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.