Dusan Hanidziar, MD Department of Anesthesiology Tufts Medical Center
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Transcript of Dusan Hanidziar, MD Department of Anesthesiology Tufts Medical Center
Dusan Hanidziar, MD
Department of Anesthesiology
Tufts Medical Center
O2 transportO2 physical solubilityHbO2 saturationHbO2 dissociation curveP502,3-diphosphoglycerateHb as a buffer
O2 transport
• Oxygen delivery (DO2) is a function of:
1. Cardiac output
2. O2 content in arterial blood
DO2 = Q x CaO2
Q=cardiac output
Q=stroke volume x heart rate
CaO2=oxygen content in arterial blood
CaO2= (1.34 x Hb x SaO2) + (0.003 x PaO2)
Adapted from Marino PL: ICU book, 2007
O2 transport
• O2 is carried in the blood in two forms:
1. bound to hemoglobin within erythrocytes
2. dissolved in plasma
• 1 L of arterial blood contains ~ 200 mL O2
• Arterial and venous blood together contain ~ 800 mL O2
Adopted from Marino PL: ICU book, 2007
• O2 is poorly soluble in plasma (3 mL O2/ 1 L plasma at 100 mm Hg PO2)
Dissolved O2= 0.003 x PaO2
0.003=solubility coefficient
• 100% FiO2 (PaO2 500-600 mmHg) increases amount of dissolved O2 to ~18 mL/L plasma
O2 physical solubility
Adapted from Marino PL: ICU book 2007
• SaO2
SaO2 = HbO2/ (HbO2 + reduced Hb + COHb + MetHb)
obtained by ABG, 97.5% at 100 mmHg PO2
• SpO2
SaO2 = HbO2/ (HbO2 + reduced Hb)
obtained by pulse oximetry
• SvO2
SvO2 = HbO2/ (HbO2 + reduced Hb + COHb + MetHb)
obtained by VBG, 75% at 40 mmHg PO2
Oxygen saturation of hemoglobin
Hb + 4O2 ↔ nH+ Hb(O2) 4
Adapted from Barash PG et al: Clinical Anesthesia, 2006
O2 partial pressures
• Partial pressure of oxygen drops as oxygen moves from inhaled air to tissues
• O2 tension clinically measured by ABG (normal PaO2 >80 mm Hg) or VBG (40-50 mm Hg)
West JB: Respiratory Physiology 2012
HbO2 dissociation curve
• Rightward shift (by ↑CO2, ↑H+, ↑Temp, ↑2,3-DPG) facilitates O2 unloading in the tissues
• Permissive hypercapnia during GA may improve tissue oxygenation and protect from stroke, MI, AKI
Adapted from Miller RD: Basics of Anesthesia, 2011
• End-product of erythrocyte metabolism, located in the central cavity of hemoglobin
• 2,3-DPG promotes release of O2 molecules from Hb
https://iwasa.hms.harvard.edu/project_pages/hemoglobin.html
• High altitude, COPD, CHF increase 2,3-DPG content in erythrocytes
2,3-diphosphoglycerate (2,3-DPG)
Adapted from West JB: Respiratory Physiology 2012
• Amino acid residues (-COO-, -NH2) of Hb bind H+ generated by hydration of CO2 in erythrocytes
• Reduced hemoglobin is a better buffer than oxygenated Hb
Hemoglobin as a buffer
Adapted from Marino PL: ICU book, 2007 and West JB: Respiratory Physiology 2012