06 - Gas Transport Part 2 Flashcards
Absorptive atelectasis occurs when oxygen is not repleted in the alveoli because
The concentration of oxygen in the blood decreases as it is deceived to tissue and continues to diffuse from the alveoli
What two ways are oxygen delivered to the body once it is in the blood?
Dissolved in the blood itself
Bound to hemoglobin
The most efficient method of oxygen transport is
Bound to hemoglobin, the desired saturation is above 95%
What is alveolar oxygen tension?
The partial pressure of oxygen in the alveoli
Decreased alveolar tension causes decreased
Arterial oxygen tension and decreased available oxygen to bind
Hemoglobin saturation is critically dependent on
Oxygen tension
What is the oxygen content equation?
CaO2 = ([0.003 ml O2/dL blood/mmHg]PO2) + SaO2Hb*1.31 ml/dL blood)
How much more oxygen is bound to hemoglobin compared to oxygen dissolved in the blood?
About 60x more
What is mixed venous oxygen?
The amount of oxygen returned to the right side of the heart
T or F. The content of any venous blood sample from one patient is the same.
False, up until the blood perfuses the alveolar beds, any venous blood sample will have subtle differences in oxygen concentration
What is the normal saturation of mixed venous oxygen?
65-75%
25% of the oxygen has been utilized
What determines what the mixed venous oxygen is?
Oxygen saturation
Concentration of hemoglobin
Oxygen consumption
Cardiac output
People with anemia compensate by __________ and ___________ to maintain cardiac output.
Increased stroke volume and heart rate
How is oxygen delivery calculated?
Oxygen delivery = oxygen content * cardiac output
DO2 = caCO2 * CO
Oxygen delivery depends on
Cardiac output
Hemoglobin concentration
PaCO2
Why does cardiac output in an anesthetized patient increase?
They are more desaturated and compensate by increasing cardiac output until the heart itself becomes ischemic
How can oxygen consumption be calculated?
O2 consumption = CO * (CaO2 - CvO2)
This is the Fick Equation
Why doesn’t the body deliver oxygen at maximum cardiac output constantly?
Energy is wasted
If oxygen consumption is more than delivery, this is
Oxygen debt
Long term anaerobic metabolism leads to
Acidosis
What is normal oxygen consumption? CO?
O2 consumption = 250 ml/min
CO = 5000 ml/min (men)
4000-4500 ml/min (women)
What is low flow anesthesia?
Flow rates are decreased to save anesthetic gas and preserve temperature (less cold gas going into patient)
Does low flow anesthesia affect O2 consumption?
No, delivery and consumption we independent at low levels.
There is a direct relationship at high levels.
What makes up oxygen stores and what is the normal amount?
Bound to hemoglobin
Remaining in lungs
Dissolved in body fluids
1500 ml O2
What is hemoglobin?
A large protein molecule with four heme groups
Each heme group can pick up ____ molecule of oxygen
1
Why is oxygen extraction from hemoglobin 25%?
On average, one heme releases it’s oxygen while the other three stay bound
Hemoglobin _________ to increase or decrease its affinity for oxygen
Changes its configuration
Oxygen dissociation depends on
2,3 - diphosphoglycerate
CO2 tension
Hydrogen ion concentration
Temperature
2,3-DPG binds to deoxyhemoglobin, stabilizing the ___________, making it ________ for oxygen to bind
Low oxygen affinity state (T state)
Harder (allows for the stereostatic change)
The T state of hemoglobin has an opening in the center that 2,3 DPG easily binds to. This opening is absent in the R state.
A right shift in the oxygen dissociation curve, _______ oxygen
Releases
R for Release!
