Oxygenation and Ventilation Flashcards
Gas Exchange
oxygen transport to the cells and carbon dioxide transport away from cells through ventilation and diffusion
Ventilation
movement of atmospheric air higher in oxygen into the lungs and the removal of the carbon dioxide produced by metabolism.
Diffusion
the movement of gases down their concentration gradients across the alveolar and capillary membranes
Perfusion
the arterial blood flow through the tissues
PO2 and PCO2 of venous blood
PO2 = 40
PCO2 = 46
PO2 and PCO2 at alveoli
PO2 = 100
PCO2 = 40
PO2 and PCO2 at end capillary
PO2 = 100
PCO2 = 40
4 Steps of Cardiopulmonary Circulation
- Pulmonary Gas Exchange: ventilation, diffusion, perfusion
- Oxygen Delivery: effected by cardiac output, HgB levels, SaO2, PaO2
- Oxygen extraction at the tissue level
- Oxygen consumption by the mitochondria
What 4 factors effect oxygen delivery?
- cardiac output
- hemoglobin levels
- SaO2
- PaO2
Respiration
Sequence of events that results in exchange of O2 and CO2 between atmosphere and body cells
Ventilation is what we think of as _______ and stimulated by ________
breathing
nerves
External respiration
Gas exchange between lungs and blood
Internal respiration
Exchange of gasses between blood and tissue cells
Cellular respiration
Cells using oxygen for activities - metabolism
Ventilation
Flow of air in and out of the alveoli
* Inspiration & expiration
Ventilation requires intact:
- CNS (brain and spinal cord) neurons,
- diaphragm,
3, skeletal muscle (i.e. intercostal muscles), - chest thorax
In ventilation, air flows from _______ to _______ pressure
Air flows from higher to lower pressure
Capnography
Non-invasive measurement of CO2 concentration in expired gasses
* Amount of CO2 exhaled
* Continuous bedside monitoring
Diffusion
Movement of gasses (O2 & CO2) across a permeable membrane from an area of higher pressure to an area of lower pressure
What 2 places does diffusion occur?
- Alveoli: pulmonary circulation (alveolar capillary membrane)
- Capillary: tissue/cells
Diffusion is dependent on what 3 things?
- Differences in pressures
- Surface area
- Thickness of wall
Normal Female Hemoglobin
120-150 mg/dL
Normal Male Hemoglobin
135-170 mg/dL
Hemoglobin
major component of RBCs - A major carrier of oxygen in blood and an important factor in tissue oxygenation– has affinity (attraction) for oxygen
What is Sa02
Percentage of oxygen-saturated hemoglobin in arterial blood
How is Sa02 measured?
ABG
Normal SaO2
> 95%
What is Sp02?
Percentage of oxygen-saturated hemoglobin in the capillary bed
How is Sp02 measured?
with pulse oximeter
What is PaO2?
Partial pressure of oxygen dissolved in arterial blood
* Amount of oxygen dissolved in plasma
Normal PaO2
80-100mmHg
How is PaO2 measured?
ABG
Hypoxemia
low blood PaO2 level (<50mmHg)
Hypoxia
inadequate cellular O2 = anaerobic metabolism
What is tissue oxygen delivery through dissociation from hemoglobin based on?
Tissues need for oxygen
The rate of oxygen unloading changes depending on:
How much oxygen is already in the tissues
Describe the top portion of the oxygen dissociation curve
This portion is representative of oxygen leaving the alveoli and saturating the hemoglobin (high SaO2)
Because the hemoglobin is saturated in oxygen, the PaO2 is also high
When blood perfuses tissues in which oxygen levels are high, hemoglobin remains tightly binded/no unloading
Describe the bottom portion of the oxygen dissociation curve
At the tissue level, there is low amounts of oxygen so hemoglobin more readily desaturates itself to transfer the oxygen to the tissue
Hemoglobin is releasing oxygen to the tissue
Low saturation (SaO2) and thus low amounts of oxygen in arterial blood (PaO2)
What is P50
The partial pressure of oxygen at which hemoglobin is 50% saturated. Normally, when Hgb is 50% saturated with oxygen, the PaO2 will be 27mmHg
What occurs at the tissue level when the oxygen saturation curve shifts to the left?
