This study was an open-label randomized controlled trial with a posttest-only control design. Due to the nature of the intervention, which involved intermittent feeding and patient positioning, blinding of participants and researchers was not feasible. The posttest-only design was selected because GRV, as the dependent variable, cannot be measured or meaningfully interpreted before the intervention. Baseline measurement of GRV was neither possible nor ethical without prior exposure to feeding or intervention. Therefore, a pretest could not be conducted.

This manuscript was prepared following the CONSORT (Consolidated Standards of Reporting Trials) 2010 guidelines to ensure transparent and comprehensive reporting of RCTs.

The population in this study consisted of all critically ill patients who were mechanically ventilated in the ICU of Persahabatan Hospital, Indonesia. Samples were obtained using consecutive sampling. The inclusion criteria were: 1) age > 18 years; 2) newly admitted ICU patients who were mechanically ventilated; 3) planned to receive enteral nutrition via a nasogastric tube (NGT) or orogastric tube (OGT); and 4) receiving enteral nutrition 24 hours after mechanical ventilation. The exclusion criteria were: 1) pregnancy; 2) receiving enteral nutrition via nasojejunal, jejunostomy, or gastrostomy tubes; 3) contraindications for lateral or right oblique positioning; and 4) BMI < 18.5 kg/m².

The sample size was calculated to achieve 80% power with a two-sided α = 0.05. Two steps of calculation were performed to justify the final sample size. First, the Lwanga & Lemeshow single-proportion formula was applied using a conservative proportion (p = 0.5) and acceptable margin of error (d = 0.20):

This resulted in 24 subjects per group for estimating a proportion with ±20% precision under maximum variance (p = 0.5). Second, because the hypothesis compared two independent groups on a continuous outcome (gastric residual volume), the two-sample t-test approach based on standardized effect size (Cohen’s d) was considered. A sample of n = 24 per group was deemed sufficient to detect a large effect (Cohen’s d ≈ 0.8) with 80% power and α = 0.05. To anticipate potential dropouts, 10% attrition was added, resulting in a final target of 26 participants per group (52 total).

Respondents were assigned to the experimental group (n = 26) and the control group (n = 26) through simple randomization to minimize bias. Simple randomization was performed by the primary researcher by randomly drawing a paper numbered 1 to 52 from a plastic cup. If the number drawn was even, the respondent was allocated to the control group; if odd, the respondent was allocated to the experimental group. To mitigate selection bias, allocation concealment was maintained by ensuring that group assignment (even or odd) was not disclosed to the research assistant or ICU staff until after the number was drawn.

The researcher provided an explanation of the study to the patient’s family member or guardian and requested their consent for participation. Those who agreed signed the informed consent form.

At the beginning of the study, 64 respondents were recruited (32 in each group) to anticipate potential dropouts. During the study, 12 respondents dropped out (5 from the intervention group and 7 from the control group) due to extubation, transfer to a regular care ward, hemodynamic instability, gastric bleeding, gastric residual volume > 500 mL, or the need to fast for surgical or diagnostic procedures. After these dropouts, 52 respondents (26 in each group) completed the study protocol. No replacements were added after dropouts; initial over-recruitment ensured the final sample met the target size.

The flow of respondent selection is shown in Fig. (1).

In this study, the data collection tools or instruments used were a respondent characteristic form and an enteral nutrition observation form. The respondent characteristic sheet contains information on respondent data regarding age, gender, Acute Physiology and Chronic Health Evaluation (APACHE) II score, and blood potassium levels. Data on age, gender, APACHE II score, and blood potassium levels were taken using initial ICU admission data obtained from electronic medical records.

The observation sheets contain monitoring of enteral nutrition provision documented at the beginning and end of administration, type of nutritional formula, and volume of enteral nutrition given at predetermined hours. This instrument also states whether the patient received catecholamine drugs (dobutamine, dopamine, norepinephrine, epinephrine) at each intervention in both the experimental and control groups.

