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.
Age ≥18 years;
Admission to the intensive care unit (ICU), with an expected ICU stay of at least 5 days;
Enteral nutrition has been initiated or is planned;
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;
An absolute contraindication to enteral nutrition, including but not limited to intestinal ischemia, gastrointestinal perforation, complete bowel obstruction, or active major gastrointestinal bleeding;
Severe cardiac arrhythmia or high-grade atrioventricular block;
An implanted cardiac pacemaker, implantable cardioverter-defibrillator, or other implanted electronic device;
Local infection, ulceration, skin injury, or another condition affecting the outer ear that makes transcutaneous auricular vagus nerve stimulation unsuitable;
Parallel
Transcutaneous auricular vagus nerve stimulation
DeviceTranscutaneous auricular vagus nerve stimulation will be delivered through surface electrodes over the cymba conchae and cavum conchae, preferably of the left ear, alongside standard ICU care. Stimulation parameters are 25 Hz, a pulse width of 200-500 microseconds, and an individually adjusted current, typically 0.5-2.0 mA. Sessions will last 60 minutes once daily for five consecutive days. Heart rate, blood pressure, and local skin reactions will be monitored. Stimulation will stop for intolerance or safety concerns and end early upon ICU discharge.
Enteral Feeding Intolerance Response Rate
Percentage of participants who achieve an enteral energy intake of at least 20 kcal/kg/day for at least 48 consecutive hours within the assessment window, without interruption of enteral feeding due to intolerance.
Change in Serum Citrulline Concentration
Change from baseline in serum citrulline concentration, used as a marker of intestinal function.
Change in Gut Microbial Diversity Measured by the Shannon Index
Change from baseline in the Shannon diversity index of gut microbiota assessed using rectal swab samples. Higher values indicate greater microbial diversity.
Change in Gut Microbial Richness Measured by the Chao1 Index
Change from baseline in the Chao1 richness index of gut microbiota assessed using rectal swab samples. Higher values indicate greater estimated microbial richness.
Changes in Gut Microbial Community Composition
Differences in gut microbial community composition over time and between groups, assessed using Bray-Curtis dissimilarity in rectal swab samples. Higher values indicate greater differences between microbial communities.
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