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Arterial blood gas

ByMaha Subih

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What is an ABGArterial Blood Gas

Drawn from artery- radial, brachial, femoral

It is an invasive procedure.

Caution must be taken with patient on anticoagulants.

Arterial blood gas analysis is an essential part of diagnosing and managing the patient’s oxygenation status, ventilation failure and acid base balance.

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What Is An ABG?pH [H+]

PCO2 Partial pressure CO2

PO2 Partial pressure O2

HCO3 Bicarbonate

BE Base excess

SaO2 Oxygen Saturation

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Acid/Base Balance The pH is a measurement of the acidity or alkalinity of the blood. no. of (H+) in the blood. The normal pH range is 7.35-7.45.in an acidic state decreases the force of cardiac contractions, decreases the vascular response to catecholamines, and a diminished response to the effects and actions of certain medications.An alkalotic state interferes with tissue oxygenation and normal neurological and muscular functioning.

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H2O + CO2 H2CO3 HCO3

+ H+

Acid/Base Relationship

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There are two buffers that work in pairs

H2CO3 NaHCO3

Carbonic acid base bicarbonate These buffers are linked to the respiratory and renal compensatory system

Buffers

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The Respiratory buffer response

• This triggers the lungs to either increase or decrease the rate and depth of ventilation , start to occur within 1-3 minutes

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The Renal Buffer Response

•The kidneys excrete or retain bicarbonate(HCO3-).

•Renal system may take from hours to days to correct the imbalance.

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ACID BASE DISORDER

Res. Acidosis• a pH less than 7.35 with a paco2

greater than 45 mmHg.

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Causes 1. Central nervous system depression

r/t medications such as narcotics, sedatives, or anesthesia.

2. Impaired muscle function r/t spinal cord injury, neuromuscular diseases, or neuromuscular blocking drugs.

3. Pulmonary disorders such as atelectasis, pneumonia, pneumothorax, pulmonary edema

4. Massive pulmonary embolus5. Hypoventilation due to pain.

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Management• Increase the ventilation. • Causes can be treated rapidly if not

treated may need M.V

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Respiratory alkalosis

• Psychological responses, anxiety or fear.• Pain• Increased metabolic demands such as

fever, sepsis, pregnancy or thyrotoxicosis.• Medications such as respiratory

stimulants.• RX: Resolve the underlying problem• Monitor for respiratory muscle fatigue

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Metabolic Acidosis

• Bicarbonate less than 22mEq/L with a pH of less than 7.35.

• Renal failure• Diabetic ketoacidosis

•Management: Treat the cause• Hypoxia → Restore tissue perfusion

to the hypoxic tissues• The use of bicarbonate is indicated

Metabolic Alkalosis

• High PH, high HCO3, high CO2.

• Caused by: prolonged vomiting or NG suctioning, prolonged diuretic.

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STEPS TO AN ABG INTERPRETATION

•Step:1•Assess the pH

–acidotic/alkalotic•If above 7.45 – alkalotic•If below 7.35 – acidotic

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Contd…..• Step 2:• Assess the paCO2 level.• pH decreases below 7.35, the paCO2

should rise.• If pH rises above 7.45 paCO2 should

fall.• If pH and paCO2 moves in opposite

direction – primary respiratory problem.

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contd

• Step:2

• Assess HCO3 value

• If pH increases the HCO3 should also increase

• If pH decreases HCO3 should also decrease

• They are moving in the same direction• primary problem is metabolic

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Step 3

Assess pao2 < 80 mm Hg - HypoxemiaFor a resp. disturbance : acute, chronic

If the change in paco2 is associated with the change in pH, the disorder is acute.

In chronic process the compensatory process brings the pH to within the clinically acceptable range ( 7.30 – 7.50)

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Respiratory acidosis

pH PaCo2 HC03

normal

Respiratory

Alkalosis

normal

Metabolic Acidosis

normal

Metabolic Alkalosis

normal

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• J is a 45 years old female admitted with the severe attack of asthma. She has been experiencing increasing shortness of breath since admission three hours ago. Her arterial blood gas result is as follows:

• pH : 7.22• paCO2 : 55• HCO3 : 25• Follow the steps• pH is low – acidosis• paCO2 is high – in the opposite direction of the pH. • Hco3 is Normal.• Respiratory Acidosis

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• Mr. D is a 55 years old admitted with recurring bowel obstruction has been experiencing intractable vomiting for the last several hours. His ABG is:

• pH : 7.5

• paCO2 :42

• HCO3 : 33

•Metabolic alkalosis

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COMPENSATION• A patient can be uncompensated or

partially compensated or fully compensated

• pH has returned within normal range- fully compensated though other values may be still abnormal

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• Mrs. H is admitted, he is kidney dialysis patient who has missed his last 2 appointments at the dialysis centre his ABG results:

• pH : 7.32• paCo2 : 32• HCO3 : 18• Pao2 : 88• Partially compensated metabolic

Acidosis

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• Mr. K with COPD.His ABG is:• pH : 7.35

• PaCO2 : 48

• HCO3 : 28

• PaO2 : 90

• Fully compensated Respiratory Acidosis

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• Mr. S is a 53 year old man presented to ED with the following ABG.

• pH : 7.51• PaCO2 : 50• HCO3 : 40• Pao2 : 40 (21%O2)• He has metabolic alkalosis

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Precautions Excessive Heparin Decreases bicarbonate

and PaCO2

Large Air bubbles not expelled from sample PaO2 rises, PaCO2 may fall slightly.

Fever may lead to erroneous lab results

Care must be taken to prevent bleeding

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It’s not magic understanding ABG’s, it just

takes a little practice!

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Practice ABG’s

1. PaO2 90 SaO2 95 pH 7.48 PaCO2 32 HCO3 242. PaO2 60 SaO2 90 pH 7.32 PaCO2 48 HCO3 253. PaO2 95 SaO2 100 pH 7.30 PaCO2 40 HCO3 184. PaO2 87 SaO2 94 pH 7.38 PaCO2 48 HCO3 285. PaO2 94 SaO2 99 pH 7.49 PaCO2 40 HCO3 306. PaO2 62 SaO2 91 pH 7.35 PaCO2 48 HCO3 277. PaO2 93 SaO2 97 pH 7.45 PaCO2 47 HCO3 298. PaO2 95 SaO2 99 pH 7.31 PaCO2 38 HCO3 159. PaO2 65 SaO2 89 pH 7.30 PaCO2 50 HCO3 2410. PaO2 110 SaO2 100 pH 7.48 PaCO2 40 HCO3 30

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Answers to Practice ABG’s

1. Respiratory alkalosis2. Respiratory acidosis3. Metabolic acidosis4. Compensated Respiratory acidosis5. Metabolic alkalosis6. Compensated Respiratory acidosis7. Compensated Metabolic alkalosis8. Metabolic acidosis9. Respiratory acidosis10.Metabolic alkalosis

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Any Questions?