Blood Gases


Core Lab Study

Arterial blood gases (ABGs), venous blood gases (VBGs), capillary blood gases, cord blood gases.

To assess oxygenation and acid-base balance.

A small group of studies in this manual have been identified as Core Lab Studies. The designation is meant to assist the reader in sorting the basic “always need to know” laboratory studies from the hundreds of other valuable studies found in the manual—a way to begin putting it all together.

Normal, abnormal, or various combinations of core lab study results can indicate that all is well, reveal a problem that requires further investigation with additional testing, signal a positive response to treatment, or suggest that the health status is as expected for the associated situation and time frame.

ABGs are 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 tests 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.

Normal Findings
Method: Selective electrodes for pH, Pco2, and Po2.

Blood Gas Value (pH)ArterialVenousCapillary
Birth, cord, full term7.11–7.367.25–7.457.32–7.49
Note: SI units (conversion factor × 1).
Pco2ArterialSI Units (Conventional Units × 0.133)VenousSI Units (Conventional Units × 0.133)CapillarySI Units (Conventional Units × 0.133)
Scalp40–50 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
Po2ArterialSI Units (Conventional Units × 0.133)VenousSI Units (Conventional Units × 0.133)CapillarySI Units (Conventional Units × 0.133)
Scalp20–30 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
HCO3Arterial Conventional and SI UnitsVenous Conventional and SI UnitsCapillary Conventional and SI Units
Birth, cord, full term17–24 mmol/L17–24 mmol/L
2 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%
Values may be at the lower end of the normal range in older adults.
Oxygen Content: ArterialOxygen Content: Venous
6.6–9.7 mmol/L4.9–7.1 mmol/L
Tco2Arterial 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
Adult/childHCO310 mmol/L40 mmol/L
Adult/childPco220 mm Hg (SI: 2.7 kPa)67 mm Hg (SI: 8.9 kPa)
Adult/childPo245 mm Hg (SI: 6 kPa)
NewbornsPo237 mm Hg (SI: 4.9 kPa)92 mm Hg (SI: 12.2 kPa)

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