Tissues need less oxygen due to a lower metabolic demand
Hemoglobin affinity increases
Oxygen being given to the tissues less easily
What is the haldane effect?
A shift of the oxygen dissociation curve to the left due to lower metabolic demand, increasing hemoglobins affinity and saturation
What occurs at the tissue level when the oxygen dissociation curve shifts to the right?
When the need for oxygen is greater in the tissues, hemoglobin will dissociate faster
Hemoglobin affinity decreases
Oxygen being given to tissues more easily
What 6 Physiologic Factors cause a left shift of the hemoglobin dissociation curve?
Left think LESS metabolic demand
- decrease altitude
- increase pH/alkalosis
- decrease pCO2
- decrease temperature
- decrease 2-3 DPG
What 5 Physiologic Factors cause a right shift of the hemoglobin dissociation curve?
Right think READILY released
- increase altitude
- decrease pH/acidosis
- increase pCO2
- increase temperature
- increase 2-3 DPG
Perfusion
Movement/flow of blood through the circulatory system that results in oxygenation of tissues
Arterial Blood Flow
What is perfusion dependent on?
Outside of other components (ventilation and diffusion)
- Pump
- Pipes
- Plasma
Describe how damage to the heart effects perfusion
Decreases ability of heart to properly function as a pump, therefore is cannot move enough blood through the body to support perfusion
Describe how damage to the vessels effects perfusion
If all the blood vessels dilate rapidly, the normal amount of blood volume is not enough to fill the system and provide adequate perfusion to the body
Describe how damage to the blood/plasma effects perfusion
If there is enough blood/plasma last, the volume of fluid in the vessels is not enough to support the perfusion needs of the body
What can inhibit perfusion?
VQ mismatch
Ventilation must match perfusion
What 2 things cause a VQ mismatch?
- When part of the lung receives oxygen (without blood flow)
- When part of the lung receives blood flow (without oxygen)
5 VQ Relationships at Alveoli
- absolute shunt: no ventilation die to fluid filling alveoli
- mismatch: ventilation partially compromised by secretions in airway
- normal lung unit
- mismatch: perfusion partially compromised by emboli obstructing blood flow
- dead space: no perfusion due to obstruction of pulmonary capillary
Oxygenation occurs as a result of what 3 processes?
- oxygen intake (ventilation)
- oxygen delivery (diffusion and perfusion)
What is FiO2 and normal value?
Fraction of oxygen in the air that is delivered to the patient
Room Air - 21%
How do nasal prongs effect FiO2?
Each additional liter of flow adds about 3% FiO2 to the inspired air (up to 6L)
How does a simple mask effect FiO2?
40-60% FiO2 @ 5-8L/min
How does a non-rebreather mask effect FiO2?
80-95% FiO2 @ 10-15L
How does an ETT w/BVM effect FiO2?
21-100% FiO2
Why do we care about oxygenation?
Oxygen is consumed to produce energy (aerobic metabolism)!
Oxygen is used for cellular processes; converting nutrients into ATP
What occurs during aerobic metabolism?
Energy using oxygen
Carbohydrates, fats, proteins broken down into substrates
What is the product of aerobic metabolism
= 36 ATP molecules, CO2, H20
What occurs during anaerobic metabolism?
Energy not using oxygen
Carbohydrates only into substrates
What is the product of anaerobic metabolism?
= 2 ATP, lactate
Small amounts of energy
What is lactate/lactic acid?
Acid metabolites (i.e. lactic acid) result from cellular breakdown and anaerobic metabolism
What is the normal lactate/lactic acid range?
0.3-2mmol/L
What drives serum lactate up rapidly>
Cellular hypoxia
Rapid rise in serum lactate usually precedes:
and can be an indicator of:
decompensatory signs
impending shock
What 7 conditions increase oxygen consumption?
- Hyperventilation
- Hyperthermia
- Trauma
- Sepsis
- Stress/anxiety
- Hyperthyroid
- Increased muscle activity
What 6 conditions decrease oxygen consumption?
- Hypoventilation
- Hypothermia
- Sedation
- Anesthesia/neuromuscular blocking agents
- Decreased activity
- Hypothyroid