Transcutaneous Auricular Stimulation Targeting Enteral Feeding Intolerance

This study will test whether electrical stimulation applied to the outer ear can improve tolerance of tube feeding in critically ill adults in the intensive care unit (ICU). Some ICU patients develop digestive problems, such as vomiting, diarrhea, or a buildup of feeding liquid in the stomach. These problems can prevent them from receiving enough nutrition through a feeding tube. This is called enteral feeding intolerance. The treatment being studied is called transcutaneous auricular vagus nerve stimulation (taVNS). It delivers small electrical pulses through electrodes placed on the skin of the outer ear, usually the left ear. It does not require surgery. The treatment targets a branch of the vagus nerve, which helps regulate digestion. Researchers want to find out whether adding this treatment to usual ICU care improves feeding tolerance and whether it causes side effects. The study will enroll 60 adults aged 18 years or older with enteral feeding intolerance at one hospital. Participants will be assigned by chance to one of two groups, with an equal chance of joining either group: * Usual ICU care alone. * Usual ICU care plus ear stimulation for 60 minutes once daily for five days. Stimulation will stop earlier if a participant leaves the ICU or the study team determines that it should be stopped for safety reasons. The main measure will be the proportion of participants whose feeding intolerance improves between 24 and 120 hours after enrollment. Improvement means receiving the study's target amount of calories through tube feeding for at least 48 consecutive hours without stopping feeding because of intolerance. Researchers will also collect blood samples and rectal swabs to study intestinal function, gut bacteria, and substances produced by the body and gut bacteria. They will record the use of pain medicines and sedatives, changes in illness severity, and possible side effects, including skin irritation, a slow heartbeat, or low blood pressure. Study assessments and sample collection in the ICU will continue for up to seven days after enrollment, ending earlier if the participant leaves the ICU. Follow-up at 28 and 90 days will assess survival and, at 90 days, new infections and hospital readmissions.

Inclusion Criteria: 1. Age ≥18 years; 2. Admission to the intensive care unit (ICU), with an expected ICU stay of at least 5 days; 3. Enteral nutrition has been initiated or is planned; 4. At least one of the following manifestations of gastrointestinal dysfunction: (1) Intra-abdominal hypertension: intra-abdominal pressure ≥12 mmHg on at least two measurements within 6 hours, or a mean pressure ≥12 mmHg based on at least four measurements within 24 hours; (2) Gastric retention: gastric residual volume \>200 mL on a single aspiration; (3) Diarrhea: more than three loose or watery stools per day, with a total volume \>250 mL/day; (4) Lower gastrointestinal paralysis: no bowel movement for at least 3 days, with bowel sounds present or absent, after exclusion of mechanical bowel obstruction; (5) Bowel dilatation on abdominal radiography, computed tomography, or bedside ultrasound: colonic diameter \>6 cm, cecal diameter \>9 cm, or small bowel diameter \>3 cm; 5. Enteral feeding intolerance confirmed during a 72-hour trial of enteral nutrition guided by the study's feeding intolerance assessment: failure to achieve an enteral energy intake of 20 kcal/kg/day within 72 hours, or discontinuation of enteral nutrition for a clinical reason, such as vomiting, diarrhea, gastrointestinal bleeding, or an intestinal fistula. Temporary interruptions for clinical procedures do not qualify; 6. Written informed consent provided by the participant or a legally authorized representative. Exclusion Criteria: 1. An absolute contraindication to enteral nutrition, including but not limited to intestinal ischemia, gastrointestinal perforation, complete bowel obstruction, or active major gastrointestinal bleeding; 2. Severe cardiac arrhythmia or high-grade atrioventricular block; 3. An implanted cardiac pacemaker, implantable cardioverter-defibrillator, or other implanted electronic device; 4. Local infection, ulceration, skin injury, or another condition affecting the outer ear that makes transcutaneous auricular vagus nerve stimulation unsuitable; 5. Pregnancy or breastfeeding; 6. Expected death within 24 hours or receipt of end-of-life care.