Oxygen Transport Flashcards
Abbreviations used in Oxygen Transport Pt 1
PA02= Alveolar Oxygen Partial Pressure
PB= Barometric Pressure (elevation from seal level)
(Obtained using a Barometric Pressure Gauge)
PH20= Water vapor (always 47)
FI02= Fraction of Inspired Oxygen (amount of Oxygen patient is receiving)
PaC02= Partial Pressure of carbon dioxide in blood. (taken from arterial blood gas)
Pa02= Partial Pressure of Oxygen in the arterial Blood (taken from arterial blood gas)
Ca02= Total Oxygen Content in Blood
Abbreviations used in Oxygen Transport Pt 2
Hb= Hemoglobin (Taken from CBC or Complete blood count)
Sa02= Hemoglobin saturation in arterial blood. (taken from arterial blood gas)
Cvo2= Total Oxygen Content in Venous Blood (must have a Swanz Ganz Catheter inserted).
Svo2= Mixed Venous Hemoglobin Oxygen saturation (must have a Swanz Ganz Catheter inserted).
Pvo2= Partial pressure of Oxygen in Venous blood. (must have a Swanz Ganz Catheter inserted).
Arterial Blood Gas
• Once drawn and ran through a machine you get the flowing results.
• PH
• PaCO2
• Pa02
• Нс03
• ВЕ
• Sa02
Complete Blood Count
• Routine blood draw taken from a patients vein. It provides a wealth of information for electorlytes, RBC, WBC, Platelet count, etc.
However, we only use the values for Hemoglobin. Normal values for Men is 14 to 16. For Women is 12 to 15.
Swanz Ganz Catheter
• Use inserted in the Subclavian vein, Femoral or Brachial arteries. The Catheter is long and the tip end typically is advanced through the right atrium, right ventricle, and ends up in the Pulmonary arterial. It’s vital when calculating a shunt. Without the values it provided a shunt can’t and wont be calculated.
alveolar oxygen tension (PA02)
• Clinically, the alveolar oxygen tension (PA02)
• Ventilation merely moves gas into and out of the lungs.
• The process that moves gas across the A-C membrane is passive diffusion.
• Diffusion is The movement of gas molecules from an area of high concentration to an area of low concentration
Barometric pressure
• Barometric pressure is the sum of all gases
• exerting pressure on the earths surface.
At sea level Atmospheric pressure is 760 mmHg.
• The primary components of this pressure is nitrogen, oxygen, argon and carbon dioxide
Dilusion of Oxygen in the Alveoli
• The partial pressure of 02 is significantly lower in the alveoli than in the atmosphere.
• If you imagine the alveoli as a micro-environment the CO2 level and water vapor content are much higher.
• By the time the atmospheric gas reaches the alveoli they are diluted by CO2 and H20
Water Vapor Ph20
• When water vapor is present in a volume of gas it exerts its own partial pressure in accordance with Daltons Law
• Alveolar gas is 100% humidified at body temp.
• It is assumed to have an absolute humidity of 44mg/l and a partial pressure of (PH20) of 47
mmHg
the alveolar gas equation
• Thus, alveolar oxygen (PAO2) is calculated using the “ideal alveolar gas equation” or “ the alveolar gas equation”
PA02=[PB-PH20]F102-Paco2(1.25)
This equation computes the total PA02
available for oxygen transfer
A and A gradient Pt1
• The Alveolar-arterial gradient (A-a gradient), is a measure of the difference between the alveolar concentration of oxygen and the arterial concentration of oxygen. It is used in diagnosing the source of hypoxemia. [1]
• A-a gradient = PAO2 - Pa02
• Where:
• PAO2 = alveolar PO2 (calculated from the alveolar gas equation)
• Pa02 = arterial PO2 (measured in arterial blood A-a gradient)
A and A gradient Pt 2
• The A-a gradient is useful in determining the source of hypoxemia. The measurement helps isolate the location of the problem as either intrapulmonary (within the lungs) or extrapulmonary (somewhere else in the body). [2]
A and A gradient (3)
• A normal A-a gradient is less than 10 mmHg, but can range from 5-20 mmHg. Normally, the
A-a gradient increases with age. For every decade a person has lived, their A-a gradient is expected to increase by 1 mmHg. An abnormally increased A-a gradient suggests a defect in diffusion, V/Q (ventilation/perfusion ratio) defect, or right-to-left shunt. [3]
Oxygen Transport
• The transport of oxygen between the lungs and the cells of the body is a function of the blood and the heart.
