Introduction

Acute kidney injury (AKI) is a clinical syndrome characterized by a sudden and potentially reversible decrease in the glomerular filtration rate, followed by an increase in serum creatinine concentration or the development of oliguria (1,2). This condition is one of the most common and dangerous complications that a patient can develop in the intensive care unit (ICU) (3). According to the literature, its incidence ranges between 20% and 65%, while its mortality, especially in more severe cases, can exceed 50% (1-5). The main complications associated with AKI include fluid overload, electrolyte disturbances, uremic syndrome, the development of chronic kidney disease, and the need for long-term renal replacement therapy (RRT) (5-8).

Since AKI is often asymptomatic, its diagnosis and staging require determining serum creatinine concentrations and quantifying urine output. To establish the diagnosis, at least one of the following criteria must be met: a ≥ 50% increase in serum creatinine concentration within less than 7 days, a ≥ 0.3 mg/dL increase in plasma creatinine within ≤ 2 days, or oliguria lasting at least 6 hours (1,2).

The severity of AKI is divided into three stages (2,9). Stage 1 corresponds to a ≥ 0.3 mg/dL increase in serum creatinine, an elevation of its baseline value by 1.5 to 1.9 times, or a urine output < 0.5 mL/kg/h for a period of 6 to 12 hours. Stage 2 is characterized by a serum creatinine increase of 2.0 to 2.9 times its baseline value or a urine output < 0.5 mL/kg/h for a period ≥ 12 hours. Finally, stage 3 presents an increase in serum creatinine ≥ 4.0 mg/dL or ≥ 3.0 times its baseline value, either alone or in combination with a urine output < 0.3 mL/kg/h for ≥ 24 hours, or anuria for at least 12 hours.

Treatment involves managing the triggering condition (obstructive nephropathy, toxicity from non-steroidal anti-inflammatory drugs, acute glomerulonephritis, sepsis, and hypovolemic shock) and implementing general therapeutic measures, such as restricting the use of nephrotoxic drugs, correcting hydroelectrolytic disorders, and providing nutritional support. RRT is indicated in the management of refractory metabolic acidosis, uremic symptoms, hyperkalemia, fluid overload, among others (2,6,10,11).

Regarding the main factors associated with AKI, a 2015 international study that included 97 ICUs and 1802 patients worldwide (244 of whom were from five Latin American countries) concluded that chronic kidney disease (CKD), liver cirrhosis, heart failure, cancer, diabetes mellitus, hypertension (HTN), acute myocardial infarction, hypovolemic shock, septic shock, ethnicity (higher incidence in patients of African descent), and age >65 years are some of the most prevalent conditions in this group of individuals (5,6,12).

In Colombia, multiple conditions, such as HTN, diabetes mellitus, CKD, acute myocardial infarction, HIV, chronic obstructive pulmonary disease (COPD), liver cirrhosis, cancer, nephrotoxic drug use, the administration of iodinated contrast agents, history of surgical procedures, and trauma, constitute the main risk factors for developing AKI (13). On the other hand, although Africa, Latin America, and Southeast Asia account for more than 85% of the global population, there is limited information on the possible risk factors associated with mortality in patients who develop AKI during hospitalization in an ICU (10). Therefore, this study presents a survival analysis and characterization of possible factors related to mortality in critically ill patients who develop AKI in the ICU.

Materials and Methods

An observational, analytical, cross-sectional study was conducted, including 76 adult patients diagnosed with AKI, hospitalized between January and December 2022 in the ICU of the Zipaquirá Regional Hospital (Colombia). Patients with unclear antecedents of chronic kidney disease (CKD) were excluded, as well as those who required RRT prior to ICU admission and patients whose families opted to limit therapeutic efforts. For diagnosis and classification of the disease, the KDIGO 2012 criteria were used. Early AKI was considered when its onset occurred within the first 48 hours of hospitalization, while late AKI was defined as occurring after this period.

The main variables analyzed in this study included age; sex; pathological and pharmacological history; exposure to potential nephrotoxic agents; values of urea, electrolytes, and arterial pH; requirement for invasive mechanical ventilation (IMV) or RRT; administration of vasopressor drugs; SOFA scores before and during ICU hospitalization; and the duration of AKI. The information obtained through the review of medical records was tabulated using Microsoft Excel 365 software (Microsoft Corporation, Redmond, Washington, USA).

Regarding the analysis plan, this was carried out using SPSS v. 29 software (SPSS Inc., Chicago, Illinois, USA). Quantitative variables were described using measures of central tendency (mean or median) and dispersion (standard deviation or interquartile range). Qualitative variables were analyzed using absolute and relative frequency distributions. Proportion comparisons were performed using the chi-square test. Potential associations between risk factors and outcomes were assessed using a multiple logistic regression model, while survival analysis was conducted using the Kaplan-Meier method.

