week 4 Oxygen Delivery and Cascade

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the approximate PaO2 in the alveolar gas mixture, and what is the main factor that reduces it from the atmospheric air value?

PaO2 is approximately 99 mmHg, and the main factor that reduces it is the dilution by CO2.

What is the A-a gradient, and how does it change with age?

The A-a gradient is the difference between alveolar and arterial PaO2, and it increases with age (7mmHg in the young, 14mmHg in the old).

How does the atmospheric pressure at sea level affect the oxygen cascade?

At sea level, the atmospheric pressure is 760mmHg, which results in a partial pressure of oxygen of 159mmHg (or 160mmHg), starting the oxygen cascade.

What happens to the oxygen cascade when the altitude increases?

At higher altitude, there is a decrease in atmospheric PaO2, affecting the whole oxygen cascade and decreasing oxygen dissolved in blood (PaO2). Signup and view all the answers

What is the effect of oxygen administration on the oxygen delivery variables?

Oxygen administration changes FiO2 and only affects two of the oxygen delivery variables: SaO2 and PaO2. Signup and view all the answers

What is the typical range of oxygen tension in the mitochondrial environment?

The oxygen tension in the mitochondrial environment is usually between 1-10 mmHg. Signup and view all the answers

What is the effectiveness of oxygen therapy dependent on?

The cause of hypoxemia and hypoxia, such as shunt or VQ. Signup and view all the answers

What is the main difference between low flow and high flow oxygen delivery systems?

Low flow systems have an oxygen flow rate less than the patient's inspiratory flow rate, while high flow systems have a gas flow rate greater than the patient's inspiratory flow rate. Signup and view all the answers

What is a characteristic of nasal cannula oxygen delivery?

FiO2 will be less in patients who are SOB or mouth breathers. Signup and view all the answers

What is the minimum oxygen flow rate required for a simple face mask to flush expired CO2?

6 L/min. Signup and view all the answers

Why does the delivery of oxygen through a tracheostomy mask depend on the status of the cuff?

Because the cuff affects the seal and delivery of oxygen. Signup and view all the answers

What is a potential disadvantage of using a simple face mask?

It can dry out the mucosa and make it uncomfortable for the patient to eat. Signup and view all the answers

How does increased WOB affect the FiO2 delivered through a simple face mask?

It reduces the FiO2. Signup and view all the answers

What is the name of the condition that develops in patients with high FiO2, where N2 is washed out, leaving only O2, which is rapidly absorbed, causing alveolar collapse?

Absorption Atelectasis Signup and view all the answers

What is the primary explanation for how oxygen causes CO2 retention in COPD patients?

Increased V/Q mismatch Signup and view all the answers

Why do non-rebreather face masks require humidification?

The answer is not provided in the given content. However, in general, non-rebreather face masks require humidification to prevent drying of the respiratory mucosa and to make the oxygen more comfortable to breathe. Signup and view all the answers

What happens to the expired gases during exhalation when using a non-rebreather face mask?

Expired gases exit through the exhalation ports. Signup and view all the answers

What is the physiological response that optimizes gas exchange in COPD patients over time?

Hypoxic vasoconstriction Signup and view all the answers

What is the Haldane effect?

The difference in the quantity of carbon dioxide carried in oxygenated and deoxygenated blood. Signup and view all the answers

What is the maximum FiO2 that non-rebreather masks can theoretically deliver?

FiO2 1.0 Signup and view all the answers

Why is it necessary to adjust the flow rate when using a non-rebreather face mask?

To prevent the reservoir bag from collapsing. Signup and view all the answers

What happens to CO2 when a patient is given high levels of oxygen, according to the Haldane effect?

CO2 is displaced by oxygen, resulting in a higher PaCO2. Signup and view all the answers

Why do patients who cannot increase their minute ventilation experience higher PaCO2 when given high levels of oxygen?

They cannot blow off the excess CO2. Signup and view all the answers

What should you do if you cannot intubate and cannot ventilate?

Not provided in the given content, but generally, it would be necessary to call for emergency assistance and consider alternative airway management techniques. Signup and view all the answers

What is the primary mechanism counteracted by oxygen therapy in patients with COPD, and what is its purpose?

Hypoxic pulmonary vasoconstriction, which optimizes the V/Q ratio to improve gas exchange. Signup and view all the answers

What is the recommended target oxygen saturation range in patients with acute exacerbation of COPD, and what is the goal of this approach?

88%-92%, to avoid oxygen-induced hypercapnia. Signup and view all the answers

What are the key factors that influence oxygen delivery to the cells?

Ventilation, diffusion of O2 into the blood, binding with haemoglobin, adequate cardiac output, and diffusion into the cell. Signup and view all the answers

What is the overall goal of oxygen therapy, and what should be considered when planning oxygen therapy for chronic CO2 retainers?

