Pre-Operative Hyponatremia in a High Dependency Cardiovascular Surgical Center of a Tertiary Health Facility in Nigeria: Risk Factors, Prevalence, Clinical Correlates and Treatment Outcome. A Retrospective Cohort Study

Introduction: Hyponatremia is the commonest electrolyte derangement seen in medical and surgical wards and in high dependency treatment units. It is associated with prolonged hospital stay, high economic burden and increased morbidity and mortality. Hyponatremia is well reported in medical and surgical conditions but literature is scanty concerning its relationship with treatment outcome in patients managed in high dependency heart and vascular surgical centers. Objectives: To determine the prevalence, determinants, clinical correlates and outcome of pre-operative hyponatremia. Methods: Retrospective study involving patients that had surgery (cardiac and vascular) between January 2015 and December 2019. Data were obtained from patients’ case files, perioperative and intensive unit charts. All participants with preoperative hyponatremia had their serum sodium corrected to ≥135 mmol before surgical incision and those with hypernatremia had their sodium corrected to <145 mmol. The socio-demographic, clinical, laboratory findings were entered. Statistical analysis was done using student’s t-test and Chi square. Results: Of the 305 participants (186 males and 119 females), pre-operative hyponatremia was found in 30.8% and normonatremia in 59.7%. Pre-operative hyponatremia was more common in advance age, overweight, those presenting for open heart and other major surgeries and those with background chronic heart failure and chronic liver disease. Participants with pre-operative hyponatremia had shortened and also prolonged hospital stay and higher risk of death than with normonatremia. Conclusion: Pre-operative hyponatremia is common in high dependency surgical unit particularly in the elderly, those with comorbidities and those presenting for major heart surgeries. It impacts negatively on the morbidity and mortality as it could shorten hospital stay through death, and could prolong hospital stay with increased health burden on patients, their care givers and the general population. The impact of this finding across different races needs further evaluation.