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The association between preoperative anemia and postoperative mortality among non-cardiac surgical patients in Northwest Ethiopia: a prospective cohort study

BMC Anesthesiology volume 25, Article number: 19 (2025) Cite this article

Abstract

Introduction

In a low-income country, the impact of preoperative anemia on postoperative mortality among noncardiac surgery patients is little understood. As a result, we aim to investigate the association between preoperative anemia and postoperative mortality in noncardiac surgery patients in Northwest Ethiopia.

Methods

This is a prospective follow-up study of 3506 noncardiac surgery patients who were included in the final analysis between June 1, 2019, and July 1, 2021. We used a propensity score-match analysis to group anemic and non-anemic patients. The propensity score match analysis took into account age, gender, comorbidities, American Society of Anesthesiologists physical status, urgency of surgery, and trauma. Patients with and without preoperative anemia were divided into a 1:1 ratio in a propensity score balance. The association between preoperative anemia and postoperative mortality was determined using adjusted odds ratios and 95% confidence interval.

Results

This study included 3506 noncardiac surgery patients, of which 1532 (43.7%) had preoperative anemia. The propensity score-matching results reveal that one-to-one nearest neighbour propensity score matching without replacement was successful for 1351 pairs of surgical patients. The postoperative 28-day mortality rate for anemic patients was 53 (3.9%), with (OR:1.63; 95% CI: 1.05–2.54).

Conclusion

The study found that patients undergoing noncardiac surgery in Northwest Ethiopia had a higher rate of preoperative anemia than those in high-income countries. Preoperative anemia had a significant association with 28-day mortality after surgery.

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Background

Anemia should be viewed clinically as a decrease in blood erythrocyte mass, which impacts tissue oxygenation and activates compensatory mechanisms. It’s also described as hemoglobin (Hb) less than 13 g/dl for men, 12 g/dl for non-pregnant women, and 11 g/dl for pregnant women [1]. This clinical understanding of anemia can considerably help surgical patients’ care during the postoperative period. The patient’s preoperative hemoglobin [Hb] and physiological reserve substantially impact the clinical manifestations of the anemic syndrome and the extent of treatment required [1, 2]. Preoperative optimization of this patients group is necessary to reduce morbidity and mortality, during preoperative assessment for a patient scheduled for elective noncardiac surgery the patient is need to be optimized [3].

Anemia affects 1.9 billion people worldwide, with Central Africa, Western Sub-Saharan Africa, and Asia having the highest prevalence (27% in 2013 vs. 33.3% in 1990) [4]. The 2016 Ethiopia Demographic and Health Survey revealed that anemia was prevalent among 23% of women of reproductive age and 18% of adult men nationwide, despite limited research conducted on preoperative anemia and its effect on postoperative mortality [5].

Preoperative anemia prevalence varies depending on the urgency of surgery (elective or emergency), the presence of comorbidities, and whether the surgery was trauma or non trauma [6, 7]. Among surgical interventions, almost one-third of patients scheduled for elective surgery are anemic [8]. Due to disparities in care and treatment approaches, surgical patients in low- and middle-income countries have a relatively high prevalence of anemia [9, 10]. The effect of preoperative anemia on postoperative mortality were found to be significantly associated in research conducted in various countries and continents including mostly Europe, North America, and Asia, data regarding patients in Africa are scarce [2, 8, 11,12,13,14].

A study conducted in high-income countries found a strong link between preoperative anemia and postoperative mortality. However, the burden is substantially higher in low- and middle-income countries [15, 16]. Even though, preoperative patients with anemia and postoperative mortality constitute a large healthcare expense in low-resource countries, like Ethiopia, studies on strategies to decrease the burden are scarce. Therefore, this study aimed to examine the association between preoperative anemia and postoperative mortality in noncardiac adult surgical patients across 28-day follow-ups in Northwest Ethiopia.

