1. ANALYSIS OF BLOOD GASES AND ELECTROLYTES
Acidemia:ph<7.35
Hco3<24 metabolic acidosis
Co2>40 respiratory acidosis.
Alkalemia:ph>7.45
Hco3>24 metabolic alkalosis.
Co2 <40 respiratory alkalosis.
In acidosis co2 decreases to same amount as Hco3.
In alkalosis co2 increases to ½ amount as Hco3.
acute change IN
Hco3 for 10 co2
chronic change in
Hco3 for 10 co2
Resp. acidosis 1 3
Resp. alkalosis 2 4/5
Calculation of Anion-gap:
SerumNa+
– (Hco3
-
+cl-
)
Normal anion gap is 8-12
Henderson-Hasselbach equation:
H=24XCo2/Hco3
values can be derived fromthis.also validity of ABG can be checked.
WINTERS FORMULA:
Pco2=(1.5x Hco3)+8+/-2
In this formula if co2 is N then no compensation is present.If notthen underlying
respiratory compensation is present.

2. ALVEOLAR- ARTERIAL O2 DIFFERENCE
Normal is 10 to 15 mmhg.Itincreases with age.
PA02-Pao2=(713 xFio2)-(Paco2 x1.25)
Common tips:
In acidemia AG dec. by 2
In alkalaemia AG inc. by 4
1 gm ↑↓in albumin ↑↓ AG by 2.
ABG and ELECTROLYTES:
In DMNa ↓by 1.6 for each 100mg/dl↑in sugar and
↓by 2.4 for each 200mg/dlif RBS is>400.
Correction of hypernatraemia:0.6xwtx12÷Na-12
Correction of hyponatraemia:wtx desired rate of correction.
For every 0.1↑in Ph; K falls by 0.3
In met. Acidosis 0.1↓in pH ↑K by 0.7
In resp.acidosis 0.1 ↓in pH ↑K by 0.3
COMMON CAUSES:
↓Na with metabolic alkalosis
Vomiting,contraction alkalosis.
↓Na with metabolic alkalosis
Diarrhoea,fistula
osteotomy

3. Metabolic acidosis with ↑Anion Gap
DKA
Lactic acidosis
Renal failure
Adrenal crisis
Drugs: paracetamol,salicylate,INH.
Metabolic acidosis with (N)Anion Gap
GITcauses
Renal cause
Excessivesaline (RL),ACE↓,heparin.
Hyperalimentation
Metabolic acidosis with ↓ Anion Gap
Multiple myeloma
Hypoalbuminemia
Lithium and bromide toxicity
↑Mg,Ca,K
How to read an ABG
Check validity of ABG
Define PH :acidosis or alkalosis
Classify into resp. or metabolic.
Work out for any compensatory change
Look at PaO2
Note down correction required and follow up orders.