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CP Phys Chap 6

Oxygen Transport

Hypoxemia An abnormal low arterial oxygen tension (PaO2) and frequently associated with Hypoxia.
Hypoxia An inadequate level of tissue oxygenation. Inadequate oxygen for cellular metabolism.
If pt is hypoxic, do they have hypoxia? Not always! It strongly suggests it but in mild hypoxic pts hypoxia does not necessarily exist.
Hypoxic Hypoxia (aka Hypoxemic Hypoxia) The condition in which there is inadequate oxygen at the tissue cells caused by low arterial oxygen tension (PaO2).
Hypoxic Hypoxia common causes are: -Hypoventilation -high altitude -Diffusion defects, i.e. interstitial fibrosis or lung disease, pulmonary edema, pneumoconiosis, -V/Q mismatch, -Pulmonary shunting.
Anemic Hypoxia PaO2 is normal but the oxygen-carrying capacity of the hemoglobin is inadequate.
Anemic Hypoxia common causes are: -Decreased hemoglobin, i.e. anemia or hemorrhage, -Abnormal hemoglobin, i.e. carboxyhemoglobinemia or methemoglobinemia.
Carbon monoxide has an affinity to hemoglobin _____ times greater than that of oxygen. 210
Methemoglobinemia Iron atoms (Fe2+) are oxidized to ferric (Fe3+) and can no longer carry oxygen in hemoglobin. This suffocates the tissue.
What is the main compensatory mechanism of anemic hypoxia? Increased cardiac output.
Circulatory Hypoxia (aka Stagnant or Hypoperfusion Hypoxia) May have normal oxygen tension but blood flow to the tissue cells is inadaquate; thus, oxygen is not adequate to meet tissue needs.
Circulatory Hypoxia common causes are: -Slow or stagnant (pooling) peripheral blood flow, -arterial-venous shunts.
Histotoxic Hypoxia Impaired ability to the tissue cells to utilize oxygen.
Histotoxic Hypoxia common cause is: Cyanide poisoning; develops in any condition that impairs the ability of tissue cells to utilize oxygen.
Hypoventilation common causes are: COPD, central nervous system depressants, head trauma, and neuromuscular disorders (i.e. myasthenia gravis or Gullain-Barre syndrome).
Diffusion Defects are what? Abnormal anatomic alterations of the lungs that result in an impedance of oxygen transfer across the alveolar-capillary membrane. Causes reduced time for oxygen equilibrium between the alveolus and pulmonary capillary.
Diffusion Defects common causes are: Chronic interstitial lung diseases, pulmonary edema, and pneumoconiosis.
Ventilation-Perfusion Mismatch is what? When the pulmonary capillary blood is in excess of the alveolar ventilation. Causes pulmonary shunting which causes < PaO2 & CaO2
Ventilation-Perfusion Mismatch common causes are: COPD, pheumonia, and pulmonary edema.
Pulmonary shunting causes what? Decreased PaO2 & CaO2.
When the oxygen tension in the arterial blood is normal but the oxygen-carrying capacity of the blood is inadaquate, what condition is this? Anemic Hypoxia
Stagnant Hypoxia (aka Hypoperfusion) Occurs when the peripheral capillary blood flow is slow or stagnant.
Stagnant Hypoxia common causes are: -Decreased cardiac output, -vascular insufficiency, -neurochemical abnormalities, -Primarily assoc with cardiovascular disorders.
Stagnant Hypoxia causes what? Sluggish blood which increases the time needed for oxygen exchange but at the same time is supplying less oxygen. The oxygen pressure gradient between the blood & tissues cells decreases causing tissue hypoxia.
Arterial-venous shunt is what? When arterial blood completely bypasses the tissue cells and moves into the venous system.
Cyanosis Severe hypoxemia. Term used to describe the blue-gray or purplish discoloration seen on the mucous membranes, fingertips, and toes whenever blood in these areas contains at least 5 g% of reduced hemoglobin per dL (100 mL).
Polycythemia means what? An increase in RBC's, increases the oxygen-carrying capacity of blood.
When pulmonary disorders produce chronic hypoxemia what is stimulated? The hormone erythropoietin stimulates the bone marrow to increase RBC production, which is called erythropoiesis.
Polycythemia causes what? Increased viscosity needing a greater driving pressure to maintain flow, which increases the work of the R & L ventricles. Can lead to L ventricular hypertrophy and failure and to R ventricular hypertrophy, and cor pulmonale.
Oxygen is carried in the blood in two forms, 1. dissolved oxygen in the blood plasma, and 2. chemically bound to hemoglobin that is encased in the RBC's.
Dissolve means, that when a gas like oxygen enters the plasma, it maintains its precise molecular structure and moves freely throughout the plasma in its normal gaseous state. This is the portion of O2 that is measured to assess pt PO2. (0.003 mL dissolved O2 factor).
The quantity of O2 that dissolves in the plasma is a function of what? Henry's Law = the amount of gas that dissolves in a liquid at a given temp is proportional to the partial pressure of gas.
Vol% represents what? The amount of O2 in mL that is in 100 mL of blood. Vol% = mL O2/100 mL blood.
RBC contains approximately ______ million hemoglobin molecules. 280
Normal adult hemoglobin consists of what? 4 heme groups, which are the pigmented, iron-containing non-protein portions of the hemoglobin molecule, and 4 amino acid chains (polypeptide chains) that collectively constitue globin (a protein).