Methods

Study design, period and setting

It is a prospective cohort study conducted from June 1, 2019, to July 01, 2021. The study setting was Bahir Dar, in northwestern Ethiopia, 580 km from Addis Ababa, Ethiopia’s capital city. Tibebe Ghion Specialized Hospital (TGSH) was established in December 2018 and offers clinical and academic services through Bahir Dar University. TGSH is a tertiary care hospital that provides medical and surgical services to more than 5 million patients. The hospital currently has over 500 beds and 14 major operating rooms for emergency and elective procedures. Surgical services include general surgery, gastrointestinal and hepatobiliary surgery, urology surgery, neurosurgery, pediatric surgery, head and neck surgery, thoracic surgery, orthopedic surgery, maxillo-facial surgery, ear, nose, and throat (ENT) surgery, obstetrics, and gynecologic surgery. Perioperative surgical services are provided by general surgeons and sub-specialty surgeons in the various units, while master anaesthetists and anesthesiologists offer perioperative anesthesia services. In general, about 1000 health professionals work across the hospital’s many service units.

This study was conducted in line with The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) Statement [17] (See Additional file 1).

Ethical consideration

The Institutional Review Board of Bahir Dar University, College of Medicine and Health Sciences, granted ethical approval to conduct this study (reference number CMHS /IRB 0163/2018). A waiver of informed consent was obtained prior to data collection. Patients aged 18 years and above who were present for surgical intervention were included. All the information obtained from the patients was kept confidential and secure from unauthorised access.

Eligibility criteria

Inclusion criteria

From June 1, 2019, to July 1, 2021, we included all adult patients aged 18 and older who underwent surgery at TGSH, as well as patients or family members who had cell phone.

Exclusion criteria

Patients who do not have cell phones are excluded.

Variables of the study

Outcome variable

The primary outcome of this study was postoperative 28-day mortality.

Independent variables

The independent factors included sex (male/female), age (≥ 18 years), type of operation (elective or emergency), ASA physical status classification (I-V), trauma (yes/no), and comorbidity (Yes/No).

Operational definition

Anemia

Defined as Hemoglobin(Hb) less than 13 g/dl for men and 12 g/dl for non-pregnant women, and 11 g/dl for pregnant women [18].

Lost to follow-up

Patients lost to follow-up within 28 days after surgery.

Outcome

The postoperative condition of patients who survived or died within 28 days of the follow-up.

Incomplete data

Missing follow-up data due to incorrect phone numbers or inability to reach the provided phone numbers.

Comorbidity

Comorbidity is defined as “a distinct additional clinical entity” that exists or may emerge during the clinical course of a patient with an index disease [19, 20].

Data collection and quality control

The data gathering methods were based on the Research Electronic Data Capture (REDCap) platform, an offline data input based on submitted questionnaires in the system [21]. The system used to collect perioperative patient information.

The anesthetist was the primary data collector at TGSH, gathering perioperative data for up to 28 days. The data manager verified that the data was complete and examined it against the hospital logbook system for inpatient mortality; if there was a discrepancy, it was cross-checked with the anesthesia and surgical logbook systems, as well as the REDCap database. After discharge, weekly follow-up phone calls were done on the 7th, 14th, 21st, and 28th postoperative days to reduce study participant dropouts. We collect multiple contact information in order to reach patients or family members. The data manager evaluated the collected data against the hospital logbook on a regular basis and filled in the gaps. The information technologist oversaw the entire REDCap database system. Prior to data collection, the anesthetist received training on the data collecting instrument as well as the ethics of recording patient data. To assure data quality, the obtained information was kept in the REDCap database system, which is only available to authorized users.

Statistical analysis

Data were extracted from the REDCap data server and analyzed using Stata Version 17. Categorical variables were reported as frequencies and percentages, while continuous data were tested for normality using the Kolmogorov–Smirnov test. The chi-square test was employed for categorical variables, and the T-test for normally distributed data. The variance infiltration factor (vif) was used to test for multicollinearity. The relationship between preoperative anemia and postoperative mortality was reported using an adjusted odds ratio and 95% confidence interval. Missing data were examined using the available case analysis. The propensity score match approach was used to compare anemic and non-anemic individuals. Variables included for propensity score match analysis included age, gender, comorbidities, ASA physical status, trauma, and urgency of surgery. The psmatch2 command in Stata was used for matching.

The quality of matching was assessed by balancing the variables between the anemia and non-anemia groups, and the quality of matching was tested by calculating the standardized bias before and after matching.

Patients with and without anemia were assigned codes 1, and 0, respectively. An adjusted estimate of the influence of preoperative anemia on postoperative 28-day mortality was produced by balancing factors classified as anemic and non-anemic based on propensity score matching. Patients with and without preoperative anemia were divided in a 1:1 ratio to balance propensity scores. To balance patients in anemic and non-anemic groups, one-to-one nearest neighbor matching was utilized with a caliber of 0.2 to estimate balancing. Standardized mean difference was used to expresses the amount of the intervention effect in each study relative to the variability found in this study. The balance of matching between anemic and non-anemic groups was also graphically assessed (Fig. 1).

