Postoperative acute kidney injury in surgical intensive care units: a multicenter study on incidence and risk profiles

Abstract

This multicenter retrospective study identifies the major risk factors associated with the development of postoperative acute kidney injury (AKI) and examines its incidence among patients in the surgical intensive care unit. The study involved adult patients (aged 18 years and older) who were admitted to surgical intensive care units (SICUs) after major surgical procedures. Data analysis was conducted using the Statistical Package for the Social Sciences 27, and tables and figures were utilized to present the results. The incidence of acute kidney injury (AKI) in surgical intensive care units (SICUs) was 53.4% (95% CI: 48.4%–58.4%). AKI was significantly associated with several factors, including sepsis (adjusted odds ratio [AOR]: 8.2, 95% CI: 5.3–12.3), trauma (AOR: 4.8, 95% CI: 3.4–7.7), chronic kidney disease (AOR: 3.3, 95% CI: 2.1–4.8), diabetes mellitus (AOR: 2.1, 95% CI: 1.1–4.2), blood transfusion (AOR: 2.5, 95% CI: 1.5–7.3), and emergency surgery (AOR: 2.6, 95% CI: 1.8–4.9). Patients hospitalized in surgical intensive care units have a significant rate of postoperative acute kidney injury (AKI). Conditions such as sepsis, trauma, pre-existing chronic renal disease, diabetes mellitus, receiving blood transfusions, and undergoing emergency surgery are independently associated with an increased risk of AKI. To reduce the burden of AKI and improve patient outcomes, early detection and targeted preventative strategies are crucial for high-risk populations in surgical intensive care units.

Introduction

Acute kidney injury (AKI) is a significant complication that can occur after major surgery, especially in patients in surgical intensive care units. It is linked to increased mortality, longer hospital stays, and higher morbidity rates¹.

The incidence of postoperative AKI varies widely, ranging from 5% to 50% among surgical populations. In high-income countries, advanced medical care has decreased this incidence; however, resource-limited settings report higher rates. AKI is especially prevalent in major surgical cases, contributing to increased mortality, dependence on renal replacement therapy (RRT), and a greater risk of chronic kidney disease².

The development of AKI in postoperative patients is influenced by a combination of preoperative, intraoperative, and postoperative risk factors. These include advanced age, preexisting chronic kidney disease (CKD), diabetes mellitus, hypertension, and other comorbidities. Key contributors to AKI include dehydration, significant blood loss, prolonged surgical durations, and the use of nephrotoxic medications^2–5.

Anesthesia and anesthetic agents significantly increase the risk of acute kidney injury (AKI) through various mechanisms. Common hemodynamic factors that heighten this risk include prolonged hypotension, reduced cardiac output, and impaired renal autoregulation⁶. Intravenous anesthetic drugs may impose renal stress, while volatile anesthetics can reduce renal blood flow and glomerular filtration rate (GFR). Additionally, anesthesia can cause renal tubular cell damage, exacerbate systemic inflammation, and alter neurohormonal and sympathetic responses. Preventive measures such as careful hemodynamic monitoring, minimizing nephrotoxic agents, and optimizing perioperative fluid management are essential for mitigating this risk^7–9.

In surgical critical care settings, postoperative acute kidney injury (AKI) remains a serious clinical issue, with incidence rates affected by variations in diagnostic criteria, demographic factors, and monitoring practices. Standardized diagnostic frameworks, real-time assessments of renal function, and routine use of biomarkers are essential for improving early detection and intervention^10–12.

Despite its clinical significance, perioperative strategies to prevent AKI are often inconsistent. Effective approaches include tailored fluid management, comprehensive hemodynamic monitoring, and the use of nephroprotective agents. Implementing consensus guidelines—such as strict glycemic control, avoidance of nephrotoxic drugs, and individualized hemodynamic goals—could substantially improve patient outcomes^13,14.

Postoperative AKI has profound implications, including increased morbidity, higher mortality rates, and progression to CKD. The long-term effects on quality of life and the associated economic burden are frequently overlooked^15,16.

By understanding the multifactorial causes of postoperative AKI, clinicians can better manage this complication. Multicenter studies are essential for defining its incidence, identifying gaps in care, and addressing regional variations^17,18. Such studies will also guide evidence-based preventive and therapeutic strategies. This study aims to investigate the incidence and factors contributing to postoperative AKI in ICU patients.

Methods

Study design and setting

Three Comprehensive Specialized Hospitals (CSHs) in the Amhara region of Ethiopia participated in this multicenter, retrospective follow-up study. These hospitals deliver life-saving healthcare and are vital components of the region’s healthcare system due to their capacity to provide specialized services, including newborn intensive care, emergency care, internal medicine, surgical services, and orthopedic and gynecological care for mothers. The hospitals included in the study are the University of Gondar Comprehensive Specialized Hospital, Debre Tabor Comprehensive Specialized Hospital, and Debre Birhan Comprehensive Specialized Hospital, all of which are renowned for their comprehensive healthcare services and equipped with advanced medical infrastructure.

