Resp Acidosis
Acute & Chronic compensation
Acute: PCO2 +10 = HCO3 +1
Chronic: PCO2 +10 = HCO3 +3
Resp Alkalosis
Acute & Chronic Compensation
Acute: PCO2 -10 = HCO3 -2
Chronic: PCO2 -10 = HCO3 -5
Metabolic Acidosis
Compensation
HCO3 -1 = PCO2 -1
Metabolic Alkalosis
Compensation
HCO3 +1 = PCO2 +0.5-0.7
Anion Gap
[Na] - [Cl] - [HCO3]
Normal: 4-12
Decrease normal limit for AG by 3 for every 10 point drop in Albumin
Delta delta
Is the fall in HCO3 equivalent to the rise in the AG? If HCO3 has dropped more, then superimposed NAG acidosis. If dropped less, then superimposed metabolic alkalosis.
Osmolar Gap
OG = Measured Osm - (2X[Na] + [BUN] + [Glu])
Normal is <10
Causes of AG acidosis
- *M**ethanol
- *U**remia
- *D**KA, AKA, starvation ketoacidosis
- *P**araldehyde
- *I**NH
- *L**actic Acidosis
- *E**thylene glycol
- *S**alicylates
Causes of Osmolar Gap
- *D**-lactic acidosis
- *M**ethanol
- *E**thylene Glycol
- *A**lcohol
- *T**oluene
Urine anion gap
If non-anion gap acidosis, check urine anion gap (Na+K)-Cl
Should be normal (negative value). If normal/negative then GI losses. If positive then renal tubular acidosis.
Causes of low AG
- increase in unmeasured cations
- lithium
- myeloma, gammopathy
- hypertriglyceridemia
- decrease in albumin
Alveolar-arterial Gradient
- P(A-a)O2 = 147 - (PaCO2 x 1.25) - PaCO2
- Normal in young adults is < 15 mmHg; older, estimate Age/4 + 4
PaO2/FiO2 ratio
- PaO2 (mm Hg)/ FiO2 (as a decimal)
- 600 normal
- 300 minimal impairment
- 250 mild
- 200 moderate
- 150 severe
- 100 very severe
Differences between ABG & VBG
- pH +- 0.05
- PCO2 +- 20 but if normal, should be normal
- HCO3 best from lytes as blood gas is calculated
- PaO2 does not correlate
- lytes and CBC on ABG not accurate if abnormal
- lactate probably better on ABG but commonly used in peripheral venous
