Blood Gases

General

Core Lab Study

Synonym/Acronym:
arterial blood gases (ABGs), venous blood gases (VBGs), capillary blood gases, cord blood gases.

Rationale
To assess oxygenation and acid-base balance.

This Core Lab Study is the gold standard for management of oxygenation levels and acid-base balance, especially in patients with severe illness. Understanding arterial blood gas results can be difficult and even complicated at times. Emergency, cardiac, and intensive care units commonly use results of ABGs and other core lab studies to inform the patient’s current clinical status and care plan.

Patient Preparation
There are no food, fluid, activity, or medication restrictions unless by medical direction. The Allen test should be performed prior to specimen collection from the radial artery. Information regarding how to perform the Allen test is presented with other general guidelines in Appendix A: Patient Preparation and Specimen Collection.

Normal Findings
Method: Selective electrodes for pH, Pco 2, and Po 2.

Allen test Note: Performed prior to use of radial artery for specimen collection
Normal Findings: Positive; where sufficient collateral blood flow in the ulnar artery is demonstratedNote: Procedure for Allen test is described and pictured in Appendix A: Patient Preparation and Specimen Collection.
Blood Gas Value (pH)ArterialVenousCapillary
Scalp——7.25–7.35
Birth, cord, full term7.11–7.367.25–7.457.32–7.49
Adult/child7.35–7.457.32–7.437.35–7.45
Note: SI units (conversion factor × 1).
Pco 2 ArterialSI Units (Conventional Units × 0.133)VenousSI Units (Conventional Units × 0.133)CapillarySI Units (Conventional Units × 0.133)
Scalp————40–50 mm Hg5.3–6.6 kPa
Birth, cord, full term32–66 mm Hg4.3–8.8 kPa27–49 mm Hg3.6–6.5 kPa——
Newborn–adult35–45 mm Hg4.7–6 kPa41–51 mm Hg5.4–6.8 kPa26–41 mm Hg3.5–5.4 kPa
Po 2 ArterialSI Units (Conventional Units × 0.133)VenousSI Units (Conventional Units × 0.133)CapillarySI Units (Conventional Units × 0.133)
Scalp————20–30 mm Hg2.7–4 kPa
Birth, cord, full term8–24 mm Hg1.1–3.2 kPa17–41 mm Hg2.3–5.4 kPa——
0–1 hr33–85 mm Hg4.4–11.3 kPa————
Greater than 1 hr–adult80–95 mm Hg10.6–12.6 kPa20–49 mm Hg2.7–6.5 kPa80–95 mm Hg10.6–12.6 kPa
HCO3 − Arterial Conventional and SI UnitsVenous Conventional and SI UnitsCapillary Conventional and SI Units
Birth, cord, full term17–24 mmol/L17–24 mmol/L—
12 mo–2 yr16–23 mmol/L24–28 mmol/L18–23 mmol/L
Adult22–26 mmol/L24–28 mmol/L18–23 mmol/L
O2 SatArterialVenousCapillary
Birth, cord, full term40%–90%40%–70%—
Adult/child95%–99%70%–75%95%–98%
Values may be at the lower end of the normal range in older adults.
Oxygen Content: ArterialOxygen Content: Venous
6.6–9.7 mmol/L 4.9–7.1 mmol/L
Tco 2 Arterial Conventional and SI Units mmol/LVenous Conventional and SI Units mmol/L
Birth, cord, full term13–22 mmol/L14–22 mmol/L
Adult/child22–29 mmol/L25–30 mmol/L
Base Excess ArterialConventional and SI Units
Birth, cord, full term(–10) – (–2) mmol/L
Adult/child(–2) – (+3) mmol/L

Critical Findings and Potential Interventions
Timely notification to the requesting health-care provider (HCP) of any critical findings and related symptoms is a role expectation of the professional nurse. A listing of these findings varies among facilities.

Consideration may be given to verification of critical findings before action is taken. Policies vary among facilities and may include requesting recollection and retesting by the laboratory.

Arterial Blood Gas ParameterLess ThanGreater Than
pH7.27.6
HCO3 − 10 mmol/L40 mmol/L
Pco 2 20 mm Hg (SI: 2.7 kPa)67 mm Hg (SI: 8.9 kPa)
Po 2 40 mm Hg (SI: 6 kPa)

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