2250 Oxygenation Assessments
Alveolar-Arterial Oxygen Tension Difference P(A-a)O2 helps determine diffusion disorders. True False
True
What is hypoxia?What are the main types of hypoxia?
-*Hypoxia refers to low or inadequate oxygen for aerobic cellular metabolism -There are four main types of hypoxia: --Hypoxic (hypoxemic) --Anemic --Circulatory --Histotoxic
Normal Oxygen Consumption (VO2) is? --250 ml/min --75% --dependent on FiO2 --greater than oxygen delivery
--250 ml/min
What is the normal degree of pulmonary shunting? --50% --3-5% --15% --20%
--3-5%
The PaO2/FIO2 Ratio of a patient is less than 200, this signifies? --Normal range --hyperventilation --Adult Respiratory Distress Syndrome --Acute Lung Injury
--Adult Respiratory Distress Syndrome
Cor Pulmonale leads to an accumulation of venous blood in the large veins, it is this severe pulmonary vasoconstriction that can cause :
--Distended neck veins --Peripheral edema and pitting edema --Enlarged and tender liver (Blood is backing up, you have extra blood in venous system ==> superior/inferior vena cava that backs up)
Why is PaO2 (the dissolved O2 in blood plasma) used in hospital settings to identify our oxygenation status?
--How much is dissolved is directly reflective of how much is bound to hemoglobin --It is pretty accurate in reflecting the O2 --As the oxyhemoglobin dissociation curve shows, hemoglobin can be misleading
Hypoxic vasoconstriction of the pulmonary vascular system commonly develops in response to decreased? --PaCO2 --CvO2 --PAO2 --Hb
--PAO2
What is a normal SvO2? --75% --97% --80-100 mm Hg --45 mmHg
75%
What is PaO2/PAO2? What are normal ranges?
-Percentage of alveolar O2 that moves into the arterial blood. -Normally 0.75 to 0.95 --Critical < 0.75
What does 10 Vol% of O2 means?
10 Vol% of O2 means that there are 10 mL of O2 in 100 mL of blood
What are normal male/female adult Hb values/concentrations? How is Hb expressed as?
Acceptable range for hemoglobin =12-16 gm/dL (LJ) -Normal adult male Hb value: -- 14-16 g/100 mL (g%) -Normal adult female Hb value: -- 12-15 g/100 mL (g%) -Clinically, the weight measurement of hemoglobin, in reference to 100 mL of blood, is referred to as either: Gram percent of hemoglobin (g% Hb), orGrams per deciliter (g/dL)
How is Total Oxygen Content of Arterial Blood calculated?
- CaO2 = oxygen content of arterial blood (Hb x 1.34 x SaO2) + (PaO2 x .003) -Acceptable range 17-20 vol% --CaO2 has the best relationship to tissues oxygenation
What is the Mixed Venous Oxygen Saturation Svo2? What are the early indicators?
- Percentage of oxygen bound to hemoglobin in mixed venous blood (pulmonary artery) -Normally the SvO2 is approximately 75% --the tissues take up 25% so you are left with 75% saturation -The SvO2 can be measured directly by obtaining a venous blood sample from a pulmonary arterial catheter. -Early indicators, changes in the SvO2 can be used to detect changes in the: --C(a-v)o2 --VO2 --O2ER
What is total oxygen delivery DO2? What is it dependent on? What is normal oxygen delivery?
- Total amount of oxygen delivered or transported to peripheral tissues-Dependent on: --Body's ability to oxygenate blood (diffusion) --Hemoglobin concentration (content) --Cardiac output -Total oxygen delivery (D O2) calculated as follows: DO2= QT x (CaO2 x 10) -Normal DO2 is about 1000 mL/min
Which of the following are true about polycythemia? (Choose all that apply) --caused by the lack of Na+ in the diet --a condition of too many red blood cells --a condition to too few red blood cells --the body's response to chronic hypoxia
--a condition of too many red blood cells --the body's response to chronic hypoxia
Oxygen is carried in which of the following ways in the blood? (choose all that apply) --bound to hemoglobin --dissolved in blood plasma --bound to NA+ --attached to WBC's
--bound to hemoglobin --dissolved in blood plasma
The three major causes of cor pulmonale include all of the following except? --decreased vascular resistance --increased vascular resistance --damage/obliteration of the pulmonary bed --increased blood viscosity (polycythemia)
--decreased vascular resistance
The C(a-v)O2 content difference directly measures? --the patient's right - to - left intracardiac shunting --how much oxygen is being used by the tissues --how much oxygen is bound to hemoglobin --how much oxygen is dissolved in blood plasma
--how much oxygen is being used by the tissues
The PaO2 may be misleading in all of the following situations EXCEPT? --increased cardiac output --CO poisoning --low Hb --pulmonary shunting
--increased cardiac output
All of the following can be caused by severe pulmonary vasoconstriction EXCEPT? --mitral valve stenosis --peripheral edema --distended neck veins --cor pulmonale
--mitral valve stenosis
When a sample of arterial blood is analyzed for the pressure of oxygen (PaO2), the value comes from the? --hemoglobin --plasma --pulmonary artery --WBC
--plasma (it is the dissolved O2 in blood plasma)
*What is hypoxemia?
