Capillary Blood Gas sampling is used to monitor neonatal patients when collecting an arterial sample is not practical.

Analyzing capillary blood yields pH and PaCO2 values that are comparable to arterial blood, which is why this measurement is useful.

We created this study guide to provide you with an overview of this topic. We included practice questions for your benefit as well. So, if you’re ready, let’s get started.

What is Capillary Blood Gas Sampling?

Capillary Blood Gas (CBG) sampling is the process of puncturing and collecting a capillary blood sample in infants. This allows the practitioner to analyze the neonate’s ventilatory status but observing the pH and PaCO2.

The lateral area of the heel is the preferred puncture site when collecting a capillary blood sample. You could potentially use the infant’s fingertip, toe, or earlobe if the lateral heel puncture is unsuccessful, but these are not the preferred sites.

The heel is the preferred and typically most effective site to stick in infants because it is highly vascularised.

Capillary Blood Gas Sampling Practice Questions:

1. Which arterial sampling sites are used for newborns?
The radial artery is the preferred site. You should avoid the brachial and femoral arteries. Also, the dorsalis pedis or posterior tibial are alternative sites.

2. What equipment is required for arterial puncture?
A 1 ml pre-heparinized tuberculin syringe, 25-gauge needle or pre-heparinized 25-gauge butterfly needle infusion kit, correctly fitting exam gloves, povidone iodine and alcohol wipes, sterile gauze, needle capping, and protection device, eye and splash shield, and patient label.

3. How much heparin do you push out before performing arterial stick?
All of it.

4. How do you insert the needle for an arterial stick?
Bevel up and insert at a 45-degree angle.

5. How long is pressure applied after an arterial stick?
At least 5 minutes.

6. What are the advantages of the capillary sample?
Used when ABG indicated but peripheral access not available, less hazardous and easier to obtain, and assess pH and CO2 disturbances.

7. What are the disadvantages of the capillary sample?
PO2 unreliable, not be done on a patient who has begun to walk or has calluses, not be done on inflamed or swollen areas, not be done on cyanotic or poorly perfused areas, and samples clot easily.

8. What should you do with air bubbles?
They should all be expelled completely.

9. What should you do with samples that are not analyzed immediately?
Place the sample on ice.

10. How long can you wait to analyze an arterial blood sample?
It is best to analyze the sample within an hour.

11. What will be prevented by alternating arms for the arterial stick and holding pressure for 5 minutes?

12. What are the contraindications for an arterial puncture?
Lack of collateral circulation, extremities previously blanched (temp blood flow lost), distal to or through a surgical shunt, signs of infection at the site, and evidence of peripheral vascular disease.

13. What are the complications for an arterial puncture?
Hematoma formation treatment– pressure and switch sites, scarring, laceration of the artery (due to the artery being so tiny), and nerve damage (brachial, femoral; posterior, tibial).

14. What is a capillary blood gas used for?
It is an alternative to an ABG.

15. What best correlates best with a capillary gas?
The arterial pH and CO2 correlate well with capillary blood gas results. The PaO2, on the other hand, does not correlate well.

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16. What are the 3 things that affect low accuracy in capillary gas samples?
Hypotension is the most important as it affects the correlation between arterial and capillary samples. Hypothermia and hypovolemia also affect low accuracy.

17. What are the puncture sites for a capillary blood gas?
Posterolateral foot, palmar or fleshy surface of distal aspects of fingers and toes, and earlobes.

18. Which puncture site for a capillary gas has the higher risk of nerve damage?
Fingers and toes.

19. What are the contraindications for capillary blood gas sampling?
If you need an accurate assessment of oxygenation, neonates <24 hours old, decreased peripheral blood flow, polycythemia, and areas that are: edematous, inflamed, infected, or calloused.

20. What are the complications of capillary blood gas sampling?
Inaccurate reflection of patient’s condition leading to mismanagement of respiratory care, burns from warming heel too much, infection, scarring, inflammatory changes, nerve and artery damage, bruising, hematoma, and bleeding.

21. The umbilical cord has one floppy vein and how many arteries?

22. What is the tip placement for umbilical artery catheterization?
High= T6-T8 and low= L3-L4.

23. What is the umbilical artery catheter connected to?
The fluid pressure transducing system.

24. What are the complications of an arterial catheter?
Infection after 72 hours, thrombosis less than 5 years old, blood volume, hemorrhage (blood transfusion may be given), ischemia (pallor, decreased pulses, poor cap refill), and air embolism (smallest amount of air can cause embolism to brain).

25. What does the placement of an arterial line allow?
The direct measurement of arterial blood pressure.

26. Blood pressure varies with age and the infant’s blood pressure is approximately what?

27. The MAP is often an indication of what?
The left ventricular afterload and resistance against the left ventricle.

28. What are the benefits of continuous invasive blood gas monitoring?
Alternative for patients requiring frequent blood gas analysis, designed for small patients with small blood volumes, and in line with an arterial or umbilical catheter.

29. What are the indications for a central venous catheter?
Cardiovascular instability, intravascular volume disturbance (dehydration, hemorrhage, increase ICP), and administration of drugs, fluids, nutritional support.

30. CVP monitoring measure the right atrial pressure helping to assess the fluid volume and also helps with what?
It helps to secure a long-term venous site in a chronically ill child.

31. What will cause the CVP measurements to rise?
Heart problems such as tricuspid and pulmonic stenosis.

32. What are the monitoring sites of the central venous catheter?
Umbilical and subclavian veins are most common, external and internal jugular, brachial, and saphenous.

