Does Pre-operative Gastric Ultrasound Influence Anaesthetic Decision-Making in Chronic Pain Patients? A Prospective Observational Cohort.

This study is the first prospective evaluation of gastric ultrasound in this high-risk, understudied population, incorporating quantitative opioid exposure and focusing on its impact on real-time anaesthetic decision-making. By linking gastric ultrasound findings to changes in peri-procedural management, this work extends gastric POCUS from a diagnostic tool to a clinically actionable risk-stratification strategy. The aim of this study is to determine whether pre-operative gastric POCUS provides decision-relevant information that influences peri-operative aspiration risk assessment and leads to modification of pre-defined anaesthetic management plans in chronic pain patients undergoing elective interventional procedures under sedation. Pre-procedural gastric ultrasound will be performed immediately before initiation of sedation by the investigators experienced in gastric point-of-care ultrasound, each having completed at least 30 supervised examinations. A standardised scanning protocol was used. Qualitative assessment of gastric contents was performed in the supine position and in the right lateral decubitus position. When patient-related factors precluded these positions, scanning was performed in a semi-recumbent position at approximately 45°. Gastric contents will be classified qualitatively as: * Empty * Fluid (homogeneous hypoechoic contents) * Solid or mixed (heterogeneous contents with echogenic material) When fluid content was identified, the gastric antral cross-sectional area (CSA) was measured at rest in a parasagittal plane at the level of the abdominal aorta using the serosal tracing method, as previously described. Gastric fluid volume was estimated using the validated Perlas mathematical model. In accordance with current literature and consensus recommendations, patients with solid or mixed gastric contents were classified as having a high aspiration risk. For patients with fluid contents, a gastric volume threshold of \>1.5 ml·kg-¹ body weight was used to define high aspiration risk. Patients with an empty stomach or fluid volumes ≤1.5 ml·kg-¹ were classified as low risk. Following completion of gastric ultrasound and prior to initiation of sedation, the responsible anaesthetist reassessed the patient's aspiration risk incorporating the ultrasound findings. The anaesthetist documented whether the original anaesthetic management plan was: * Unchanged * Modified to a more conservative approach (additional measures to reduce aspiration risk) * Modified to a more liberal approach Anaesthetic management modifications were made at the discretion of the responsible anaesthesiologist to ensure patient safety. The anesthesiologist responsible for patient care will not be blinded to ultrasound findings, consistent with the observational nature of the study.