-Abnormally low arterial oxygen tension (PaO2) -Frequently associated with hypoxia --Which is an inadequate level of tissue oxygenation (hypoxia can be caused by other conditions also).
What is oxygen consumption VO2? If normally an individual has a cardiac output of 5 L/min and a C(a-v)O2 of 5 vol% whats the normal oxygen consumption?
-Amount of oxygen extracted by the peripheral tissues during the period of ONE MINUTE -Also called oxygen uptake (VO2) -Calculated as follows: VO2= QT (C(a-v)O2 x 10)5 L/min x 5 vol% x 10=250 mL O2/min --Total amount of oxygen metabolized by the tissue cells in one minute will be *250* mL (normal)
Total oxygen content can be calculated for the following:
-Arterial Oxygen Content (CaO2) [normal 17-20 vol%] -Mixed Venous Oxygen Content (CvO2) [normal 14-16 vol%] -Oxygen Content of Pulmonary Capillary Blood (CcO2)
What are the Oxygen Tension-Based Indices?
-Arterial oxygen tension (PaO2) -Alveolar-arterial oxygen tension difference (P[A-a]O2) -Ideal alveolar gas equation (PAO2) -arterial-Alveolar pressure ratio (PaO2 / PAO2 ratio) -Arterial oxygen tension to fractional concentration of oxygen ratio (PaO2 /FIO2 ratio)
How saturated is Hb at a normal PaO2 of 100 mm Hg? Why is this so?
-At a normal PaO2 of 100 mm Hg the Hb saturation (SaO2) is 97% due to the following three normal physiologic shunts:--Thebesian venous drainage into the left atrium--Bronchial venous drainage into pulmonary veins--Alveoli that are under ventilated relative to pulmonary blood flow
What is cyanosis?
-Blue-gray or purplish discoloration seen on the mucous membranes, fingertips, and toes --Severe hypoxemia --Blood in these areas contain at least 5 g% of reduced hemoglobin per dL (100mL)
What are the Oxygen Saturation- and Content-Based Indices?
-CaO2 = (Hb × 1.34 × SaO2) + (PaO2 × 0.003) -CvO2 = (Hb × 1.34 × SvO2) + (PvO2 × 0.003) -CcO2 = (Hb × 1.34) + (PAO2 × 0.003) -Total oxygen delivery (Do2) --Amount of O2 delivered to peripheral cells --Normal = 1000mL/min -Arterial-venous oxygen content difference (C[a-v])O2 --Good early indication of oxygenation issues --Normal is 5 vol% -Oxygen consumption (Vo2) --Amount of O2 consumed by the peripheral tissues 250mL/min -Oxygen extraction ratio (O2ER) --Amount of O2 consumed by tissue cells divided by total amount delivered --Normal is 25% -Mixed venous oxygen saturation (Svo2) --Normal is 75% -Pulmonary shunting (QS/Qt) --Normal is 3-5%
How is Total Oxygen Content of Pulmonary Capillary Blood calculated?
-CcO2 = oxygen content of pulmonary capillary blood (Hb x 1.34) + (PAO2 x .003)
How is Total Oxygen Content of Mixed Venous Blood calculated? What can affect the CvO2? Where is the best place to obtain a CvO2?