This study complies with national and international bioethical principles as endorsed by Colombian law through Resolution 08430 of 1993. The research was evaluated, approved, and supervised by the Ethics Committee of the Samaritana University Hospital. Regarding the use of personal data, this study adheres to the provisions of Colombia's Law 1581 of 2012, ensuring privacy and security of the information.

Results

Clinical Characterization

A total of 76 patients diagnosed with AKI who were hospitalized between January and December 2022 in the ICU of the Zipaquirá Regional Hospital were analyzed. The average age was 65.3 ± 16.1 years. 64.5% (n = 49) of the patients were male, 93.4% (n = 71) had at least one comorbidity, and 19.7% (n = 15) required RRT. Regarding the values of various laboratory tests, the median creatinine level before ICU admission was 1.28 mg/dL (IQR = 0.91-2.10 mg/dL). The maximum creatinine level reached in the ICU was, on average, 4.49 mg/dL (95% CI = 4.01-4.96 mg/dL), while the median creatinine level at discharge was 2.20 mg/dL (IQR = 1.16-4.15 mg/dL). On the other hand, the maximum blood urea nitrogen (BUN) and potassium levels reached during ICU hospitalization were, on average, 85.1 mg/dL (95% CI = 78.5-91.7 mg/dL) and 5.59 mEq/L (95% CI = 5.37-5.81 mEq/L), respectively. Table 1 presents the main clinical characteristics and demographic data of the sample.

Factors Associated with the Use of Renal Replacement Therapy

Of the total number of individuals, 19.7% (n = 15) required RRT, half of whom received it within approximately 36 hours of ICU admission (IQR = 18-72 hours). The presence of fluid overload (OR = 13.2; 95% CI = 5.6-30.6; p ≤ 0.001), refractory metabolic acidosis (OR = 9.7; 95% CI = 4.8-19.5; p ≤ 0.001), and uremic encephalopathy (OR = 7.7; 95% CI = 4.2-14.3; p ≤ 0.001) were the main conditions associated with its use. Other potential risk factors for RRT included age ≤ 61 years (OR = 4.2; 95% CI = 1.2-13.7; p = 0.029), a history of autoimmunity (OR = 5.1; 95% CI = 1.1-23.9; p = 0.044), and serum potassium and creatinine levels during ICU hospitalization ≥ 6 mEq/L (OR = 3.8; 95% CI = 1.1-12.4; p = 0.028) and 5 mg/dL (OR = 5.1; 95% CI = 1.5-17.3; p = 0.007), respectively.

Mortality Analysis During the First 28 and 60 Days

The mortality rate during the first 28 days was 61.8% (n = 47), and it reached 68.4% (n = 52) by day 60. Sex-adjusted mortality by day 28 was 69.4% (n = 34) for males and 48.1% (n = 13) for females. After 60 days, these values increased to 75.5% (n = 37) for males and 55.6% (n = 15) for females, respectively. No statistically significant differences were observed between the sexes during the mentioned periods (p = 0.087 vs. p = 0.121). It is noteworthy that the overall mortality risk was significantly higher during the first 28 days compared to the period from day 29 to day 60 (61.8% vs. 6.6%; p ≤ 0.001).

Regarding patients who required RRT, the mortality rate reached 60% in the first 28 days and increased to 66.6% by day 60. In this subgroup, a significant difference in the mortality risk was also observed during the first 28 days (60% vs. 6.7%; p ≤ 0.001). The main factors associated with an increased risk of mortality in the bivariate model were the need for IMV, a history of CKD, the development of late AKI, a SOFA score > 5 at ICU admission or after one week of hospitalization (Table 2). Other conditions, such as early or late initiation of RRT and prolonged ICU stay, were not linked to a change in mortality risk.

After applying a logistic regression model, it was determined that being male (adjusted OR = 3.3; 95% CI = 1.1-9.8; p = 0.035) and having a SOFA score greater than 7 prior to ICU admission (adjusted OR = 3.8; 95% CI = 1.2-11.8; p = 0.020) are possible independent risk factors for mortality. Other variables, such as advanced age, serum creatinine levels, the presence of comorbidities, and the administration of nephrotoxic agents, were not associated with a significant change in mortality risk.

Survival Analysis

The overall median survival was 13.0 days (95% CI = 9.1-16.8). The main variables associated with a significant reduction in survival were age ≥ 65 years, the requirement for IMV, the presence of COPD or CAD, an arterial pH < 7.2, and a SOFA score > 5 before or during the first seven days of ICU hospitalization (Figure 1, Table 3). Other variables, such as sex, a history of HTN or CKD, and the use of early RRT, were not associated with a significant change in survival.

