L11 - Gas Transport and Gas Exchange Flashcards
What is the main process of gas exchange?
Gas exchange refers to the process where oxygen (O2) is brought into the body and carbon dioxide (CO2) is expelled.
What are the three major factors needed for effective gas exchange?
Chest wall expansion
Gas transport
Lung compliance
Why is chest wall expansion important for breathing?
- When the chest expands, the lungs increase in volume, reducing pressure inside the lungs and allowing air (including oxygen) to flow in.
- Without proper chest wall movement, breathing becomes difficult, and gas exchange is compromised.
What is the role of the mechanics of breathing in gas exchange?
- The mechanics of breathing involve the diaphragm and intercostal muscles, which help expand and contract the chest cavity.
- This expansion allows air to flow into the lungs (inspiration), and contraction forces air out (expiration).
- Efficient breathing mechanics are vital for adequate gas exchange.
What is the conducting zone and its role in gas transport?
- The conducting zone includes the airways (trachea, bronchi, and bronchioles) that carry air into and out of the lungs.
- While it doesn’t participate in gas exchange directly, it plays a crucial role in transporting oxygen to the respiratory zone, where actual exchange takes place.
What is the respiratory zone, and what happens there?
- The respiratory zone is where gas exchange occurs. It consists of the alveoli where oxygen diffuses into the blood and carbon dioxide diffuses out of the blood to be expelled.
- This is the key site of gas exchange.
What is lung compliance, and why is it important?
- Lung compliance refers to the lung’s ability to expand and contract easily.
- High compliance means the lungs expand easily, allowing efficient oxygen intake.
- Low compliance makes breathing more difficult and reduces the efficiency of gas exchange.
How is gas exchange related to lung compliance?
- For gas exchange to happen effectively, the lungs must be able to expand and recoil properly.
- Lung compliance ensures that the lungs can fill with air during inspiration (bringing in O2) and expel air during expiration (removing CO2).
- Poor compliance impairs this process.
What two zones are involved in gas transport and exchange?
Conducting zone: transports air in and out of the lungs.
Respiratory zone: where actual gas exchange occurs.
What is the normal oxygen saturation range in healthy individuals?
95-99%.
What does oxygen saturation (SpO2) measure?
the proportion of oxygen molecules bound to the haemoglobin (Hb) in the red blood cells
What is the partial pressure of oxygen (PO2)?
Partial pressure of oxygen (PO2) refers to the total amount of oxygen in the blood at any given time. This includes:
Oxygen attached to haemoglobin (Hb)
Oxygen dissolved in plasma
How is the partial pressure of oxygen (PO2) measured, and what are the normal values?
Normal values:
10.6 - 13.5 kPa
What is the significance of the partial pressure gradient in oxygen diffusion?
Oxygen diffuses from the lungs into the blood due to a partial pressure gradient. The partial pressure is highest in the lungs and low in tissues, driving oxygen to move from the alveoli into the bloodstream and then to cells where it is needed.
How does oxygen travel from the lungs to the heart?
Oxygen binds to haemoglobin (Hb) in the blood after diffusing across the alveolar-capillary membrane in the lungs. The oxygenated blood is then carried to the left side of the heart via the pulmonary veins.
How is oxygen transported to tissues after leaving the heart?
Once oxygenated blood reaches the left side of the heart, it is pumped through the aorta and arteries. Oxygen is then released from haemoglobin into tissues and cells where the partial pressure of oxygen is lower.
What are the two main forms of oxygen in the blood?
Oxygen in the blood exists in two forms:
Bound to haemoglobin (Hb)
Dissolved in plasma
What drives oxygen to be released from haemoglobin into tissues?
Oxygen is released from haemoglobin when it reaches tissues because the partial pressure of oxygen (PO2) is lower in tissues compared to the blood. This creates a gradient that allows oxygen to diffuse into cells.
What role does haemoglobin (Hb) play in oxygen transport?
