Arterial blood gases

1. ABGs
11
Dr .fateh addin alemad

2. An arterial blood gas (ABG)
• An arterial blood gas (ABG) is a test that
measures the oxygen tension (PaO2), carbon
dioxide tension (PaCO2), acidity (pH),
oxyhemoglobin saturation (SaO2), and
bicarbonate (HCO3) concentration in arterial
blood.
• Some blood gas analyzers also measure the,
carboxyhemoglobin, and hemoglobin levels.
• Such information is vital when caring for patients
with critical illness, respiratory, or metabolic
diseases.

3. INDICATIONS
• Identification and monitoring of acid-base
disturbances
• Measurement of the partial pressures of oxygen
(PaO2) and carbon dioxide (PaCO2)
• Assessment of the response to therapeutic
interventions (eg, insulin in patients with diabetic
ketoacidosis)DKA
• Procurement of a blood sample in an acute
emergency setting when venous sampling is not
feasible (most tests can be performed from an
arterial sample)

4. CONTRAINDICATIONS
of ABG NEEDLE PUNCTURE
• An abnormal modified Allen test
• Local infection or distorted anatomy at the
puncture site (eg, previous surgical
interventions, congenital or acquired
malformations, burns, aneurysm, stent,
arteriovenous fistula, vascular graft)
• Supra therapeutic coagulopathy and infusion of
thrombolytic agents are relative
contraindications to arterial needle stick.

16. Definitions
 Acidosis: process that lowers the pH by a fall in
HCO3 or elevation in PCO2
 Alkalosis: process that raises pH by an elevation
in HCO3 or fall in PCO2
 Met Acidosis: low pH and low bicarb
 Met Alkalosis: high pH and high bicarb
 Resp Acidosis: low pH and high PCO2
 Resp Alkalosis: high pH and low PCO2

17.  Simple acid-base disorder – a single
primary process of acidosis or alkalosis
 Mixed acid-base disorder – presence
of more than one acid base disorder
simultaneously

18.  Compensation – the normal response of the
respiratory system or kidneys to change in
pH induced by a primary acid-base disorder
 No overcompensation ( except occasionally
primary resp. alkalosis)
 Kidneys slow, lungs fast
 Lack of compensation (or over) determines a
second primary disorder
 The degree of appropriate compensation is
predictable

20. Serum Anion Gap
• Na-(Cl+HCO 3
)
• Normal Value= 12±2 mEq/L

21. Steps for ABG analysis
1. Are the data consistent
2. What is the pH? Acidemic or Alkalemic?
3. What is the primary disorder present?
4. Is there appropriate compensation?
5. Is the compensation acute or chronic?
6. Is there an anion gap?

22. DETERMINE
PRIMARY DISORDER
 Check the trend of the pH, HCO3, pCO2
 The change that produces the pH is the
primary disorder
pH = 7.25 HCO3 = 12 pCO2 = 30
ACIDOSIS ACIDOSIS ALKALOSIS
METABOLIC ACIDOSIS

23. DETERMINE
PRIMARY DISORDER
 Check the trend of the pH, HCO3, pCO2
 The change that produces the pH is the
primary disorder
pH = 7.25 HCO3 = 28 pCO2 = 60
ACIDOSIS ALKALOSIS ACIDOSIS
RESPIRATORY ACIDOSIS

24. DETERMINE
PRIMARY DISORDER
 Check the trend of the pH, HCO3, pCO2
 The change that produces the pH is the
primary disorder
pH = 7.55 HCO3 = 19 pCO2 = 20
ALKALOSIS ACIDOSIS ALKALOSIS
RESPIRATORY ALKALOSIS

25. DETERMINE
PRIMARY DISORDER
 If the trend is the same, check the percent
difference
 The bigger % difference is the 10 disorder
pH = 7.25 HCO3 = 16 pCO2 = 60
ACIDOSIS ACIDOSIS ACIDOSIS
RESPIRATORY ACIDOSIS
(16-24)/24 = 0.33 (60-40)/40 = 0.5

26. DETERMINE
PRIMARY DISORDER
 If the trend is the same, check the percent
difference
 The bigger %difference is the 10 disorder
pH = 7.55 HCO3 = 38 pCO2 = 30
ALKALOSIS ALKALOSIS ALKALOSIS
METABOLIC ALKALOSIS
(38-24)/24 = 0.58 (30-40)/40 = 0.25

27. ANION GAP
Na – (HCO3 + Cl) = 10-12 mmol/L
Na = 135 HCO3 = 15
Cl = 97 RBS = 100 mg%
Anion Gap = 135 – (15 + 97)
=135 -112 = 23

28. Case 1
 A 55-year-old woman is admitted with a
complaint of severe vomiting for 5 days. Physical
examination reveals postural hypotension,
tachycardia, and diminished skin turgor.
 The lab. Findings include:
Plasma [Na+] = 140 meq/L [K+] = 3.4meq/L
[Cl-] = 77 meq/L HCO3 = 9 meq/L
pH = 7.23 Pco2 = 22 mmHg

29. Analysis
 pH 7.23 acidemia
 HCO3 9 metabolic acidosis
 Pco2 22 appropriate comp.
 Ag = 140 – (77 + 9 ) = 54
 Ag 54 – 12 = 42
metabolic alkalosis

30. Case 2
 A 58-year-old man with a history of chronic
bronchitis developed severe diarrhea
caused by pseudomembranous colitis.
 Lab results
[Na+] = 138 meq/L [K+] = 3.8
[Cl-] = 117 meq/L HCO3 = 9 meq/L
pH = 6.97 Pco2 = 40 mmHg

31.  pH6.97 acidemia
 HCO3 9 metabolic acidosis
 Pco2 40 ( 20.5 ) respiratory acidosis
 Anion gap = 138-(9+117) = 12 nL
 Ag 12 – 12 = 0

32. Thank You