• Oxygen is carried in the blood in two forms:
- as dissolved oxygen in the blood plasma
- chemically bound to the hemoglobin (Hb) that is encased in the erythrocytes, or RBC’s
02 Dissolved in Plasma
• As 02 diffuses from the alveoli into the pulmonary capillary blood, it dissolves in the plasma of the blood.
• At normal body and temperature about 0.003 ml of 02 will dissolve in 100 ml of blood for every I mm Hg of Poz
• Vol% represents the amount of 02 in milliliters that is in 100 ml of blood.
• In terms of total oxygen transport, a relatively small percentage of 02 is transported in the form of dissolved 02.
Dissolved Oxygen
• Henry’s Law states that the amount of gas that dissolves is proportional to its partial pressure.
• Dissolved Oxygen=.003 mls x PA02.003 x
100=.3mls of dissolved 02
Oxygen Bound to Hemoglobin
• Most of the 02 that diffuses into the pulmonary capillary blood rapidly moves into the RBC’s and chemically attaches to the hemoglobin.
Each RBC contains about 280 million Hb molecules, which are highly specialized to transport 02 and CO2.
• The normal hemoglobin value for the adult male is 14 to 16 g% and female is 12 to 15 g%.
• Normal adult hemoglobin consists of:
-four hemo groups which are the pigmented, iron-containing non-protein portions
-four amino chains that collectively constitute globin (a protein)
form oxyhemoglobin:
- Hb + 02 = Hb02
• The amount of 02 bound to Hb is directly related to the partial pressure of 02.
• The globin, or protein portion of each adult Hb molecule consists of two identical alpha chains and two identical beta chains.
• Normal fetal Hb
• Normal fetal Hb (Hb F) has two alpha chains and two gamma chains.
• These gamma chains increase hemoglobin’s attraction to 02 and facilitates transfer of maternal 02 across the placenta.
• Fetal Hb is gradually replaced with adult Hb (Hb A) over the first year of postnatal life
Quantity of 02 Bound to Hb
• Each g% of Hb is capable of carrying approximately 1.34 ml of 02 thus: 02 bound
to Hb = 1.34 ml 02 x g% Hb
• At a normal Pao2 of 100 MM Hg, hemoglobin saturation (Sao2) is about 97% because of normal physiologic shunts:
-thebesian veins (Coronary circ.)
-bronchial venous drainage
-V/Q mismatch
• The total oxygen content of specific blood is calculated as
• To determine the total amount of 02 in 100 ml of blood, the dissolved 02 and the 02 bound to Hb must be added together.
• The total oxygen content of specific blood is calculated as follows:
Cao2: (Hb x 1.34 x Sao2) + (Pao2 x 0.003)
CVO2 calculation
Co2: (Hb x 1.34 x Svo2) + (Po2 × 0.003)
Cv2 is the total oxygen content of Oxygen in the venous system.
SVO2
• measurement of oxygenation saturation from mixed venous blood in the pulmonary artery
• requires Pulmonary Artery Catheter insertion in most clinical settings
• DESCRIPTION
• measures the end result of 02 consumption and delivery
METHOD OF INSERTION AND/OR USE
02 flux = (cardiac output x (Haemoglobin concentration x Sp02 × 1.34) + (Pa02 × 0.003)) - oxygen consumption
• Sv2 = mixed venous oxygen saturation
• measured via a sample of blood from a pulmonary artery catheter (PAC)
• measures the end result of 02 consumption and delivery
• is used in ICU as a measure of 02 extraction by the capillaries
• normal Sv02 = 65-70%
• PVO2
• Normal mixed venous oxygen tension (PvO,) is approximately 40 mmHg, representing the balance between oxygen consumption and oxygen delivery. A true PvO, measurement must come from a mixed venous blood sample containing venous drainage from the SVC, IVC, and the heart.
• C(a-v)02
• The arteriovenous oxygen difference, or a-vO, diff, is the difference in the oxygen content of
the blood between the arterial blood and the venous blood. It is an indication of how much oxygen is removed from the blood in capillaries as the blood circulates in the body. The a-vo, diff and cardiac output are the main factors that allow variation in the body’s total oxygen consumption, and are important in
usually measured in milires of otogen per 100, dit is
millilitres of blood (mL/100 mL)
The Shunt Equation
• Pulmonary shunting and venous admixture are common complications in respiratory disorders, knowledge of the degree of shunting is often desirable when developing patient care plans.
