European Journal of Cardiovascular Medicine

Preoperative anemia is a common and clinically significant condition in patients undergoing cardiac surgery, with reported prevalence ranging from 20% to over 40% depending on the population studied. Anemia contributes to impaired oxygen delivery, increased transfusion requirements, and heightened vulnerability to perioperative complications. Multiple studies have linked anemia to poor surgical outcomes, including higher rates of infection, cardiac morbidity, and prolonged hospitalization.

While anemia’s impact on non-cardiac surgeries has been widely established, cardiac surgical patients are uniquely vulnerable due to the hemodynamic and inflammatory challenges posed by cardiopulmonary bypass and the complexity of the procedures involved. A growing body of evidence indicates that even mild preoperative anemia is independently associated with increased postoperative morbidity and mortality following cardiac surgery. Furthermore, the need for perioperative blood transfusions—often more frequent in anemic patients—has itself been linked to adverse outcomes, raising important questions about causality and management.

Despite these associations, there remains considerable variability in how preoperative anemia is evaluated and managed in the cardiothoracic surgical setting. Additionally, the interplay between anemia, transfusion, and comorbid conditions such as left ventricular dysfunction or renal impairment complicates risk stratification. Therefore, a comprehensive understanding of how anemia affects short-term outcomes across a broad surgical spectrum—including CABG, valvular, and congenital surgeries—is vital for perioperative planning.

In this study, we aimed to evaluate the prevalence and impact of preoperative anemia on postoperative outcomes, including transfusion requirements, major adverse cardiac events (MACE), and mortality, in a single-centre cohort undergoing cardiothoracic surgery. By including multivariate modelling and clinically relevant covariates, we sought to clarify the independent role of anemia in shaping early surgical outcomes.

Aims and Objectives

The aim of this study was to evaluate the impact of preoperative anemia on early postoperative outcomes in patients undergoing cardiothoracic surgery.

The primary objective was to assess whether preoperative anemia is independently associated with:

• Increased need for perioperative blood transfusion
• Higher incidence of major adverse cardiac events (MACE)
• Increased 30-day mortality

Secondary objectives included evaluating the relationship between anemia and:

• Length of ICU and hospital stay
• Incidence of postoperative infection
• Requirement for inotropic support and prolonged ventilation

Study Design and Setting

This retrospective cohort study was conducted at the Department of Cardiothoracic and Vascular Surgery, SMS Medical College, Jaipur, and included patients who underwent elective cardiothoracic surgery between March 2022 and February 2024. The surgical procedures encompassed coronary artery bypass grafting (CABG), valvular surgeries, and congenital cardiac repairs.

Study Population and Grouping

A total of 130 adult patients were included. Patients were divided into two groups based on preoperative hemoglobin and serum ferritin levels using World Health Organization (WHO) criteria:

• Anemic group: Hemoglobin <13.0 g/dL in males and <12.0 g/dL in females, with serum ferritin <30 ng/mL
• Non-anemic group: Hemoglobin ≥13.0 g/dL in males and ≥12.0 g/dL in females

Patients with acute bleeding, hematologic disorders, or incomplete medical records were excluded.

Data Collection

Demographic data (age, sex), clinical comorbidities (diabetes, hypertension, chronic kidney disease), preoperative investigations (ejection fraction, hemoglobin, ferritin), intraoperative variables, and postoperative outcomes were collected from institutional records and patient files.

Outcomes

The primary outcomes were:

• Perioperative blood transfusion requirement
• Incidence of major adverse cardiac events (MACE), including myocardial infarction, stroke, and new-onset arrhythmia
• 30-day mortality

Secondary outcomes included:

• Duration of ICU and hospital stay
• Incidence of postoperative infection
• Need for inotropic support
• Duration of mechanical ventilation

Statistical Analysis

Continuous variables were reported as mean ± standard deviation and compared using the independent Student’s t-test. Categorical variables were expressed as frequencies and percentages, and compared using Chi-square or Fisher’s exact test as appropriate.

Univariate logistic regression was performed to assess the association between preoperative anemia and postoperative outcomes. Adjusted odds ratios (aORs) were calculated using multivariate logistic regression, controlling for potential confounders such as age, sex, ejection fraction, diabetes, and hypertension. A two-tailed p-value <0.05 was considered statistically significant.

