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RTT 193 - Ch. 6
Oxygen Transport
| Question | Answer |
|---|---|
| The transport of oxygen between the lungs and the cells is a function of what? | The blood and the heart |
| How is oxygen carried in the blood? | 1. As dissolved oxygen in the blood plasma 2. bound to hemoglobin that is encased in RBC |
| What are the normal blood gas value ranges? | Arterial: Venous: PH - 7.35-7.45 PH - 7.30-7.40 PCO2 - 35-45mmHg PCO2 - 42-48mmHg HCO3 - 22-28mEq/L HCO3 - 24-30mEq/L PO2 - 80-100mmHg PO2 - 35-45mmHg |
| What does DISSOLVE mean? | 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. |
| What portion of the oxygen is measured to assess the patient's partial pressure of oxygen? | The part of oxygen that is dissolved in the blood plasma |
| The quantity of oxygen that dissolves in the plasma is a function of what law? | Henry's law (the amount of gas that dissolves in a liquid at a given temperature is proportional to the partial pressure of gas) |
| How many mL of oxygen will dissolve in 100mL of blood every 1 mmHg PO2? | 0.003mL |
| What does most of the oxygen that diffuses into the pulmonary capillary blood do? | Rapidly moves into the RBCs and chemically attaches to the hemoglobin. |
| How many hemoglobin molecules do each RBC contain? | Approximately 280 million |
| What does a normal adult hemoglobin consist of? | 1. Four heme groups (pigmented, iron-containing non-protein portions) 2. Four amino acid chains [polypeptide chains] (collectively constitue globin, a protein) |
| A total of four oxygen molecules can combine with each Hb molecule, what percent is Hb saturated when four oxygen molecules are bound to one Hb molecule? Three? Two? One? | 100%; 75% 50%; 25% |
| What is it called when hemoglobin is bound with oxygen? | Oxyhemoglobin |
| What is it called when hemoglobin is not bound with oxygen? | Deoxyhemoglobin or reduced hemoglobin |
| What is the amount of oxygen bound to Hb directly related to? | The partial pressure of oxygen |
| What does the globin portion of each Hb molecule consist of? | Two identical alpha chains (each with 141 amino acids) and two identical beta chains (each with 146 amino acids) |
| What does normal fetal hemoglobin consist of? | Two alpha chains and two gamma chains. |
| What does the normal fetal hemoglobin do? | Increases Hb's attraction to oxygen and facilitates transfer of maternal oxygen across the placenta. It is gradually replaced with normal adult hemoglobin over the first year. |
| When does the hemoglobin become abnormal? | When the precise number, sequence, or spatial arrangement of the globin amino acid chains is altered. |
| What changes the iron molecule in heme from FERROUS STATE to the FERRIC STATE? | Various drugs and chemicals, such as nitrites. |
| What does changing the iron molecule in the heme from the ferrous state to ferric state do for hemoglobin? | It eliminates its ability to transport oxygen. (Known as methemoglobin) |
| What is the normal hemoglobin value for the adult male? Adult female? Infant? | 14-16 g/100mL; 12-15 g%; 14-20 g% |
| How much is each g% of Hb capable of carrying? | Approximately 1.34 mL of O2. |
| What is the formula for oxygen bound to hemoglobin? | O2 bound to Hb = 1.34 x Hb x SaO2 |
| What is the hemoglobin saturation at a NORMAL ARTERIAL OXYGEN PRESSURE (PA02) of 100mmHg? | 97% |
| Why is the hemoglobin saturation only 97% at a normal arterial oxygen pressure of 100mmHg? | Because of these normal physiologic shunts: 1. Thebesian venous drainage into the left atrium 2. Bronchial venous drainage into the pulmonary veins 3. Alveoli that are underventilated relative to pulmonary blood flow |
| When is a person in respiratory distress? | When their respiratory rate is greater than 25 breaths/min. |
| What is the total oxygen content of the arterial blood (CaO2) formula? | Oxygen bound to hemoglobin: (1.34 x Hb x SaO2) + Dissolved in O2:(0.003 x PaO2) |
| Oxygen content of mixed venous blood (CvO2) Formula: | (Hb x 1.34 x SvO2) + (PvO2 x 0.003) |
| Oxygen content of pulmonary capillary blood (CcO2) Formula: | (Hb x 1.34) + (PAO2 x 0.003) |
| Ideal Alveolar Gas Equation (PAO2) Formula: | (BP - PH2O)FIO2 - PaCO2(1.25) |
| What does the oxygen dissociation curve illustrate? | Left-hand side: percentage of hemoglobin that is chemically bound to oxygen Bottom portion: at each oxygen pressure Right-hand side: precise oxygen content that is carried by the Hb at each oxygen pressure |
| What is the measurements of the steep slope of the curve? Flat portion? | 10-60mmHg; 70-100mmHg |
