Know How To Perform Pulse Oximetry - Prescribing And Administering Oxygen

1. When should you use an ear lobe probe?

Cyanide poisoning

Poor peripheral circulation

Carbon monoxide poisoning

Emergency situations

Patients with carbon dioxide retention

Poor peripheral circulation leads to false reading due to the lack of haemoglobin in the extremities. The earlobe is more central so retains its blood supply.
Cyanide and CO will give false readings from any probe due to thier effect on haemoglobin. CO binds to haemoglobin to form carboxyhaemoglobin which cannot be distinguished from oxyhaemoglobin by oximetry. Oximetry will indicate a higher % arterial saturation of oxygen than is actually present.
Oximetry should be applied as soon as possible in an emergency and regularly monitored to ensure early management of hypoxaemia.

Explanation

Poor peripheral circulation leads to false reading due to the lack of haemoglobin in the extremities. The earlobe is more central so retains its blood supply.
Cyanide and CO will give false readings from any probe due to thier effect on haemoglobin. CO binds to haemoglobin to form carboxyhaemoglobin which cannot be distinguished from oxyhaemoglobin by oximetry. Oximetry will indicate a higher % arterial saturation of oxygen than is actually present.
Oximetry should be applied as soon as possible in an emergency and regularly monitored to ensure early management of hypoxaemia.

2. The same man's ABGs come back. They show that he is severely hypercapnic and acidotic. How would you treat him?

100% administered oxygen via non-rebreather

Treat with the lowest concentration of oxygen required to maintain target saturation

Immediately begin non-invasive ventilation

Use no oxygen at all

Wait for a senior colleague before proceeding

In cases of hypercapnia oxygen should be limited but titrated so that enough is administered to prevent hypoxia (keep arterial saturation within target range)
Non-invasive ventilation should be considered but only if the patients breathing becomes inadequate (infrequent and shalloe)
A senior colleague should be immediately informed but do not hesitate to provide essential treatment provided you are qualified.

Explanation

In cases of hypercapnia oxygen should be limited but titrated so that enough is administered to prevent hypoxia (keep arterial saturation within target range)
Non-invasive ventilation should be considered but only if the patients breathing becomes inadequate (infrequent and shalloe)
A senior colleague should be immediately informed but do not hesitate to provide essential treatment provided you are qualified.

3. An 80 year old man comes to the emergency department with severe shortness of breath, he is exhibiting an obvious tremor and appears distressed and unsure of where he is or who he is. His pulse rate is 94bpm. What is his target oxygen saturation?

92-98%

88-92%

Unknown until ABGs taken

Depends on the presence of asterixis

This man is exhibiting enough factors to classify him as at risk of type 2 hypercapnic respiratory failure. Remember:
Hypercapnia is indicated by:
-Tremor
-Asterixis
-Confusion
-Drowsiness
-Increased pulse rate
Although asterixis is an indicator for hypercapnia it is not always present
ABGs should be taken as a routine and used to confirm the diagnosis at this point. But for the time being 88-92% is the most appropriate target.

Explanation

This man is exhibiting enough factors to classify him as at risk of type 2 hypercapnic respiratory failure. Remember:
Hypercapnia is indicated by:
-Tremor
-Asterixis
-Confusion
-Drowsiness
-Increased pulse rate
Although asterixis is an indicator for hypercapnia it is not always present
ABGs should be taken as a routine and used to confirm the diagnosis at this point. But for the time being 88-92% is the most appropriate target.

4. A patient's breathing has become noticeably shallow and at a severely reduced rate, his latest ABG results show high arterial CO₂ saturation, acidosis and hypoxaemia. How should he be treated?

Non-rebreather mask 15L/min

Lowest concentration of inspired oxygen to maintain O2 sats with non-invasive ventilation

Lowest concentration of inspired oxygen to maintain O2 sats

Venturi mask with 24% filter

No oxygen administered

If a patient's breathing becomes inadequate non-invasive ventilation hould be considered
Hypercapnia-lowest concentration required to maintain dose

Explanation

If a patient's breathing becomes inadequate non-invasive ventilation hould be considered
Hypercapnia-lowest concentration required to maintain dose

5. Which of the following is/are not true:

Venturi masks can be used in non-COPD patients to titrate a correct dose

Nasal cannulae are used at flow rates of up to 6L/min

Humidifiers reduce the risk of nasal infection

Pure water should not be used in a humidifier

If a patient is carrying their own oxygen mask the mask should be used

Nasal cannulae are only used up to 4L/min (even though they have the capacity to be used up to 6L/min) as they are unreliable at higher flow rates.

Explanation

Nasal cannulae are only used up to 4L/min (even though they have the capacity to be used up to 6L/min) as they are unreliable at higher flow rates.

6. A 35 year anaemic old woman in hospital with bronchiectasis shows dropping oxygen sats. ABGs come back and her CO₂levels are normal. You're superior tells you to prescribe oxygen. What do you specify?

