Blood Gases, Respiratory Failure and Acid Base Disorders

Question 1

What are the SpO2 and PaO2 features of end-stage respiratory disease?

Answer 1

Question 2

What are the different biochemical adaptations to acute and chronic respiratory failure?

Answer 2

• Respiratory compensations happen quickly (mins to hrs)
• Metabolic compensations happen slowly (hrs to days)
• Greated compensation in chronic than acute
• Compensation includes buffers (Hb, plasma proteins, bicarbinate, phosphate), ventilatory response and renal response

Question 3

How is the anion cap calculated?

Answer 3

• Anion gap = [Na⁺] – ([Cl^-] + [HCO₃^-])
• Normal is 8-16mmol/L

Question 4

What causes a raised anion cap?

Answer 4

• Excess production of H+ or inability to excrete it
• Renal failure
• Lactic acidosis
• Diabetic or other ketoacidosis
• Tocins (i.e. salucylate, some IEM)

Question 5

What leads to a normal anion gap?

Answer 5

• Excess HCO3-
• Renal tubular acidosis
• Diarrhoea
• Carbonic anhydrase inhibitors
• Ureteric diversion

Question 6

What is serum osmolal gap?

Answer 6

• Measures osmolality -calculated osmolality
• Calculated = 2x(Na+ + K+) + urea + glucose
• Normal <10mOsm/kg
• If elevated then something else dissolved in the serum