The study aimed to evaluate the incidence and risk factors for acute kidney injury (AKI) following surgery in patients hospitalized in the surgical intensive care units (SICUs) of these institutions. The study period was from January 1, 2021, to December 30, 2024.

Study population

All adult surgical patients admitted to the surgical intensive care units of the selected hospitals who met the inclusion criteria were included in the study.

Inclusion and exclusion criteria

Inclusion criteria

All adult patients (aged 18 years and older) who were admitted to the intensive care units after surgical procedures during the study period were included.

Exclusion criteria

The study excluded patients with a history of end-stage renal disease (ESRD) or chronic kidney disease (CKD) stages IV and V, as defined by KDIGO criteria. Additionally, patients requiring renal replacement therapy, such as dialysis, those who survived less than 48 h after surgery, and those lacking data on postoperative kidney function or relevant clinical variables were also excluded.

Variables

Dependent variable

Postoperative AKI in SICUs.

Independent variables

The study’s independent variables comprise socio-demographics (age, sex, and comorbidities such as diabetes mellitus, hypertension, and cardiovascular diseases), surgical parameters (type of operation, procedure duration, and anesthesia duration), and postoperative factors (length of ICU stay, duration of mechanical ventilation, and use of nephrotoxic drugs, including aminoglycosides and contrast agents).

Data collection

Data were collected through a retrospective evaluation of medical records from eligible patients by anesthetists at comprehensive specialized hospitals. The retrieved data included demographic characteristics such as age, sex, and comorbidities (diabetes mellitus, hypertension, and cardiovascular diseases). Surgical parameters documented included the type of operation, procedure duration, and duration of anesthesia.

To evaluate the postoperative course, data were recorded on the length of stay in the ICU, duration of mechanical ventilation, and use of nephrotoxic drugs, including aminoglycosides and contrast agents. Renal function was assessed by measuring blood creatinine levels both preoperatively and postoperatively.

The primary clinical outcome of interest was the incidence of acute kidney injury (AKI), diagnosed according to the Kidney Disease: Improving Global Outcomes (KDIGO) criteria. Postoperative AKI was defined as an increase in serum creatinine of at least 0.3 mg/dL within 48 h, a urine output of less than 0.5 mL/kg/h for six hours, or an elevation in serum creatinine to at least 1.5 times the baseline value within the previous seven days.

Sample size and sampling technique

Sample size determination

The single population proportion formula was used to determine the sample size. This calculation considered a proportion of p = 40.4% (from previous studies¹⁹, a Z-score of Za/2 = 1.96 for a 95% confidence interval, and a margin of error (D) of 5%.

n= (za/2)²p (1-p)/(d) ².

n= (1.96)² 0.404 (1-0.404)/ (0.05)².

n = 3.84*0.24/0.0025 = 370.

The total sample size was 370. After accounting for a 10% non-respondent rate, the final sample size increased to 407.

Sampling procedure

The study participants were selected using a proportional allocation algorithm designed to distribute the sample size (ns = 407) across three different surgical intensive care units (SICUs) based on the proportion of admissions at each unit from January 1, 2021, to December 30, 2024. During this period, a total of Nt = 1800 SICU patients were admitted. The process for calculating the sample size for each ICU is as follows:

Average Number of Surgical Patients in Each ICU per year:

• DBCSH (n1) = 84.

• DTCSH (n2) = 96.

• GCSH (n3) = 420.

Proportional allocation formula: The number of participants allocated to each ICU (nICU) is calculated using the formula:

Where:

• ns = Total sample size (407).

• nICU​ = Average number of surgical patients admitted to each ICU.

• Nt = Total number of surgical patients admitted across all ICUs (1,800).

Calculations for Each ICU:

• For DBCSH: nDBCSH = 407 × 252/1,800 = 57.

• For DTCSH: nDTCSH = 407 × 288/1,800 = 65.

• For GCSH: nGCSH = 407 × 1260/1,800 = 285.

• Total Sample Size 57 + 65+285 = 407.

Where;

DBCSH: Debre Birhan Comprehensive Specialized Hospital.

DTCSH: Debre Tabor Comprehensive Specialized Hospital.

GCSH: Gondar Comprehensive Specialized Hospital.

A simple random sampling method was used to select the required number of participants from all newly admitted surgical patients in the surgical ICU between January 1, 2021, and December 30, 2024. Participants were chosen using a lottery method (Fig. 1).

Fig. 1.