Fig. 1
figure 1

Assessment of matching balance in Propensity score match analysis among anemic and non anemic patients

Full size image

Before and after matching, the propensity scores suggest comparable groups of anemic and non-anemic patients. The presence of preoperative anemia and its impact on surgical outcomes were assessed using an odds ratio and confidence interval. We considered balancing for statistically significant results (p-value < 0.05). A receiver operating characteristic (ROC) curve has been generated for models of preoperative hemoglobin and 28-day mortality.

Results

Baseline demographic and clinical characteristics

This study included 3506 surgical cases in the final analysis. The number of patients who were lost to follow-up was 103 (2.85%) (Fig. 2).

Fig. 2
figure 2

Study population profile

Full size image

The median age of the patients in this cohort was 42.5 [35, 50], and 61.2% were male. 66.4% were ASA physical status classification I, 78% had no comorbidity, 68.5% were non-trauma, and 52.3% were elective cases. Prior to surgery, 1532 (43.7%) of the total patients were anemic. In this study, the median age of anemic patients was 38 years, and preoperative anemia was more common in female patients (47.6%) than male patients (41%). Preoperative anemia was observed in 57.9% of patients with ASA physical status I. Preoperative anemia occurred in 27.8% of comorbid patients. Preoperative anemia was seen in 50.5% of emergency patients and 37.1% of trauma patients (Table 1).

Table 1 Univariable analysis of patients demographic and clinical characteristics before matching of non-cardiac surgical patients in Northwest Ethiopia, June 1, 2019, to July 01, 2021
Full size table

There was a significant difference in baseline characteristics between the anemia and non-anemia group in age, sex, surgical category, ASA physical status, comorbidity, and trauma (p = < 0.05). Using a one-to-one nearest neighbour propensity score matching without replacement, 1351 pairs of surgical patients were successfully matched (Table 2).

Table 2 Propensity score analysis after matching of non-cardiac surgical patients in Northwest Ethiopia, June 1, 2019, to July 01, 2021
Full size table

Preoperative anemia significantly correlates with the odds of 1.63 times increase the mortality of surgical non-cardiac patients (Table 3).

Table 3 Association of preoperative anemia on mortality after adjusting of anemia in non-cardiac surgical patients in Northwest Ethiopia, June 1, 2019, to July 01, 2021
Full size table

The mortality of anemic and non anemic patients after matching in the follow-up of 7th day, 14th day, 21 day and 28-days was illustrated on (Fig. 3).

Fig. 3
figure 3

Weekly mortality pattern

Full size image

The receiver operating characteristic (ROC) curve for preoperative hemoglobin and postoperative 28-day morality demonstrates the proportion of correct classifications (Fig. 4).

Fig. 4
figure 4

Receiver operating characteristic (ROC) curve

Full size image

Discussion

Our prospective study found that preoperative anemia in noncardiac surgical patients is prevalent at 43.7%, with anemic patients having higher postoperative 28-day mortality. The association between preoperative anemia and postoperative mortality in non-cardiac surgical patients shows that patients who were anemic before surgery had 1.63 times higher postoperative 28-day mortality than non-anemic patients.

In this study, the prevalence of preoperative anaemia among non-cardiac surgical patients (43.7%) was higher than studies conducted in Canada [22], Singapore [23], China [24], Germany [25], United Kingdom [26], and Madagascar [27]. The possible explanation for this discrepancy is a difference in sample size, access and quality of healthcare services. The prevalence of preoperative anemia among non-cardiac surgery patients was in line with the study conducted in South Africa surgical Outcome Studies [16]. One probable explanation is the utilization of a relatively equal sample size. In contrast to our findings, research conducted in the Northern part of Ethiopia reported a lower prevalence of preoperative anemia among noncardiac surgery patients [28]. One probable explanation is a difference in sample size, and the patients included were scheduled for elective noncardiac surgical procedures.

