Sun14November0130PM 9

A 76-year-old man has had a transurethral resection of a large prostate gland under spinal anaesthesia.

He has a medical history of hypertension and hypothyroidism. Medication includes hydrochlorothiazide, aspirin and ramipril. The duration of surgery was 90 minutes. 1.5% glycine has been used as irrigation by the surgeon.

You are called to the recovery room because the patient cannot see properly. The patient has not experienced headache, speech disturbance, weakness, ophthalmic pain or other visual disturbances.

Clinical examination the patient reveals a severe reduction in visual acuity of both eyes. There are no focal neurological signs.

The patient is urgently referred to a neuro-ophthamlologist.

Laboratory results show:

Na 127 mmol/L (135-145)

K 5.9 mmol/L (3.5-5.1)

Cl 105 mmol/L (99-101)

Bic 29 mmo/L (22-29)

Urea 16.4 mmol/L (1.7-8.3)

Creatinine 100 µmol/L (44-80)

Glucose 11.1 mmol/L (3.5-5.5)

Hb 102 g/L (115-145)

Hct 0.31 (0.37-0.47)

Which one of the following options is the most likely cause of visual loss in this patient?

(Please select 1 option)

Hyponatraemia Incorrect answer selected

Ocular migraine

Amaurosis fugax

Acute angle-closure glaucoma

Hyperglycinaemia This is the correct answer

Explanation

Glycine is a non-essential amino acid with a plasma concentration of 0.3 mmol/L and is metabolised by the liver into ammonia.

1.5% glycine is used as an irrigation solution for endoscopic urological and gynaecological procedures. It is non-conductive, non-haemolytic and has good optical properties. However it is hypotonic with an osmolality of approximately 220 mOsm/Kg, less than that of plasma.

Systemic absorption is associated with:

fluid overload

acute hyponatraemia

cardiac toxicity (myocardial ischaemia/infarction)

acute kidney injury in susceptible patients (hyperoxaluria), and

transient blindness (minutes - 24 hours).

This patient has had a prolonged procedure that may have resulted in significant glycine absorption. The initial electrolyte and haematological abnormalities in this case are not unusual. Hyponatraemia is unlikely to be the cause of this patient's blindness.

Glycine is an inhibitory neurotransmitter to the retina and absorption of large amounts can lead to the slowing of neurotransmission from the retina to the visual cortex. Prolongation of visual-evoked potentials and deterioration of vision can occur following the absorption of as little as 200 mL 1.5% glycine.

The patient may present with acute angle closure glaucoma crisis which is characterised by

sudden ocular pain

seeing halos around lights

red eye

very high intraocular pressure (>30 mmHg)

nausea and vomiting

suddenly decreased vision, and

a fixed, mid-dilated pupil.

Acute angle closure is an emergency.

The patient is not experiencing any of these symptoms but the ocular pressure will need to be measured.

Whilst ocular migraine and amaurosis fugax cause visual disturbances and transient blindness the symptoms and signs are usually unilateral in nature.

Answer Statistics

1

28%

2

1%

3

5%

4

7%

5

62%

Times answered: 259