Lab. ~ Short Answer

Question 1.

A 23 year old male with a decreased level of consciousness is being assessed in your ED. His arterial blood gas results with reference ranges are:

Lab Med Graph 7

A.) List the 4 major abnormalities in this blood gas including calculations.

Show Answer

  • Anion gap metabolic acidosis
    • AG = 140-(105+2) = 33
    • If include K = 39
  • High lactate
  • Hyperkaelameia

 

  • High osmolar gap
    • OG = actual – calculated (2 x Na + BSL + Urea + ETOH)
    • = 360 – (280 + 5.2 + 4.8 + ?)
    • = 360-290
    • = 70
    • = high

(6 marks; abnormalities + calculations) 

B.) What is the likely cause of these abnormalities?

Show Answer

  • Toxic alcohols most likely causing AGMA and OG and depressed LOC
  • Lactic acidosis may be due to ethanol, hypovolaemic shock, seizures

(4 marks; Dx and explanations) 

  1. What is your differential diagnosis for this type of acid-base disturbance?

Show Answer

AGMA DDX

  • Toxic alcohols
  • Metformin
  • CO
  • Cyanide
  • Paracetamol
  • Fe
  • Salicylates
  • Alcoholic ketoacidosis
  • Diabetic ketoacidosis
  • Toluene
  • Uraemia
  • Paraldehyde
  • Isoniazid
  • Lactic acidosis

(3 marks; should have at least 6 differentials) 

Author: J Haire

 


Question 2.

A 59 year old obese man receives 5 mg of intravenous morphine for analgesia for abdominal pain. Thirty minutes later, his GCS has fallen to 12 and investigations are performed.

Lab Med Graph 8

A.) Describe the acid-base abnormality including calculations.

Show Answer

  • Respiratory acidosis
    • Low pH and raised CO2
  • Renal compensation
    • If acute compensation then expect HCO3 to be 29 mmol/l (for every 10 mmHg CO2 raised, HCO2 should increase by 1 mmol/L)
    • If chronic then expect HCO3 to be 44 mmol/L (for every 10 mmHg CO2 raised, HCO2 should increase by 4 mmol/L)
    • Actual HCOs is raised by 52 mmol/L = likely acute on chronic compensation
    • Therefore has metabolic alkalosis as well

(3 marks)

B.) List the other abnormalities

Show Answer

  • Profoundly hypoxic
  • Chloride low
  • BSL moderately raised
  • Hb slightly raised
  • COHb slightly raised

(4 marks)

C.) What is the likely cause for these metabolic abnormalities and why?

Show Answer

  • Chronic CO2 retention secondary to obesity causing background metabolic alkalosis + raised Hb and COHb
  • Opiates have caused a depressed LOC, acute hypoxia, CO2 retention and respiratory acidosis
  • Mild metabolic alkalosis may also be due to vomiting, renal loss or dehydration
  • Low chloride due to chronic respiratory acidosis

(3 marks; must have bold + one other)

Author: J Haire

 


Question 3.

A 65 year old woman with a history of osteoporosis and depression presents with two weeks of increasing confusion and malaise.

Observations on arrival

Lab Med Graph 9

Lab Med Graph 10

A.) List the metabolic abnormalities in this biochemistry

Show Answer

  • Metabolic alkalosis
    • HCO3 raised slightly
  • Urea greatly increased
  • Creatinine normal
  • Calcium markedly raised with normal phosphate

(4 marks)

B.) What are the likely causes of the major abnormalities?

Show Answer

  • Metabolic alkalosis
    • GIT loss ? vomiting
    • Uric acid loss ? diuretics, hyperaldosteronism
  • Severe hypercalcaemia secondary to malignancy casing bony metastases
  • Raised urea and normal creatinine due either to pre-renal failure (dehydration) or high protein breakdown (due to malignancy/tissue necrosis)

(6 marks; each abnormality + explanation)

C.) What is the differential diagnosis for the major electrolyte abnormality?

Show Answer

  • Malignancy
  • Hyperparathyroidism (primary, secondary, tertiary)
  • Calcium supplementation

(3 marks)

Author: J Haire

 


Question 4.

A 45 year old man with type 1 diabetes mellitus conscious state is brought in by ambulance with an altered conscious state

Lab Med graph 11

A.) List the acid – base abnormalities in these investigations including calculations.

Show Answer

  • Respiratory acidosis
    • Low pH
    • Raised pCO2
  • Raised anion-gap metabolic acidosis
    • Low pH
    • Low HCO3
    • AG = 131- (18 + 92) = 20 = raised
  • No NAGMA component
    • Delta ratio = 10/6 = 1.5

(3 marks)

B.) List the other abnormalities and their significance or cause.

Show Answer

  • Low Cl due to acidosis
  • Moderately increase urea and creatinine indicating renal failure
  • Severely raised glucose indicating DKA

(3 marks)

  1. What is the true Na?

Show Answer

  • Na = Na + (0.3 x (BSL – 5.5)) = 145

(1 mark)

C.) What is the likely explanation for all these abnormalities

Show Answer

  • Severe DKA causing AGMA
  • Depressed LOC causing hypoventilation leading to respiratory acidosis
  • Dehydration leading to renal failure

(3 marks)

Author: J Haire

 

 

 

 

 

 

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