Flow diagram illustrating the sample size allocation for surgical patients admitted to the SICU at CSHs.

Operational definition

AKI: defined according to KDIGO criteria as.

1. Increase in serum creatinine by ≥ 0.3 mg/dL within 48 h, or.

2. Urine output < 0.5 mL/kg/h for 6 h.

3. Elevation of serum creatinine to ≥ 1.5 times baseline, which could have happened in the last 7 days at any point during this period^20,21.

KDIGO AKI staging criteria

Stage	Serum Creatinine Criteria	Urine Output Criteria
Stage 1	Increase to 1.5–1.9× baseline, OR - Increase by ≥ 0.3 mg/dL (≥ 26.5 µmol/L) within 48 h	< 0.5 mL/kg/h for 6–12 h
Stage 2	Increase to 2.0–2.9× baseline	< 0.5 mL/kg/h for ≥ 12 h
Stage 3	Increase to 3.0× baseline, OR - Increase to ≥ 4.0 mg/dL (≥ 353.6 µmol/L), OR - Initiation of renal replacement therapy, OR - In patients < 18 years: eGFR < 35 mL/min/1.73 m²	< 0.3 mL/kg/h for ≥ 24 h, OR Anuria for ≥ 12 h

Post-surgical anemia in ICU

Anemia that develops at any point during a stay in the intensive care unit²².

Delayed awakening

Defined as the inability to regain consciousness within 30 min of stopping the administration of anesthesia and adjuvant drugs²³.

Nephrotoxic medications

Drugs that can harm the kidneys, potentially leading to chronic kidney disease (CKD) or acute kidney injury (AKI). Nephrotoxic drugs used in anesthesia and surgery can cause acute kidney injury or exacerbate pre-existing renal dysfunction. Common agents include etomidate, propofol, inhalational agents, aminoglycosides, cisplatin, methotrexate, diuretics, ACE inhibitors (ACEIs), contrast media, nonsteroidal anti-inflammatory drugs (NSAIDs), and immunosuppressants^24,25.

Postoperative AKI

Acute kidney injury occurring at any time within seven days following surgery^26,27.

Statistical analysis

Clinical and demographic features were summarized using descriptive statistics. Continuous variables were presented as means ± standard deviations (SD) or medians with interquartile ranges (IQR), depending on their distribution. Categorical variables were represented using frequencies and percentages.

Multivariate logistic regression was employed to identify factors independently associated with postoperative acute kidney injury (AKI). The multivariate model included variables that were clinically significant or had a p-value < 0.2 in the univariate analysis. Results are reported as odds ratios (OR) with 95% confidence intervals (CI).

All statistical analyses were conducted using IBM SPSS Statistics, Version 27 (https://www.ibm.com/products/spss-statistics). A p-value of less than 0.05 was considered statistically significant.

Result

Sociodemographic characteristics of surgical patients admitted to the SICUs

The patient group in this comprehensive study of 407 individuals admitted to surgical intensive care units following major procedures represented a diverse array of backgrounds and characteristics. The average age of the patients was 57 years, ranging from young adults to the elderly. Men comprised a slight majority at 56.8%, while more than half of the patients (56.1%) came from rural areas. Most participants (69%) were married, and a significant portion (40%) worked as farmers. Education levels varied widely; over one-third of patients (34.1%) lacked formal education, indicating potential gaps in health literacy (Table 1).

Table 1.

Sociodemographic characteristics of surgical patients admitted to SICUs at CSHs in Amhara, Ethiopia.

Variables	Categories / Values	Frequency (n)	Percentage (%)
Age (years)	Mean ± SD		57.0 ± 15.7
	Median (IQR)		58 (46–69)
Sex	Male	232	56.8
	Female	175	43.2
Residence	Urban	179	43.9
	Rural	228	56.1
Marital Status	Married	281	69.0
	Single	59	14.5
	Widowed / Divorced	67	16.5
Educational Status	No Formal Education	139	34.1
	Primary (Grades 1–8)	127	31.2
	Secondary (Grades 9–12)	83	20.4
	Tertiary (College/University)	58	14.3
Occupation	Farmer	163	40.0
	Government/Private Employee	97	23.8
	Daily Laborer	83	20.4
	Unemployed / Retired	64	15.7

Clinical characteristics of surgical patients admitted to the SICUs

Among the 407 surgical patients admitted to the ICU, 54.3% (n = 221) had a history of prior surgery, while 45.7% (n = 186) had not undergone previous surgical procedures. According to the American Society of Anesthesiologists (ASA) physical status classification, 21.2% of patients were classified as ASA I, 29.7% as ASA II, 33.2% as ASA III, and 15.9% as ASA IV.

