ABG

Question 1

DDx HAGMA

Answer 1

Lactate - A: shock, sepsis, anaemia, B: leuk/lymph, liver failure, toxins, IEM
Toxins - paracetamol, iron, metformin, ETOH & toxic alcohols, cyanide, CO
Ketoacids - DKA, starvation, alcoholic
Renal - failure, uraemia

Question 2

DDx NAGMA

Answer 2

Renal - RTA, addisons
Acetazolamide
Chloride
Extra loss - ureterostomy, pancreatic fistula

Question 3

DDx Metabolic alkalosis

Answer 3

Loss H+
- GIT: vomiting, NG, ileostomy
- Renal: Diuretics, Barters/Gittlemans synd 
Gain HCO3 
- endogenous: ketoacid metabolism 
- exogenous: citrate, bicarb, laxatives, antacids 
Steroid
- Cushings and hyperaldosteroinism

Question 4

Respiratory Acidosis

Answer 4

Obstructive - COPD, asthma  
Decreased resp drive 
- CNS: CVA, tumour, infection
- Drugs: opioids, benzodiazepines 
Decreased chest wall movement 
- Neurological: NMJ, GBS, myasthenia 
- Drugs: muscle relaxant, organophosphates 
- Acute resp dis: trauma, tension pneumothorax

Question 5

DDx Respiratory Alkalosis

Answer 5

Increased rep drive: 
- CNS: CVA, ICH 
- Increased metabolic state: hyperthyroidism, pregnancy, sepsis, anxiety, pain
- Compensation: DKA
- Environmental: hyperthermia 
- Liver failure 
Iatrogenic 
Hypoxia: Pneumonia, PE, CHD, altitude

Question 6

Explain compensation in metabolic acidosis

Answer 6

Determine degree of expected respiratory comensation with Winters formula.
Expected CO2 = 1.5 x HCO3 + 8
+/- 2

Question 7

Explain compensation in metabolic alkalosis

Answer 7

To compensation for metabolic alkalosis, there is a respiratory acidosis.
Expected CO2 = 0.7 x HCO3 + 20
+/- 5

Question 8

Explain compensation for respiratory acidosis

Answer 8

In respriatory acidosis the CO2 goes up, and the bicarb will increase as compensation.
Expected bicarb calculated for an acute or chronic change.
In acute acidosis, for every 10 the CO2 goes up above 40, the HCO3 will go up 1
In chronic acidosis, for every 10 the CO2 goes up above 40, the HCO3 will go up 4

Question 9

Explain metabolic compensation for a respiratory alkalosis

Answer 9

In a respiratory alkalosis, the CO2 goes down, and so does the HCO3.
In an acute alkalosis, for every 10 the CO2 goes down, we expect the bicarb to go down by 2.
In a chronic alkalosis, for every 10 the CO2 goes down, the bicarb goes down by 5.

Question 10

Corrected Sodium calculation

Answer 10

Na + (glucose - 5 / 3)

Question 11

Anion gap calculation

Answer 11

AG = Na - (Cl + HCO3) 
Normal = 12 +/- 4

Question 12

Delta gap calculation

Answer 12

Change in AG / Change in Bicarb
Pts AG - 12 / 2 4- HCO3

0.4-1 NAGMA + HAGMA
1-2 pure HAGMA
> 2 HAGMA, resp acidosis or metabolic alkalosis

Question 13

A-a gradient

Answer 13

Pts PAO2 - Calculated PAO2
Calc PAO2 = FiO2 (Patm - Pwv) - PaCO2 / R

Patm - Pwv = 713 at sea level, on room air, = 150
Normal A-a gradient = Age / 4 + 4

Question 14

Urea:Creatinine ratio

Answer 14

Divide creatinine by 1000 (mmol)
Pre-renal: > 100:1
Post-renal: 40-100:1
Renal: < 40:1