Discussion

This study analyzed the potential factors associated with mortality in critically ill patients who developed AKI during their hospitalization in the ICU. Additionally, a time-to-event analysis was conducted to determine the possible factors linked to changes in the median survival.

As reported in the literature, this study observed an average age >50 years, a higher proportion of male patients, and a significant comorbidity burden. Also, nearly 50% of the patients were exposed to nephrotoxic agents, and there was a high frequency of vasopressor administration and IMV prior to ICU admission (13-16).

Other notable findings include a SOFA score > 5 in approximately 45% of patients after one week of hospitalization, average BUN and creatinine values exceeding 80 mg/dL and 4.0 mg/dL, respectively, and 50% of patients having an ICU stay ≥ 9 days. Compared to other studies, the urea nitrogen levels in our sample were higher, while the average ICU hospitalization time was similar. Regarding the SOFA score, only one study published in Colombia by Fonseca et al. (13) incorporated this information in their analysis, reporting a median score of 4 points (IQR 2-7) (12,14,17-19).

Concerning the use of RRT, 19.5% of the patients included in this study required its implementation. The frequency of this intervention in our sample was lower than reported internationally (19.5% vs. 23.5%) but higher than observed in Colombia (19.5% vs. 12.4%) (12,13). The main factors associated with its use were the presence of fluid overload, refractory metabolic acidosis, and uremic encephalopathy. Other authors, such as Ríos Valbuena (19), also reported a potential relationship with the presence of sepsis, the use of iodinated contrast agents, and a history of surgical procedures. This is consistent with what was published by Larrarte et al. (18), who state that sepsis, cardiac surgery, rhabdomyolysis, and severe trauma are possible risk factors for the development of AKI requiring RRT.

Compared to the literature, this study showed a higher proportion of mortality, especially during the first 28 days (19,20), with men being the most affected, as well as those who had a SOFA score > 7 prior to ICU admission. The median survival in our sample was 13.0 days (95% CI = 9.1-16.8), with age ≥ 65 years, the need for IMV, COPD or CAD, an arterial pH < 7.2, and a SOFA score > 5 before or during the first seven days of ICU hospitalization being the main factors associated with a reduction in survival. As reported by Chaïbi et al. (21), more than 50% of deaths in our study occurred before day 60, which constitutes a higher proportion of mortality compared to other studies (9,22).

From a clinical perspective, our findings support the use of a dynamic surveillance model focused on the prevention of complications through the sequential calculation of the SOFA score as a risk stratification tool. Scores greater than 7 points at ICU admission or greater than 5 points during the first week of hospitalization should trigger early alerts and renal protection strategies to mitigate the risk of complications. Simultaneously, public policies should prioritize the development of protocols based on local evidence to improve the outpatient management of comorbidities and ensure timely access to necessary care, thus optimizing clinical outcomes and ensuring the financial sustainability of the healthcare system (1,23-24).

Conclusions

AKI in critically ill patients represents a frequent complication with high mortality. In this study, mortality exceeded 60% at 28 days and approached 70% at 60 days, figures higher than those reported in developed countries. The factors independently associated with an increased risk of death were being male and having a SOFA score greater than 7 prior to ICU admission. Although the requirement for RRT was similar to that described in the international literature, its relationship with mortality was not significant after multivariate adjustment, highlighting the importance of the overall clinical condition rather than the intervention itself. Overall survival was limited, with a median of 13 days, and was primarily conditioned by age, cardiovascular and respiratory comorbidities, metabolic acidosis, and multiple organ dysfunction. These findings underscore the need to implement prevention strategies, early diagnosis, and optimization of comprehensive management in patients at risk of AKI in the ICU. They also highlight the importance of generating more local evidence in developing countries, where resources are limited, and clinical conditions differ from those in developed countries, in order to guide health policies and improve clinical outcomes.

References

Notes

Funding The authors did not receive funding for the development of this research.

Conflict of Interest he authors declare that they have no conflicts of interest.

Author notes

a Correspondence author: airamcabrera89@gmail.com

Additional information

How to cite: Ruiz-Barrera MA, Cifuentes M. Ramírez Maldonado AF, Bernate F, Rosario A, Pedraza Cortés GA, Riveros Orjuela HJ, Sánchez Veloza C, Buitrago Gutiérrez CT. Survival and mortality analysis in patients with acute kidney injury admitted to the intensive care unit. Univ Med. 2026;67. https://doi.org/10.11144/Javeriana.umed67.sarf

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