This document provides information on arterial blood gas (ABG) analysis, including indications, contraindications, sampling procedures, normal values, terminology, and how to interpret ABG results. It discusses assessing adequacy of oxygenation, classifying acid-base disturbances as metabolic or respiratory, evaluating compensation and identifying mixed acid-base abnormalities. Key steps in ABG interpretation are outlined, such as using the anion gap and osmolal gap to identify causes of metabolic acidosis.

1. ABG Analysis
Dr. Gaurav Jain

2. Indications
Assess the adequacy of ventilation and oxygenation
Diagnosis of severity of respiratory failure
Assess prognosis in critically ill
Cardiopulmonary surgery
Sleep studies
Exercise testing

3. CONTRAINDICATIONS
Negative results of a modified Allen test
Arterial puncture should not be performed through a lesion or
through or distal to a surgical
femoral punctures should not be performed outside the
hospital
A coagulopathy or medium-to-high-dose anticoagulation (eg,
heparin or coumadin, streptokinase, and TPA but not aspirin)
a relative contraindication for arterial puncture
Distal to AV fistula

4. Sampling
Steady state of oxygenation
10 min (healthy)
20 min (COPD)
Site (order of choice) (Don’t forget to apply LA)
Radial (check for collateral)
Dorsalis pedis
Bracheal
Femoral
Arterialized ear lobe samples: in neonate/small children
AARC Clinical Practice Guideline. RESPIRATORY CARE [Respir Care 1992(8);37:891–897]

5. Arterial or venous
Sampling
arterial
Person who draw sample Blood pulsate in syringe
syringe plunger rise on its own
Pao2/O2 conc >40/>75%
Calculate the value of H+ using equation and compare it with ABG values

6. Sampling
Excess heparin cause (keep <8 units) (Rinse)
a drop in PaCO2 (dilutional)
Rise in PaO2 (dilutional)
No change in PH
.
Arterial blood gas syringe including filter member United States Patent 5807344

7. Sampling
The pH, remains unchanged because of the vast buffering
potential of oxyhemoglobin and plasma proteins;
for a hemoglobin concentration of 15 grams per dl, 1.62
X107 nm of hydrogen are required to lower the pH from
7.40 to 7.15.
Arterial blood gas syringe including filter member United States Patent 5807344

8. Air bubble
If sample PaO2<160 – rise
If sample PaO2>160 – fall
Delay in running the sample
Decrease in PaO2
At 0 deg C- stable for 1 hr
Acceptable- 10-15 min at room temp
The PaO2 from subjects with elevated WBC dec
very rapidly. Immediate chilling is necessary
Arterial Blood Gas Analysis by Susan Blonshine, BS, RRT, RPFT. AARC Tımes February 1999
Sampling

9. Volume of blood requirement: a
blood sample of 2-4 mL be drawn
After drawing the sample firm
pressure must be applied for at
least 2 min
Sampling
AARC Clinical Practice Guideline. RESPIRATORY CARE [Respir Care 1992(8);37:891–897]

10. FREQUENCY:
depend on the clinical status of the
patient and the indication for
performing the procedure
Arterial line placed if>4 sample
drawn/day
not on an arbitrarily designated time
or frequency.
Sampling
AARC Clinical Practice Guideline. RESPIRATORY CARE [Respir Care 1992(8);37:891–897]
Browning JA, Kaiser DL, Durbin CG. The effect of guidelines on the appropriate use of arterial blood gas analysis in the intensive
care unit. Respir Care 1989; 34:269-276.

11. HAZARDS/COMPLICATION
Hematoma
Arteriospasm
Air or clotted-blood emboli
Anaphylaxis from local anesthestic
Introduction of contagion
Hemorrhage
Trauma to the vessel
Arterial occlusion
vasovagal response
Pain

12. Documentation in record
When a sample is obtained,
date,
time,
patient's body temperature,
position,
activity level,
respiratory rate,
sample site,
results of Allen test,
inspired oxygen concentration
mode of supported ventilation.