Hypoxia is defined as
<60 mmHg O2 in the blood
A decrease in temperature causes a higher O2 affinity because
Metabolic rates decrease
An increase in pH
Increases O2 affinity
At a lower pH! more o2 is released to restore balance
5 categories of hypoxia
Hypoxic: 5 categories
Cardiac: low perfusion due to heart not functioning well
Hemic: low hemoglobin even with increased CO or deranged Hgb
Demand: increased consumption of O2
Histotoxic: O2 delivery and CO are adequate, but tissue can not use the oxygen
Oxygen is in the blood, but there is a. Problem with getting the blood circulated. This is an example of what kind of hypoxia?
Cardiac
Malignant hyperthermia is an example of what kind of hypoxia?
Demand
What is an example of hemic hypoxia?
Binding of hemoglobin to carbon monoxide
What is an example of histotoxic hypoxia?
Cyanide poisoning mitochondria ch disrupts ETC function
What are the methods of carbon dioxide transport?
Dissolved in plasma
Bicarbonate (carbonic acid)
Carbamino compounds (bound to proteins)
T or F. There is no good way to transport carbon dioxide in the blood.
True, carbon dioxide does not have a hemoglobin equivalent.
How is carbonic acid buffered with water in the blood?
Carbonic acid = [CO2 + H2O] [H + HCO3-] (bicarbonate)
How does the carbon dioxide dissociation curve compare to the oxygen dissociation curve?
It behaves more linearly
Removal of carbon dioxide from the blood is a self perpetuating cycle. What does this mean?
In order to allow more carbon dioxide to enter a RBC to be converted to carbonic acid, carbon dioxide needs to be removed.
Adequate alveolar ventilation and perfusion are required
Describe the process of the chloride shift (hamburger shift)
Carbon dioxide generated in the tissues diffuses into the capillaries and enters red blood cells. RBCs contain carbonic anhydride which converts the CO2 into carbonic acid. The carbonic acid dissociates to form hydrogen ions and bicarbonate. The fall of CO2 in the call allows more CO2 to enter the cell (self perpetuating cycle). Bicarbonate ions are exchanged for chloride (hydrogen ions can not cross the membrane). This bicarbonate export and chloride intake is referred to as the chloride shift.
What is the Haldane effect?
A property of hemoglobin to increase its affinity for carbon dioxide as blood is more deoxygenated
What is deoxygenated hemoglobin’s affinity to CO2?
3.5x
Venous blood carries _______ carbon dioxide tha arterial blood
More
Large amounts of carbon dioxide is stored primarily as __________
Bicarbonate
About 120 L
How long does it cake to equilibriate an imbalance in carbon dioxide production or elimination.
20-30 min
What factors contribute to our control of breathing?
Respiratory rhythm generators Chemoreceptors Arterial PO2 Lung and airway receptors Vasal pulmonary stretch receptors
What are the respiratory rhythm generators?
Dorsal and ventral respiratory group on the brainstem
Group responsible for the rate of expiration
Ventral
Group responsible for the rate of inspiration
Dorsal
What do the chemoreceptors measure and where are they located?
Oxygen, carbon dioxide, acid state
Located at different parts of the arterial system
Chemoreceptors can be impacted by
Anesthesia
Pain
The hypercapnic drive is _______ than the hypoxic drive
Stronger
Examples of airway reflexes
Bronchospasm
Laryngospasm
What are the vagal pulmonary stretch receptors?
Activation of these receptors helps to prevent over inflation of the lungs.
Inhibits the inspiratory area and the apneustic center, inhibiting the activation of inspiration. Allows expiration to begin.
Extubation criteria
TV > 5 cc/kg VC > 10 cc/kg Adequate motor strength Neg inspiratory pressure < -25 cmH2O PaO2 > 65 mmHg on FiO2 < 0.40 PaCO2 < 50 mmHg RR < 30/min TV/RR > 10 RSBI < 105
Too many breaths causes inadequate
Tidal volumes
This is why RR < 30 for extubation
What is RSBI?
Rapid shallow breathing index
RSBI = RR/TV
A low RSBI indicates
Less effort to breathe