Based on a propensity score matching analysis and adjusting for potential confounding variables of 3506 non-cardiac surgical patients, we found that preoperative anaemia had 1.63 times increased the odds of postoperative 28-day mortality. Our findings were consistent with an Austrian study that revealed that non-cardiac surgical patients with uncorrected preoperative anaemia had a higher postoperative mortality rate [12]. Similarly, a study in Lebanon found a significant association between preoperative anaemia and postoperative mortality rate in non-cardiac surgical patients [2]. Furthermore, a study conducted on 30-day postoperative follow ups among non-cardiac surgery in the United Kingdom [26], Singapore [29], and also a one weeks follow-ups study of South Africa perioperative surgical outcome studys [16] found that the presence of preoperative anaemia in a patients come for non-cardiac surgery had association with postoperative mortality rate. According to several guidelines, preoperative anemia has a direct impact on the outcome of surgical patients, necessitating tailored preoperative optimization, prevention, and management of preoperative anemia for improved postoperative outcomes [3, 11].

This study’s clinical importance will be a foundation for understanding the association between preoperative anemia and postoperative mortality in non-cardiac surgical patients in North West Ethiopia. Our findings will assist clinicians and stakeholders working in perioperative care to understand the magnitude of preoperative anemia and its impact on postoperative mortality and use it as a baseline for future national surgical outcome studies. Furthermore, clinicians should screen patients for anemia before surgery, prioritizing management with an accurate identification of the etiology, and initiating the most appropriate preoperative therapy.

Strengths and limitations of this study

To highlight the strength of this study, first, a prospective data set with a long follow-up period is used to demonstrate mortality after surgical intervention. Second, propensity score-matched analysis was used to adjust for potential confounders and assess the relationship between preoperative anemia and postoperative mortality. Despite the strengths mentioned above, this study has limitations. To begin with, this was a single-centre study, which may impact the generalizability and magnitude of the problem. In addition, we analysed mixed surgical cohort that could influence the association between preoperative anemia and postoperative outcome. Furthermore, we did not include other potential confounding variables which might affect the relationship between preoperative anemia and postoperative mortality, such as nutritional status, transfusion, intraoperative blood loss, and perioperative managment.

Conclusions

The study found that patients undergoing noncardiac surgery in Northwest Ethiopia had a higher rate of preoperative anemia than those in high-income countries. Preoperative anemia had a significant association with 28-day mortality after surgery.

Data availability

The data used for analysis for this research is available from the corresponding author on reasonable request.

Abbreviations

Hb:

Hemoglobin

TGSH:

Tibebe Ghion Specialized Hospital

ASA:

American Society of Anesthesiologists

IQR:

Inter Quartile Range

SMD:

Standardized Mean Difference

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Acknowledgements

We thank Bahir Dar University, College of Medicine, and Health Science, Anesthesia Department staff for their unlimited support.

Provenance and peer review

Not commissioned; externally peer reviewed.

Funding

Impact Africa Perioperative Outcome Project supported this work by allowing to use the collected data, but the funder has no role in the study’s design, analysis of the study, interpretation, and preparation of the manuscript. The grant number or award is not applicable (N/A).

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Authors and Affiliations

  1. Department of Anesthesia, College of Medicine and Health Sciences, Bahir Dar University, PO Box 79, Bahir Dar, Ethiopia

    Misganew Terefe Molla, Amanuel Sisay Endeshaw, Gebrehiwot Asfaw & Fantahun Tarekegn Kumie

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  1. Misganew Terefe Molla
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Contributions

MT contributed to the study’s conception, design, data curation, data analysis, visualization, and manuscript preparation. AS contributed to the study’s design, data analysis, manuscript review, and manuscript editing. GA contributed to the paper’s revision, editing, and methodology. And FT were involved in figure preparation. All author reviewed the manuscrpit.

Corresponding author

Correspondence to Misganew Terefe Molla.

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Ethics approval and consent to participate

The Institutional Review Board of Bahir Dar University, College of Medicine and Health Sciences granted ethical permission for this study, including a waiver of informed consent, with reference number CMHS /IRB 0163/2018.

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The authors declare no competing interests.

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Molla, M.T., Endeshaw, A.S., Asfaw, G. et al. The association between preoperative anemia and postoperative mortality among non-cardiac surgical patients in Northwest Ethiopia: a prospective cohort study. BMC Anesthesiol 25, 19 (2025). https://doiorg.publicaciones.saludcastillayleon.es/10.1186/s12871-025-02900-x

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BMC Anesthesiology

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