Lab case 253 answes

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Answers:

Question 1:

PH = 7.26 that is moderate acidaemia.

PCO2 = 52 mmHg, that is high. So we have respiratory acidosis.

Next step is calculating the compensation. We don’t have enough information in the history to decide if this respiratory acidosis is acute or chronic. So we will calculate both

 First option:

If it is a case of acute respiratory acidosis then the expected HCO3 should increase by 1 mmol/L for every 10 PCO2 above 40.

Accordingly expected HCO3 should be 24 + (0.1 x 12) = 25.2. In this case we have HCO3 of 23 that is a bit lower than the expected HCO3 however it is still within an accepted range.

However, the PH in this case is too low for PCO2 of 52. pH drops by 0.08 units and HCO3 increases by 1 mmol/L for 10 mmHg increase in PaCO2 above 40 (up to a PCO2 of 70) .

If this case was well compensated acute respiratory acidosis then the expected PH should be 7.32.

 Second option:

If this respiratory acidosis id chronic, then expected HCO3 show increase by 4 for every 10 PCO2 above 40. Accordingly expected HCO3 will be 24 + (0,4 x 12) = 28.8. Since we have HCO3 of 23, that is outside the accepted range then we have additional metabolic acidosis.

Next we need to calculate the anion gap, [Na – (HCO3 + Cl)] = 6. So we have normal anion gap metabolic acidosis.

This will fit better with PH of 7.26

Other findings in these blood gases,

Cl = 114, that is high. hyperchloremia (usual level is 95 – 105 mmol/L).

Cr = 189, that is elevated. Creatinine of 189 in 58 year old female will give us GFR of 25. Then this patient has stage IV chronic kidney disease.

The most probable final conclusion is Chronic respiratory acidosis with hyperchloremic  NAGMA.

 

Question 2:

The commonest cause of chronic respiratory acidosis is COPD

Other causes:

  •  Obesity hypoventilation syndrome
  • Neuromuscular disorders such as amyotrophic lateral sclerosis.
  • Severe restrictive respiratory disease – interstitial lung disease
  • Thoracic deformities

Hyperchloremic metabolic acidosis is usually caused by a loss of base, either a Gl loss or a renal loss.

Gastrointestinal loss of HCO3:

  •  Severe diarrhea
  • Pancreatic fistula with loss of bicarbonate rich pancreatic fluid
  • Naso-jejunal tube losses in cases of small bowel obstruction and loss of alkaline proximal small bowel secretions.
  • Chronic laxative abuse.

Renal Causes:

  • Proximal renal tubular acidosis with failure of HCO3 resorption.
  • Distal renal tubular acidosis with failure of H+ secretion.
  • Long-term use of a carbonic anhydrase inhibitor such as acetazolamide.

Other causes:

  • Ingestion of ammonium chloride, hydrochloric acid, or other acidifying salts.
  • The treatment phase and recovery phase of diabetic ketoacidosis.
  • Volume resuscitation with 0.9% normal saline provides a chloride load, so that infusing more than 3L can cause acidosis.
  • Hyperalimentation (i.e., total parenteral nutrition).

Still we don’t have enough information about this case to make the definite conclusion about the cause but most probably it is a combination of COPD and CRF.

 

***** This patient discharged herself early from the emergency department very shortly after presenting as she was feeling well.