Lab case 356 Interpretation

Question 1:

PH = 7.55, that is moderate alkalaemia.

pCO2 = 23 mmHG, so we have respiratory alkalosis.  This can be acute or chronic respiratory alkalosis.

Next we need to calculate the compensation…

• For acute respiratory alkalosis, we expect HCO3 to drop by 2 mmol/L for every 10 pCO2 less than 40. Accordingly expected HCO3 will be 24 – 17 x 0.2 = 20.6, that is very close to the value we have here (20).
• For chronic respiratory alkalosis, we expect HCO3 to drop by 5 mmol/L for every 10 pCO2 less than 40. Accordingly expected HCO3 will be 24 – 17 x 0.5 = 15.5.

This case doesn’t fit with well compensated acute respiratory alkalosis, as this patient had moderate alkalaemia. If it was a case of well compensated alkalosis then we expect the PH to be close to normal. Also (We will read later), this patient has high anion gap meaning, there is an associated HAGMA.

On further history taking, this patient had symptoms (Anxiety, nausea, vomiting and abdominal pain) for 5 days. Now, we will consider his respiratory alkalosis to be chronic. and since HCO3 is higher than the expected then patient has additional metabolic alkalosis.

Anion Gap = Na – (Cl + HCO3) = 17. So we have additional HAGMA.

Other abnormal findings:

Hb = 192 g/L. that is to the high side.

Lactate = 6.8, severe hyperlactataemia.

Creatinine = 253, that is high. In a 25 year old man, this will give him eGFR of 29.

This patient has Combined Chronic respiratory alkalosis and metabolic alkalosis plus HAGMA.

For the causes of  respiratory alkalosis, we use the mnemonic CHAMPS

• C = CNS diseases
• H = Hypoxia
• A = Anxiety/Pain
• M = Mechanical ventilation/ over ventilation
• P = Progesterone
• S = Salicylates / sepsis

This patient was anxious and was complaining of abdominal pain for 5 days.

For the differential diagnosis of metabolic alkalosis we use the mnemonic CLEVER PD.

• C – contraction (dehydration)
•  L – liquorice (diuretic), laxative abuse
•  E – endocrine (Conn’s, Cushing’s)
•  V – vomiting, GI loss (villous adenoma)
•  E – excess alkali (antacids)
•  R – renal (Bartter’s), severe K depletion
•  P – post hypercapnia
•  D – diuretics

This patient had been vomiting for 5 days and he was dehydrated (Elevated Hb and Creatinine).

For HAGMA we use the mnemonic CAT MUDPILES

• C = cyanide, carbon monoxide
• A = alcoholic ketoacidosis and starvation Ketoacidosis.
• T = toluene
• M = methanol, metformin
• U = uraemia
• D = diabetic ketoacidosis
• P = phenformin, pyroglutamic acid, paraldehyde, propylene glycol, paracetamol
• I = iron, isoniazid
• L = lactate
• E = ethanol, ethylene glycol
• S = salicylates

This patient had very high lactate level secondary to poor tissue perfusion due to dehydration. ( Lactate level more than 5 = HAGMA).

Question 2:

Cyclic vomiting syndrome is a condition that presents as recurrent episodes of severe nausea and vomiting lasting from few hours to several days followed by symptoms free periods.

Although nausea and vomiting are the main features of cyclic vomiting syndrome, researchers believe that the primary system affected is the nervous system (the brain and peripheral nerves_. There are more nerve cells in the abdomen than in the head, and symptoms of the disorder develop due to abnormalities in the interaction between neurons in the brain and in the gut (thus, brain-gut disorder).

Cyclic vomiting syndrome has 4 phases:

• Prodrome phase: like aura, that patient feels the episode is coming. Patient usually becomes anxious, develops sweating, nausea and may develop abdominal pain.
• Vomiting phase: severe nausea, vomiting and retching.
• Recovery phase: Vomiting and retching stops and patient has less nausea. Gradually starts to feel better.
• Well phase: between episodes.

For further information about cyclical vomiting syndrome, there are multiple articles online.