| What is the clinical significance of the flat portion of the curve? | The PO2 can fall from 100 to 60mmHg and the Hb will still be 90% saturated with oxygen. Thus, the upper curve plateau illustrates that Hb has an excellent safety zone for the loading of oxygen in the lungs. It also means that increasing the PO2 beyond 100 |
| What is the clinical significance of the steep portion of the curve? | PO2 below 60mmHg produces rapid decrease in the amount of O2 bound to Hb. When PO2 falls below 60mmHg, the quantity of O2 delivered to the tissue cells is reduced. |
| What does the P50 represent? | The partial pressure at which the Hb is 50% saturated with O2. |
| Normally, the P50 is about? | 27mmHg |
| Explain what happens to the P50 when the curve shifts. | P50 increases when the curve shifts to the right (affinity of Hb for O2 decreases). P50 decreases when the curve shifts to the left (affinity of Hb for O2 increases) |
| What are the factors that shift the oxygen dissociation curve? | pH, temperature, carbon dioxide, 2,3-Diphosphoglycerate (DPG), fetal hemoglobin, and carbon monoxide hemoglobin |
| What does pH do to the curve? | As blood hydrogen-ion concentration increases (decreased pH), the curve shifts to the right. As the blood hydrogen-ion concentration decreases, the curve shifts to the left. |
| What does temperature do to the curve? | Body temperature increases, the curve shifts to the right. Body temperature decreases, the curve shifts to the left. |
| What does carbon dioxide do to the curve? | PCO2 increases, the oxyhemoglobin saturation decreases, curve shifts to the right. PCO2 decreases, curve shifts to the left. |
| What is the Bohr effect? | The effect if PCO2 and pH on the oxyhemoglobin curve. (Most active in the capillaries of the working muscles, particularly myocardium) |
| What is the 2,3-DPG? And what does it do to the curve? | A metabolic intermediary that is formed by the RBCs during anaerobic glycolysis. As it increases, it shifts the curve to the right. |
| What are the conditions that affect the level of 2,3-DPG? | Hypoxia (increases 2,3-DPG); Anemia (2,3-DPG increases as Hb concentration decreases); pH changes (pH increases, 2,3-DPG increases and vice versa); Stored blood (very low concentration of 2,3-DPG) |
| What does the fetal hemoglobin do to the curve? | Greater affinity to oxygen, shifts curve to the left (reducing the P50) |
| What does carbon monoxide hemoglobin do to the curve? | (CO has 210 times the affinity of O2 for Hb) The affinity of Hb for O2 increases and shifts curve to the left. |
| Where do shifts below the normal pressure range occur? | The steep portion of the curve |
| Describe right shifts - loading of oxygen in the lungs. | The total oxygen delivery may be much lower than indicated by a particular PaO2 value when a disease process is present that cause the oxygen dissociation curve to shift to the right. |
| Describe right shifts - unloading of oxygen in the lungs. | The total oxygen delivery decreases, the plasma PO2 at the tissue sites does not have to fall as much to unload oxygen from the Hb. |
| Describe left shifts - loading of oxygen in the lungs. | Curve shifts to the left, when PAO2 is 60mmHg, the Hb will be about 95% saturated with O2 as it leaves alveoli. |
| Describe the left shifts- unloading of oxygen in the lungs. | The plasma PO2 at the tissue sites must decrease more than normal in order for oxygen to dissociate from the hemoglobin. |
| What is the total amount of oxygen delivered or transported to the peripheral tissues dependent on? | 1. The body's ability to oxygenate blood 2. The hemoglobin concentration 3. The cardiac output |
| Total oxygen delivery (DO2) Formula: | DO2 = QT x (CaO2 x 10) (QT - total cardiac output, CaO2 - the oxygen content of arterial blood) |
| When does oxygen delivery decrease? | When there is a decrease in blood oxygenation, hemoglobin concentration, or cardiac output. |
| Arterial-Venous oxygen content difference Formula: | C(a-V)O2 = CaO2 - CvO2 (normal is about 5vol%) (CaO2 - the oxygen content of the arterial blood, CvO2 - the oxygen content of the mixed venous blood) |
| Clinically, the mixed venous blood needed to compute the CvO2 is obtained from the patient's what? | Pulmonary artery |
| What are the factors that increase the C(a-v)O2? | Decreased cardiac output, periods of oxygen consumption, exercise, seizures, shivering, hyperthermia |
| What are the factors that decrease the C(a-v)O2? | Increased cardiac output, skeletal muscle relaxation, peripheral shunting, certain poisons, hypothermia |
| What is the oxygen consumption (oxygen uptake)? | The amount of oxygen extracted by the peripheral tissues during the period of 1 minute. |
| Oxygen Consumption (oxygen uptake) Formula: | VO2 = QT [C(a-v)O2 x 10] (QT - total cardiac output, C(a-v)O2 - arterial-venous oxygen content difference) |
