ABG Sampling Errors

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Questions and Answers

What is the recommended practice to prevent dilution error in blood sampling?

Using any anticoagulant without checking for acidity
Using saline without considering dead space
Mixing the sample with sodium bicarbonate
Discarding at least 3 times the dead space (correct)

Which factor does NOT influence the bias caused by air bubbles in a sample?

Original PAO2
Extent of mixing
Duration of exposure
Type of anticoagulant used (correct)

What is a consequence of failing to mix the sample immediately after collection?

Increased temperature of the sample
Lower sodium concentration in the sample
Clots forming that block the syringe (correct)
Improved accuracy of the blood gas values

How should a blood sample be stored if it cannot be analyzed within 30 minutes?

Place it on ice (A)

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What effect does higher body temperature have on blood gas values?

Increases both PaO2 and PaCO2 (D)

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Which practice should be adopted to avoid contamination of venous blood in arterial sampling?

Ensure proper catheter flushing (B)

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What happens to CO2 solubility when blood is cooled?

Becomes more soluble, reducing PaCO2 (A)

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What is an effective method for expelling air bubbles from a blood sample?

Visually inspect and remove before mixing (A)

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Which heparin characteristic can directly influence sample acidity?

Heparin is more acidic than blood (D)

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What is the recommended temperature setting for an ABG machine during analysis?

Body temperature of the patient (B)

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Flashcards

Dilution Error (ABG)

Occurs when too much sodium chloride (NaCl) or heparin solution is added to the blood sample, affecting the blood gas results.

Air Bubbles (ABG)

Air bubbles in the blood sample can alter the partial pressures of oxygen and carbon dioxide, leading to inaccurate results.

Clotting (ABG)

Blood clotting in a sample makes it impossible to analyze, leading to false readings.

Prolonged Storage (ABG)

Analyzing blood gas samples (ABGs) after 30 minutes at room temperature can produce differing results.

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Venous Blood Contamination (ABG)

Mixing venous blood into an arterial blood sample gives inaccurate ABG values.

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Temperature Correction (ABG)

ABG machine must account for patient temperature to get accurate results; incorrect temperature leads to inaccurate values.

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Blood Gas Sampling

Blood gas sampling is a method of obtaining blood to measure pH, partial pressure of oxygen, and partial pressure of carbon dioxide in arterial blood.

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Dead Space (ABG)

The part of a catheter that does not contain blood during sample collection (ABG).

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Pre-heparinized (ABG)

Blood already treated to prevent clotting by using dry, balanced electrolyte heparin during ABG collection.

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Correct Heparin (ABG)

Using the correct type of electrolyte balanced heparin is crucial to avoid dilution and clotting problems during ABG sampling.

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Study Notes

ABG Sampling Errors

Dilution Error: Too much saline flush with heparin in the blood sample. Discard at least 3 times the dead space in the catheter. Use the correct amount of dead space to withdraw blood. Always use heparinized electrolyte-balanced solution. Heparin is more acidic. Dilution lowers PCO2, increases pH, increases low partial pressure of oxygen (pO2), or decreases high partial of oxygen (pO2).
Air Bubbles in Sample: Remove air bubbles as soon as the sample is obtained; the bias depends on the size of the bubble and duration of exposure. Visually inspect the sample, remove air bubbles before mixing, blood gas samplers with vented tip caps are helpful. Air lowers PCO2, increases pH, increases low partial pressure of oxygen (PO2), and decreases high partial of oxygen (PO2). Push up on syringe until blood occupies the cap.
Clotting: Mix sample immediately and expel air bubbles. Clots block syringes, preventing analysis. Use pre-heparinized electrolyte-balanced heparin. Mix the sample before putting it into the blood gas machine. Clotting increases cellular potassium.
Prolonged Storage: Analyze samples within 30 minutes. If unable to analyse within 30 minutes, place the sample on ice. After 30 minutes at room temperature, results may vary. Prolonged storage increases PCO2, decreases pH, and decreases the partial pressure of oxygen (PO2).
Venous Blood Contamination: Avoid getting venous blood in arterial samples. Use self-filling syringes, short beveled needles, and a 45-degree puncture angle. Venous contamination increases PCO2, decreases pH, and significantly lowers the partial pressure of oxygen (PO2).
Temperature Correction: Higher body temperature results in a higher PaCO2 and PaO2. Get the patient's temperature when obtaining the ABGs. Set the ABG machine to this temperature, and adjust the values accordingly. Cooler blood results in more soluble CO2, which decreases PaCO2. pH increases because hemoglobin acts as a buffer, accepting more H+ ions when cooled. When blood is rewarmed, H+ ions are released from hemoglobin, returning blood to normal. The table shows the effect of temperature on blood gas values.