Haemoglobin (Hb) is a protein in red blood cells that binds oxygen in the lungs and transports it through the bloodstream. It releases oxygen to tissues where it is needed, especially in areas of low partial pressure.
What is the oxygen dissociation curve?
The oxygen dissociation curve is a graphical representation that shows the relationship between the partial pressure of oxygen (PO2) and the percentage of haemoglobin saturation (SpO2) with oxygen. It describes how readily haemoglobin binds to or releases oxygen.
What does the shape of the oxygen dissociation curve indicate?
The curve has an S-shape (sigmoidal), which indicates that:
- At low PO2, haemoglobin has a lower affinity for oxygen.
- As PO2 increases, haemoglobin binds oxygen more readily.
- At high PO2 (as in the lungs), haemoglobin becomes almost fully saturated with oxygen.
What does a right shift in the oxygen dissociation curve represent?
A right shift in the curve means haemoglobin has a lower affinity for oxygen, making it easier to release oxygen to the tissues.
what causes a right shift in the oxygen dissociation curve
- Increased CO2 levels
- Increased acidity (low pH)
- Increased temperature
- Increased 2,3-BPG (a byproduct of red blood cell metabolism)
What does a left shift in the oxygen dissociation curve represent?
A left shift in the curve means haemoglobin has a higher affinity for oxygen, making it harder to release oxygen to the tissues.
what causes a left shift in the oxygen dissociation curve
- Decreased CO2 levels
- Increased pH (alkalinity)
- Decreased temperature
- Decreased 2,3-BPG
What is the clinical importance of understanding the oxygen dissociation curve?
Understanding the oxygen dissociation curve helps clinicians predict how oxygen will behave under different conditions (like changes in pH, temperature, and CO2 levels). This is critical for managing conditions like respiratory diseases, shock, and exercise physiology.
In what three forms is CO2 found in the blood?
- Dissolved CO2 (10%): CO2 is 20 times more soluble in blood than oxygen.
- Bound CO2 (22%): Binds to proteins as carbamino compounds.
- As bicarbonate ions (68%): Formed through the CO2 hydration reaction, which is accelerated by carbonic anhydrase.
How is carbon dioxide measured in the blood, and what are the normal levels?
Normal values:
- 4.5 - 6 kPa
What can cause CO2 levels in the blood to increase?
- Increased metabolic rate ⇨ leads to increased CO2 production.
- Impaired gas exchange ⇨ reduces the body’s ability to eliminate CO2, leading to its buildup.
What can cause CO2 levels in the blood to decrease?
- Hyperventilation: Causes increased CO2 elimination, leading to lower CO2 levels in the blood.
What is respiratory insufficiency?
Respiratory insufficiency is a condition where the pulmonary system fails to maintain adequate gas exchange, which can lead to low oxygen levels (pO2) and elevated or normal CO2 levels (pCO2). It can progress into respiratory failure.
What causes respiratory insufficiency?
- It can occur due to conditions that impair lung function, such as:
- Obstructive lung diseases (e.g., COPD)
- Restrictive lung diseases
- Severe pneumonia
- Pulmonary edema
How is respiratory insufficiency identified?
- Respiratory insufficiency is identified using an arterial blood gas (ABG) reading. Key indicators include:
- Low pO2 levels (hypoxemia)
- Normal or high pCO2 levels (hypercapnia)
What is the difference between respiratory insufficiency and respiratory failure?
- Respiratory insufficiency is a precursor to respiratory failure if not managed properly.
What role does carbonic anhydrase play in CO2 transport?
- Carbonic anhydrase is an enzyme that accelerates the conversion of CO2 into bicarbonate ions (HCO3-) in the blood. This reaction is key for transporting the majority (68%) of CO2 in the blood.
What is Type I respiratory failure?
Type I respiratory failure is a failure of oxygenation,
* where PaO2 (partial pressure of oxygen) is less than 8kPa.
* often reversible
* commonly caused by V/Q mismatch (ventilation/perfusion mismatch) due to intrapulmonary causes, such as postoperative atelectasis or sputum retention.
