Gastric POCUS has been validated and shown to be an accurate diagnostic tool in both healthy individuals and medically complex patient populations. Regional anaesthesiologists and pain management physicians frequently provide sedation or anaesthetic care for medically complex patients who fall outside the limited applicability of existing fasting guidelines, including patients with chronic pain, poor acute-on-chronic pain control, and those receiving acute or chronic opioid therapy. These patients are at risk of delayed gastric emptying and may therefore benefit from additional pre-procedural assessment using gastric ultrasound prior to elective interventions

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.

Inclusion Criteria: Patients were eligible for inclusion if they met all of the following criteria:

• Age ≥18 years
• Scheduled for elective chronic pain interventional procedures under procedural sedation
• Adherence to standard preoperative fasting guidelines (≥6 hours for clear fluids and ≥8 hours for solids)
• Presence of at least one clinical factor associated with delayed gastric emptying or increased risk of pulmonary aspiration, including:
• Chronic opioid use (≥2 weeks)
• Acute opioid administration within 24 hours prior to the procedure
• Poorly controlled acute-on-chronic pain
• Diabetes mellitus without established autonomic neuropathy
• Symptoms of gastroesophageal reflux
• Reduced functional mobility
• ASA physical status II-III

Exclusion Criteria: Patients will be excluded if any of the following present:

• Age <18 years
• Previous gastric or esophageal surgery
• Known pregnancy
• Known hiatal hernia
• Severe neurological disorders affecting swallowing or gastric motility
• Established autonomic neuropathy affecting gastric emptying (e.g. advanced diabetic gastroparesis)
• Morbid obesity (body mass index ≥35 kg·m-²), due to known limitations in gastric ultrasound image acquisition and reduced validity of volume estimation models
• Inability to provide informed consent

This will be a single-center, prospective observational cohort study conducted at Danat Al Emarat Hospital, Abu Dhabi, UAE. Adult patients scheduled for elective chronic pain interventional procedures under procedural sedation will be screened for eligibility.