, and higher in-hospital mortality. These findings support careful preoperative haemostatic assessment, optimization of modifiable risk factors, minimization of unnecessary CPB duration, meticulous surgical haemostasis, close postoperative monitoring of high-risk patients, and timely re-exploration when clinically significant postoperative bleeding persists.

Re-exploration for postoperative bleeding remains an important complication following open heart surgery and is associated with increased postoperative morbidity and mortality. In the present study, 10.0% of patients required surgical re-exploration. Lower preoperative platelet count, prolonged cardiopulmonary bypass duration, and urgent or emergency surgery were identified as independent predictors of re-exploration. Renal dysfunction, lower haemoglobin, redo surgery, complex procedures, and greater perioperative blood-product requirements were also more frequently observed among patients who required re-exploration.

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