To avoid tissue hypoxia; consider different approaches for chronic CO2 retainers. Signup and view all the answers

If we live in higher areas for long times, develop compensatory mechanisms

Increased RBC Increased lung capacity Reason for high altitude training Signup and view all the answers

Indications for Oxygen Administration

Correction or prevention of hypoxemia • SaO2<90%&PaO2<60mmHg • Respiratory Failure • Cardio-respiratory arrest • Shock • Severe Trauma • Acute myocardial infarction with low SpO2 • Anaesthesia / procedural sedation Signup and view all the answers

Absorption Atelectasis

Develops in patients with high FiO2 • N2is the most abundant gas in the alveoli • The pressure exerted by N2 splints the alveoli open • FiO2 1.0 “washes out” all the N2 • Leaves only O2 which is rapidly absorbed  alveolar collapse • Develops in < 1 hr  worsening hypoxemia Signup and view all the answers

Study Notes

Oxygen Delivery and Therapy

Oxygen administration changes FiO2 and affects two oxygen delivery variables: SaO2 and PaO2
The Oxygen Cascade from Atmosphere to Mitochondria:
- Atmosphere to Alveoli: PaO2 of 159 mmHg, diluted by water vapor and CO2 to 99 mmHg
- Capillary to Mitochondria: PaO2 of 99 mmHg, diluted by venous admixture to 92 mmHg, and further decreased by diffusion distance

Oxygen Therapy

Goals of oxygen therapy:
- Reduce or correct hypoxemia
- Reduce the body's compensatory mechanisms
- Reduce tachycardia
Effectiveness of oxygen therapy depends on the cause of hypoxemia and hypoxia
- Shunt (VQ): oxygen administration generally more effective as ventilation is ok

Oxygen Delivery Systems

Low-flow/Variable Performance Systems:
- Oxygen flow rate is less than the patient's inspiratory flow rate
- Do not provide all the gas necessary to meet inspiratory demand
- Room air is entrained to make up the difference, resulting in a variable FiO2
High-flow/Fixed Performance Systems:
- Gas flow rate > patient's inspiratory flow rate
- Gas flow sufficient to meet patient's demand
- Delivers a fixed FiO2 not affected by the patient's ventilatory pattern

Devices and Their Characteristics

Nasal Cannula:
- Inexpensive, comfortable
- FiO2 will be less in patients who are SOB
- FiO2 may be reduced in mouth breathers
Simple Face Mask (Hudson Mask):
- Provides 100-200ml reservoir
- Higher concentration of oxygen
- Some rebreathing of CO2
- A minimum of 6LPM is required for all face masks to flush expired CO2
Tracheostomy Mask:
- Similar to a simple face mask
- Delivery is dependent on the status of the cuff
Non-Rebreather Face Mask:
- Contain a 750ml reservoir bag that stores O2 during expiration
- On inspiration, the patient draws pure O2 from the reservoir bag
- Increases O2 concentration
- Theoretically can deliver up to FiO2 1.0, but in reality, the FiO2 is nearer 0.6-0.8
Manual Resuscitation Bag:
- Self-refilling, non-rebreathing resuscitators
- Normally disposable
- Can deliver very close to FiO2 of 1.0

Oxygen Toxicity and Side Effects

Absorption Atelectasis:
- Develops in patients with high FiO2
- N2 is the most abundant gas in the alveoli
- The pressure exerted by N2 splints the alveoli open
- FiO2 1.0 "washes out" all the N2, leaving only O2 which is rapidly absorbed, causing alveolar collapse
Oxygen and CO2 Retention:
- The traditional theory is that oxygen administration to CO2 retainers causes loss of hypoxic drive, resulting in hypoventilation and type 2 respiratory failure. This is a myth.
- The real explanation involves:
  - Increased V/Q mismatch (most important)
  - The Haldane effect
How Oxygen Causes CO2 Retention:
- V/Q mismatch:
  - In COPD, over time patients optimize their gas exchange by hypoxic vasoconstriction
  - Administering a high level of oxygen will increase oxygen tension, reducing hypoxic pulmonary vasoconstriction
  - Results in increased perfusion to areas where ventilation is poor
- The Haldane effect:
  - Describes the difference in the quantity of carbon dioxide carried in oxygenated and deoxygenated blood
  - CO2 has a higher affinity for deoxygenated Hb than oxygenated Hb
  - Giving a patient high levels of oxygen will decrease the affinity of CO2 for Hb, resulting in a higher PaCO2

Nursing Care and Considerations

Mouth care/nasal care
Pressure area care – observe ears and nares
Ensure treatment/medication order unless it is an emergency
Oxygen is a medication with positive and negative effects
Take home messages:
- Overall goal of oxygen therapy is to avoid tissue hypoxia
- The devices are different and terms are used interchangeably
- Faced with a hypoxic patient, ALWAYS think Oxygen first
- Long-term oxygen therapy is not without side effects
- Consider different approaches for the chronic CO2 retainer when planning oxygen therapy

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Understand how oxygen is delivered from the atmosphere to the mitochondria, including the effects of oxygen administration on FiO2 and oxygen delivery variables. Explore the oxygen cascade from atmosphere to alveoli, including the changes in PaO2 at each stage.