ABG’s
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Indications
Technique
Complications
Analysis
Summary
Indications
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Respiratory illness
Critical illness
Unwell patients
Other circumstances
Technique
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Right pt?
Any artery : commonly radial
Allens test
Preparation pre test
Monitoring
Caution
Don’t loose it
Arterial lines and monitoring of IABP
Complications
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Bleeding
Bruising
Thrombosis
AV fistula
Complication of arterial lines
Analysis
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pH
PaCO2
PaO2
HCO3
O2 sats
Electrolytes
Lactate
Hb, Meth Hb, Carboxy Hb
Normal values
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pH: 7.35 – 7.45
PaCO2: 4.7 – 6 kPa
PaO2: 11 – 13 kPa
HCO3: 22 – 26 mEq/L
Lactate: <2
O2 sats: >96%
Step wise analysis
• What is the pH?
• Normal: 7.35 – 7.45
• Acidosis: < 7.35( more acid ie H+)
• Alkalosis: > 7.45( less acid ie H+)
What is the PaCO2
• Normal: 4.7 – 6.0
• Hypercapnoea: > 6 ( more CO2)
• Hypocapnoea: < 4.7( less CO2)
What is PaO2
• Normal?
• High: > 13 on room air
• Low: < 11 on room air
What is the HCO3
• Normal: 22 – 26
• Low: < 22
• High: > 26
Is it metabolic or respiratory?
Acidosis
Respiratory
pH
PaCO2
Acidosis
Metabolic
pH
PaCO2
Alkalosis
Respiratory
pH
PaCO2
Alkalosis
Metabolic
pH
PaCO2
Is there compensation?
• Respiratory pathology the compensation is
renal
• Renal pathology the compensation is
respiratory
Is there compensation?
Disorder
pH
Primary problem
Compensation
Metabolic acidosis
in HCO3
in PaCO2
Metabolic alkalosis
in HCO3
in PaCO2
Respiratory acidosis
in PaCO2
in HCO3
Respiratory alkalosis
in PaCO2
in HCO3
Anion gap
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Na – ( Cl+HCO3)
Normal 12
Metabolic acidosis with normal anion gap
Metabolic acidosis with increased anion gap
Respiratory acidosis
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Airway obstruction - Upper - Lower: COPD, asthma
CNS depression
Sleep disordered breathing
Neuromuscular impairment
Ventilatory restriction
Increased CO2 production: shivering, rigors, seizures,
malignant hyperthermia, hypermetabolism
• Incorrect mechanical ventilation settings
Respiratory alkalosis
• CNS stimulation: fever, pain, fear, anxiety, CVA, cerebral
edema, CNS infection
• Hypoxemia or hypoxia: lung disease, profound anemia,
low FiO2
• Stimulation of chest receptors: pulmonary edema,
pleural effusion, pneumonia, pneumothorax,
pulmonary embolus
• Drugs, hormones: salicylates, catecholamines,
medroxyprogesterone, progestins
• Pregnancy, liver disease, sepsis, hyperthyroidism
• Incorrect mechanical ventilation settings
Metabolic alkalosis
• Hypovolemia with Cl- depletion
• GI loss of H+Vomiting, gastric suction, villous
adenoma, diarrhea with chloride-rich fluid
• Renal loss H+Loop and thiazide diuretics
• Renal loss of H+: edematous states (heart
failure, cirrhosis, nephrotic syndrome),
hyperaldosteronism, hypercortisolism, excess
ACTH, exogenous steroids, severe
hypokalemia bicarbonate administration
Metabolic acidosis with elevated anion
gap
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M
U
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P
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L
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Metabolic acidosis with normal anion
gap
• GI loss of HCO3-Diarrhoea, ileostomy, proximal
colostomy
• Renal loss of HCO3-proximal RTA
• carbonic anhydrase inhibitor (acetazolamide)
• Renal tubular disease, ATN, Chronic renal
disease, Distal RTA, NaCl infusion
Metabolic acidosis with elevated anion
gap
• Methanol intoxication
• Uremia
• Diabetic ketoacidosis, alcoholic ketoacidosis,
starvation ketoacidosis
• Paraldehyde toxicity
• Isoniazid
• Lactic acidosis
• Ethanol
• Salicylate intoxication
ABG’s
pH:
7.38
PaCO2
8.0
PaO2
8.0
HCO3
32
Sats
88
O2
2L
Lac
1.5
Na
138
Cl
99
• What is the abnormality?
• What might this patient have?
ABG’s
pH:
7.50
PaCO2
3.0
PaO2
8.0
HCO3
22
Sats
88
O2
Room air
Lac
1.5
Na
138
Cl
99
• What is the abnormality?
• What might this patient have?
ABG’s
pH:
7.50
PaCO2
3.0
PaO2
13.0
HCO3
23
Sats
98
O2
Room air
Lac
1.5
Na
138
Cl
99
• What is the abnormality?
• What might this patient have?
ABG’s
pH:
7.20
PaCO2
12
PaO2
8.0
HCO3
30
Sats
88
O2
2L
Lac
1.5
Na
138
Cl
99
• What is the abnormality?
• What might this patient have?
ABG’s
pH:
7.10
PaCO2
3.0
PaO2
12
HCO3
10
Sats
96
O2
2L
Lac
1.5
Na
138
Cl
99
• What is the abnormality?
• What might this patient have?
• What other blood tests may you want to do?
ABG’s
pH:
7.10
PaCO2
6.5
PaO2
9.0
HCO3
15
Sats
96
O2
2L
Lac
4.5
Na
148
Cl
94
Summary
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Systematic approach in analysis of ABG’s
Can help you in difficult situations
Always co relate clinically
Should not be abused
Get slick at it
Thanks