A nasogastric (NG) tube is a medical device inserted through the nose into the stomach to deliver nutrition, hydration, medication, or perform decompression. When used for feeding, the stomach may not empty completely. The Gastric Residual Volume (GRV) is the amount of liquid remaining in the stomach, consisting of formula, water, and digestive secretions. Historically, measuring GRV monitors the stomach’s ability to empty and assesses tolerance to the feeding regimen. This practice also aims to reduce the risk of pulmonary aspiration, which occurs if stomach contents are inhaled into the lungs.
Necessary Equipment and Patient Preparation
The procedure requires several items for accuracy and cleanliness. You will need clean examination gloves and a large, catheter-tip syringe (typically 60 mL) that connects directly to the NG tube. A graduated container, such as a measuring cup, is necessary to accurately measure the total volume of aspirated contents. Finally, clean water or saline should be available for flushing the tube after the procedure, which helps prevent occlusion.
Proper patient positioning is necessary before beginning aspiration. The head of the patient’s bed must be elevated to at least 30 degrees, preferably 45 degrees (semi-Fowler’s position). This elevated position uses gravity to keep stomach contents lower and minimize the risk of reflux or aspiration. Explaining the process to an alert patient reduces anxiety and encourages cooperation, contributing to a smoother measurement.
Step-by-Step Procedure for Measuring Residual Volume
Begin by performing hand hygiene and donning clean gloves to reduce pathogen risk. If the patient is receiving a continuous infusion, the enteral feeding pump must be temporarily stopped and disconnected from the NG tube. This pause ensures no new formula enters the stomach while the residual volume is checked, providing an accurate snapshot of current capacity.
Next, securely attach the catheter-tip syringe to the NG tube end. The tube should be gently kinked or clamped below the connection site to prevent leakage. Draw out the aspirate by slowly pulling back on the syringe plunger until slight resistance is felt. This gentle technique is important because forceful aspiration can pull the tube tip against the stomach lining, potentially causing inaccurate readings or tissue damage.
If the volume exceeds the syringe capacity, empty the contents into the graduated measuring container. Repeat aspiration until no more contents can be easily withdrawn. Note the total volume collected, along with the fluid’s appearance, color, and consistency. In most clinical settings, the next step is to re-instill the entire measured residual volume back into the stomach, provided the volume is not excessively high according to facility protocol.
Re-instilling the gastric contents is important because the aspirated fluid contains vital electrolytes, digestive enzymes, and nutrients that the body needs. Discarding the residual contents can lead to fluid and electrolyte imbalances. After the residual contents are returned, flush the NG tube with the pre-measured water to ensure the tube remains patent before the feeding infusion is resumed.
Interpreting Results and Clinical Guidelines
Current clinical guidance suggests that routine monitoring of GRV may not be necessary for all patients receiving enteral nutrition, as the practice has not been shown to consistently reduce aspiration risk or improve patient outcomes. However, when GRV is checked, the measured volume serves as an indicator of gastric emptying, and the interpretation depends on established facility protocols, which can vary widely. There is no single, globally accepted cutoff volume, but many institutions use 250 mL or 500 mL as a threshold for concern, especially in critically ill patients.
If the measured GRV is below the established threshold, the feeding tube is flushed, the residual is re-instilled, and the tube feeding is resumed at the ordered rate. If the measured volume exceeds the high-volume threshold, such as a single measurement over 500 mL, the feed is typically held temporarily, and the healthcare provider must be notified immediately. In the absence of other signs of feeding intolerance, such as abdominal distension, nausea, or vomiting, a high GRV alone may not be enough to stop feeding, and the decision should be made based on a comprehensive assessment.
Accurate documentation is necessary regardless of the volume obtained. The exact time the residual was checked, the total volume measured, and the color and consistency of the aspirate must be recorded. If a large volume is obtained, the patient should be monitored for other physical signs of intolerance, and the healthcare team may consider adjusting the feeding rate or using medications to enhance gastric motility before the next check.