33. What are the complications of central venous monitoring?
Catheter sepsis in over 72 hours (fungal issue), pulmonary embolism, cardiac dysrhythmias (due to catheter slipping into RV), and perforation of the trachea (catheter may slip into jugular vein).

34. What does the central venous catheter measure?
Right atrial pressure.

35. A decreased CVP indicates what?
Hypovolemia and/or shock.

36. An increased CVP indicates what?
Hypervolemia and/or LV failure.

37. Pulmonary artery catheters are also known as what?
Swan Ganz catheter.
38. What is the pulmonary artery catheter used for?
It measures left ventricular function, guide fluid management, aid in diagnosing pulmonary disease and cardiac dysfunction, and CO and mixed venous O2.

39. What are the complications of a pulmonary artery catheter?
Bleeding, pneumothorax, heart valve damage, heart chamber perforation, and cardiac arrhythmias (PVC’s).

40. What does the pulmonary artery pressure measure?
Right atrial pressure (RAP), Pulmonary artery pressure (PAP), Pulmonary capillary wedge pressure (PCWP), and cardiac output.

41. What is the normal cardiac output for a baby?
0.6 L/min.

42. Fetal hemoglobin causes a shift to which direction of the oxygen dissociation curve?
It shifts to the left and consequently an increase affinity of HB for O2.

43. When does methemoglobin form?
When HB is oxidized to the ferric (iron) state.

44. What causes a baby to develop methemoglobinemia (MetHb)?
Medications and nitric oxide.

45. Carbon monoxide poisoning causes Hb to combine with what?
CO, not oxygen.

46. What is the CaO2 equation?
(Hb x 1.34 x SaO2) + (PaO2 x 0.003).

47. What is the most accurate way to detect changes in oxygen levels of the blood?

48. What method for obtaining ABG should be tried initially in a neonate?
Umbilical artery catheter.

49. The high placement of umbilical artery catheter should be which landmark on X-ray?

50. What is the most important advantage of continuous in-line blood gas sampling compared with umbilical blood gas sample in neonates?
Decreased amount of blood wasted.

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51. What is the cardiac index?
Cardiac output/BSA.

52. What is a common factor that can reduce PVR?
Nitric oxide.

53. Which measurement requires a Swan-Ganz catheter?
Pulmonary Wedge Pressure (PCWP).

54. What are the complications associated with a dwelling vascular catheter?
Infection and air embolism.

55. What are the arterial sample sites for neonates?
Radial artery and umbilical artery.

56. What is the capillary sampling site for neonates?
The lateral portion of heal.

57. What is the umbilical artery catheter placement?
It is inserted through umbilicus into 1 of the 2 Umbilical arteries. Heparinized isotonic saline solution is attached to prevent clotting. It is secured by suturing or umbilical tape.

58. What are the advantages of an ABG sample?
It provides reliable values for pH, oxygen, and CO2, and arterial lines make for easy and quick access.

59. What are the disadvantages of an ABG sample?
They are hard to obtain, can damage the artery, infection/ clotting, and stimulation of the infant will affect the values.

60. What are the complications of an ABG sample?
Technique, instrument (analyzer), and post puncture care.

61. What are indications for transcutaneous monitoring?
Monitor adequacy of arterial oxygenation and ventilation. Evaluate response to diagnostic & therapeutic interventions. It is useful for continuous monitoring. Last, it is useful when direct measurement of ABG is not available.

62. What are the contraindications for transcutaneous monitoring?
Poor skin integrity and adhesive allergy (relative contraindication).

63. What are the hazards of transcutaneous monitoring?
False negative or positive results and tissue injury.

64. What are the advantages of transcutaneous monitoring?
Continuous monitoring of O2 or CO2 and non-invasive.

65. What are the disadvantages of transcutaneous monitoring?
Burns and erythema, frequent calibration, equilibration time, and oxygen values become less reliable on older infants.

66. What is capnography?
Used with ventilated patients, special neonatal adapter needed, smaller ETCO2 adapters, accurately measure smaller volumes, moisture and secretions affect readings, and ETCO2 values usually 2-3 torr lower than ABG values.

67. What is a pneumogram and apnea monitor?
It measures heart rate and respiratory rate. Electrodes placed in mid-axillary line and held in place with a flexible belt. Monitor senses the changing impedance as chest moves and calculates respiration.

68. What are the indications for a pneumogram?
It is used with babies at risk for Sudden Infant Death Syndrome (SID), bradycardia, or apnea spells.

69. What is the preferred puncture site for a capillary blood gas?
The heel is preferred.

70. How long should you warm the site before puncture?
Warm the site for 10 minutes using a compress, heat lamp, or commercial hot pack.

71. What are the alternative puncture sites if the heel is unavailable?
The earlobe, big toe, and finger.

72. What is used to puncture the skin?
A lancet should be used.

73. What should you do with the first drop of blood?
You should wipe away the first drop of blood before collecting a sample.

74. How long do you have to analyze the sample?
The sample should be analyzed within 10-15 minutes.

75. What parameters should you look at during the analysis of a capillary sample?
The pH and PaCO2 correlate well with an arterial sample. The PaO2, however, does not. Only look at the infant’s ventilatory parameters during a capillary blood gas analysis.

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Final Thoughts

Capillary Blood Gas sampling is an important topic in the field of respiratory care. This is especially true for those who want to work with neonatal and pediatric patients.

Hopefully, this study guide can help make the learning process easier for you.

We have a similar guide that covers Arterial Blood Gas Interpretation in adults as well that I think you will enjoy. Thank you so much for reading and as always, breathe easy my friend.


The following are the sources that were used while doing research for this article: