Nasogastric tube insertion and verification — formative SAQs

SAQ 1 — The verification rule and the deprecated methods (10 marks, 15 minutes)

Stem: A clinical audit on a paediatric ward finds that several nurses are still using the whoosh test to confirm nasogastric tube position before feeds. Outline the accepted bedside verification method, the pH threshold and its physiological basis, the deprecated methods and why each is unsafe, and the action when the pH is above 5.5 or no aspirate can be obtained. [1] [4]

Model answer

The accepted method and the threshold (4 marks). The accepted bedside method is aspirate pH measured with a CE-marked indicator strip. A reading of 5.5 or less confirms gastric placement and is the green light to feed; a reading above 5.5, or no aspirate, means do not feed and obtain a radiograph. The physiological basis is that gastric contents are acidic, with a pH typically between 1 and 5.5, because parietal cells secrete hydrochloric acid, whereas respiratory secretions and small-intestinal contents have a pH of 6 or more. So a strip of pH paper held to a drop of aspirate separates the stomach from the airway, which is exactly the distinction that prevents a feed entering the lung. [4] [6]

The deprecated methods and why each is unsafe (4 marks). The deprecated methods are the whoosh or air-insufflation test, listening over the stomach with a stethoscope while pushing air in; the bubbling test, observing whether air bubbles appear when the tube end is held under water; litmus and blue litmus paper; auscultation used alone; and reliance on the volume or appearance of the aspirate. They are unsafe because none reliably separates a gastric from a respiratory tube: the whoosh sound and the auscultatory bubble transmit across the chest whether the tube is in the stomach or the lung, litmus is too coarse to read in the critical range around 5.5, and the bubbling test can expose staff to secretions. Using any of these as the sole check is itself part of the Never Event. [4] [9]

The action when pH is above 5.5 or there is no aspirate (2 marks). Reposition the tube and re-attempt aspiration once. If the pH is still above 5.5 or aspirate is still absent, request a radiograph that shows the whole course of the tube and its tip below the diaphragm over the stomach, interpret it, and document before any feed. Record the exact pH value, the radiograph result, the length at the naris, and the date and time. [1] [4]