-CvO2 = oxygen content of mixed venous blood (Hb x 1.34 x SvO2) + (PvO x .003) -Acceptable range 14-16 vol% -Decreasing values relate to decreasing cardiac output -Best place to obtain mixed venous blood is from the pulmonary artery
Case study Automobile Accident Victim A 22-year-old man is on a volume-cycled mechanical ventilator on a day when the barometric pressure is 755 mm Hg. The patient is receiving an FIO2 of 0.60. -Hb: 15 g/dL -Pao2 : 65 mm Hg (Sao2 = 90%) -Paco2: 56 mm Hg -Pvo2 : 35 mm Hg (Svo2 = 65%) Calculate the following: PAO2 CaO2 CvO2 CcO2 Shunt %
-PAO2= (755-47).60 - 56 x 1.25 424.8 - 70 PAO2 = 354.8 -CaO2= (15 x 1.34).90 + (65 x 0.003) 18.09 + 0.195 CaO2= 18.29 -CvO2= (15 x 1.34).65 + (35 x 0.003) 13.07 + 0.105 CvO2= 13.18 -CcO2= (15 x 1.34) + (354.8 x 0.003) 20.1 + 1.06 CcO2= 21.16 -Qs/QT= CcO2 - CaO / CcO2-CvO2 21.16 - 18.29 / 21.16 - 13.18 = 2.87 / 7.98 = .3596 QS/QT = 36%
What does it mean when oxygen is dissolved in the blood plasma?How much O2 is dissolved in blood plasma? How is this expressed?
-Dissolve means that the gas maintains its precise molecular structure -At normal body temperature, about .003 mL of O2 will dissolve in 100 mL of blood for every 1 mm Hg of PO2 (partial pressure of oxygen). --Relatively small percentage of oxygen is transported in the form of dissolved oxygen. Ex. if PaO2 of 100 100 mm Hg x .003= .3 mL of O2 dissolves in 100 mL of blood OR .3 volumes percent (vol%) --Vol% represents amount of O2 (in mL) in 100 mL of blood --Vol% = mL O2/100 mL bd
Oxygen is carried from the lungs to the tissues in 2 forms:
-Dissolved in blood plasma (.003 mL of O2 dissolves in 100 mL of blood for every 1 mm Hg) --referred to as our PaO2 -Chemically bound to hemoglobin (Hb) --Most oxygen is carried to the tissue cell bound to the hemoglobin.
How much can each Hb carry?
-Each g% Hb can carry 1.34 mL of oxygen (what it CAN carry if fully saturated) Thus if the Hb level is 12 g% and if the Hb is fully saturated with oxygen, about 16.08 vol% of O2 will be bound to the Hb: O2 bound to Hb = 1.34 mL O2 × 12 g% Hb = 16.08 vol% O2 At a normal PaO2 of 100 mm Hg, however, the Hb saturation (SaO2) is only about 97% because of these normal physiologic shunts: --Thebesian venous drainage into the left atrium --Bronchial venous drainage into the pulmonary veins Thus the amount of arterial oxygen in the calculation must be adjusted to 97%: 16.08 vol% O2 × 0.97 = 15.60 vol% O2
What factors increase the C(a-v)O2? What factors decrease the C(a-v)O2?
-Factors that increase the C(a-v)O2 "tissues use more": -Decreased cardiac output -Periods of increased oxygen consumption --Exercise --Seizures --Shivering --Hyperthermia -Factors that decrease the C(a-v)O2 "tissues use less" : -Increased cardiac output -Skeletal relaxation (Induced by drugs) -Peripheral shunting (Sepsis, trauma) -Hypothermia -Certain poisons (cyanide) (arterial-venous oxygen content different)
What is the Arterial Oxygen Tension (Pao2)? When can PaO2 be misleading?
-Good indicator of the patient's oxygenation status, pressure of oxygen from the arterial blood plasma -The PaO2, however, may be misleading in these clinical situations: --Low Hb --Decreased cardiac output --Peripheral shunting --Carbon monoxide exposure
What occurs when there is a shift to the left at the lung level and tissue?
-Hemoglobin has a higher affinity for O2 "fun bus" -At lung level --Easier to load --takes a lower PaO2 than normal to get the same saturation -At tissue level --Harder to unload, O2 doesnt want to unbind --takes more of a PaO2 drop to unload O2 from hemoglobin
What occurs when there is a shift to the right at the lung level and tissue?
-Hemoglobin has a lower affinity for O2 -At lung level --Harder to load --takes higher PaO2 than normal to get the same saturation, you need higher pressure to make O2 want to load --O2 still goes in blood but doesn't want to load as much -At tissue level --Easier to unload, O2 didn't want to load in the first place so they unload faster --takes less of a PaO2 drop to unload O2 from hemoglobin(if an issue/condition is added to a right shift it really affects content and ability to load)
If you had 15 g% of Hb how much O2 would you have?
