Gastric Emptying and Enteral Nutrition Tolerance According to Vasopressor Dose in ICU Patients

Overview

This study investigates whether the dose of vasopressor medications (drugs that maintain blood pressure in shock) affects gastric emptying during tube feeding in the intensive care unit (ICU). Critically ill patients receiving vasopressors often develop impaired gastric motility, which reduces the effectiveness of enteral nutrition and increases the risk of aspiration. Gastric emptying will be objectively measured using bedside point-of-care ultrasound - a safe, painless imaging method - at three time points: before feeding (T0), at 1 hour (T1), and at 2 hours (T2) after restarting enteral nutrition following a 2-hour fasting period. Patients will be stratified into three groups based on norepinephrine equivalent dose (NEQ): Group 1 (no vasopressor, NEQ=0), Group 2 (low-to-moderate dose, NEQ \>0 to \<0.3 μg/kg/min), and Group 3 (high dose, NEQ ≥0.3 μg/kg/min). The primary outcome is gastric emptying rate (GER = (T0 volume - T2 volume) / 2 hours). Gastroparesis is defined as GER ≤0 mL/hour. Secondary outcomes include antrum cross-sectional area, agreement between ultrasound and aspirated gastric residual volume (Bland-Altman analysis), and enteral nutrition intolerance incidence. A subgroup analysis by shock type (septic, cardiogenic, hypovolemic, obstructive) will also be performed. The study aims to identify the vasopressor dose threshold at which gastric emptying is significantly impaired, and to support the use of bedside gastric ultrasound as an objective, non-invasive monitoring tool for enteral nutrition management in the ICU.

Enteral nutrition (EN) is a cornerstone of critical care management; however, feeding intolerance occurs in 30-60% of ICU patients and is associated with prolonged ICU stay and increased mortality. Vasopressor/inotrope use is a recognized risk factor for impaired gastric motility, yet the dose-dependent relationship between vasopressor dosing and objective gastric emptying measurements remains poorly characterized. Existing studies rely primarily on clinical intolerance criteria rather than objective, non-invasive gastric emptying assessments. Point-of-care gastric ultrasonography (POCUS) is a validated, non-invasive bedside method for assessing gastric content and volume. Antrum cross-sectional area (CSA) is measured using the formula π × (dAP/2) × (dCC/2) in both supine and right lateral decubitus positions, and gastric volume is calculated using the Perlas formula (27 + 14.6 × CSA right lateral decubitus). Measurement Protocol (Protocol B): Enteral nutrition is stopped 2 hours before measurement. At T0 (baseline, 06:00-08:00), gastric ultrasound is performed first, followed immediately by nasogastric aspiration to record gastric residual volume (GRV). Enteral nutrition is then restarted, and ultrasound measurements are repeated at T1 (+1 hour) and T2 (+2 hours). Gastric emptying rate (GER) is calculated as (T0 volume - T2 volume) / 2 hours. Gastroparesis is defined as GER ≤0 mL/hour. All ultrasound measurements are performed by a single blinded ICU fellow with ≥1 year of gastric ultrasound experience, who is unaware of the patient's vasopressor group, NEQ dose, and clinical data. Intraobserver reliability will be assessed during the first month (pilot phase) using intraclass correlation coefficient (ICC), with ICC \>0.80 considered acceptable.