EC Pharmacology and Toxicology

Background: Sodium is the principal extracellular cation responsible for maintaining fluid balance, osmotic pressure, and cellular homeostasis. Postoperative dysnatremia, particularly hyponatremia, is a common complication following surgery due to perioperative stress, hormonal imbalance, fluid therapy, and underlying comorbidities. Abnormal sodium levels are associated with prolonged hospitalization, neurological complications, and increased mortality.

Aim: This study assessed serum sodium levels and their clinical impact among postoperative patients at Obafemi Awolowo University Teaching Hospitals Complex (OAUTHC), with emphasis on the prevalence and magnitude of sodium abnormalities, gender differences, and associations with different surgical conditions.

Methodology: A hospital-based descriptive cross-sectional study was conducted at OAUTHC between April and June 2026. A total of 197 adult postoperative patients aged 18 years and above were recruited using consecutive sampling. Ethical approval and informed consent were obtained. Venous blood samples were collected within 24 - 72 hours postoperatively, and serum sodium levels were analyzed using standard biochemical methods. Demographic and clinical data were obtained using structured questionnaires.

Results: There was a significant reduction in mean plasma sodium concentration from 140.48 ± 2.71 mmol/L pre-operatively to 129.24 ± 5.19 mmol/L post-operatively (t = 13.40, p < 0.001), indicating a high prevalence of postoperative hyponatremia. Male patients showed a decline from 140.98 ± 2.77 mmol/L to 129.74 ± 5.55 mmol/L (p < 0.001), while females decreased from 139.94 ± 3.19 mmol/L to 130.45 ± 4.51 mmol/L (p < 0.001). However, the difference in sodium reduction between males and females was not statistically significant (p = 0.109). Disease-specific analysis revealed the greatest sodium decline among post-Endoscopic Retrograde Cholangiopancreatography (ERCP) patients (140.5 ± 3.20 to 124.5 ± 6.16 mmol/L, p < 0.001). Significant reductions were also observed in appendectomy, bowel surgery, breast cancer surgery, and craniopharyngioma surgery patients (p < 0.05). Linear regression analysis demonstrated a weak positive correlation between pre-operative and post-operative sodium levels (R = 0.2245, R² = 0.050, p = 0.0344).

Conclusion: Postoperative hyponatremia is highly prevalent among surgical patients at OAUTHC and occurs across multiple surgical conditions. Routine perioperative electrolyte monitoring, proper fluid management, and early correction of sodium imbalance are essential to reduce postoperative complications and improve patient outcomes.

Keywords: Post-Operative; Dysnatremia; Antidiuretic Hormone (ADH); Perioperative Fluid Management

Abbreviations; OAUTHC: Obafemi Awolowo University Teaching Hospital; ERCP: Post-Endoscopic Retrograde Cholangiopancreatography; ADH: Antidiuretic Hormone

1. Adrogué HJ and Madias NE. “Renal tubular acidosis and sodium metabolism”. New England Journal of Medicine6 (2020): 543-554.
2. Verbalis JG., et al. “Efficacy and safety of oral tolvaptan therapy in patients with the syndrome of inappropriate antidiuretic hormone secretion”. European Journal of Endocrinology5 (2011): 725-732.
3. Liamis G., et al. “Aldosterone activation in postoperative patients and its impact on sodium balance”. Hormones 2 (2022): 205-215.
4. Brown E and Paloian NJ. “Perioperative electrolyte management and sodium balance in surgical patients”. Journal of Surgical Research 1 (2023): 1-11.
5. Webb AR., et al. “Prevalence and clinical impact of postoperative hyponatremia in major surgery”. BJA: British Journal of Anaesthesia4 (2025): 912-922.
6. Sanada H., et al. “Incidence and risk factors of postoperative hyponatremia in patients undergoing spinal surgery”. Spine 6 (2023): E96-E103.
7. McCausland FR., et al. “Increased dietary sodium is independently associated with greater mortality among prevalent hemodialysis patients”. Clinical Journal of the American Society of Nephrology3 (2022): 435-442.
8. Gilder ME., et al. “Postoperative dysnatremia and prolonged hospital stay: A prospective cohort analysis”. Perioperative Medicine1 (2020): 22.
9. Waikar SS and Mount DB. “Sodium homeostasis in clinical practice: An evidence-based review”. New England Journal of Medicine25 (2022): 2399-2410.
10. Adebayo O., et al. “Electrolyte abnormalities among hospitalized patients in a Nigerian tertiary hospital: Prevalence and clinical correlates”. Nigerian Journal of Clinical Practice5 (2021): 683-689.
11. Okoye HC., et al. “Postoperative electrolyte monitoring in Nigerian teaching hospitals: Current practices and gaps”. African Health Sciences3 (2023): 571-580.
12. Huang G., et al. “Dysnatremia and clinical outcomes in intensive care and surgical populations: A meta-analysis”. Critical Care Medicine 6 (2024): e298-e309.
13. Coşkun Yavuz G., et al. “Methodological heterogeneity in postoperative sodium monitoring studies: A systematic review”. Surgical Research and Practice (2025): 6628071.
14. “Anatomy and physiology (2^nd edition)”. OpenStax (2021).
15. Oni ES., et al. “Impact of ERCP on cholestatic liver enzymes in patients with obstructive jaundice at Obafemi Awolowo University Teaching Hospital, Ile-Ife, Osun, Nigeria”. Asian Journal of Research and Reports in Hepatology1 (2026): 1-8.