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  • Blood Gas Basics

  • Normal Blood Gas Values

  • Venous Blood Gases

  • Capillary Blood Gases

  • General Principles of Blood Gas Determinations

  • Acid-Base Disorders: Definition

  • Mixed Acid-Base Disorders

  • Interpretation of Blood Gases

  • Metabolic Acidosis: Diagnosis and Treatment

  • Metabolic Alkalosis: Diagnosis and Treatment

  • Respiratory Acidosis: Diagnosis and Treatment

  • Respiratory Alkalosis: Diagnosis and Treatment

  • Hypoxia

  • Sample Acid-Base Problems

Chapter update by Steven Haist, MD, MS


Blood gases provide information concerning the oxygenation, ventilatory, and acid-base status of the patient. Blood gas results are usually given as pH, PO2, PCO2, [HCO3], base excess or deficit (base difference), and O2 saturation. This test gives information on acid-base homeostasis (pH, PCO2, HCO3, and base difference) and on blood oxygenation (PO2, O2 saturation). Arterial blood gases (ABGs) are most commonly measured; venous, mixed venous, and capillary blood gases are less often measured. Indications for blood gas determinations are as follows:

  • To determine a patient’s ventilator status (PaCO2), acid-base balance (pH and PaCO2), and oxygenation and O2-carrying capacity (PaO2 and O2Hb)

  • To quantitate the response to therapeutic interventions (e.g., supplemental O2 administration, mechanical ventilation) or diagnostic evaluation (e.g., exercise desaturation)

  • Monitoring the severity and progression of documented disease processes (e.g., COPD)


Normal values for blood gas analysis are given in Table 14-1 below, and capillary blood gases are discussed in a following section. Mixed venous blood gases are reviewed in Chapter 28, Pulmonary Artery Catheters (Swan–Ganz Catheter) and Additional Functions and Measurement Capabilities of PA Catheters. The bicarbonate concentration ([HCO3]) from the blood gas is a calculated value and should not be used in interpretation of blood gases; the [HCO3] from a concurrent chemistry panel should be used. Note: The HCO3 values on the chemistry panel and those calculated from the blood gases should be about the same. A major discrepancy (>10% difference) means one or more of the three values is in error (pH, PCO2, or [HCO3]) or the blood gas and the chemistry panel were not collected at the same time. ABGs and chemistry panels [HCO3] should be obtained at the same time for the most accurate interpretation.

Table 14-1Normal Blood Gas Values (Adult)

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