Hb + O2 <-----> HbO2 (oxyhemoglobin)
Four heme/iron groups in each Hb molecule = Four O2 molecules that combine w/each Hb molecule.
When 4 O2 are combined w/one Hb molecule it is said to be ______% saturated. 100
Hb not bound to O2 is called what? Reduced hemoglobin or deoxyhemoglobin.
The amount of O2 bound to Hb is ______ related to the partial pressure of O2. Directly.
Globin portion of each Hb molecule consists of what? 2 identical alpha chains, each with 141 amino acids, and 2 identical beta chains, each with 146 amino acids.
Normal hemoglobin values: Adult male - 14 - 16 g/100 mL of blood (g%) Adult female - 12 - 15 g% Infant - 14 - 20 g%
g% = gram percent of hemoglobin
g/dL grams per deciliter
Quantity of O2 bound to Hb vol% O2 = 1.34 mL O2 x Yg% (.97 or SaO2)
Hb saturation is only about 97% because of what normal physiologic shunts? 1. Thebesian venous drainage into the left atrium, 2. bronchial venous drainage into the pulmonary veins, and 3. alveoli that are underventilated relative to pulmonary blood flow.
Dissolved O2 + O2 bound to Hb = Total amount of O2 in 100 mL of blood
Dissolved O2 YmmHg x 0.003
O2 bound to Hb Yg% x 1.34 (SaO2)
CaO2 (O2 content of arterial blood) = (Hb x 1.34 x SaO2) + (PaO2 x 0.003)
CVO2 (O2 content of mixed venous blood) = (Hb x 1.34 x SVO2) + (PVO2 x 0.003)
CCO2 (O2 content of pulmonary capillary blood) (Hb x 1.34) + (PAO2 x 0.003)
The total amount of O2 delivered or transported to the peripheral tissues is dependent on, 1. the body's ability to oxygenate blood, 2. the hemoglobin concentration, and 3. the cardiac output.
Total oxygen delivery (DO2) (tells what is available to the cells) = Qt (total cardiac output, L/min) x (CaO2 x 10) -- multiply by 10 to convert CaO2 from mL to L.
CvO2 tells, how much O2 has been consumed by the cells. Average is 15 vol%.
Oxygen delivery decreases when there is a decline in, 1. blood oxygenation, 2. hemoglobin concentration, or 3. cardiac output.
An individual's hemoglobin concentration or cardiac output will often ______ in an effort to compensate for a reduced oxygen delivery. Increase
Arterial-venous oxygen content difference = C(a - V)O2 or CaO2 - CVO2 -- CVO2 obtained from pt pulmonary artery.
CaO2 - CVO2 norms = 20 vol% - 15 vol% = 5 vol% (arterial-venous diff)
O2 Consumption = O2 used in 1min time. Amount of O2 extracted by the periperal tissues during 1min.
O2 Consumption Calculation = VO2 = Qt [C(a-V)O2 x 10]
Average cardiac output (Qt) 5 L/min
Factors that increase C(a-V)O2 - decreased cardiac output, - periods of increased O2 consumption, i.e. exercise, seizures, shivering, hyperthermia
Factors that decrease C(a-V)O2 - Increased cardiac output, - skeletal muscle relaxation (by drugs), - peripheral shunting, - certain poisons, - hypothermia
Oxygen consumption is usually related to the pt ______? BSA - Body Surface Area -- found on a chart, we cannot calculate.
Normal BSA 125 - 165 mLO2/m squared
Pt O2 consumption index is derived by what? VO2/BSA
Factors that increase VO2 - exercise, - seizures, - shivering, - hyperthermia
Factors that decrease VO2 - skeletal muscle relaxation (drugs), - peripheral shunting, - certain poisons, - hypothermia
Oxygen concentration ratio (O2ER) the amount of O2 extracted by the peripheral tissues divided by the amount of O2 delivered to the peripheral cells. Aka oxygen coefficient ratio or oxygen utilization ratio.
O2ER calculation C(a - V)O2/CaO2
Normally, a pts Hb returns to the alveoli approximately _____% saturated with O2. 75
Factors that increase O2ER - dec cardiac output, - periods of inc O2 consumption, i.e. exercise, seizures, shivering, hyperthermia, - anemia, - dec arterial oxygenation.
Factors that decrease O2ER - inc cardiac output, - skeletal muscle relaxation (drugs), - peripheral shunting, - certain poisons, - hypothermia, - inc Hb concentration, - inc arterial oxygenation.
Mixed venous oxygen saturation (SVO2) Continuous monitoring of SVO2 is often used to detect changes in the pts C(a-V)O2, VO2, and O2ER. Norm is 75%, about 65% is acceptable.
Factors that decrease SVO2 - dec cardiac output, - periods of inc oxygen cunsumption, i.e. exercise, seizures, shivering, hyperthermia.
Factors that increase SVO2 - inc cardiac output, - skeletal muscle relaxation (drugs), - peripheral shunting, - certain poisons, - hypothermia.
Shunt perfusion without ventilation
Pulmonary Shunting That portion of the cardiac output that moves from the right side to the left side of the heart without being exposed to alveolar oxygen (PAO2). Divided by 1. absolute (true) shunts and 2. relative shunt (aka shunt-like effects).
Absolute Shunt Does NOT respond to O2 therapy because there is no gas exchange. Divided by 1. anatomic shunts and 2. capillary shunts.
Created by: mfredenburg