OSCE - Poisoning

Question 1

What is the anion gap and what is a normal anion gap

Answer 1

Na + K - (Cl + HCO)

Varies with texts but between 8-6 without potassium and 10-20 with

Question 2

How does albumin alter the anion gap

Answer 2

Albumin is a major unmeasured anion

1g/l decrease in albumin decreases the anion gap by 0.25

Therefore - a high anion gap may appear like a normal AG if albumin is low

Question 3

Causes of a high anion gap metabolic acidosis

Answer 3

Reason - accumulation of organic acids OR loss of H excretion

LTKR
Lactate, toxin, ketones, renal

CATMUDPILES

CO or cyanide
Alcoholic ketoacid (and starvation)
Toluene
Metformin / methanol
Ureamia
DKA
Pyglutamic, propoylene glycol, para-aldehyde
Iron
Lactic Acidosis
Ethylene Glycol
Salicylate

Question 4

Calculated Osmolality

Osmolar gap

Answer 4

2x (Na) + glucose + urea

OG = Measured = calculated

> 10 abnormal

Question 5

Causes of a normal anion gap met acidosis

Answer 5

Loss of HCO

CAGE 
Chloride excess
Acetazolamide /Addisons
GI - , DV, ileus, fistula 
Extra - rental tubule acidosis

ABCD
Addisons
Bicarbonate loss
Chloride excess
Dieuretics - acetazolamide

Question 6

Features of ethylene glycol poisoning

Answer 6

Neuro - similar to alcohol.
Inebriation, slurred speech, euphoria, drowsiness —> oedema, conclusions, coma

Cardio - myocardial depression, hypotension, failure, severe acidosis

Renal - ATN —glycolate is directly toxic and Calcium oxalate crystals

Alternative way:
30 min to 12 hours - confusion,ataxia, lethargy, coma, N/V, seizures, cranaial nerve defect

12-24: cardio failure

24-72 - renal failure from ATN

Question 7

Why do you get a high lactate in ethylene glycol poisoning

Answer 7

Common lab error.

Common analysers measure glycolate as L-lactate, leading to misdiagnosis of lactic acidosis

BUT - may be hypoperfusion

Question 8

Investigations for EG poisoning

Answer 8

Ethylene glycol level (delays result)
Ethanol/methanol/paracetamol

Lactate gap
Osmolar gap
Met acidosis

Urine microscopy - oxalate crystals

Question 9

Treatment of EG poisoning

Answer 9

Tube, MV and inotropic suppler

Conisder bicarbonate
Consider RRT

Antidote - ethanol/fomepizole

Question 10

How does fomepazole work

Answer 10

Competitive antagonists of Alcohol Dehydrogenase

RRT then aids elimination

Question 11

Sources of ethylene glycol

Answer 11

De-icer
Anti freeze
Radiator coolant
Brake fluid
Cleaning polishes

Question 12

Metabolism of EG

Answer 12

EG metabolised by alcohol dehydrogenase to

Glycoaldehyde then by Aldehyde dehrdorgenase to

Glycolic Acid and Oxalic Acid