revision

Question 1

List the five diagnostic criteria for ARDS

Answer 1

Acute onset
Gas exchange abnormality (PaO2/FiO2 < 200mmHg/26.7kPa)
Bilateral infiltrates on CXR
Non-cardiogenic in origin (PAWP < 18mmHg)
Known causative condition

Question 2

List the four broad indications for mechanical ventilation

Answer 2

Hypoxaemia
Hypercarbia
Exhaustion
Increase in work of Breathing

Question 3

long-term oxygen therapy (LTOT)

Answer 3

LTOT criteria are:
PaO2 less than 7.3 kPa when stable.
OR…
PaO2 greater than 7.3 and less than 8.0 kPa when stable AND with any of:
Secondary polycythaemia
Peripheral oedema
Nocturnal hypoxaemia
Pulmonary hypertension

if they do not meet criteria - Lifestyle advice and smoking cessation of necessary.

Question 4

What is the Ddx for raised anion gaps with metabolic acidosis

Answer 4

‘MUDPILES’:
Methanol
Uraemia
Diabetic ketoacidosis (and alcoholic/starvation ketoacidosis)
Propylene glycol
Isoniazid
Lactate
Ethylene glycol
Salicylates
However, another way is to think about the mechanism of acidosis:

Excess production of acids
DKA, lactic acidosis (produced by poorly perfused tissues)
Ingestion of acids
Methanol, ethanol, ethylene glycol
Inability to clear acids
Renal failure

Question 5

What is the differential diagnosis for a metabolic acidosis with normal or decreased anion

Answer 5

Loss of bicarbonate:
From the GI tract (diarrhoea or high-output stoma)
From the kidneys (renal tubular acidosis)

Question 6

aspirin overdose. ABG picture

Answer 6

initial respiratory alkalosis due to central respiratory centre stimulation causing increased respiratory drive.
In the later stages a metabolic acidosis develops along side the respiratory alkalosis as a result of direct effect of the metabolite salicylic acid and more complex disruption of normal cellular metabolism.

Question 7

Presentation of aspirin overdose

Answer 7

Hyperventilation
Sweating
Nausea & vomiting
Epigastric pain
Tinnitus
Deafness
ARDS (rare)
Hypoglycaemia (children in particular)

Question 8

Investigations in aspirin overdose

Answer 8

Plasma salicylate concentration (initial and repeats)
Paracetamol levels (always check in any case of poisoning by anything)
ABG
Urea and electrolytes
Renal failure (rare) sometimes other electrolyte imbalances
Chest x-ray
If dropping sats or any suspicion of ARDS (non-cardiogenic pulmonary oedema)

Question 9

Management of aspirin overdose

Answer 9

ABCDE and supportive care
Gastric lavage within 1h of ingestion (although no evidence for mortality reduction)
Activated charcoal
Correct electrolyte abnormalities
In mild/moderate cases (plasma concentration 500-700mg/l)
Alkalinise urine
Give 225ml of 8.4% bicarbonate solution over 1hr
Ensure urine pH over 7.5 (use indicator paper)
Bicarbonate will increase any pre-existing hypokalaemia – so don’t let it happen
Additional boluses of bicarbonate to maintain alkalinisation
N.B. Acidosis increases salicylate transfer across the blood brain barrier
Monitor U+Es regularly
In severe cases (plasma concentrations >700mg/l)
Haemodialysis