RESPIRATORY 221 WEEK 4 CH.8

Oxygen transport Mixed venous blood – pulmonary capillary - PvO2 40mmHg - PAO2 100mmHg – diffuses through pressure gradient into blood - carried in blood HOW?

How Does Blood Carry Oxygen? 1. Oxygen Dissolved in Plasma Expressed as mL of oxygen dissolved in 100 mL of plasma PO 2 x = mL/dL dissolved oxygen 2. COMBINED WITH HEMOGLOBIN (Hb)

Henry’s Law In physics, Henry's law is one of the gas laws formulated by William Henry in It states: "At a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid.“ An equivalent way of stating the law is that the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid.

How Does Blood Carry Oxygen? Fig. 8-2

How Does Blood Carry Oxygen? 2. Oxygen Combined with Hemoglobin 1 gram Hb carries max. of 1.34 mL of O 2 Normal Hb level is ? (12-16 g/dL) At 15 g/dL and 100% saturation, Hb carries 20.1 mL oxygen Mixed venous blood at 75% saturation carries 0.75 x 20.1 = 15.1 mL/dL (vol %) Arterial-venous content difference ≈ 5 mL/dL (vol%)

How much oxygen is dissolved in arterial plasma? pH 7.40 PaCO2 40mmHg PaO2 90mmHg90 x =.27 ml/dl SaO2 94% HCO3 24mEq/L PO2 in blood plasma Hgb 15g/dL called blood’s O2 tension SvO2 71% PvO2 37mmHgpg 143

What is the arterial oxyhemoglobin? pH 7.40 PaCO2 40mmHg PaO2 90mmHg SaO2 94% 15g/dl x 1.34 ml = HCO3 24mEq/L20.1 ml/dL Hgb 15g/dL SvO2 71% PvO2 37mmHg pg 146

Calculate the total arterial oxygen content pH 7.40 PaCO2 40mmHg PaO2 90mmHg SaO2 94% HCO3 24mEq/L Hgb 15g/dL SvO2 71% PvO2 37mmHg CaO2 = (Hgb x 1.34) x SaO2 + (PaO2 x 0.003) 15 x 1.34) = 20.1 x.94 = (90 x 0.003).27= 19.6ml/dL

How much oxygen is dissolved in venous plasma? pH 7.40 PaCO2 40mmHg PaO2 90mmHg SaO2 94% HCO3 24mEq/L Hgb 15g/dL SvO2 71%.71 x 20.1 = 15.1 ml/dL of O2 PvO2 37mmHg pg 146

What is the venous oxyhemoglobin? pH 7.40 PaCO2 40mmHg PaO2 90mmHg SaO2 94% HCO3 24mEq/L Hgb 15g/dL SvO2 71% PvO2 37mmHg

Calculate the total venous oxygen content pH 7.40 PaCO2 40mmHg PaO2 90mmHg SaO2 94% HCO3 24mEq/L Hgb 15g/dL SvO2 71% PvO2 37mmHg

Calculate the arterio-venous (a-v) oxygen content pH 7.40 PaCO2 40mmHg PaO2 90mmHg SaO2 94% HCO3 24mEq/L Hgb 15g/dL SvO2 71% PvO2 37mmHg

Clinical Significance The a-v difference reflects ________________________ The larger the difference, the more oxygen transported to the tissues, drawing from the venous so less venous PvO2 is returning to heart

Calculate the Volume of oxygen consumed (VO2) VO2 = QT x C(a-v)O2 x 10 Normal = 250mL Equation = Fick’s Equation Can also be rearranged to solve for Cardiac Output

Fick’s equation for cardiac output QT = VO 2 [C(a-v)O 2 x 10] If oxygen consumption remains constant, increased oxygen transport (  C(a-v)O 2 ) implies a  in cardiac output. What else can cause an increase in oxygen being extracted?

How can you saturate the blood? Increase the pressure of O2 molecule By increasing your carrying capacity: Increase Hemoglobin, and FIO2, reduce factors effecting Oxyhemoglobin curve

Oxyhemoglobin Curve Fig. 8-4

Oxyhemoglobin Curve pg 147 Fig. 8-6

Using the previous graph How much saturation is lost when the pressure of O2 decreases from 100mmHg to 60mmHg? = Safety Margin. In other words, the patient is not in significant danger. However, what happens if pressure decreases from 60mmHg to 20mmHg? Pg 148

Acid Base: pH, PaCO2, Hco-3 Oxygenation: Dissolved & Bound to hg CaO2: (Hb x 1.34 xSaO2) + (PaO2x 0.003) Oxygen Dissociation Curve: Right Shift: –Increasing unloading at the cellular level Left shift: –Decreasing unloading at the cellular level O2 Delivery CaO2 x 10x QT ml/min Acid Base, Oxygenation, ABNL Hb

Key Findings pg 149 P 50 (normal = 27 mm Hg) –measure of Hb’s affinity for oxygen –PO 2 at which Hb is 50% saturated with O 2 HbO 2 curve shifts –lower P 50 = left shift  PCO 2,  pH,  temperature,  2,3-DPG  Hb’s affinity for O 2 = less O 2 to tissues Hypoxic; not hypoxemic –higher P 50 = right shift  PCO 2,  pH,  temperature,  2,3-DPG  Hb’s affinity for O 2 = release O 2 into tissues Hypoxemic; not hypoxic

Signs of low oxygen? Cyanosis Blue-greyish discoloration of the skin/mucosa/lips Tachypnea RR>20/min Tachycardia HR > 100/min