Concepts Related to Oxygenation James Barnett, RN, MSN Vanderbilt University Medical Center May 2007

Measurements PaO 2 (partial pressure of arterial 0 2 ) PaO 2 (partial pressure of arterial 0 2 ) SaO 2 (arterial oxygen saturation) SaO 2 (arterial oxygen saturation) SpO 2 (pulse oximeter saturation) SpO 2 (pulse oximeter saturation) SvO 2 (mixed venous blood saturation) SvO 2 (mixed venous blood saturation)

PaO 2 Partial pressure of oxygen dissolved in arterial blood Partial pressure of oxygen dissolved in arterial blood Dependent on Dependent on Altitude Altitude Age Age Normal (sea level) = 80 – 100 mmHg Normal (sea level) = 80 – 100 mmHg

PaO2 Abnormally low PaO 2 = hypoxemia Abnormally low PaO 2 = hypoxemia Causes Causes Inability to ventilate appropriately (paralysis, rib fractures, secretions) Inability to ventilate appropriately (paralysis, rib fractures, secretions) Low cardiac output states (CHF, MI, Shock) Low cardiac output states (CHF, MI, Shock) Alveolar diffusion failure (pneumonia, ARDS) Alveolar diffusion failure (pneumonia, ARDS) Low environmental oxygen states (high-altitude) Low environmental oxygen states (high-altitude)

SaO 2 Measures percentage of arterial hemoglobin sites saturated with oxygen Measures percentage of arterial hemoglobin sites saturated with oxygen Direct measure from an arterial sample Direct measure from an arterial sample Normal > 93% Normal > 93% Remember: hemoglobin carries oxygen to the tissues Remember: hemoglobin carries oxygen to the tissues

SpO 2 Measures percentage of arterial hemoglobin sites saturated with oxygen Measures percentage of arterial hemoglobin sites saturated with oxygen Indirect measure from pulse oximeter technology Indirect measure from pulse oximeter technology Normal range is > 93% Normal range is > 93%

SvO 2 Percent of hemoglobin sites saturated with oxygen after tissue oxygenation has occurred Percent of hemoglobin sites saturated with oxygen after tissue oxygenation has occurred Indicates adequacy of tissue oxygenation Indicates adequacy of tissue oxygenation Methods Methods Pulmonary artery catheter access Pulmonary artery catheter access Venous access Venous access

SvO 2 Normal = 60 – 80% Normal = 60 – 80% Formula: (dual oximetry) Formula: (dual oximetry) SaO 2 – SvO 2 = % of O 2 removed from the hgb by the tissues SaO 2 – SvO 2 = % of O 2 removed from the hgb by the tissues Usually 20 – 40% Usually 20 – 40%

Low SvO 2 Decreased oxygen delivery (DaO 2 ) Decreased oxygen delivery (DaO 2 ) Low hematocrit Low hematocrit Hypoxemia Hypoxemia Low cardiac output Low cardiac output Shock (SvO 2 < 40% can  profound shock) Shock (SvO 2 < 40% can  profound shock) Increased tissue demand for oxygen Hyperthermia Pain Stress Shivering Seizures

High SvO 2 Increased oxygen supply Increased oxygen supply High FiO 2 High FiO 2 Technical problems with reading Technical problems with reading Wedged Swan - Ganz Wedged Swan - Ganz Decreased oxygen demand Hypothermia Anesthesia Hypothyroidism

Finished You have completed this in-service. Please complete the post-test titled: You have completed this in-service. Please complete the post-test titled: Concepts Related to Oxygenation Concepts Related to Oxygenation