The mean duration of anesthesia was 5.45 ± 1.25 h, and the mean surgical duration was 5.23 ± 1.30 h. Patients remained in the ICU for an average of 10 ± 5 days and required mechanical ventilation for 9.0 ± 5.0 days. The estimated mean blood loss was 1,350 ± 830 mL. Hemoglobin levels increased from9.3 ± 4.2 g/dL at baseline to 10.2 ± 2.4 g/dL at discharge (Table 2).

Table 2.

Clinical variables of SICU patients at CSHs in Amhara, Ethiopia.

Variables		Values
History of previous surgery	Yes	221 (54.3%)
	No	186 (45.7%)
ASA physical status	ASA I	86 (21.2%)
	ASA II	121 (29.7%)
	ASA III	135 (33.2%)
	ASA IV	65 (15.9%)
Duration of Surgery		5.23 (± 1.30) hours
Duration of Anesthesia		5.45 (± 1.25) hours.
Estimated blood loss		1350 ± 830 milliliter
Length of stay in SICU		10 ± 5 days
Duration on MV		9.0 ± 5.0 days
Baseline hemoglobin		9.3 ± 4.2 mg/dL
Hemoglobin at discharge		10.2 ± 2.4 mg/dL

Preoperative and intraoperative medications administered

All patients (100%) received vecuronium and antibiotics. The most commonly used anesthetics and analgesics included pethidine (92.8%), propofol (83.3%), suxamethonium (88.7%), isoflurane (81.8%), and ketamine (74.4%). Opioid administration varied, with morphine (73.9%), fentanyl (24.3%), and tramadol (25.3%) being utilized.

NSAIDs were used more frequently in 66.1% of cases, followed by antiretroviral therapy (ART) at 18.9% and chemotherapeutic agents preoperatively at 19.4%. Cardiovascular medications were selectively administered, including beta-blockers (9.6%), calcium channel blockers (24.8%), ACE inhibitors (23.6%), and diuretics (27.8%). Additionally, thiopental (48.9%) and halothane (73.5%) were used as general anesthetics. A broad spectrum of other medications was reported in 32.7% of cases (Table 3).

Table 3.

Common preoperative and intraoperative medications for SICU patients at CSHs in the Amhara Region, Ethiopia.

Drugs	N (%)
Antibiotics	100 (100)
NSAIDs	269 (66.1)
Chemotherapy	79 (19.4)
Diuretics	113 (27.8)
ACEIs	96 (23.6)
CCBs	101 (24.8)
BBs	39 (9.6)
ART	77 (18.9)
Morphine	301 (73.9)
Fentanyl	99 (24.3)
Pethidine	378 (92.8)
Tramadol	103 (25.3)
Ketamine	303 (74.4)
Propofol	339 (83.3)
Thiopental	199 (48.9)
Vecuronium	100 (100)
Suxamethonium	361 (88.7)
Isoflurane	333 (81.8)
Halothane	299 (73.5)
Other	133 (32.7)

The study included patients who underwent various surgical procedures, with general surgery being the most common, accounting for 29.2% (n = 119) of the cases. Neurologic surgery followed at 21.2% (n = 86), while orthopedic and trauma procedures comprised 17.4% (n = 71). Urologic procedures made up 13.3% (n = 54), and gynecologic and obstetric surgeries represented 11.3% (n = 46). Thoracic surgery was the least frequent, constituting 7.6% (n = 31) of all cases (Fig. 2).

Fig. 2.

Types of Surgical Procedures Performed on ICU-Admitted Patients at CSHs in Amhara, Ethiopia.

The data illustrates the distribution of critical circumstances leading to ICU admissions. Shock (28.3%) and respiratory failure (23.8%) are the most prevalent causes, reflecting their significant role in potentially fatal situations. Serious neurological issues also contribute substantially, with delayed awakening (19.9%) and severe brain injury (16.8%) being major factors. Myocardial infarction/ischemia (5.2%) and diabetic ketoacidosis (2.6%) indicate metabolic and cardiovascular crises. Although less common, neuromuscular diseases (1.3%) can significantly impact respiratory and motor function. The category labeled “Others” (2.1%) encompasses less common conditions (Fig. 3).

Fig. 3.

Causes of ICU Admissions at CSHs in the Amhara Region, Ethiopia.

Postoperative complications and medication used in ICU

More than half of the patients had anemia (51.8%), making it the most common complication. Among critically ill surgical patients, sepsis (19.9%) was the second most frequent complication and posed a significant risk. The notable prevalence of surgical site infections (SSI, 8.1%) and ventilator-associated pneumonia (VAP, 11.6%) underscores the necessity of stringent infection control protocols in intensive care units. A smaller proportion of patients developed stress ulcers (5.2%), highlighting the importance of preventive measures. Finally, a very small subset of patients (0.7%) experienced other complications (Fig. 4).

