Subclinical Hypothyroidism Increases the Requirement of Renal Replacement Therapy After Cardiac Surgery

Abstract

Background: Subclinical or biochemically diagnosed hypothyroidism (SCH) is defined as an elevated serum thyroid-stimulating hormone (TSH) with normal free thyroxine (FT4) levels. Thyroid hormones play a major role in the normal function of the heart and vascular physiology. Atherosclerosis, increased systemic vascular resistance, and decreased arterial compliance are common pathophysiological changes that may occur in hypothyroidism. Acute kidney injury (AKI) is one of the devastating complications after cardiac surgery. Age, diabetes mellitus (DM), preexisting renal dysfunction, hypertension, impaired left ventricular function, and severe arteriosclerosis are the major risk factors for the development of AKI. The purpose of the current study was to analyze the influence of SCH on AM and the requirement of renal replacement therapy (RRT) after isolated coronary artery bypass graft surgery (CABG). Methods: We retrospectively reviewed the prospectively collected data of 336 adult patients who underwent isolated CABG surgery with normal renal function (baseline serum creatinine value <1.4 mg/dL) from January 2017 to January 2019. The patients were divided into two groups either having the diagnosis of SCH (Group I, N = 47) or not (Group II, N = 289). SCH was diagnosed based on preoperative serum TSH and FT4 levels. Kidney injury was interpreted, according to RIFLE classification. The effect of SCH on AM and the need for RRT after CABG was determined using logistic regression analysis and the results were expressed as odds ratio (OR) with a 95% confidence interval (CI). A P value < .05 was considered statistically significant. Results: Subclinical hypothyroidism was diagnosed in 14% of all patients. Postoperative AKI occurred in 15 patients (31.9%) in Group I, whereas there were 42 patients (14.5%) in Group II. On logistic regression analysis, the presence of SCH was shown to be associated with an increased incidence of postoperative AKI (OR, 0.363; 95% CI, 0.181-0.727; P = .004). RRT was used in 2.97% of patients (seven patients in Group I and three patients in Group II, P < .001). The 30-day mortality was 2.1%. Conclusion: The presence of SCH seems to be associated with an increased incidence of AKI and increased requirement for RRT after cardiac surgery.