Nephrology · Medical Literature
The Effect of Preoperative Hydration on Cardiac Surgery-Associated Acute Kidney Injury.
Abstract
The aim of this study was to determine the effect of preoperative intravenous saline hydration on postoperative renal functions and the prevention of acute kidney injury subsequent to open-heart surgery. Our investigation was designed as a prospective, randomized, and controlled single-center trial. We included 110 patients with basal renal functions that were not disrupted and who were undergoing cardiac surgery from October to December 2020. The first group (control) had fluid restriction for 12 hours prior to surgery (n = 55), and the second group (case) was hydrated with 0.9% normal saline for 12 hours before surgery (n = 55). In the hydration group, creatinine values dropped below the preoperative values (P = 0.008) and the glomerular filtration rate values rose above the preoperative levels (P = 0.003). The early-term mortality rates were 0% for the hydration group and 5.45% for the control group (n = 3). Besides, in the hydration group, the glomerular filtration rate values on the 30th day and 360th day after surgery increased to levels even higher than those recorded preoperatively. As a result of much effort, we showed that preoperative hydration can prevent severe cardiac surgery-associated acute kidney injury and related in-hospital mortality.
Clinical relevance
In adult patients with normal baseline renal function undergoing open-heart surgery, does preoperative intravenous 0.9% normal saline hydration for 12 hours reduce postoperative acute kidney injury compared with 12-hour preoperative fluid restriction? __SNAPSHOT__ {"studyDesign":"Prospective, randomized, controlled, single-center trial","setting":"Single center; country not specified in the abstract (journal origin: Brazil); institutional type not reported","sampleSize":"n = 110 (hydration group: n = 55; control/fluid-restriction group: n = 55)","population":"Adult patients with intact baseline renal function undergoing elective open-heart (cardiac) surgery; patients with preoperative renal dysfunction were excluded. Enrolled October–December 2020.","intervention":"Preoperative intravenous 0.9% normal saline hydration for 12 hours before surgery (rate, total volume, and infusion protocol not specified in the abstract)","comparator":"Preoperative fluid restriction for 12 hours prior to surgery (standard perioperative fasting/NPO approach)","primaryOutcome":"Postoperative renal function as measured by serum creatinine and glomerular filtration rate (GFR); prevention of cardiac surgery-associated acute kidney injury (CSA-AKI). Specific AKI diagnostic criteria (e.g., KDIGO staging) not reported in the abstract.","followUp":"Short-term (immediate postoperative), 30-day, and 360-day GFR measurements reported; exact duration of primary outcome assessment not explicitly defined","fundingSource":"Not reported"}
Key findings
In the hydration group, postoperative serum creatinine values fell below preoperative baseline values (p = 0.008), and postoperative GFR values rose above preoperative levels (p = 0.003). GFR at 30-day and 360-day follow-up in the hydration group also exceeded preoperative baseline values; no statistical comparisons for these time points versus the control group are reported in the abstract. Early-term (presumably 30-day) mortality was 0% in the hydration group versus 5.45% (3/55) in the control group; no p-value, confidence interval, or relative risk for this mortality difference is reported in the abstract. Absolute risk reduction for early mortality = 5.45% (calculated); NNT to prevent one early death = 18.3 (calculated). The abstract is truncated and the complete primary AKI incidence rates, absolute between-group differences in creatinine and GFR, and all secondary outcome data are not reported in the available text. No adverse events related to the hydration protocol (e.g., fluid overload, pulmonary edema) are mentioned in the abstract.
Practice implications
This small single-center RCT suggests that preoperative IV normal saline hydration for 12 hours may preserve or improve renal function (creatinine, GFR) and reduce early mortality after open-heart surgery compared with standard preoperative fluid restriction in patients with normal baseline renal function. However, several critical interpretive cautions apply: (1) Only the abstract is available; complete outcome data, AKI incidence rates, precise GFR and creatinine values, effect sizes with confidence intervals, and the full methodology cannot be assessed. (2) The abstract is truncated, and the primary conclusion sentence is incomplete, making the full scope of findings uncertain. (3) The study enrolled only 110 patients from a 3-month window, raising concerns about statistical power for mortality and rare AKI endpoints. (4) The hydration protocol (infusion rate, total volume) is not specified, limiting reproducibility. (5) The study excluded patients with preoperative renal dysfunction—the population at highest risk for CSA-AKI—limiting generalizability to the most clinically important subgroup. (6) The AKI diagnostic criteria used are not stated; it is unclear whether a validated definition (e.g., KDIGO) was applied. (7) Creatinine and GFR are surrogate endpoints; patient-centered outcomes (dialysis requirement, long-term renal survival, hospital length of stay) are not reported in the abstract. (8) Blinding status is not reported. (9) The 3-patient difference in early mortality, while numerically striking, is underpowered to draw definitive mortality conclusions. Practice should not change based on this abstract alone; however, findings are directionally consistent with pathophysiologic rationale and prior smaller trials suggesting benefit of preoperative hydration in cardiac surgery populations. __LIMITATIONS__ Only the abstract is available, and it is truncated—the complete dataset and statistical analysis cannot be evaluated.,Small sample size (n = 110 total; n = 55 per arm) limits statistical power, particularly for low-frequency endpoints such as mortality.,Enrolled exclusively over a 3-month period (October–December 2020), introducing potential seasonal or institutional confounding.,Hydration protocol (infusion rate, total volume, monitoring parameters) not specified, limiting reproducibility.,Patients with preoperative renal dysfunction were excluded, restricting generalizability to the highest-risk group for CSA-AKI.,AKI diagnostic criteria not stated; validated staging systems (KDIGO, RIFLE) not confirmed as applied.,Surrogate endpoints (creatinine, GFR) used without reporting clinically meaningful outcomes such as dialysis requirement, ICU length of stay, or long-term renal function trajectories.,Blinding status not reported; open-label design likely, introducing performance and detection bias.,No p-values or confidence intervals reported for mortality difference or for 30-day/360-day GFR comparisons between groups.,Funding source and conflicts of interest not reported, precluding assessment of sponsorship bias.,Single-center design limits external validity and generalizability across institutions and healthcare systems. __BOTTOM_LINE_CATEGORY__ promising_but_preliminary __BOTTOM_LINE__ This small single-center RCT provides preliminary signal that 12 hours of preoperative IV 0.9% normal saline hydration may improve postoperative renal function markers and reduce early mortality in cardiac surgery patients with normal baseline renal function, but the truncated abstract, small sample, unreported AKI incidence rates, and absence of confidence intervals substantially limit confidence in these findings. Clinicians should interpret results as hypothesis-generating rather than practice-changing. Larger, adequately powered, multi-center RCTs with validated AKI definitions, standardized hydration protocols, and patient-centered outcomes are needed before this strategy can be routinely recommended.