Parameters and Reference Ranges
These are typical reference ranges, although various analysers and laboratories may employ different ranges.
| Analyte | Range | Interpretation |
|---|---|---|
| pH | 7.34-7.44 | The pH or H+ indicates if a patient is acidemic (pH < 7.35; H+ >45) or alkalemic (pH > 7.45; H+ < 35). |
| H+ | 35–45 nmol/L (nM) | See above. |
| Arterial oxygen partial pressure (PaO2) | 11-13 kPa or 75-100 mmHg | A low PaO2 indicates that the patient is not oxygenating properly, and is hypoxemic. (Note that a low PaO2 is not required for the patient to have hypoxia.) At a PaO2 of less than 60 mm Hg, supplemental oxygen should be administered. At a PaO2 of less than 26 mmHg, the patient is at risk of death and must be oxygenated immediately. |
| Arterial carbon dioxide partial pressure (PaCO2) | 4.7-6.0 kPa or 35-45 mmHg | The carbon dioxide partial pressure (PaCO2) is an indicator of CO2 production and elimination: for a constant metabolic rate, the PaCO2 is determined entirely by its elimination through ventilation. A high PaCO2 (respiratory acidosis, alternatively hypercapnia) indicates underventilation (or, more rarely, a hypermetabolic disorder), a low PaCO2 (respiratory alkalosis, alternatively hypocapnia) hyper- or overventilation. |
| HCO3− | 22–26 mEq/L | The HCO3− ion indicates whether a metabolic problem is present (such as ketoacidosis). A low HCO3− indicates metabolic acidosis, a high HCO3− indicates metabolic alkalosis. As this value when given with blood gas results is often calculated by the analyzer, correlation should be checked with total CO2 levels as directly measured (see below). |
| SBCe | 21 to 27 mmol/L | the bicarbonate concentration in the blood at a CO2 of 5.33 kPa, full oxygen saturation and 37 Celsius. |
| Base excess | −2 to +2 mmol/L | The base excess is used for the assessment of the metabolic component of acid-base disorders, and indicates whether the patient has metabolic acidosis or metabolic alkalosis. Contrasted with the bicarbonate levels, the base excess is a calculated value intended to completely isolate the non-respiratory portion of the pH change. |
| total CO2 (tCO2 (P)c) | 23-30 mmol/L or 100-132 mg/dL | This is the total amount of CO2, and is the sum of HCO3− and PCO2 by the formula: tCO2 = + α*PCO2, where α=0.226 mM/kPa, HCO3− is expressed in millimolar concentration (mM) (mmol/l) and PCO2 is expressed in kPa |
| O2 Content (CaO2, CvO2, CcO2) | vol% (mL oxygen/dL blood) | This is the sum of oxygen dissolved in plasma and chemically bound to hemoglobin as determined by the calculation: CaO2 = (PaO2 * 0.003) + (SaO2 * 1.34 * Hgb) where hemoglobin concentration is expressed in g/dL. |
Contamination of the sample with room air will result in abnormally low carbon dioxide and possibly elevated oxygen levels, and a concurrent elevation in pH. Delaying analysis (without chilling the sample) may result in inaccurately low oxygen and high carbon dioxide levels as a result of ongoing cellular respiration.
Read more about this topic: Arterial Blood Gas
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