Fig. 4.

Common Complications in ICUs at CSHs in the Amhara Region, Ethiopia.

All 407 ICU patients (100%) received both an antibiotic and an analgesic. Intravenous anesthetic agents were administered to 312 patients (76.7%), while inotropes and vasopressors were used in 279 cases (68.6%). Diuretics were prescribed for 153 patients (37.6%), and benzodiazepines were administered to 243 patients (59.8%). Muscle relaxants were the least commonly used medication, given to 102 patients (25.1%) (Table 4).

Table 4.

Common Pharmacologic agents used in SICUs at CSHs in the Amhara Region, Ethiopia.

Variable	N (%)
Antibiotics	407 (100)
Analgesics	407 (100)
Diuretics	153 (37.6)
Inotropes and vasopressors	279 (68.6)
Benzodiazepines	243 (59.8)
IV anesthetic agents	312 (76.7)
Muscle relaxants	102 (25.1)

Incidence and associated factors of AKI in SICUs

In this study, the incidence of AKI in surgical intensive care units was found to be 53.4% with 95% CI of 48.4–58.4 (Fig. 5).

Fig. 5.

Pie Chart Illustrating the Incidence of AKI in SICU Patients at CSHs in the Amhara Region, Ethiopia.

Factors associated with AKI

Both bivariable and multivariable logistic regression analyses were conducted to identify factors associated with acute kidney injury (AKI). In the bivariable analysis, several factors were significantly associated with AKI (p < 0.2), including preexisting chronic kidney disease (CKD), diabetes mellitus, hypertension, cerebrovascular disease, congestive heart failure, malignancy, retroviral infection (RVI), mean arterial pressure (MAP) < 65 mmHg, shock, sepsis, procedural urgency, case type, vasopressor use, nephrotoxic medication use, and blood transfusion.

In the multivariable analysis, the most significant predictors of AKI (p < 0.05) included preexisting CKD, diabetes mellitus, blood transfusion, sepsis, emergency surgery, and trauma.

AKI was most strongly associated with sepsis (adjusted odds ratio [AOR]: 8.2, 95% confidence interval [CI]: 5.3–12.3), trauma (AOR: 4.8, 95% CI: 3.4–7.7), chronic kidney disease (AOR: 3.3, 95% CI: 2.1–4.8), diabetes mellitus (AOR: 2.1, 95% CI: 1.1–4.2), blood transfusions (AOR: 2.5, 95% CI: 1.5–7.3), and emergency surgical procedures (AOR: 2.6, 95% CI: 1.8–4.9) (Table 5).

Table 5.

Bivariable and multivariable logistic regression analysis of factors associated with AKI in SICU patients at CSHs in the Amhara Region, Ethiopia.

Variables	Category	AKI		COR (95% CI)	AOR (95% CI)	P - Value
		Yes	No
Underlying CKD	Yes	113	63	2.2 (1.4-4)	3.3 (2.1–4.8) **	0.001
	No	105	126
Diabetes Mellitus	Yes	110	68	2.1 (1.2–2.9)	2.1 (1.1–4.2) **	0.008
	No	101	128
Hypertension	Yes	111	54	2.3 (1.4–3.4)	0.8 (0.4–1.6)	0.11
	No	110	125
Cerebrovascular disease	Yes	93	50	1.9 (1.5–4.2)	0.6 (0.3–1.2)	0.18
	No	135	139
Congestive cardiac failure	Yes	103	67	1.63 (1.1–2.8)	1.9 (0.9–3.8)	0.15
	No	115	122
Malignancy	Yes	108	63	2 (1.4–3.5)	4.2 (2.8–7.8)	0.1
	No	110	126
Retroviral disease	Yes	109	67	1.8 (1.3–3.2)	5.1 (3.1–8.8)	0.3
	No	109	122
MAP < 65 mmHg	Yes	122	76	1.9 (1.3–3.2)	2(1.2–2.9)	0.11
	No	96	113
Blood transfusion	Yes	145	80	2.7 (1.8–5.2)	2.5 (1.5–7.3) **	0.01
	No	73	109
Nephrotoxic exposure	Yes	134	81	2.1 (1.5–3.8)	3.8 (2.6–5.3) **	0.0002
	No	84	108
Urgency of the procedure	Emergency	120	80		2.6 (1.8–4.9) **	0.002
	Elective	98	109	1.7 (1.1–2.8)
Nature of the case	Traumatic	107	71	2.2 (1.1–4.9)	4.8 (3.4–7.7) **	0.0001
	Nontraumatic	94	135
Sepsis	Yes	111	71	1.9 (1.2–4.3)	8.2 (5.3–12.3) **	0.03
	No	102	123

Discussion

In our study, we found that 53.4% of patients in surgical intensive care units (SICUs) developed acute kidney injury (AKI) (95% CI: 48.4%–58.4%). This finding aligns with previous studies conducted in various healthcare settings, highlighting the high incidence of AKI among critically ill surgical patients. AKI is a well-recognized complication in postoperative patients admitted to intensive care, often resulting from a combination of factors, including perioperative hemodynamic instability, extensive surgical trauma, and pre-existing comorbidities.

