Postoperative Antibiotic Escalation After Major Free-Flap Reconstruction Requiring ICU Admission: Associations with Day-1 Procalcitonin, Shock, and Microbiological Positivity

Major reconstructive free-flap surgery often requires ICU admission, yet early signals associated with postoperative antibiotic escalation remain poorly characterized. We conducted a single-center retrospective cohort study of 119 consecutive postoperative ICU admissions after major free-flap reconstruction. Exposures were postoperative day-1 procalcitonin (PCT) and documented postoperative shock; the primary endpoint was clinician-initiated antibiotic escalation ("upgrade"), and secondary endpoints were documented microbiological positivity and ICU mechanical ventilation duration. Escalation occurred in 85/119 admissions (71.4%). Day-1 PCT was higher with escalation (median 0.25 vs. 0.135 ng/mL; <i>p</i> = 0.033), and shock was more frequent (59/85 [69.4%] vs. 13/34 [38.2%]; <i>p</i> = 0.003). Escalation was associated with longer ventilation (median 3515 vs. 2170 min; <i>p</i> < 0.001) and higher rates of any positive culture (54/85 [63.5%] vs. 8/34 [23.5%]; <i>p</i> < 0.001). In multivariable logistic regression adjusting for operative time and intraoperative IV volume, shock remained independently associated with escalation (adjusted OR 3.52, 95% CI 1.48-8.36; <i>p</i> = 0.004), whereas log-transformed PCT was not (<i>p</i> = 0.224). PCT showed modest apparent discrimination for escalation (AUC 0.63), improving to 0.71 when combined with shock. These findings should be interpreted as observational associations with escalation behavior, supporting prospective evaluation of physiology-plus-biomarker stewardship approaches.