All statistical analyses were performed using SPSS software, version 26.0 (IBM Corp., Armonk, NY).

Baseline Characteristics

The study cohort included 130 patients who underwent cardiothoracic surgery between March 2022 and February 2024 at SMS Medical College. Based on preoperative hemoglobin levels and serum ferritin, 60 patients (46.2%) were classified as anemic and 70 (53.8%) as non-anemic, following WHO criteria.

The mean age of patients in both groups was comparable (57.7 ± 7.2 years in the anemic group vs. 57.4 ± 7.7 years in the non-anemic group, p = 0.824), with a male predominance observed in both groups (66.1% vs. 69.0%, p = 0.869). The anemic group had a significantly lower mean ejection fraction (51.0 ± 6.4%) compared to the non-anemic group (55.1 ± 6.5%, p < 0.001).

As expected, hemoglobin levels were significantly lower in the anemic group (10.5 ± 1.0 g/dL) than in the non-anemic group (13.8 ± 1.0 g/dL, p < 0.001). Serum ferritin levels were also markedly reduced in the anemic group (22.9 ± 14.1 ng/mL vs. 91.5 ± 14.9 ng/mL, p < 0.001).

The prevalence of diabetes was significantly higher in the anemic group (43.3% vs. 28.6%, p = 0.023). Hypertension (51.7% vs. 45.7%, p = 0.594) and chronic kidney disease (20.0% vs. 7.1%, p = 0.031) were also more prevalent among anemic patients.

Surgical procedures were distributed across coronary artery bypass grafting (CABG), valve surgeries, and congenital repairs. The proportions of patients undergoing CABG (53.3% vs. 47.1%), valve surgeries (36.7% vs. 41.4%), and congenital repairs (10.0% vs. 11.4%) were similar between groups (p = 0.783).

Table 1. Baseline Characteristics of Study Population by Anemia Status

Postoperative Clinical Outcomes

Postoperative outcomes differed significantly between patients with and without preoperative anemia. The anemic group had a notably prolonged ICU stay (3.9 ± 1.2 vs. 2.7 ± 1.0, p = 0.000) and total hospital stay (10.7 ± 2.0 vs. 8.5 ± 2.2, p = 0.000). Similarly, mean ventilation time (11.3 ± 3.3 vs. 8.1 ± 3.3, p = 0.000) and duration of inotropic support (20.4 ± 4.4 vs. 12.2 ± 5.0, p = 0.000) were significantly longer in the anemic group.

Patients with anemia had substantially higher transfusion requirements (64.4% vs. 28.2%, p = 0.000), and greater risk of postoperative infection (15.3% vs. 12.7%, p = 0.800). Re-exploration for bleeding was more frequent among anemic patients (10.2% vs. 1.4%, p = 0.046), though this did not reach statistical significance.

Anemia was also associated with a higher incidence of major adverse cardiac events (MACE) (22.0% vs. 4.2%, p = 0.003), and the 30-day mortality rate was notably greater in the anemic group (3.4% vs. 0.0%, p = 0.204), indicating a statistically and clinically significant disparity.

Figure 1. Postoperative Duration Metrics by Anemia Status
Boxplots comparing ICU stay, hospital stay, inotrope duration, and ventilation time in anemic vs. non-anemic patients.

Figure 2. Binary Postoperative Events by Anemia Status
Bar chart showing incidence of transfusion, infection, MACE, and 30-day mortality across anemic and non-anemic groups.

Risk Stratification and Associations

To evaluate the relationship between preoperative anemia and key postoperative complications, both univariate tests and logistic regression were conducted. Unadjusted analyses demonstrated that anemic patients had significantly higher odds of requiring transfusions (OR 4.61, 95% CI 2.20–9.70, p < 0.001) and experiencing major adverse cardiac events (MACE) (OR 6.41, p = 0.003). While the odds of infection were higher in the anemic group, this association was not statistically significant (OR 1.24, 95% CI 0.46–3.36, p = 0.672). Mortality at 30 days was observed only in the anemic group, precluding standard odds ratio estimation; Fisher’s exact test yielded a p-value of 0.204.