Our findings are consistent with previous studies that have reported similar AKI incidence rates among SICU patients. A large multicenter study in Asia²⁸ reported an AKI incidence of 51.2% among intensive care unit (ICU) patients, highlighting a substantial burden of renal impairment among critically ill postoperative patients in the region. Similarly, a retrospective study in South America²⁹ found an incidence of 55.6%, further reinforcing the notion that postoperative AKI remains a significant global clinical concern. In a nationwide cohort study conducted in Australia³⁰ and New Zealand³¹, AKI incidence in SICUs was reported at 55.3%, while a study in South Korea³² found that 52.7% of critically ill surgical patients developed AKI. The latter study attributed these findings to institutional differences in fluid resuscitation strategies, the implementation of advanced renal monitoring, and variations in perioperative hemodynamic management.

According to our research, the incidence of acute kidney injury (AKI) among patients in the surgical intensive care unit (SICU) was higher than that reported in several studies conducted in sub-Saharan Africa, India, and other low- and middle-income countries (LMICs). For example, a study in West Africa³³ reported an AKI incidence of 45.3%, which may be attributed to differences in patient characteristics, perioperative fluid management, and early AKI detection. Similarly, a study in Southeast Asia²⁸ reported a lower incidence of 42.7%, potentially due to variations in intraoperative monitoring protocols and SICU admission criteria.

An Indian³⁴ study reported an AKI incidence of 38.5% and attributed this to delayed ICU admissions, limited access to renal replacement therapy (RRT), and differences in sepsis management strategies. Likewise, a study conducted in sub-Saharan Africa³⁵ reported an incidence of 35.2%, with contributing factors including delays in surgical interventions, inadequate nephroprotective measures, and restricted access to critical care services.

The lower AKI rates observed in these studies may be partly explained by differences in critical care practices, resource limitations, and patient selection criteria. These variations underscore the influence of patient demographics, perioperative management strategies, and healthcare infrastructure on AKI incidence in SICUs.

However, compared to other studies, our findings indicate a lower incidence of acute kidney injury (AKI). A large North American cohort study reported an AKI incidence of 60.8% in surgical intensive care units (SICUs)³⁶, which was associated with prolonged ICU stays, a higher incidence of pre-existing comorbidities, and frequent use of nephrotoxic medications. A study conducted in European tertiary hospitals also reported an incidence of 58.9%³⁷, suggesting that such factors contribute significantly. These variations in incidence may be influenced by differences in surgical complexity, postoperative care protocols, and patient demographics.

Similarly, a multicenter study in Canada found an AKI incidence of 62.3%, emphasizing the role of fluid resuscitation strategies and perioperative hypotension³⁸. In the UK, a retrospective analysis identified sepsis and vasopressor use as major risk factors, with AKI occurring in 64.1% of SICU patients³⁹. Furthermore, a comprehensive database analysis from the United States reported an incidence of 65.7%, underscoring the impact of complex surgical interventions and prolonged mechanical ventilation on AKI development⁴⁰.

The observed heterogeneity in AKI incidence across studies may be attributable to differences in study populations, AKI definitions (e.g., KDIGO, RIFLE, or AKIN criteria), and variations in healthcare infrastructure. In contrast, the higher incidence observed in these studies may be driven by multiple factors, including suboptimal fluid resuscitation strategies, delayed presentation of surgical cases, and limited access to nephrology consultations. Additionally, pre-existing renal dysfunction, exposure to nephrotoxic medications, and postoperative hemodynamic instability were likely key contributors to AKI development in our study cohort.

AKI was most strongly associated with sepsis (AOR: 8.2, 95% CI: 5.3–12.3), trauma (AOR: 4.8, 95% CI: 3.4–7.7), chronic kidney disease (AOR: 3.3, 95% CI: 2.1–4.8), diabetes mellitus (AOR: 2.1, 95% CI: 1.1–4.2), blood transfusions (AOR: 2.5, 95% CI: 1.5–7.3), and emergency surgery (AOR: 2.6, 95% CI: 1.8–4.9).