24% venturi

28% venturi

40% venturi

Nasal Cannulae 4L/min

Non-rebreather 15L/min

Remember- if hypoxaemia without hypercapnia 40-60% oxygen should be administered-this is most accurately achived with a venturi device.
Non-rebreathers can be used but carry an increased risk of precipitating type 2 respiratory failure and oxygen toxicity.
Nasal cannulae will only provide up to 35%. This may not be adequate to reverse severe hypoxamia. It is indicate in less severe situations.

Explanation

Remember- if hypoxaemia without hypercapnia 40-60% oxygen should be administered-this is most accurately achived with a venturi device.
Non-rebreathers can be used but carry an increased risk of precipitating type 2 respiratory failure and oxygen toxicity.
Nasal cannulae will only provide up to 35%. This may not be adequate to reverse severe hypoxamia. It is indicate in less severe situations.

7. You are in A&E. A 20 year old woman is brought in from a recent RTA. There is a deep laceration running the length of her left leg. She is fully conscious and in severe pain. What Oxygen treatment is indicated assuming the airway is clear?

None

15L/min non-rebreather

Venturi with 60% filter

4L/min nasal cannulae

Monitor her oxygen saturation with oximetry and titrate if required

In an emergency situation the standard response is to provide high flow oxygen with a non-rebreather mask to ensure highest possible oxygen saturation. The exception is the presence of an alert card or clear signs of type 2 hypercapnic respiratory failure.
She can then be assessed once stabilised and her oxygen dose titrated accordingly.

Explanation

In an emergency situation the standard response is to provide high flow oxygen with a non-rebreather mask to ensure highest possible oxygen saturation. The exception is the presence of an alert card or clear signs of type 2 hypercapnic respiratory failure.
She can then be assessed once stabilised and her oxygen dose titrated accordingly.

8. The following are situations in which you should use a non-rebreather mask:

Cardiac arrest

Facial trauma

COPD patients

Oxygen toxicity

Acute respiratory episode

Remember, a non-rebreather is used in cardiac and respiratory arrest.
The mask is contraindicated in facial trauma.
The mask may precipitate type 2 respiratory failure in COPD patients.
Oxygen toxicity occurs when too much oxygen is delivered so using a non-rebreather will just make things worse.

Explanation

Remember, a non-rebreather is used in cardiac and respiratory arrest.
The mask is contraindicated in facial trauma.
The mask may precipitate type 2 respiratory failure in COPD patients.
Oxygen toxicity occurs when too much oxygen is delivered so using a non-rebreather will just make things worse.

Submit

9. The following is a/are danger(s) with Nasal Cannulae:

Mucosal Dermatitis

Ear pressure sores

Carbon Dioxide re-breathing

Non-adherence

Oxygen toxicity

Foreign objects in the nose coupled with the drying effect on the mucosa from dry oxygen flowing past increases the risk of dermatitis and pressure sores.
Cannulae are not masks so there is no-where for CO2 to be trapped so no chance of rebreathing.
Cannulae can become uncomfortable and many patients will remove them.
The % oxygen administered is only up to 35%. this is too low the cause oxygen toxicity.

Explanation

Foreign objects in the nose coupled with the drying effect on the mucosa from dry oxygen flowing past increases the risk of dermatitis and pressure sores.
Cannulae are not masks so there is no-where for CO2 to be trapped so no chance of rebreathing.
Cannulae can become uncomfortable and many patients will remove them.
The % oxygen administered is only up to 35%. this is too low the cause oxygen toxicity.

Submit

10. Which of the following is/are true?

Non-rebreather prevents rebreathing using a one way valve

Nasal cannulae prongs curve upwards to the roof of the nasopharynx to slow oxygen before it reaches the trachea and thus prevent mucosal drying

Pure water in a humidifier can precipitate bronchoconstriction

Oxygen should be prescribed in an emergency

Some normal, healthy elderly individuals can have arterial oxygen saturation values of

Nasal cannulae prongs should always face downwards towards the trachea to ensure a direct flow of oxygen into the lungs-even if they are more prone to falling out this way around.
0.9% saline should be used in a humidifier
Never prescribe oxygen in an emergency-you will waste precious time filling out forms. Instead administer it as soon as possible or needed and once the patient is stable document all the care he has recieved including a full account of the oxygen therapy in the patient's notes.
It is true that many elderly patients have normal arterial oxygen saturation scores below the target range for normal patients. I such cases titrate oxygen to maintain the target arterial oxygen concentration and be vigilant for signs of hypercapnia or hypoxia.

Explanation

Nasal cannulae prongs should always face downwards towards the trachea to ensure a direct flow of oxygen into the lungs-even if they are more prone to falling out this way around.
0.9% saline should be used in a humidifier
Never prescribe oxygen in an emergency-you will waste precious time filling out forms. Instead administer it as soon as possible or needed and once the patient is stable document all the care he has recieved including a full account of the oxygen therapy in the patient's notes.
It is true that many elderly patients have normal arterial oxygen saturation scores below the target range for normal patients. I such cases titrate oxygen to maintain the target arterial oxygen concentration and be vigilant for signs of hypercapnia or hypoxia.

Submit