Situation: A 57-year-old woman is on post-operative day 3 after surgery for a small bowel obstruction. She has a nasogastric (NG) tube on low intermittent suction that drained 1,800 mL in the past 24 hours, and she receives 5% dextrose in water at 80 mL/h. She is on subcutaneous enoxaparin to prevent venous thrombosis. This morning she reports numbness and tingling of her fingers. The nasogastric (NG) tube stops draining, and the physician orders irrigation of the tube. Which solution should the nurse use?

Nasogastric tubes are irrigated with isotonic 0.9% sodium chloride. Water and other electrolyte-poor solutions draw electrolytes into the stomach, where suction removes them, which worsens her electrolyte and acid-base losses.

Why 0.9% sodium chloride is the correct irrigation solution

The NG tube in this patient is draining large volumes of gastric contents — 1,800 mL in 24 hours — under low intermittent suction. Gastric fluid is rich in hydrogen ions, chloride, potassium, and sodium. When the tube stops draining and irrigation is ordered, the goal is to clear the obstruction without adding further electrolyte shifts. Irrigating with an isotonic solution such as 0.9% sodium chloride prevents an osmotic gradient that would pull additional electrolytes from the gastric mucosa into the lumen, where suction would then remove them.

Using sterile water or hypotonic solutions creates a concentration gradient: water moves into the gastric lumen and draws sodium, potassium, and chloride out of the interstitial and intracellular compartments. Because the NG tube is on suction, those electrolytes are then aspirated out of the body. In a patient who has already lost 1,800 mL of gastric drainage, this would accelerate hypochloremia, hypokalemia, and metabolic alkalosis. Watch out! The numbness and tingling of the fingers reported by the patient is a classic sign of hypocalcemia, which commonly accompanies the metabolic alkalosis and electrolyte depletion seen with prolonged gastric suctioning.

Irrigation solution	Tonicity	Effect on gastric electrolyte loss	Clinical suitability
0.9% sodium chloride	Isotonic	No osmotic gradient; minimizes further electrolyte shift into the lumen	Preferred for NG tube irrigation
Sterile water	Hypotonic	Draws electrolytes into gastric fluid; suction removes them	Avoid in patients with large NG losses
0.45% sodium chloride	Hypotonic	Same risk as sterile water, though less severe	Not appropriate for NG irrigation
5% dextrose in water	Isotonic in bag, but dextrose is metabolized leaving free water	Functions as hypotonic solution in the body; promotes electrolyte loss	Avoid for NG irrigation

The patient is already receiving 5% dextrose in water intravenously at 80 mL/h, which provides free water after dextrose metabolism and does not replace the sodium and chloride being lost through the NG tube. This makes the choice of irrigation solution even more important: adding hypotonic fluid directly into the stomach would compound the electrolyte depletion. Isotonic saline irrigation is consistent with the principle of minimizing additional electrolyte and acid-base disturbances in a patient whose gastric drainage is already substantial.

Key point! NG tube irrigation is not simply about mechanical patency. The tonicity of the irrigation solution matters because the stomach is not a closed container — suction continuously removes whatever enters the lumen. An isotonic solution such as 0.9% sodium chloride clears the tube while protecting the patient from further electrolyte losses that could worsen the existing metabolic alkalosis and hypocalcemia suggested by the finger numbness and tingling.