What clinical signs are associated with Type I respiratory failure?
- Low SpO2 (oxygen saturation)
- Peripheral cyanosis (bluish discoloration of the extremities)
- Central cyanosis (bluish discoloration around the mouth and mucous membranes)
- Increased respiratory rate (RR): The body compensates for low oxygen levels by increasing the breathing rate to attempt to expel more CO2.
- Note: RR isn’t driven by oxygen levels until PO2 drops below 6.7 kPa.
What is the main underlying cause of Type I respiratory failure, and how is it treated?
- Type I respiratory failure often results from a V/Q mismatch due to intrapulmonary causes such as atelectasis or sputum retention.
Treatment involves addressing the underlying cause:
* Reinflate the alveoli (e.g., through deep breathing exercises)
* Clear sputum to improve ventilation
What is Type II respiratory failure, and what causes it?
- Type II respiratory failure is a failure of ventilation, where the patient experiences low PaO2 (oxygen) and an inability to clear CO2 (hypercapnia).
- It occurs due to reduced alveolar ventilation, and can be caused by both:
- Intrapulmonary factors (e.g., sputum retention, asthma, COPD)
- Extrapulmonary factors (e.g., neuromuscular insufficiency, rib fractures).
What are the clinical signs of Type II respiratory failure?
- Increased respiratory rate (RR)
- Increased work of breathing (WOB)
- Tremors
- Increased heart rate (HR)
- Drowsiness, dizziness, confusion, and headache
- These symptoms occur as the body struggles with high CO2 levels (hypercapnia) and low oxygen levels.
How should Type II respiratory failure be managed?
- Management focuses on treating the underlying cause, such as clearing sputum or improving alveolar ventilation.
- In some cases, treatments may need to be adapted based on the patient’s underlying condition (e.g., asthma, COPD).
- Careful consideration is needed for oxygen therapy due to the risk of further elevating CO2 levels (hypercapnia).
Why is it crucial to monitor PCO2 levels in Type II respiratory failure?
- Rising PCO2 on an arterial blood gas (ABG) reading indicates that the patient is unable to clear CO2 effectively, which can lead to hypercapnia.
- Prompt management is necessary to prevent worsening respiratory failure and complications.
What is the difference between Type I and Type II respiratory failure?
- Type I failure involves low oxygen levels (hypoxemia) but normal or low CO2 levels and is often due to V/Q mismatch.
- Type II failure involves low oxygen levels (hypoxemia) and high CO2 levels (hypercapnia), typically due to reduced alveolar ventilation.
What is a V/Q mismatch, and how does it relate to Type I respiratory failure?
- V/Q mismatch stands for ventilation/perfusion mismatch, which occurs when certain areas of the lung receive air (ventilation) but are poorly perfused with blood, or vice versa.
- This imbalance leads to reduced oxygenation of the blood, a key feature of Type I respiratory failure.
What are the intrapulmonary causes of Type I and II respiratory failure?
- For Type I failure, intrapulmonary causes include conditions like postoperative atelectasis and sputum retention, which affect oxygenation.
- For Type II failure, intrapulmonary causes can include asthma, COPD, or sputum retention, which reduce alveolar ventilation and impair CO2 clearance.
What are some extrapulmonary causes of Type II respiratory failure?
- Extrapulmonary causes include conditions that affect the ability to ventilate, such as:
- Neuromuscular insufficiency (e.g., muscular dystrophy, ALS)
- Rib fractures, which limit chest wall movement
- Obesity hypoventilation syndrome, where excess weight interferes with breathing.
What is the impact of respiratory failure on oxygen therapy choices?
- In Type I failure, oxygen therapy can be administered to correct hypoxemia.
- In Type II failure, oxygen therapy must be used cautiously because high oxygen levels can reduce the drive to breathe and worsen CO2 retention (hypercapnia). Careful monitoring is essential.
What is the bicarbonate buffer system and its role in acid-base balance?
