A nasogastric (NG) tube is a slender, flexible plastic tube inserted through the nose, down the esophagus, and positioned in the stomach. The tube provides temporary access to the gastrointestinal tract, primarily used for delivering liquid nutrition, medications, or removing stomach contents. Aspiration is the process of gently drawing fluid, known as aspirate, from the NG tube. The primary purpose is to confirm the tube’s tip remains safely seated in the stomach before administering anything through it, preventing pulmonary aspiration. Aspiration is also performed to check for gastric residual volume, which measures the amount of fluid remaining in the stomach before a scheduled feeding.
Preparation and Necessary Supplies
Before beginning the aspiration process, gather all required materials, ensuring a clean workspace and meticulous hand hygiene. Essential equipment includes a 60-milliliter (mL) syringe with an appropriate tip, specialized pH indicator strips designed for gastric fluid, clean disposable gloves, and a small container or basin for any aspirated fluid.
Proper patient positioning is crucial for success; the patient should be in a semi-Fowler’s position, meaning the head of the bed is elevated to at least 30 to 45 degrees. This position helps prevent reflux and promotes the pooling of gastric contents near the tube’s tip.
Before proceeding, check the tube’s external measurement, which is often marked in centimeters near the nostril. Comparing this measurement to the length recorded after insertion helps detect tube migration. A significant change suggests the tube has moved out of its intended placement, requiring further investigation before aspiration proceeds.
Step-by-Step Aspiration Technique
The physical act of aspirating fluid requires a gentle, deliberate approach to ensure patient comfort and obtain a reliable sample. Begin by gently flushing the tube with 10 to 20 mL of air using the syringe to help dislodge the tube tip from the stomach wall or clear the contents. Next, securely attach the empty 60 mL syringe to the end of the NG tube.
Slowly and steadily pull back on the syringe plunger to create negative pressure and draw a small fluid sample. Only 1 to 5 mL is needed to perform the necessary placement tests. If resistance is felt or no fluid is obtained, gently repositioning the patient or injecting a small bolus of air and waiting a few minutes may help encourage fluid return.
Once the sample is collected, detach the syringe and immediately cap or clamp the NG tube to prevent air from entering or contents from leaking. If checking for gastric residual volume, the total fluid withdrawn must be carefully measured and recorded. The practice is to return the aspirated fluid to the stomach to maintain electrolyte balance, unless specific instructions dictate otherwise.
Interpreting the Aspirate Results
After aspirating a fluid sample, analyze it to confirm the tube’s location. The most reliable bedside method involves testing the sample’s acidity using specialized pH indicator strips. A small drop of the aspirate is placed onto the strip, and the resulting color change is compared to the chart provided on the strip container.
Gastric contents in an adult who is not receiving acid-suppressing medication typically have a pH between 1.0 and 5.5. A reading within this range provides strong evidence that the tube is correctly positioned in the stomach. If the tube has migrated to the small intestine, the aspirate will be more alkaline, with a pH of 6.0 or higher due to pancreatic secretions.
If the tube were accidentally placed in the respiratory tract or lungs, the aspirate would also resemble respiratory secretions, which are generally more alkaline, often with a pH of 7.0 or higher. While the visual appearance of the fluid can offer a hint—gastric aspirate is often cloudy, green, tan, or clear—color alone is not a definitive placement indicator, making the pH test the primary method for confirmation.
Troubleshooting and Safety Guidelines
A common challenge is the inability to obtain fluid, often caused by the tube tip resting against the stomach lining or being temporarily blocked. If this occurs, repositioning the patient, such as turning them onto their left side, may move the tube tip away from the mucosal wall. Waiting 15 to 30 minutes before trying to aspirate again can also allow more gastric secretions to accumulate.
If the pH reading is above 5.5, or if placement remains uncertain after troubleshooting, do not use the tube for feeding or medication administration. A high pH reading may be due to acid-reducing drugs or a recent feeding, but it signals potential misplacement. In such situations, the gold standard for final confirmation is a chest X-ray, which visually verifies the tube’s tip location.
Proceeding with feeding or medication when placement is unconfirmed carries a significant risk of pulmonary aspiration, potentially leading to severe pneumonia and other respiratory complications. Any sign of patient distress, such as coughing, choking, or sudden difficulty breathing during the procedure, warrants immediate cessation of the aspiration attempt and medical evaluation. Always contact a healthcare provider if the tube’s position cannot be definitively confirmed by both the external measurement and the pH test.