-If Hb level is 15 g%, and if Hb is fully saturated, about 20.1 vol% of O2 will be bound to the Hb O2 bound to Hb= 1.34 mL O2 x 15 g% Hb = 20.1 vol% O2
What does an increased P(A-a)o2 indicate?
-Increased indicates --Oxygen diffusion disorders --V/Q ratio mismatching --Right-to-left shunting --Age
What is the most common cause of hypoxic vasoconstriction of the pulmonary vascular system?
-Low PAO2
What are the different classifications of hypoxemia and their PaO2 levels?
-Normal 80-100 mm Hg -Mild Hypoxemia 60-80 mm Hg -Moderate hypoxemia 40-60 mm Hg -Severe hypoxemia <40 mm Hg
What is normal pulmonary shunting level? What occurs as pulmonary shunting increases?
-Normal Pulmonary shunt level is 3-5% - <10 percent --Normal status -10 to 20 percent --Indicates intrapulmonary abnormality but is not significant in terms of cardiopulmonary support -20 to 30 percent --Significant intrapulmonary diseases, may be life threatening. Possibly requiring cardiopulmonary support - > 30 percent --Serious life-threatening condition, almost always requiring cardiopulmonary support
What is the Oxygen Extraction Ratio (O2ER)?
-Oxygen extraction ratio (O2ER) is the amount of oxygen extracted by the peripheral tissues divided by the amount of oxygen delivered to the peripheral cells -Also called: --Oxygen coefficient ratio --Oxygen utilization ratio -Normally CaO2 of 20 vol% and CvO2 of 15 vol% -- O2ER= CaO2-CvO2 / CaO2= 20 vol% - 15 vol% / 20 vol%= 5 vol% / 20 vol%= .25O2ER is about 25%(if tissues take up 5 of the 20 than that is 25%)
What is Cor Pulmonale and what does it denote?
-Right-sided heart failure arising from chronic lung disease -The term used to denote: --Pulmonary arterial hypertension --Right hypertrophy --Increased right ventricular work --Right ventricular failure
What is arterial-venous oxygen content difference?
-The C(a-v)O2 is the difference between the O2 content in the arteries (CaO2) and the O2 content in the veins (CvO2) -Acceptable value 4-5 vol% - *Directly measures how much oxygen is being used by the tissues* C(a-v)O2 = CaO2 - CvO2
What is the Alveolar-Arterial Oxygen Tension Difference (P[A-a]o2)? How is it calculated? What are normal values?
-The P(A-a)o2 is the oxygen tension difference between the alveoli and arterial blood. -To calculate this, first we must find the PAO2 using the alveolar air equation: PAO2 = (PB − PH2O)FiO2 − PaCO2/RQ PAO2= (PB- PH2O)FIO2 - PaCO2 (1.25) -The normal P(A-a)o2 on room air ranges from 7 to 15 mm Hg and should not exceed 30 mm Hg. -On 100% normal range is 25-65 mm Hg (>350 is critical) --*The P(A-a)o2 loses sensitivity in patients breathing high FIO2
What is the Arterial Oxygen Tension to Fractional Concentration of Oxygen Ratio (PaO2/FIO2 Ratio)? What are normal ranges and what does it tell us?
-The PaO2/FIO2 Ratio (also called oxygenation ratio) is useful in determining the extent of lung diffusion defects (acute respiratory distress syndrome) --at a certain FiO2 you should have a certain PaO2 -Normal is 380 or greater (LJ pg.10) --300 or less signifies Acute Lung Injury (ALI) --200 or less signifies Adult Respiratory Distress Syndrome (ARDS), inability of oxygenate
What are the three major causes of Cor Pulmonale?
-Three major causes: -Increased viscosity of blood (polycythemia) --Increased red blood cell level --Chronic hypoxia leads to renal cells increasing release of erythropoietin which stimulates bone marrow to increase RBC production. --An adaptive mechanism to increase the O2 carrying capacity of the blood. -Increased vascular resistance --Hypoxic vasoconstriction commonly develops in response to the decreased PAO2 that occurs in chronic respiratory disorders. --Causes smooth muscle of pulmonary arterioles to constrict. -Obliteration of the pulmonary capillary bed --Primarily in emphysema
What is oxygen content? How is it calculated?