The researcher conducted the Interclass Correlation Coefficients (ICC) test calculation on the respondent characteristics instrument using SPSS to align perceptions with the research assistant regarding filling out the instrument and monitoring the research procedure, and obtained a result of 0.889. This ICC score indicates excellent inter-rater reliability, which means the agreement between the researcher and assistant is considerably high.

Respondents were divided into two groups: the experimental group (n = 26) and the control group (n = 26). Researchers and research assistants ensured that hemodynamic conditions were stable before administering enteral nutrition. Criteria for stable hemodynamics included a mean arterial pressure (MAP) > 65 mmHg, no abdominal distension, diarrhea, or gastric bleeding. Additionally, the patency of the NGT, the use of catecholamine drugs (dobutamine, dopamine, norepinephrine, epinephrine), and the presence of bowel sounds were checked. Both intervention and control groups received enteral nutrition 24 hours after ICU admission. The type of daily enteral nutrition formula followed the regimen recommended by a nutrition specialist.

Respondents were positioned in a semi-recumbent/ semi-Fowler position 15 minutes before the start of nutrition administration. Gastric residual volume (GRV) measurements were performed in the same manner for both groups. GRV was measured by aspirating gastric contents using a 50 mL syringe (catheter tip). If the GRV was <500 mL, enteral nutrition was administered unless the patient experienced nausea, vomiting, bloating, abdominal distension, or severe abdominal pain, in which case nutrition was temporarily withheld. If the GRV was >500 mL, enteral nutrition was postponed, and the GRV was re-evaluated after 2 hours. Nutrition was resumed when GRV was <500 mL; if GRV remained >500 mL, nutrition continued to be postponed, and consultation with a nutrition specialist or dietitian was conducted.

In the experimental group, after measuring gastric residual volume and confirming that enteral nutrition could be administered, patients were positioned in the right lateral position with a 45-degree head elevation. Enteral nutrition was delivered using the intermittent feeding method over 60 minutes via gravity drip/infusion (feeding burette) suspended on an infusion pole approximately 30 cm above the NGT insertion site. The feeding burette was a 100 mL nutrient container made of safe, BPA-free material, equipped with measurement lines, a hose, and a roll clamp at the bottom. The administration rate was controlled by adjusting the roll clamp, and the volume was given according to the patient’s nutritional needs six times per day. The volume of enteral nutrition administered started at 50 mL per feeding on the first day, 100 mL on the second day, and 150 mL on the third day of the study, at 07:00, 11:00, 15:00, 19:00, and 03:00.

The right lateral position was maintained for 60 minutes after each intermittent feeding, after which the patient was returned to the semi-recumbent position. To minimize observer variability, all procedures were performed by trained ICU nurses under the supervision of the research team according to a standardized protocol. Patient positioning, feeding setup, and drip regulation were continuously monitored to ensure uniformity across participants.

In the control group, respondents received standard care, which consisted of maintaining a semi-recumbent position with a 45-degree head elevation both before measuring gastric residual volume and during enteral nutrition. Enteral nutrition was administered using the bolus feeding method via a catheter tip with a short gravity drip (3–5 minutes). The volume and timing of enteral nutrition administration were the same as in the experimental group.

The study was conducted in the ICU ward of Persahabatan Hospital, East Jakarta, from March 16 to June 14, 2024. After obtaining ethical approval from the Health Research Ethics Committee (HREC) of Persahabatan Hospital, the researcher recruited three adult ICU nurses as research assistants. Inclusion criteria for research assistants were: holding a Bachelor's degree in Nursing, at least three years of adult ICU experience, working in shifts, and having a schedule aligned with the study period.

To ensure consistency, the researcher provided training and guidance to the research assistants on general research procedures, administering enteral nutrition using the intermittent feeding method, positioning patients in the right lateral position, and documenting respondent characteristics and observation data. The researcher and assistants identified eligible patients for inclusion in the study.

Respondents were then assigned to the experimental or control group using simple randomization. After obtaining consent from the patient’s family member or guardian, the research team collected baseline data including age, gender, APACHE II score, type of enteral nutrition formula, and blood potassium levels from electronic medical records. Additionally, the use of catecholamine drugs (dobutamine, dopamine, norepinephrine, epinephrine), the volume of enteral nutrition administered, and gastric residual volume measurements were recorded on the observation sheet.

