BackgroundIntraoperative hypotension is a risk factor for postoperative complications. Preoperative dehydration is a major contributor, although it is difficult to estimate its severity. Point-of-care ultrasound offers several potential methods, including measurements of the inferior vena cava. The addition of lung ultrasound may offer a safety limit. We aimed to evaluate whether the implication of an ultrasound-based preoperative fluid therapy protocol can decrease the incidence of early intraoperative hypotension.MethodsRandomised controlled study in a tertiary university department involves elective surgical patients of ASA 2–3 class, scheduled for elective major abdominal surgery under general anaesthesia with intubation. We randomised 40–40 patients; 38–38 were available for analysis. Conventional fluid therapy was ordered on routine preoperative visits. Ultrasound-based protocol evaluated the collapsibility index of inferior vena cava and lung ultrasound profiles. Scans were performed twice: 2 h and 30 min before surgery. A high collapsibility index (≥ 40%) indicated a standardised fluid bolus, while the anterior B-profile of the lung ultrasound contraindicated further fluid. The primary outcome was the incidence of postinduction and early intraoperative (0–10 min) hypotension (MAP< 65 mmHg and/or ≥ 30% of decrease from baseline). Secondary endpoints were postoperative lactate level, urine output and lung ultrasound score at 24 h.ResultsThe absolute criterion of postinduction hypotension was fulfilled in 12 patients in the conventional group (31.6%) and 3 in the ultrasound-based group (7.9%) (p= 0.0246). Based on composite criteria of absolute and/or relative hypotension, we observed 17 (44.7%) and 7 (18.4%) cases, respectively (p= 0.0136). The incidence of early intraoperative hypotension was also lower: HR for absolute hypotension was 2.10 (95%CI1.00–4.42) in the conventional group (p= 0.0387). Secondary outcome measures were similar in the study groups.ConclusionWe implemented a safe and effective point-of-care ultrasound-based preoperative fluid replacement protocol into perioperative care.Trial registrationThe study was registered to ClinicalTrials.gov on 10/12/2021, registration number: NCT05171608 (registered prospectively on 10/12/2021).Supplementary InformationThe online version contains supplementary material available at 10.1186/s13741-023-00320-4.