ABG formulas Flashcards
In a metabolic acidosis, what is the expected PaCO2?
PaCO2 expected = 1.5 x HCO3 +8 (+/-2)
In a metabolic alkalosis, what is the expected PaCO2?
PaCO2 expected = 0.7 x HCO3 +20 (+/-5)
In low albumin how do you correct the anion gap?
For every 10 below normal, add 2.5 to the anion gap.
How do you calculate the urine anion gap?
Na + K - Cl
but can only do if urine pH over 6.5 and urine sodium over 20 otherwise have to check urine osmolal gap
Causes of a negative urine anion gap?
Diarrhea, sodium infusion, prox RTA
Positive Urine AG causes?
RTA type 1 or 4
New causes HAGMA?
GOLDMARK glycols (propylene, ethylene) 5-oxoprolene D-lactic L-lactic Methanol Aspirin Renal failure Rhabdo Ketoacidosis
D type lactic acidosis caused by?
Short bowel
L type lactic acidosis caused by?
Type A- hypoxia ie in hypovolaemia, CO poisoning, sepsis, mesenteric ischaemia
Type B- non hypoxic ie thiamine def, seizures, NNRTIs, metformin, isoniazid, aspirin intox
Type 1 RTA causes?
Type 1 is distal
Autoimmune disease- classically Sjogren’s
Drugs- lithium , amphotericin B
Sickle cell
Chronic UT obstruction
Nephrocalcinosis from vit D intoxication (can cause not just be a consequence)
Cirrhosis
Type 2 RTA causes?
Type 2 is proximal
Wilsons Cysteinosis Amyloid MM, PNH Vit D deficiency Heavy metals Tenofovir, aminoglycosides
The widely used test for ketones checks for what?
Acetoacetate not beta hydroxybutyrate
Hyperchloraemic metabolic acidosis usually caused by what in hospital?
Normal saline
What is milk alkali?
Cause of metabolic alkalosis when there is severe hypercalcaemia or exogenous alkali.
A-a gradient?
At sea level on ambient air
150- (PaO2- 1.25 x PaCO2)
If under 10 (under 20 in elderly) says that there is hyperventilation without intrinsic lung disease
If over 10 or over 20 in the elderly, says there is intrinsic lung disease, VQ mismatch or both
