LECTURE 13 (Oxygen therapy)

Question 1

What is the equation to calculate Cardiac Output?

Answer 1

Cardiac Output = Heart rate X Stroke volume

Question 2

Describe the Oxygen-dissociation curve

Answer 2

RIGHTWARD SHIFT:
A higher PO2 is required to achieve a similar level of haemoglobin saturation -> haemoglobin molecules has LESS affinity for oxygen and is MORE willing to unload oxygen at the tissue level

LEFTWARD SHIFT:
Less PO2 can achieve a higher haemoglobin saturation compared to the baseline -> Haemoglobin has a HIGHER affinity for oxygen and is LESS willing to give up oxygen molecules

Question 3

What are the different oxygen delivery systems?

Answer 3

• Variable-performance systems (Nasal cannula, Hudson mask, T pieces and Y connectors)
• Fixed-performance systems (Venturi mask, oxygen blenders)
• 100% oxygen systems

Question 4

Describe Variable-performance oxygen delivery systems

Answer 4

Deliver a variable FiO2 which is altered by:
- Inspiratory flow rate
- Minute volume (how deeply + rapidly the patient breathes)

INDICATIONS:
- Patients with arterial oxyhemoglobin saturation of less than 94%
- Patients with minimal respiratory/oxygenation problems
- Patients who cannot tolerate a face mask

Question 5

In a __________ _____ ______ oxygen flow rate of at least 6L/min is needed to prevent rebreathing of exhaled CO2 and to maintain increased inspired oxygen concentration

Answer 5

Oxygen Face Mask

Question 6

What are the properties of a partial non-rebreathable mask?

Answer 6

• Covers both the nose and mouth
• 100% oxygen enters the mask
• One two-way valve connecting the mask and the reservoir bag
• The two-way valve allows about 1/3 of exhaled air to get into the bag

[compared to a non-rebreather mask, it allows 2/3 of air to be expelled into the atmosphere]

Question 7

What is the use of T pieces or Y connectors in emergency medicine?

Answer 7

To supplement an existing oxygen supply with
- Extra oxygen
- Nebulised medication
- Humidification

Question 8

Describe Non-invasive ventilation

Answer 8

INDICATIONS:
- severe hypoxia

FUNCTION:
- Reduces work breathing -> increased oxygenation + CO2 clearance
- Allows alveolar recruitment
- Redistributes alveolar fluid

Question 9

How does CPAP (Continuous positive airway pressure) reduce the need for ET intubation?

Answer 9

CPAP provides fixed positive pressure throughout the respiratory cycle without pause by utilising constant flow to generate pressure

Question 10

What are the properties of Bilevel positive airway pressure?

Answer 10

• Delivers different levels of pressure during inspiration and expiration
• Each cycle triggered by patient initiation of inhalation
• Inspiratory +ve pressure exceeds expiratory +ve pressure
• Prevents alveolar collapse