Interventions in the experimental group, consisting of intermittent feeding combined with the right lateral position, were conducted six times per day (every four hours) for three consecutive days, as long as enteral nutrition could be provided in the ICU. Standard interventions were provided to the control group according to protocol.

Univariate analysis for numerical data used measures of central tendency, including mean, median, and standard deviation, while categorical data were analyzed using proportions or percentages. The normality of numerical data was assessed using the Kolmogorov-Smirnov test, as the number of respondents was greater than 50. Bivariate analysis for numerical data employed Spearman’s rank correlation, while categorical data were analyzed using the Mann-Whitney U test; for categorical data with more than two groups, the Kruskal-Wallis test was used. Statistical decisions were based on the significance value (p-value), with p ≤ 0.05 considered statistically significant. Linear regression analysis was employed to determine the effect of independent variables on gastric residual volume. All analyses were performed using IBM SPSS Statistics software version 25.

This study received ethical approval from the Health Research Ethics Committee (HREC) of Persahabatan Hospital (letter number 0031/KEPK-RSUPP/02/2024) and was conducted in accordance with the Declaration of Helsinki. However, the study was not registered in a public clinical trial registry, as it was a single-site academic study and registration was not required by the ethics committee at the time of approval.

Table 1 shows that the average age of respondents in the experimental group was 58.08 years (SD = 14.05) and in the control group was 58.81 years (SD = 10.97). The youngest respondent in the experimental group was 26 years and the oldest was 81 years, while in the control group, ages ranged from 31 to 74 years. Male and female respondents were evenly distributed, with a proportion of 50% each. In the experimental group, the average APACHE II score was 20.27 (SD = 7.31), compared with 17.92 (SD = 8.80) in the control group. The majority of respondents received catecholamine drugs (57.7%) and other types of enteral nutrition formulas (53.8%). Analysis of blood potassium levels showed an average of 4.47 mEq/L (SD = 0.78) in the experimental group and 4.17 mEq/L (SD = 0.92) in the control group.

Graphic 1 illustrates the mean GRV across study days, showing a slightly lower trend in the experimental group, although confidence intervals overlapped widely. Table 2 provides a description of respondents based on gastric residual volume measured from the first to the third day of the study. The average cumulative GRV was similar between groups: 306.35 ± 302.94 mL in the experimental group and 315.38 ± 342.16 mL in the control group.

The Mann-Whitney U test showed no significant difference in gastric residual volume between the experimental and control groups on the first day (p = 0.910), the second day (p = 0.887), the third day (p = 0.699), or cumulatively during the study period (p = 0.927). Although the differences were not statistically significant, the average gastric residual volume on the second and third days, as well as cumulatively, was lower in the experimental group than in the control group.

Table 2 also reports 95% confidence intervals (CI) and effect sizes (Cohen’s d) for the differences in GRV between groups. The CIs for mean differences across all days and cumulative values crossed zero, indicating no statistically significant differences between the experimental and control groups. The effect sizes were very small (Cohen’s d < 0.20).

Table 3 shows that there was no significant relationship between age and gastric residual volume (p = 0.143), with a weak correlation strength (r = 0.296). Similarly, the APACHE II score was not significantly associated with gastric residual volume (p = 0.573), showing a very weak correlation (r = 0.116). In contrast, blood potassium levels were significantly associated with gastric residual volume (p = 0.022), with a moderate correlation strength (r = 0.447).

Table 4 shows that there is no significant relationship between gender and gastric residual volume (p = 0.692) and between the type of enteral nutrition formula and gastric residual volume (p = 0.447). Meanwhile, there is a significant relationship between the use of catecholamine drugs and gastric residual volume (p = 0.035).

Table 5 shows the relationship between age, gender, APACHE II score, use of catecholamine drugs, type of nutritional formula, and serum potassium levels using linear regression analysis. The analysis results showed that all cofounding variables did not significantly influence the effectiveness of the intervention.