Question 1

Because of an extremely low PO₂, you suspect that an arterial blood sample taken from a patient's brachial artery might have been contaminated with venous blood. Which of the following might help to confirm your suspicion?

Accepted Answer

The answer of Because of an extremely low PO₂, you...

Question 2

A mixed venous blood sample obtained from a pulmonary artery catheter sample has a PO₂ of 85 mm Hg and a hemoglobin saturation of 95%. Which of the following is likely? 1) The pulmonary artery catheter balloon was not deflated. 2) The sample was drawn from the proximal, not distal port. 3) The blood sample was withdrawn too quickly.

Accepted Answer

A mixed venous blood sample obtained from a pulmonary artery catheter should have a hemoglobin saturation of around 75%, indicating oxygen extraction by the tissues. The high saturation of 95% suggest the blood sample was drawn too quickly from the pulmonary artery, without allowing sufficient time for oxygen to be extracted by the tissues. The PO₂ of 85 mm Hg is consistent with a normal mixed venous oxygen tension. The other options are less likely explanations.

Question 3

What is a normal level for CaO₂?

Accepted Answer

A normal CaO₂ is 18 to 20 ml of oxygen per 100 ml of arterial blood.

Question 4

All of the following are true about capillary blood gas sampling except:

Accepted Answer

Sometimes capillary blood gas sampling is used as an alternative to direct arterial access in infants and small children. Properly obtained capillary blood from a well-perfused patient can provide rough estimates of arterial pH and PCO₂ levels. However, the capillary PO₂ is of no value in estimating arterial oxygenation. For this reason, direct arterial access is still the preferred approach for assessing gas exchange in infants and small children. Respiratory therapists must exercise extreme caution when using capillary blood gases to guide clinical decisions.

Question 5

Which of the following can help avoid the problem of arterial blood sample contamination with air?
1) Discarding frothy samples
2) Fully expelling any bubbles
3) Mixing before expelling air
4) Capping syringe quickly

Accepted Answer

Discarding frothy samples (1) can help avoid the problem of arterial blood sample contamination with air, as frothy samples are likely to have air bubbles. Fully expelling any bubbles (2) is also important, as even small amounts of air can significantly alter the test results. Capping the syringe quickly (4) can prevent air from entering the sample after it has been drawn. Mixing before expelling air (3) may actually introduce more air into the sample, so it is not necessary to avoid arterial blood sample contamination with air.

Question 6

Through which pulmonary artery catheter port would you obtain a mixed venous blood sample?

Accepted Answer

First, ensure that the balloon is deflated and prepare to draw the sample directly from the catheter's distal port (no three-way stopcock).

Question 7

What is the best site for capillary puncture in an infant?

Accepted Answer

The most common site for sampling is the heel, specifically the lateral aspect of the plantar surface.

Question 8

After obtaining an arterial blood sample from an arterial line, you would do all of the following except:

Accepted Answer

Aspirating at least 5 ml of fluid or blood is typically done before obtaining the sample to clear the dead space of any diluted or clotted blood, not after obtaining the sample. The steps after obtaining a sample usually involve flushing the line to ensure patency and prevent clotting, confirming the system is correctly set up for continuous monitoring, and ensuring the waveform on the monitor is accurate, indicating the arterial line is functioning properly.

Question 9

Possible complications of capillary blood gas sampling include which of the following?
1) Infection
2) Hematoma
3) Hemorrhage
4) Hypotension

Accepted Answer

Capillary blood gas sampling can lead to infection due to the break in skin integrity, hematoma from bleeding into the tissue, and hemorrhage from the puncture site. Hypotension is not a typical complication of capillary sampling due to the minimal volume of blood drawn.

Question 10

When is capillary blood gas sampling indicated?

Accepted Answer

To guide practitioners in providing quality care, the AARC has published Clinical Practice Guideline: Capillary Blood Gas Sampling for Neonatal and Pediatric Patients. Modified excerpts from the AARC guideline appear on p. 379.

Question 11

Analysis of an arterial blood sample taken from a healthy athlete reveals a pH of 7.36, a PCO₂ of 45 mm Hg, and a PO₂ of 43 mm Hg. Which of the following analytic errors should you suspect?

Accepted Answer

The PCO₂ and PO₂ values indicate low levels of oxygen and high levels of carbon dioxide, suggesting that the blood sample contains venous blood in addition to arterial blood. This could occur if the sample was contaminated during collection with venous blood or if there was a mixture due to a faulty arterial puncture or damage to the arterial wall. The other options, such as excessive heparin or exposure to air, would not affect the levels of oxygen and carbon dioxide in the sample.

Question 12

Capillary puncture should be performed at or through what location?
1) Edematous tissue
2) Areas with new signs of infection
3) The heal of neonates
4) Previous puncture sites

Accepted Answer

Capillary puncture is commonly performed on the heel of neonates because their fingers are too small for this procedure, and it is a recommended site. Performing capillary puncture on areas with new signs of infection, edematous tissue, or previous puncture sites is not recommended due to the risk of infection, inaccurate test results, and pain or injury to the patient.

Question 13

Before connecting the sample syringe to an adult's arterial line stopcock, what would you do?

Accepted Answer

Before connecting the sample syringe to an adult's arterial line stopcock, it is important to aspirate 1 to 2 ml of fluid or blood using a waste syringe to remove any stagnant blood or air that might have accumulated near the catheter tip or connection site. This ensures an accurate result and reduces the risk of contamination. Therefore, option B is the best choice. Flushing the line and stopcock with the heparinized intravenous solution, aligning the stopcock off to the patient and on to the flush solution, or increasing the flush-solution bag pressure by 20 to 30 mm Hg are not necessary steps before connecting the sample syringe.

Question 14

To assess gas exchange at the tissues, you would obtain a blood sample from which of the following?

Accepted Answer

The answer of To assess gas exchange at the tissues,...

Question 15

Warming a capillary bed to 42° C has which of the following effects?
1) It constricts the underlying blood vessels.
2) It increases blood flow well above tissue needs.
3) It "arterializes" the capillary blood.

Accepted Answer

Warming a capillary bed to 42° C increases blood flow by causing vasodilation, not constriction, thereby increasing blood flow well above tissue needs. This increased blood flow also "arterializes" the capillary blood, meaning it makes the blood in the capillaries have oxygen levels more similar to arterial blood.

Question 16

You determine that a blood gas sample that requires analysis has been sitting in ice slush for 90 min. What should you do?

Accepted Answer

Even chilled samples should be discarded if they are not analyzed within 60 min.

Question 17

The advantage that point-of-care testing has over traditional laboratory testing is that point-of-care testing:

Accepted Answer

The answer of The advantage that point-of-care testing has over...

Question 18

Which of the following are true about a blood gas analyzer's waste fluids?
1) A strong disinfectant should be added to waste fluid containers.
2) Waste fluids should be handled as if they were blood samples.
3) Waste fluids should be treated as potentially infectious.

Accepted Answer

The answer of Which of the following are true about...

Question 19

Which blood gas analyzer electrode uses a separate reference electrode?

Accepted Answer

The answer of Which blood gas analyzer electrode uses a...

Question 20

The total instrument error (inaccuracy) of a blood gas analyzer equals which of the following?

Accepted Answer

The answer of The total instrument error (inaccuracy) of a...

Quiz 19: Analysis and Monitoring of Gas Exchange

Because of an extremely low PO2, you suspect that an arterial blood sample taken from a patient's brachial artery might have been contaminated with venous blood. Which of the following might help to confirm your suspicion?

What is a normal level for CaO2?