Factors associated with the ionized-to-total magnesium ratio in major hepatobiliary-pancreatic surgery: a single-center prospective observational study

Purpose To identify perioperative factors associated with the ionized-to-total magnesium (iMg/tMg) ratio at intensive care unit (ICU) admission and on postoperative day (POD) 1 after major open hepatobiliary-pancreatic surgery. Methods This single-center prospective observational study enrolled adults undergoing elective surgery. Paired iMg and tMg measurements were obtained at ICU admission and on POD 1. The primary analyses evaluated perioperative factors associated with the iMg/tMg ratio at each time point using univariable linear regression and multivariable linear regression with backward elimination. Exploratory analyses assessed temporal changes using paired t tests. Results Of 150 enrolled patients, 141 were analyzed. At ICU admission, the ratio was positively associated with iMg immediately after anesthesia induction (P = 0.007) and low-density lipoprotein cholesterol (P = 0.041), and negatively associated with anesthesia time (P = 0.005) and total cholesterol (P = 0.018). On POD 1, the ratio was positively associated with intraoperative non-Mg-containing fluid volume (P = 0.016), and negatively associated with operation time (P < 0.001), hypertension (P = 0.013), and albumin (P = 0.007). Model R 2 values were 0.10 and 0.20 at ICU admission and on POD 1, respectively. In exploratory analyses, the mean ratio increased between postoperative measurements (0.659 to 0.713; P < 0.001). Mean iMg decreased from 0.589 mmol/L after induction to 0.545 at ICU admission, then increased to 0.640 on POD 1 (all P < 0.001). Conclusion Perioperative factors associated with the iMg/tMg ratio differed between ICU admission and POD 1 after major open hepatobiliary-pancreatic surgery. Both models had limited explanatory power. These findings should be interpreted in relation to sampling time and require independent validation before informing clinical management.