-the total amount of oxygen in 100 mL of blood -It is calculated by combining the dissolved oxygen and the oxygen bound to hemoglobin
Case study If a patient is receiving an FIO2 of 0.30 on a day when the barometric pressure is 750 mm Hg, and if the patient's PaCO2 is 70 mm Hg and PaO2 is 60 mm Hg The P(A-a)O2 can be calculated as follows:
1. PAO2 = (PB − PH2O) FIO2 − PaCO2/RQ = (750 − 47) 0.30 − 70 x 1.25 = (703) 0.30 − 87.5 = (210.9) − 87.5 = 123.4 mm Hg 2. Using the calculated PAO2 and the PaO2 obtained from the ABG: 123.4 (PAO2) − 60.0 (PaO2) = 63.4 mm Hg [P(A-a)O2]
Case Study -27-year-old woman --Long history of anemia (decreased hemoglobin concentration) --Showing signs of respiratory distress --Respiratory rate 36 breaths/min --Heart rate 130 beats/min --Blood pressure 155/90 mm Hg --Hemoglobin concentration is 6 g% --PaO2 is 80 mm Hg --SaO2 90% -Based on these data, the patient's total oxygen content is determined as follows:
1. Dissolved O2 -- 80 PaO2 x .003 (dissolved O2 factor) =.24 vol% O2 2. Oxygen bound to hemoglobin -- 6 g% Hb x 1.34 (O2 bound to Hb factor) =8.04 vol% O2 (at SaO2 of 100%) Above answer is then followed by the SaO2 factor: -- 8.04 vol% O2 x .90 SaO2 =7.24 vol% O2 3. Total arterial oxygen content -- 7.24 vol% O2 (bound to hemoglobin) + .24 vol% O2 (dissolved O2) =7.48 vol% O2 (total amount of O2/100 mL of blood) -Patient's total arterial oxygen content is less than 50 percent of normal (normal is 17-20 vol%) --Her hemoglobin concentration, which is the primary mechanism for transporting oxygen, is very low (normal is 12-15) --Once problem is corrected, respiratory distress should no longer be present
Case Study A 44-year-old woman with a long history of asthma arrives in the emergency room in severe respiratory distress. Her vital signs are respiratory rate 36 breaths/min, heart rate 130 bpm, and blood pressure 160/95 mm Hg. Her hemoglobin concentration is 10 g%, and her PaO2 is 55 mm Hg (SaO2 85%). -Based on these data, the patient's total oxygen content is determined as follows:
1. Dissolved O2 55 PaO2 × 0.003 (dissolved O2 factor) = 0.165 vol% O2 2. Oxygen Bound to Hemoglobin 10 g% Hb × 1.34 (O2 bound to Hb factor) = 13.4 vol% O2 (at SaO2 of 100%) Above answer is then followed by the SaO2 factor: 13.4 vol% O2 × 0.85 SaO2 = 11.39 vol% O2 (at SaO2 of 85%) 3. Total Oxygen Content 11.39 vol% O2 (bound to hemoglobin) +0.165 vol% O2 (dissolved O2) = 11.55 vol% O2 (total O2/100 mL of blood)
If normally CaO2 is approximately 20 vol% and CvO2 is 15 vol% what is normal arterial-venous oxygen content difference?
C(a-v)O2 = CaO2 - CvO2 = 20 vol% - 15 vol% = 5 vol%
Hypoxia refers to abnormally low arterial oxygen tension? True False
False
What is the pulmonary shunt equation? Normal values? What information is needed and what is its role?
Qs/QT= CcO2 - CaO / CcO2-CvO2 Acceptable range 3 - 5% -Can calculate the amount/degree of shunt (% of CO not getting oxygenated) -Information needed: --PB (Barometric Pressure) --PaO2, SaO2 --PvO2, SvO2 --Hb concentration --FIO2 -- *PAO2 (partial pressure of alveolar oxygen) -Pulmonary shunting and venous admixture are frequent complications of respiratory disorders --Knowing the degree of shunting can help develop patient care plans
What is the oxyhemoglobin dissociation curve?
The oxyhemoglobin dissociation curve (Hbo2 curve), also called the oxyhemoglobin equilibrium curve, is the S-shaped curve on a nomogram that illustrates the percentage of hemoglobin (left-hand side of the graph) that is chemically connected to oxygen at a specific oxygen pressure (Po2) (bottom portion of the graph).