| What is the oxygen consumption usually related to? | The patient's body surface area (BSA) |
| What is the oxygen extraction ratio? | The amount of oxygen extracted by the peripheral tissues divided by the amount of oxygen delivered to the peripheral cells. |
| What are the two other names for the oxygen extraction ratio? | 1. oxygen coefficient ratio 2. oxygen utilization ratio |
| Oxygen extraction ratio formula: | O2ER = (CaO2 - CvO2) / CaO2 |
| What are the factors that increase VO2? | Exercise, seizures, shivering, hyperthermia |
| What are the factors that decrease VO2? | Skeletal muscle relaxation, peripheral shunting, certain poisons, hypothermia |
| Under normal circumstances, how much is an individual's Hb saturation after it returns to the alveoli? | 75% saturated with oxygen |
| What are the factors that increase the O2ER? | Decreased cardiac output, periods of increased oxygen consumption, exercise, seizures, shivering, hyperthermia, anemia, and decreased arterial oxygenation |
| Normally, the SvO2 is about how much? | 75% |
| What is the continuous monitoring of mixed venous oxygen saturation used for? | Detect changes in the patient's C(a-v)O2, Vo2, and O2ER |
| What are the factors that decrease the SvO2? | Decreased cardiac output, periods of increased oxygen consumption, exercise, seizures, shivering, hyperthermia |
| What are the factors that increase the SvO2? | increased cardiac output, skeletal muscle relaxation, peripheral shunting, certain poisons, hypothermia |
| What is 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. |
| What are the two pulmonary shunting groups? | 1. Absolute shunts (True shunts) 2. Relative shunts (shunt-like effect) |
| What are the two absolute shunts (true shunts) categories? | 1. Anatomic shunts 2. Capillary shunts |
| What is an anatomic shunt? | When blood flows from the right side of the heart to the left side without coming in contact with the alveolus for gas exchange. |
| What is the normal anatomic shunt? | 3% of cardiac output |
| What is the normal anatomic shunt caused by? | Non-oxygenated blood completely bypassing the alveoli and entering the pulmonary vascular system by means of the bronchial venous drainage and the left atrium by way of the thebesian veins. |
| What are the abnormalities that cause anatomic shunting? | 1. Congenital heart disease 2. Intrapulmonary fistula 3. Vascular lung tumors |
| Effects of congenital heart disease on anatomic shunting: | Certain congenital defects permit blood to flow directly from the right side of the heart to the left side without going through the alveolar capillary system for gas exchange. |
| What are two of the congenital heart defects? | 1. Ventricular septum defect 2. Newborns with persistent fetal circulation |
| Effects of intrapulmonary fistula on anatomic shunting: | A right-to-left flow of pulmonary blood does not pass through the alveolar-capillary system. (Caused by chest trauma or disease) |
| Effects of vascular lung tumors on anatomic shunting: | Some lung tumors permit pulmonary arterial blood to move through the tumor mass and into the pulmonary veins without passing through the alveolar-capillary system. |
| What is a capillary shunt commonly caused by? | 1. Alveolar collapse or atelectasis 2. Alveolar fluid accumulation 3. Alveolar consolidation |
| What is the sum of the anatomic shunt and capillary shunt referred to as? | Absolute, or true shunt. |
| How do patients respond with absolute shunting respond to oxygen therapy? | Poorly, since alveolar oxygen does not come into contact with the shunted blood. Absolute shunting is REFRACTORY to oxygen therapy. |
| What does refractory (doesn't respond to oxygen therapy) to oxygen therapy mean? | The reduced arterial oxygen level produced by this form of pulmonary shunting cannot be treated simply by increasing the concentration of inspired oxygen. |
| What are the two reasons why absolute shunting is refractory? | 1. The alveoli are unable to accommodate any form of ventilation 2. The blood that bypasses functional alveoli cannot carry more oxygen once it has become fully saturated (except for small amount in plasma) |
| When pulmonary capillary perfusion is in excess of alveolar ventilation, what exists? | A relative shunt, or shunt-like effect |
| What are the common causes of relative shunting? | 1. Hypoventilation 2. Ventilation/perfusion mismatches 3. Alveolar-capillary diffusion defects |
| When else can a relative shunting occur? | 1. Following the administration of drugs that cause an increase in cardiac output or dilation of the pulmonary vessels. |
