Oxygen+Transport

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=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)

•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 = = = O2 physical solubility =

<span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;">•O2 is poorly soluble in plasma (3 mL O2/ 1 L plasma at 100 mm Hg PO2)

<span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;"> Dissolved O2= 0.003 x PaO2

<span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;"> 0.003=solubility coefficient

<span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;">•100% FiO2 (PaO2 500-600 mmHg) increases amount of dissolved O2 to ~18 mL/L plasma

=<span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;"> HbO2 saturation = <span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;">

<span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;">Hb + 4O2 ↔ nH+ Hb(O2) 4 <span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;">•SaO2 <span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;"> SaO2 = HbO2/ (HbO2 + reduced Hb + COHb + MetHb) <span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;"> obtained by ABG, 97.5% at 100 mmHg PO2

<span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;">•SpO2 <span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;"> SaO2 = HbO2/ (HbO2 + reduced Hb) <span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;"> obtained by pulse oximetry <span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;"> <span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;">•SvO2 <span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;"> SvO2 = HbO2/ (HbO2 + reduced Hb + COHb + MetHb) <span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;"> obtained by VBG, 75% at 40 mmHg PO2 <span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;">

=<span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;"> HbO2 dissociation curve = <span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;">•Partial pressure of oxygen drops as oxygen moves from inhaled air to tissues <span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;"> <span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;"> <span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;"> •Rightward shift (by ↑CO2, ↑H+, ↑Temp, ↑2,3-DPG) facilitates O2 unloading in the tissues <span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;"> •Permissive hypercapnia during GA may improve tissue oxygenation and protect from stroke, MI, AKI <span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;">

=<span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;">2,3-diphosphoglycerate = <span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;"> •End-product of erythrocyte metabolism, located in the central cavity of hemoglobin

<span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;"> •

<span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;"> •2,3-DPG promotes release of O2 molecules from Hb

<span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;"> []

<span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;"> •High altitude, COPD, CHF increase 2,3-DPG content in erythrocytes <span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;">

=<span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;">Hemoglobin as a Buffer = <span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;">= <span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;">

<span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;"> •Amino acid (-COO-, -NH2) of Hb bind H+ generated by hydration of CO2 in erythrocytes <span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;"> •Reduced hemoglobin is a better buffer than oxygenated Hb

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