1 Oxygenation Monitoring At the end of this self study the participant will: 1. Describe the difference between SpO 2 and SaO 2 2. Describe the relationship between hemoglobin and oxygenation

2 Pulse Oximetry (SpO 2 ) Adequate Tissue Oxygenation depends on three things: –Adequate Oxygenation – look at the PaO 2 –Adequate Hemoglobin – to carry the O 2 –Adequate Circulation Pulse Oximetry measures: –The ability of the blood to bind to oxygen –Gas exchange in the lungs Pulse Oximetry does not measure the oxygen delivery to the tissues

3 Hemoglobin’s role Hemoglobin –oxygen carrier –normal gm/dl –Critical threshold = less than 10 gm/dl –Physician alert value <4 gm/dl High binding capacity with –oxygen –carbon dioxide –carbon monoxide

4 Oxyhemoglobin = functional oxygen % of available oxygen sites on hemoglobin that are attached to an oxygen molecule Oxygen Saturation –normal % –critical threshold normally <90% SaO 2 is Arterial saturation SpO 2 is Pulse oximetry Skin color is NOT a reliable indicator of oxygenation Central Cyanosis

5 Dysfunctional Hemoglobin 97% of oxygen is attached to hemoglobin –2-4% is normally dysfunctional Carboxyhemoglobin (COHb) –Carbon monoxide has a greater infinity to bind to Hgb than oxygen, therefore the oxygen carrying capacity of Hgb is reduced –Expected values: % (non-smokers) % (average smokers) % (heavy smokers) –Physician alert value (automatic callback): ≥20%

6 Dysfunctional Hemoglobin Methemoglobin (MetHb) –heme protein changes state (ferrous to ferric)- thus is incapable of binding with oxygen –Normal <2% –Physician alert value (automatic call- back): ≥5.0% Causes include –Local anesthetics –Environmental 10-20% metHb - Skin discoloration only (most notably on mucus membranes) 20-30% metHb - Anxiety, headache, dyspnea on exertion 30-50% metHb - Fatigue, confusion, dizziness, tachypnea, palpitations 50-70% metHb - Coma, seizures, arrhythmias, acidosis Greater than 70% metHb - Death

7 Pulse Oximetry (SpO 2 ) Process –Light shone through tissue –Oxygenated and reduced hemoglobin absorbs different amount of light –amount of light detected on other side of tissue determines SpO 2 Indirect measurement –Is an estimation of SaO 2

8 SpO 2 Normal % Critical Threshold <90% Should correlate with SaO 2 –If correlation present, can use for ventilator effectiveness

9 Pulse Oximetry Limitations May cause inaccurate readings Low perfusion state –shock Vasoconstriction –vasopressors, hypothermia Dysfunctional hemoglobin –carboxyhemoglobin, methemoglobin Motion artifact Compression of artery –during BP External Light Sources IV dyes Nail polish Inconsistent pulse detection Hyperlipidemia or hyperbilirubinemia