When To Use This Protocol:

Use this protocol if entonox therapy is to be administered for greater than 20 minutes per day for a period greater than one week.

When Not To Use Entonox Therapy:

Do Not use entonox therapy if the patient has any of the following conditions:

•  Confined airspace disease: eg pneumothorax, intracranial gas/air, bowel obstruction, middle ear or sinus obstruction, gas embolism.

•  Severe respiratory disease

•  Bone marrow failure  eg. leukaemia, chemotherapy

•  Folic acid deficiency

•  Vitamin B12 deficiency (pernicious anaemia)

•  Chronic neurological disease eg multiple sclerosis

•  Known hyperhomocysteinaemia

•  Pregnancy

 Screening Tests

 All patients should be screened and monitored as follows:

 Haematologic

•  Baseline Full blood picture, differential and film. Repeat weekly

 Metabolic

•  Baseline fasting homocysteine level. Repeat weekly

 Neurologic

• Baseline neurologic examination and lower limb “scratch test”** Repeat weekly

 Consider pregnancy test  (BHCG) in women of child bearing age.

Prescribe The Following During Entonox Therapy  

• Folinic acid  15 mg  p.o. daily

• Vitamin B12  1000 mcg  imi  weekly

Prescribing Entonox Therapy

ENTONOX ™  50:50 N₂O AND 0₂ FOR ……..MIN ; ……… TIMES PER DAY

 FOR ……….  DAYS  (MAXIMUM 7 days BEFORE REVIEW)

Entonox therapy should be kept to a minimum and ceased as soon as possible

 Cease entonox therapy and review if any of the following develops:

 1.  Significant decrease in blood cell counts and/ or macrocytosis, megaloblastosis  develops on haematological screening

 2.  Abnormal neurological signs and symptoms develop, particularly in the lower limbs. 

And/or

    If patient gets more than 2/10 directions of scratch incorrect on “scratch testing” *** see below

3.  Change in homocysteine levels of greater than  30 % from baseline.

 **** Neurological examination  Hankey and Edis J Neuro 1989; 395-398.

Baseline neurological examination of lower limbs including power, reflexes, proprioception and vibration is necessary. This should be repeated weekly.

The “scratch test” developed by Hankey and Edis in 1989 for assessment of posterior column pathology, is a standardized, repeatable objective test of posterior column neurological function.

Equipment:  a tongue depressor is split in half in the long axis and the “sharp end” is used as the instrument.

Method:

·     A 2 cm long vertical “scratch” is performed over the anterior shin half way    between the medial malleolus and the tibial tuberosity.

·     10 scratches are performed in a vertical direction.

·     The direction of scratch should be randomised.

·     The number of correct directional assessments is recorded.

·     Significant impairment is denoted if greater than 2/10 errors are made.

·     If significant impairment, stop N20 and consult neurologist.

·     The test should be performed and recorded weekly.

Reproduced with kind permission of Dr Eric Visser, Royal Perth Hospital

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