The bicarbonate buffer system is the primary system in the body that helps regulate blood pH. It works through the interaction of CO2 (carbon dioxide), which is acidic, and HCO3- (bicarbonate), which is alkaline. By adjusting the levels of these substances, the body can control the concentration of H+ ions, which determines the pH of the blood.
How does CO2 and HCO3- influence pH?
- CO2 is acidic and its levels affect the amount of H+ ions in the blood, lowering pH (more acidic).
- HCO3- (bicarbonate) is alkaline and can buffer against the acidity caused by CO2, raising pH (more alkaline).
- The balance between these two is key in maintaining a normal pH range in the body.
Which systems control acid-base balance in the body?
Two main systems control acid-base balance:
- Respiratory system – controls CO2 levels (acid).
- Metabolic system – controlled by the kidneys, which regulate HCO3- (bicarbonate) (alkaline).
How does the respiratory system affect blood pH?
The lungs control the amount of CO2 in the blood:
- Increased respiratory rate (RR) eliminates more CO2, reducing acidity and raising pH.
- Decreased RR allows CO2 to accumulate in the blood, increasing acidity and lowering pH.
- The lungs primarily control blood pH through the carbonic acid system.
How does the metabolic system control acid-base balance?
The kidneys regulate blood pH by:
- Reabsorbing bicarbonate (HCO3-) from the urine back into the blood, increasing alkalinity.
- Secreting hydrogen ions (H+) into the urine, reducing acidity in the blood.
- This process helps maintain long-term pH balance.
Can physiotherapy influence acid-base balance through the respiratory system?
Yes, physiotherapy can impact the respiratory system, which controls CO2 (acid) levels. By manipulating breathing techniques, physiotherapists can help patients eliminate CO2, potentially raising blood pH and improving oxygenation.
Can physiotherapy influence acid-base balance through the metabolic system?
No, physiotherapy cannot directly influence the metabolic system because it is controlled by the kidneys, which regulate HCO3- (bicarbonate) and pH in the blood over a longer period. This system is independent of physiotherapeutic interventions.
What happens to pCO2 levels when respiratory rate increases?
- When respiratory rate (RR) increases, more CO2 is expelled from the lungs, resulting in a decrease in pCO2 levels in the blood.
- This raises the blood pH (makes it more alkaline).
What happens to pCO2 levels when respiratory rate decreases?
When respiratory rate (RR) decreases, less CO2 is expelled, allowing pCO2 levels to build up in the blood. This lowers the blood pH (makes it more acidic).
How do the kidneys regulate blood pH?
The kidneys regulate pH by:
- Reabsorbing bicarbonate (HCO3-) into the blood, increasing its alkalinity.
- Secreting hydrogen ions (H+) into the urine, reducing acidity in the blood.
What is the role of hydrogen ions (H+) in acid-base balance?
Hydrogen ions (H+) determine the acidity of the blood.
- Increased H+ ions lower blood pH (more acidic).
- Decreased H+ ions raise blood pH (more alkaline).
- The kidneys control H+ ions by secreting them into the urine.
What is the primary metabolic byproduct and how is it eliminated from the body?
CO2 (carbon dioxide) is a byproduct of cell metabolism. It is eliminated during the expiratory phase of breathing.
What happens to CO2 levels with changes in metabolic rate?
An increase in metabolic rate leads to an increase in CO2 production.
How does impaired gas exchange affect CO2 elimination?
Impaired gas exchange results in decreased CO2 elimination, leading to higher levels of CO2 in the blood.
How does hyperventilation affect CO2 levels and blood pH?
Hyperventilation increases CO2 elimination, causing low CO2 in the blood, a decrease in H+ ions, and an increase in pH (leading to respiratory alkalosis).
What is respiratory alkalosis?
Respiratory alkalosis occurs when hyperventilation leads to increased CO2 elimination, causing low CO2 levels, decreased H+ ions, and increased pH.
How does hypoventilation affect CO2 levels and blood pH?
