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pH Testing to confirm Nasogastric Tube Position on
ICU.Are we wasting our time?
Mr. Samuel George
Intensive Therapy Unit, Morriston HospitalSwansea
Background
• ESPEN guidelines 2006– All patients not expected to achieve oral diet in 3 days
- started on enteral nutrition
• NG feeding - main route on ICU
• NPSA Guidelines 2005 – “Placement of NG tubes together with confirmation
of correct placement can carry significant risks. “
Background
• NPSA alert 2011 – 21 deaths and 79 cases of harm between 2005 and 2010 – Main causal factor – misinterpretation of X-ray– 7 cases (2 deaths) from feeding despite obtaining aspirate
pH of between 6-8– ‘Whoosh’ tests, litmus paper, or interpretation of the
appearance of aspirate should NEVER be used• NPSA guidelines – Measuring pH of aspirate 1st line - “Only reliable method
of confirming NG tube position” (safe range - 1 and 5.5)– X-rays 2nd line - when aspirate unattainable or high pH
pH Testing
• Colorimetric pH strips – (Blue litmus paper insufficient and unsafe)
• 0.5 gradations• Colour change - easily distinguishable (esp.
between 5-6)• Aspirate between 0.5-1ml required
Frequency of pH Testing
• Position checked:– Following insertion– Before each feed/medication– At least once daily during continuous feed– Suspicion of displacement (vomiting, coughing,
etc)
Aims/Objective
• To assess usefulness of pH testing of NG aspirate in ICU patients
• Proforma for data – Medication– Type of tube– Type of feed – Volume of aspirate– pH readings on first insertion– pH readings on daily /routine checks– Any change in management?
Materials and Methods
Morriston ICU Protocol
• All new NG’s – CXR
• Daily / routine pH testing - although in protocol – not strictly adhered to…
Results
• 168 separate pH readings - 41 ICU patients receiving continuous enteral nutrition – 18 readings from new NG– 150 readings from “old” NG
Results
• 141 (84%) had Ryles tubes
• 27 (16%) had fine bore feeding tubes.
Results – Type of NG
Volume of Aspirate – Large v’s Fine Bore
• 36/141 (25%) of large bore tubes - less than 10mls aspirated
• 10/27 (37%) fine bore tubes - less than 10mls aspirated
Results – New NG tubes
• 14 / 18 (77%) new tube insertions – on PPI’s
• 18 readings were taken after a new NG tube was inserted
Results – Replacement of NG
• In 2/85 high pH readings– feed stopped and new NG inserted– pH in these 2 cases - 6 and 7.5
• Remaining 83 high pH readings – feed was continued and no action taken
• Despite this - NO adverse events
Discussion
• Most ICU patients - continuous feed and PPI’s
• Significant numbers have very low aspirate volumes – especially fine bore tubes
• Old tubes - 50% have a high pH
• New tubes - 28% have a high pH
Discussion
• NPSA guidelines – pH 6 or more feed should be stopped for an hour then retested
• 50.5% of readings were pH 6 – but in the majority feed was continued
• BUT – NO adverse events – i.e. probable falsely high readings
• Stopping feed would have caused unnecessary interruption of patients nutrition
Conclusions
• High pH readings in ICU patients probably reflects continuous feeding and stress ulcer prophylaxis regimes.
• The value of pH testing in these patients is limited.….especially in daily checks
• ICU specific guidelines needed…..
Other Welsh ICU’s
A Telephone Survey
Other Welsh ICU’s
• 13 units contacted
• Data obtained from 12 units
• 1 unit declined to participate
Other Welsh ICU’s
• Initial insertion– All units obtain X-rays
Other Welsh ICU’s
• Routine / daily testing.– 4 units confirm NG position routinely by pH
testing (1-4 times a day)– 3 units routinely aspirate only to confirm position– 2 units routinely measure tube length at nose– 4 units do not routinely check NG position with
patients on continuous feeding
Other Welsh ICU’s
• Routine / daily testing (cont.)– All but 1 unit use X-rays as a 2nd line method of
confirming NG position – One unit uses litmus paper
Summary of Survey
• Wide variation in practice
• NPSA Guidelines not being followed
• Patients at risk
Possible Guideline for ICU’s• New NG – use pH as 1st line and x-ray as 2nd line
•Daily / routine checks - Screening tool– 1. No reason to suspect displacement i.e. no prolonged
coughing or retching etc – 2. NG tapes or fixation devices are secure and have not
moved.– 3. Identical insertion length to that recorded on initial
placement
– Only if all three of above are satisfied -further use of the NG can occur.