Lab case 342 interpretation

PH = 7.255, that is moderate acidaemia

HCO3 = 19 mmol/L. That is low. Accordingly, we have metabolic acidosis.

Next step is to calculate the compensation and anion gap.

For compensation we use Winter’s formula, that is: Expected pCO2 = 1.5 x HCO3 + 8 (+/- 2). Accordingly, expected pCO2 for this patient = 1.5 x 19 + 8 = 36.5 (34.5 – 38.5). We can argue that this is within accepted range or the patient might have mild respiratory acidosis (especially when the sample was venous) – It is not going to affect the management of this patient.

Anion Gap = Na – (Cl + HCO3), that is 146 – (118 +19) = 9. So, we have NAGMA.

Other abnormal findings.

Na = 146 mmol, slightly to the high side of the scale

K = 2.7, That is moderate hypokalaemia. However, K level is affected by PH. K level will falsely increase by 0.6 for every 0.1 PH below 7.35. Since PH for this patient is 7.25, the corrected K level will be 2.1 mmol/L (2.7 – 0.6). This will put the patient is severe hypokalaemic state.

Cl = 118, so we have Hyperchloraemia.

Lactate = 1.9, mild hyperlactataemia, reflection of mild impairment of tissue perfusion.

The Final conclusion, the patient has hypokalaemic, hyperchloraemic metabolic acidosis (NAGMA).

For the potential causes of NAGMA we use mnemonic USED CARP

  • U = Ureteroenterostomy
  • S = Small bowel fistula
  • E = Extra chloride
  • D = Diarrhoea
  • C = Carbonic anhydrase inhibitors
  • A = Adrenal insufficiency/ Addison’s disease
  • R = Renal tubular acidosis
  • P = Pancreatic fistula.

This patient has high chloride.

The usual cause of hyperchloraemia is loss of body fluid that is low is Cl relative to Na and K when compared to the ratios of these ions in the extracellular fluids.

Looking at the list of causes above. Since this patient didn’t receive any fluids before the blood for these tests was taken then extra chloride is unlikely to be iatrogenic.

The only two potential causes from the list above are Diarrhoea and RTA.

This patient had diarrhoea

 Question 2:

Management of this patients should focus on 2 aspects,

  • Rehydration
  • Safe electrolytes replacement

For rehydration we can use N/S or Ringer’s Fluid.

To treat hypokalaemia, remember it is frequently associated with hypomagnesemia. In these patient’s K level will be corrected unless we correct the Mg level first.

Accordingly, for this patient, since we don’t know the Mg level. We might consider giving the patient 10 mmol of Mg while we are correcting K level

For this patient, consider 40 mmol of KCl in 1 L N/S over 4 hours then check K and Mg levels again, if still low and then repeat the therapy.

This patient should be cardiac monitored during the replacement of K and Mg.


 Question 3

The body losses K either through urinary tract or GIT. To differentiate between these two routes we need to check urinary K level.

If the urine K level is more than 15 mmol/day then the cause is renal. Otherwise, if urinary K is < 15 mmol/day then the cause is the GIT