• The amount of intrapulmonary shunting can be calculated by using the classic shunt equation:
• QS/QT = (A-aD02) .003
————————————
(A-aD02) .003 + C(a-v)02
How much more affinity does HB have for CO2 over O2
210 more times
Mechanics of Pulmonary Shunting
• Pulmonary shunting is defined as that portion of the cardiac output that enters the left side of the heart without exchanging gases with alveolar gases (true shunt) or as blood that does exchange gases with alveolar gases but does not obtain a PO2 that equals that of normal alveolus (shunt-like effect).
• Regardless of the type of shunt the physiologic effect is the same, hypoxemia.
Absolute Shunt also called True Shunt
(anatomic Shunt)
• Common Causes of Absolute Shunting
• Congenital heart disease
• Intrapulmonary fistula
• Vascular lung tumors
• Capillary shunting is commonly caused by:
• Alveolar collapse or atelectasis
• Alveolar fluid accumulation
• Alveolar consolidation
• Key Concept: True shunts are refractory to supplemental oxygen. Refractory means that it does not respond to increased oxygen delivery.
Relative Shunt, also called shunt-like effects
• When pulmonary capillary perfusion is in excess of alveolar ventilation, a shunt-like effect is said to exist.
• Common Causes of Relative Shunt
• When pulmonary capillary perfusion is in excess of alveolar ventilation, a relative or shunt-like effect is said to exist
• Hypoventilation
• Ventilation/perfusion mismatches
• Chronic emphysema, bronchitis, asthma
• Alveolar-capillary diffusion defects
• Alveolar fibrosis or alveolar edema
• Key Concept: Relative or Shunt-Like effects can be corrected by supplemental oxygen
Venous Admixture
• The end result of pulmonary shunting is venous admixture.
• Venous admixture is the mixing of shunted, non-reoxygenated blood with reoxygenated blood distal to the alveoli.
• When venous admixture occurs, shunted and oxygenated blood mixes until the PO2 throughout all plasma of the newly mixed blood is in equilibrium and all the Hb molecules carry the same number of oxygen molecules.
Clinical Significance of Shunts
• Pulmonary shunting below 10% reflects normal lung status.
• A shunt between 10 and 20% is indicative of an intrapulmonary abnormality, but is seldom of clinical significance.
• Pulmonary shunting between 20 and 30% denotes significant intrapulmonary disease and may be life-threatening.
• Pulmonary shunting greater than 30% is a potentially life-threatening situation and aggressive support is needed.
Tissue Hpoxia
• Tissue hypoxia means that the amount of oxygen available for cellular metabolism is inadequate.
• There are four main types of hypoxia:
• hypoxic hypoxia
- circulatory hypoxia
• anemic hypoxia
- histotoxic hypoxia
• Hypoxia leads to anaerobic mechanisms that eventually produces lactic acid and cause the blood pH to decrease.
Hypoxic hypoxia
• Hypoxic hypoxia or hypoxemic hypoxia refers to the condition in which the Pa02 and Ca02 are abnormally low.
• This form of hypoxia is better known as hypoxemia (low oxygen concentration in the blood).
• This form of hypoxia can develop from:
• pulmonary shunting
- low alveolar PO2
• diffusion impairment
- V/Q mismatch
Anemic Hypoxia
• Anemic hypoxia is when the oxygen tension in the arterial blood is normal, but the oxygen-carrying capacity of the blood is inadequate.
• This form of hypoxia can develop from:
• a low amount of Hb in the blood
• a deficiency in the ability of Hb to carry 02
• Increased cardiac output is the main compensatory mechanism for anemic hypoxia.
Circulatory Hypoxia
• In circulatory hypoxia, the arterial blood that reaches the tissue cells may have a normal 02 tension and content, but the amount of of blood–and therefore the amount of 02–is not adequate to meet tissue needs.
• The two main causes of circulating hypoxia are:
• stagnant hypoxia
• arterial-venous shunting
Histotoxic Hypoxia
• Histotoxic hypoxia develops in any condition that impairs the ability of tissue cells to utilize oxygen.
• Clinically, the Pa02 and CaO2 in the blood are normal, but the tissue cells are extremely hypoxic.
• The PvO2, CvO2 and SvO2 are elevated because oxygen is not utilized.
• One cause of this type of hypoxia is cyanide poisoning.