Sepsis patients are 8.2 times more likely to develop acute kidney injury (AKI) compared to non-sepsis patients (AOR: 8.2, 95% CI: 5.3–12.3). The pathophysiology of sepsis-induced AKI is multifaceted, involving cellular dysfunction, hemodynamic instability, and systemic inflammation. Hemodynamic failure leads to hypotension, reduced renal perfusion, and systemic vasodilation, exacerbating renal injury. Additionally, immune-mediated responses and endothelial dysfunction further aggravate ischemic damage, contributing to the progression of AKI^41,42.

The risk of acute kidney injury (AKI) is also 4.8 times higher in trauma patients compared to non-trauma individuals. One of the primary mechanisms is direct renal injury, which occurs when the kidneys sustain damage from blunt or penetrating trauma, leading to ischemia, contusion, or hemorrhage⁴³ . Hypovolemia resulting from bleeding or fluid loss further exacerbates ischemic injury by reducing renal perfusion. Additionally, rhabdomyolysis, triggered by severe muscle damage, releases myoglobin into the bloodstream, which can obstruct renal tubules and induce oxidative stress, further contributing to AKI⁴⁴ . The combined effects of these factors significantly increase the likelihood of renal impairment in trauma patients^45,46.

Compared to patients without chronic kidney disease (CKD), those with pre-existing renal impairment have a 3.3-fold increased risk of developing acute kidney injury (AKI) (AOR: 3.3). This heightened susceptibility is primarily due to a reduced renal reserve, meaning fewer functional nephrons are available to compensate for additional insults⁴⁷. Chronic inflammation and fibrosis impair the kidney’s ability to recover from injury, while dysregulated autoregulation of renal blood flow increases susceptibility to ischemic and hemodynamic disturbances. Furthermore, endothelial dysfunction, oxidative stress, and impaired electrolyte homeostasis are common in CKD patients, making them even more vulnerable to AKI when exposed to nephrotoxic medications, infections, or hemodynamic instability^51,52.

Patients with diabetes mellitus have a 2.1-fold increased risk of developing acute kidney injury (AKI) compared to those without the disease (AOR: 2.1). This elevated risk is primarily driven by endothelial dysfunction, chronic metabolic stress, and pre-existing diabetic nephropathy. Chronic hyperglycemia induces progressive renal damage through glomerular hyperfiltration, oxidative stress, and inflammation. Endothelial dysfunction reduces nitric oxide availability, impairing vasodilation and increasing susceptibility to ischemic injury. Additionally, glomerulosclerosis and tubulointerstitial fibrosis, hallmarks of diabetic nephropathy, further diminish renal reserve, limiting the kidneys’ ability to withstand subsequent insults such as infections, dehydration, nephrotoxic medications, or hypotension. Collectively, these factors increase both the likelihood and severity of AKI in individuals with diabetes^53,54.

Patients who receive blood transfusions have a 2.5-fold increased risk of developing acute kidney injury (AKI) compared to those who do not (AOR: 2.5). This heightened risk is primarily attributed to hemolysis, iron overload, and immune-mediated responses. Free hemoglobin, released during hemolysis, contributes to renal injury through oxidative stress, nitric oxide depletion, and tubular obstruction. Iron overload from multiple transfusions generates free radicals, exacerbating renal inflammation and oxidative damage. Additionally, immune-mediated transfusion reactions, including hemolytic responses and inflammatory cytokine release, can lead to renal hypoperfusion and endothelial dysfunction. Collectively, these mechanisms increase the risk of AKI following blood transfusions^55,56.

Emergency surgery is associated with a 2.6-fold increased risk of acute kidney injury (AKI) compared to non-emergency procedures (AOR: 2.6, 95% CI: 1.8–4.9). Several factors contribute to this elevated risk, including hemodynamic instability (unpredictable blood pressure fluctuations leading to renal hypoperfusion), delayed diagnosis and treatment (resulting in limited preoperative optimization), and greater illness severity, often due to conditions such as trauma, sepsis, or gastrointestinal perforation^7,57.

Clinical implications

The high rate of postoperative AKI in SICUs emphasizes the need for targeted preventative measures and early risk assessment. Clinicians should closely monitor patients with sepsis, trauma, diabetes, chronic kidney disease, those undergoing emergency surgery, or receiving blood transfusions. In surgical critical care settings, minimizing nephrotoxic exposures, implementing rapid hemodynamic optimization, and following evidence-based perioperative guidelines can reduce the risk of AKI and enhance patient outcomes.

Conclusion

Acute kidney injury (AKI) is highly prevalent in surgical intensive care units (SICUs), affecting 53.4% of patients. Key risk factors for AKI include sepsis, trauma, diabetes mellitus, chronic renal disease, blood transfusions, and emergency surgery. These findings highlight the importance of early risk assessment, prophylactic care, and effective perioperative management to reduce the incidence of AKI and improve outcomes in SICUs.