13. ABG feeding
Check if required parameters correctly fed in ABG
machine
Pt. temp
Hb
Fio2
Barometric pressure

14. Normal values
blood PaCO2 pH PaO2 SpO2 Bicarb BE
arterial 35-45 7.36-7.44 80-100 >95% 22-26 ±3
venous 42-50 7.34-7.42 37-42 71-78 ±3
Normal range
Anion Gap (meq/l) 10-14
Osmolar gap (meq/l) 10
PaO2/Fio2 (%) >3

15. Terminology
Acidemia
increase in H+ and a fall in arterial pH
Alkalemia
decrease in H+ and a rise in arterial pH
Acidosis
acidifies body fluids (lowers plasma HCO3
- ) and if
unopposed leads to fall in pH
Alkalosis
alkalinizes body fluids (raises plasma HCO3
- ) and if
unopposed leads to rise in pH

16. Adequacy of oxygenation (step 1)
PaO2 (mmHg) SaO2 (%)
Normal values >80 >95
Mild hypoxemia 60-79 90-94
Moderate 40-59 75-89
Severe <40 <75

17. Adequacy of oxygenation (step 1)
New born
Pao2 – 60-90 mmHg- normal
50-59- mild hypoxemia
40-49- moderate
<40- severe
Above 60yr-normal Pao2 dec by 1mm Hg/yr from 80
mmHg.

18. Adequacy of oxygenation (step 1)
Predicted Pao2
Healthy lung 5* Fio2
COPD lung 3*Fio2
Uncorrected hypoxemia PaO2<60
Corrected 60-100
overcorrected >100
Alveolar arterial O2 Difference not affected by fiO2

19. Acidemia/alkalosis (step 2)
Classify pH: 7.4 correspond to H conc. of 40
Mild 7.3-7.34 7.46-7.5
Moderate 7.20-7.29 7.51-7.54
Severe <7.2 7.55-7.8
Incompatible with life <6.8 >7.8

20. Metabolic/respiratory (step 3)
Metabolic disorders:
Initiated by Primary changes in Bicarbonate.
If Bicarb<22/>26 = metabolic
Respiratory disorders:
Initiated by Primary changes in pCO2.
If PaCO2<35/>45 = respi

21. If Respiratory (acute or chronic) (step 4)
Acute respiratory acidosis/alkalosis (pH~7.4)
∆pH = 0.008* ∆paCO2
Chronic respiratory acidosis/alkalosis (pH~7.4)
∆pH = 0.003* ∆paCO2

22. Compensation (step 5)
Respi acidosis High paco2 High bicarb
Respi alkalosis low paco2 low bicarb
Meta acidosis low bicarb low paco2
Meta alkalosis High bicarb High paco2

23. Compensation (step 5)
Acute respiratory acidosis
Chronic respiratory acidosis
10 inc in Paco2-1 inc in HCO3
10 inc in Paco2-4 inc in HCO3
If measured higher – coexist Malk
If low than normal- coexist Macid
Is equivalent – Comp Malk
Acute respiratory alkalosis
Chronic respiratory alkalosis
10 dec in Paco2-2 dec in HCO3
10 dec in Paco2-5 dec in HCO3
Metabolic acidosis Predicted paCO2= 1.5 HCO3 value + 8±2
If measured higher – coexisting Racid
If low – coexist R alk
Is equivalent – Comp R alk
Metabolic Alkalosis Predicted paCO2= 0.7 HCO3 value+ 21 ± 2

24. Compensation (step 5)
Respiratory compensation start in 6-12 hrs
Start in 6-12 hrs
At the level of lung
Metabolic compensation
At the level of kidney
Start in 3-5 days
Before compensation-acute
After compensation- chronic

25. Metabolic acidosis (high/normal AG)(step 6)
Anion gap or UA-UC = Na- Cl + HCO3
Normal range= 12±2 meq/l
Influence of albumin= for each gm decrease in albumin
AG decreases by 2.5
Adjusted AG= observed AG+2.5[4.5-albumin]

26. Gap-gap analysis/corrected bicarb (step 7)
AG excess/HCO3 deficit= measured AG-12/24- measured
HCO3
High anion gap GG~1-2
If >2 in High anion gap MA indicate coexistant met alkalosis
Concomitant non anion gap<0.4-0.8
Normal AG<0.4
Corrected bicarb=observed bicarb+ (AG-12)
If 24 - High AG
If >24 in High AG Macid indicate coexistant met alkalosis
If <24 Non AG Macid also present

27. Osmolal gap
difference between the plasma osmolality (POsm)
measured and that calculated
POsm (mOsm/kg) = 2Na+ + glucose/18 + BUN/2.8
Normally, measured-cal Posm <15 mOsm per kg.
If ethanol, lactate, or ketones cannot be identified in a
patient with an AG metabolic acidosis with an high
osmolal gap, the diagnosis of ethylene glycol or methanol
intoxication should be strongly suspected.

28. Base excess
Index of magnitude of metabolic contribution to an acid –base
disturbance
It is quantity of acid/base in meq needed to titrate 1 litre of blood
to a pH of 7.4 at a temp of 37 deg and PaCo2 of 40 mm Hg.
Normal range ±2 meq/l.
<-2 indicate metabolic acidosis
>+2 indicate metabolic alkalosis

29. Thank you