Hypoventilation decreases CO2 elimination, causing high CO2 in the blood, an increase in H+ ions, and a decrease in pH (leading to respiratory acidosis).
What is respiratory acidosis?
Respiratory acidosis occurs when hypoventilation leads to decreased CO2 elimination, causing high CO2, increased H+ ions, and decreased pH.
What are the normal blood gas values for pH, pCO2, and pO2?
pH: 7.35 – 7.45
pCO2: 4.5 – 6.0 kPa
pO2: 10.6 – 13.5 kPa
What does high CO2 in the blood indicate in terms of pH?
High CO2 causes a decrease in pH, leading to respiratory acidosis.
What does low CO2 in the blood indicate in terms of pH?
Low CO2 causes an increase in pH, leading to respiratory alkalosis.
How does oxygen affect pH?
Oxygen does not affect pH, as it is pH neutral.
What is the role of bicarbonate (HCO3-) in acid-base balance?
Bicarbonate (HCO3-) helps to neutralize acids in the blood. The kidneys regulate the levels of bicarbonate to maintain acid-base balance.
How do the kidneys affect acid-base balance?
The kidneys control acid-base balance by:
- Excreting HCO3- into the urine if the blood is too alkaline.
- Retaining HCO3- if the blood is too acidic.
What causes metabolic alkalosis?
Metabolic alkalosis is caused by high HCO3- levels, which lead to a high pH. It can be due to vomiting (loss of stomach acid) or diuretic therapy.
What causes metabolic acidosis?
Metabolic acidosis occurs when low HCO3- levels lead to a low pH. It can be caused by diabetic ketoacidosis, lactic acidosis, renal failure, or intoxication with acids.
What is base excess?
Base excess represents the amount of base (HCO3-) in the blood. A +ve number indicates too much base, and a -ve number indicates too little base. The normal range is -2 to +2.
What is respiratory compensation in metabolic acidosis?
In metabolic acidosis, the body compensates by increasing respiratory rate (RR) (hyperventilation) to clear more CO2, reducing H+ ions, and returning pH to normal.
What is respiratory compensation in metabolic alkalosis?
In metabolic alkalosis, the body compensates by reducing respiratory rate (RR) (hypoventilation) to retain CO2, increasing H+ ions, and returning pH to normal.
What is metabolic compensation in respiratory acidosis?
In respiratory acidosis, the kidneys compensate by retaining more HCO3-, which helps to “mop up” excess H+ ions and return pH to normal.
What is metabolic compensation in respiratory alkalosis?
In respiratory alkalosis, the kidneys compensate by excreting more HCO3- into the urine, reducing the amount in the blood, and returning pH to normal.
What are the 6 steps to interpret an ABG?
- Know normal values
- Look at the pH first (acidic, alkalotic, or normal?)
- Look at PCO2 (high, low, or normal?)
- Look at HCO3- and base excess (high, low, or normal?)
- Identify any compensations
- Look at PO2 to identify respiratory failure
what are normal ABGs
break down step 2 of interpreting ABGS
Always look at the pH first
- is it an acidosis or alkalosis (or normal!)
- if the sample is acidic it is either
- a respiratory acidosis (⭡ CO2) or
- a metabolic acidosis (⭣ HCO3)
- if the sample is alkalotic it is either
- a metabolic alkalosis (⭡ HCO3) or
- a respiratory alkalosis (⭣ CO2)
break down step 3 of interpreting ABGs
look at PCO2
- Is it high, low or normal
- is the cause of the change in pH respiratory?
break down step 4 of interpreting ABGs
look at the HCO3- and base excess/deficit
- Is it high, low or normal
- is the cause of the change in pH metabolic?
break down step 5 of interpreting ABGs
identify any possible compensations
- once you have identified the primary cause go back and see if there is a compensation
break down step 6 of interpreting ABGs
look at the pO2 in the light of the FiO2 (to identify any respiratory failure)
- Is it normal, low or high?
- Type I or Type II respiratory failure