Strength, and limitation

Strength

The study’s strength lies in its thorough analysis of intensive care unit (ICU) admissions across various surgical specialties in a resource-limited context. By incorporating both sociodemographic and clinical characteristics, it offers a comprehensive overview of the challenges faced by surgical ICU patients in Amhara, Ethiopia. The large sample size enhances the reliability of the findings, while the multicenter design increases the study’s generalizability.

Limitation

One limitation of the study is its retrospective design, which may have introduced information bias and restricted access to certain clinical and sociodemographic data. Additionally, the study did not assess long-term outcomes, such as mortality rates, renal recovery, and quality of life. Furthermore, several important variables that could have influenced the outcomes, including patients’ socioeconomic status and living situations, were not documented in the medical records. Despite these limitations, the study offers valuable insights into the magnitude and risk factors of postoperative acute kidney injury (AKI) in surgical intensive care unit patients within a resource-limited setting.

Recommendations

Risk stratification

Implement regular AKI risk assessment procedures in intensive care units, particularly for patients with diabetes mellitus, sepsis, trauma, or chronic kidney disease.

Sepsis management

To reduce the risk of AKI, enhance aggressive hemodynamic stabilization techniques and improve early sepsis detection.

Trauma and blood transfusion protocols

Develop guidelines to minimize the risk of AKI by optimizing blood transfusion strategies and reducing unnecessary transfusions.

Abbreviations

ACEIs

Angiotensin Converting Enzyme Inhibitors

AKI

Acute Kidney Injury

ART

Antiretroviral Therapy

ASA

American Society of Anesthesiologist

BBs

Beta Blockers

BDZs

Benzodiazepines

BMI

Body Mass Index

BUN

Blood Urea Nitrogen

CCBs

Calcium Channel Blockers

CIN

Contrast-Induced Nephropathy

CKD

Chronic Kidney Disease

COPD

Chronic Obstructive Pulmonary Disease

CSHs

Comprehensive Specialized Hospitals

DBCSH

Debre Birhan Comprehensive Specialized Hospital

DKA

Diabetic Ketoacidosis

DTCSH

Debre Tabor Comprehensive Specialized Hospital

DAW

Delayed Awakening

GCSH

Gondar Felegehiwot Comprehensive Specialized Hospital

Gyn-Obs

Gynecology Obstetrics

HIC

High Income Countries

HIV

Human Immunodeficiency Virus

ICU

Intensive Care Unit

KDIGO

Kidney Disease Global Outcome

LIC

Low Income Countries

MAP

Mean Arterial Pressure

mL

Milliliter

mmHg

Millimeter Mercury

MV

Mechanical Ventilator

NMDs

Neuromuscular Diseases

NSAIDs

Non-steroidal Anti-inflammatory Drugs

RF

Respiratory Failure

RRT

Renal Replacement Therapy

SCr

Serum Creatinine

SICU

Surgical Intensive Care Unit

SPSS

Statistical Packages for Social Science

SSI

Surgical Site Infection

TBI

Traumatic Brain Injury

TIVA

Total Intravenous Anesthetics

UO

Urine Output

UTI

Urinary Tract Infection

VAP

Ventilator-Associated Pneumonia

Author contributions

HB planned the study and collected, processed, and analyzed the data under the direction of NZ, TB, GM, AA, WA, BY, and GD. All authors were responsible for the final manuscript, with AG, DG, MA, AT, AD, and TM overseeing data collection, conducting a critical review of the text, and granting publication approval.

Funding

This work did not receive any grants or other funding from the public, private, or nonprofit sectors.

Data availability

Due to institutional and ethical constraints, the datasets generated and/or analyzed in this study are not publicly accessible. However, they can be obtained from the corresponding author upon reasonable request. Access will be granted following approval from the relevant ethics committees and in compliance with the ethical guidelines of the participating institutions.

Declarations

Competing interests

The authors declare no competing interests.

Ethical approval and informed consent

This retrospective study was reviewed and approved by the Debre Tabor University (DTU) Institutional Review Board (IRB) to ensure compliance with ethical research standards. The DTU IRB evaluated the study’s objectives, methodology, potential risks, and benefits to participants, confirming that all necessary safeguards were in place to protect the rights, privacy, and welfare of the individuals whose data were analyzed. The DTU IRB granted approval for this study under reference number CHS/63/2024. All study procedures were conducted in accordance with the ethical standards of the institution and the Helsinki Declaration. Informed consent was waived due to the study’s retrospective nature, with this waiver granted by the DTU Institutional Review Board. The study exclusively utilized anonymized data extracted from existing medical records. No additional interventions or procedures were performed, and no direct contact with patients was required. Strict confidentiality protocols were followed to ensure the protection of patient privacy, and all data were de-identified prior to analysis.