| Are relative shunts responsive to oxygen therapy? | Yes, they are not refractory to oxygen therapy. |
| What is a venous admixture? | The end result of pulmonary shunting; the mixing of shunted, non-reoxygenated blood with reoxygenated blood distal to the alveoli. |
| What happens when the venous admixture occurs? | The shunted, non-reoxygenated blood gains oxygen molecules while, at the same time, the reoxygenated blood loses oxygen molecules. |
| The venous admixture process continues until what? | 1. The PO2 throughout all of the plasma of the newly mixed blood is in equilibrium 2. All of the Hb molecules carry the same number of oxygen molecules. |
| What is the end result of a venous admixture? | A blood mixture that has a higher PO2 and oxygen content than the original shunted, non-reoxygenated blood, but a lower PO2 and oxygen content than the original reoxygenated blood. |
| What is the final outcome of venous admixture? | A reduced PaO2 and CaO2 returning to the left side of the heart. |
| Clinically, the venous admixture is what? | It is this oxygen mixture that is evaluated downstream to determine an individual's arterial blood. |
| What is the classic shunt equation and what is it used to calculate? | Qs/Qt = (CcO2 - CaO2)/(CcO2 - CvO2); The amount of intrapulmonary shunting. |
| What is the clinical significance of pulmonary shunting? | <10% - normal lung status; 10-20% - intrapulmonary abnormality; 20-30% - significant intrapulmonary disease and may be life-threatening in patients w/ limited cardiovascular function; >30% - life-threatening |
| What kind of patient's make calculating the degree of pulmonary shunting not reliable? | Patients who demonstrate: 1. a questionable perfusion status 2. a decreased myocardial output 3. an unstable oxygen consumption demand |
| What is HYPOXEMIA? | It refers to an abnormally low arterial oxygen tension. |
| What is the hypoxemia classifications? | Normal: 80-100 Mild hypoxemia (stimulates the oxygen peripheral chemoreceptors to increase the patients RR and HR): 60-80 Moderate hypoxemia: 40-60 Severe hypoxemia: <40 |
| What is HYPOXIA? | Low or inadequate oxygen for cellular metabolism (inadequate level of tissue oxygenation) |
| What is hypoxia characterized by? | Tachycardia, hypertension,peripheral vasoconstriction, dizziness, and mental confusion |
| What are the four main types of hypoxia? | 1. Hypoxic (Hypoxemic hypoxia) 2. Anemic hypoxia 3. Circulatory hypoxia (Stagnant hypoxia) 4. Histotoxic hypoxia |
| What is hypoxic hypoxia? | Refers to the condition in which there is inadequate oxygen at the tissue cells caused by low arterial oxygen tension (PaO2). |
| What are causes of hypoxic hypoxia? | 1. low alveolar oxygen tension (PAO2) 2. diffusion defects 3. ventilation-perfusion mismatches 4. pulmonary shunting 5. high altitudes |
| What are conditions that cause hypoventilation? | COPD, central nervous system depressants, head trauma, neuromuscular disorders |
| What are diffusion defects? | Abnormal anatomic alterations of the lungs that result in an impedance of oxygen transfer across the alveolar-capillary membrane. |
| What is anemic hypoxia? | The oxygen tension in the arterial blood is normal but the oxygen-carrying capacity of the blood is inadequate. |
| What are causes of anemic hypoxia? | low amount of hemoglobin in the blood; a deficiency in the ability of hemoglobin to carry oxygen. |
| What is the main compensatory mechanism for anemic hypoxia? | increased cardiac output |
| What is circulatory (stagnant) hypoxia? | the arterial blood that reaches the tissue cells may have a normal oxygen tension and content, but the amount of blood - and therefore, the amount of O2 - is not adequate to meet tissue needs. |
| What are the two main causes of circulatory hypoxia? | 1. slow or stagnant peripheral blood flow 2. arterial-venous shunting |
| What is an arterial-venous shunt? | When arterial blood completely bypasses the tissue cells and moves into the venous system. |
| What is histotoxic hypoxia? | It develops in any condition that impairs the ability of tissue cells to utilize oxygen. |
| What are the causes of histotoxic hypoxia? | cyanide poisoning and alcohol poisoning |
| What is cyanosis? | The term used to describe the blue-gray or purplish discoloration seen on the mucous membranes, fingertips, and toes whenever the blood in these areas contains at least 5g% of reduced Hb per dL. |
| What does the hormone erythropoietin do? | Responds by stimulating the bone marrow to increase RBC production. |
| What is the RBC production known as? | Erythropoiesis |
| What is polycethemia? | An increased level of RBCs. |
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