ARTERIAL BLOOD GAS ANALYSIS (ABG)
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I have been given this case to solve in an attempt to understand the topic of " patient clinical data analysis" to develop my competency in reading and comprehending clinical data including history, clinical findings, investigations and come up with diagnosis and treatment plan.
ARTERIAL BLOOD GAS ANALYSIS (ABG)
Normal values of ABG
PH: 7.36-7.44 (7.40)
HCO : 24-26 mEq/L (24)
PCO2: 35-45 (40)
H+ : 36-44 meq/L (40 mEq/L)
PH<7.2 Severe acidosis
PH > 7.6 Severe alkalosis
How to say sample for ABG is valid or invalid?
First calculate bicarbonate using the below formula
HCO3 = 24 X pCO2/H+
Now the calculating bicarbonate is compared with bicarbonate of venous blood
The measured value should be with in +/-2 value compared to bicarbonate of venous blood
ABG interpretation:
pH: 7.2--- acidosis
HCO3: 22.4-- acidosis
pCO2 : 55.5-- acidosis
Respiratory and metabolic acidosis
HCO decrease by 1 meq/L = PCO decrease by 1.2 mmHg
HCO3 decrease by 1.6
Pco2 decreased should be 1.6 x 1.2 =1.92
That is 40-1.92= 38.08
But pco2 raise is 55.5
Uncompensated Respiratory and metabolic acidosis
pH: 7.217-- acidosis
HCO3: 20.9-- acidosis
pCO2 : 70.0-- acidosis
Respiratory and metabolic acidosis
HCO decrease by 1 meq/L = PCO decrease by 1.2 mmHg
HCO3 decrease by 3.1
Pco2 decreased should be 3.1x 1.2 =3.72
That is 40-3.72= 36.28
But pco2 raise is 70
Uncompensated
pH: 7.43-- alkalosis
HCO3: 31.1-- alkalosis
pCO2 : 48.8-- acidosis
metabolic alkalosis
Compensation
HCO decrease by 1 meq/L = PCO decrease by 1.2 mmHg
HCO3 decrease by 7.1
Pco2 decreased should be 7.1x 1.2 =8.52
That is 40-8.52= 31.48
But pco2 raise is 48.8
Uncompensated metabolic alkalosis
pH: 7 -- acidosis
HCO3: 10 -- acidosis
pCO2 : 73-- acidosis
Respiratory and metabolic acidosis
Compensation
HCO decrease by 1 meq/L = PCO decrease by 1.2 mmHg
HCO3 decrease by 14
Pco2 decreased should be 14 x 1.2 =17
That is 40-17= 23
But pco2 raise is 73
Uncompensated
pH: 7.47-- alkalosis
HCO3: 21-- acidosis
pCO2 : 25.6-- alkalosis
Respiratory alkalosis
Compensation
HCO decrease by 1 meq/L = PCO decrease by 1.2 mmHg
HCO3 decrease by 3
Pco2 decreased should be 3 x 1.2 =3.6
That is 40-3.6= 36.4
But pco2 is 25.6
Uncompensated respiratory alkalosis/ metabolic acidosis with mild respiratory acidosis
Learning points
1.Contraindications for ABG?
•Abnormal modified Allen test
•Local infection/distorted anatomy at the puncture site
•Severe peripheral vascular disease of the artery
• Active Raynaud's syndrome
2 how much heparin should be used in abg?
Flush the syringe with 0.5 ml of 1:1000 heparin
Don't leave excess heparin in the syringe as it may decrease HCO3, decrease pCO2
3 Preferred arteries?
Radial artery
Femoral artery
4 what precautions should be taken
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