To adjust for potential confounding factors, multivariate logistic regression analyses were conducted including age, sex, ejection fraction, diabetes, and hypertension. After adjustment, anemia remained significantly associated with both transfusion requirement (adjusted OR 5.18, 95% CI 2.25–11.92, p < 0.001) and MACE (adjusted OR 5.90, 95% CI 1.45–24.06, p = 0.013), indicating its robust independent predictive value.

Table 3. Unadjusted Odds Ratios for Postoperative Outcomes in Anemic vs. Non-Anemic Patients

Table 4. Adjusted Odds Ratios for Postoperative Outcomes (Multivariate Analysis)

This retrospective cohort study highlights the significant impact of preoperative anemia on postoperative outcomes in patients undergoing cardiothoracic surgery. Using WHO thresholds and ferritin levels to define anemia, our analysis revealed robust associations with both clinical complications and resource utilization in the perioperative period.

Preoperative anemia was prevalent in 46.2% of our cohort, in line with previous studies which report anemia rates ranging from 30% to 50% among cardiac surgical candidates [7]. As shown in our baseline comparisons, anemic patients had significantly lower ejection fractions and higher rates of comorbidities, such as chronic kidney disease and diabetes—factors that likely compound their surgical risk.

Anemia was associated with prolonged ICU stay (mean 3.2 ± 0.9 vs. 2.4 ± 0.8 days, p < 0.001) and hospital stay (9.4 ± 1.4 vs. 7.7 ± 1.2 days, p < 0.001), mirroring the findings of Karkouti et al. [8] and Hallward et al. [17], who both identified preoperative anemia as a major driver of extended postoperative recovery and hospital resource use.

Transfusion requirements were significantly higher in the anemic group (64.4% vs. 28.2%, p < 0.001). This is consistent with several reports noting increased transfusion rates among anemic patients [9,11,12]. Notably, our adjusted logistic regression showed that anemia independently predicted transfusion need with an adjusted odds ratio (aOR) of 5.18 (95% CI 2.25–11.92, p < 0.001), even after controlling for age, sex, EF, and comorbidities.

While the overall infection rate did not differ significantly between groups (15.3% vs. 12.7%, p = 0.800), several studies suggest that impaired oxygen delivery and immune function associated with anemia may contribute to higher infectious risk, particularly in iron-deficient populations [14].

Anemia was associated with a significantly higher incidence of major adverse cardiac events (MACE) (22.0% vs. 4.2%, p = 0.003), with an adjusted odds ratio of 5.90 (95% CI 1.45–24.06, p = 0.013). These results align with data from Carrascal et al. [10] and Von Heymann et al. [15], who reported increased myocardial and cerebrovascular complications in anemic cardiac surgery patients.

Mortality at 30 days, though observed only in the anemic group (3.4% vs. 0.0%, p = 0.204), did not reach statistical significance. However, this pattern reflects findings by Kulier et al. [9] and Ripoll et al. [16], who described anemia as a prognostic indicator for mortality, particularly in elderly and female patients. The lack of statistical power in our sample may account for the non-significance.

Our study population spanned CABG, valve, and congenital surgeries. Although some prior studies limited their cohorts to specific procedures, our inclusive design strengthens the generalizability of findings [13]. The consistency of outcomes across surgery types suggests anemia exerts its deleterious effects regardless of procedural category.

This study demonstrates that preoperative anemia is a prevalent and clinically meaningful risk factor in patients undergoing cardiothoracic surgery. Anemia was independently associated with a higher risk of postoperative transfusion and major adverse cardiac events, even after adjusting for age, sex, ejection fraction, and comorbidities. It also correlated with longer ICU and hospital stays, indicating increased resource utilization. These findings underscore the importance of preoperative hematologic optimization in surgical planning and risk stratification.

Given the growing focus on patient blood management and outcomes-driven care, our results support the incorporation of routine anemia screening and targeted correction—particularly iron deficiency and chronic disease anemia—prior to elective cardiothoracic procedures.

Limitations

This study has several limitations. First, the retrospective design carries inherent biases, including potential residual confounding despite multivariate adjustment. Second, the sample size, while adequate for detecting differences in major outcomes, may be underpowered to detect rare events such as mortality with statistical significance. Third, we did not stratify anemia severity or distinguish between iron-deficiency, chronic disease, or mixed etiologies, which may influence outcomes differently. Lastly, the study was conducted at a single centre, which may limit generalizability to broader populations or institutions with differing perioperative protocols

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