Before we explore oxygen delivery devices, it is important to understand why we are applying oxygen. The main reason is to correct hypoxia.

What is hypoxia and how does it involved in COPD?


Patients who present with an exacerbation of COPD are often hypoxic. As you will have discovered earlier, they already have dyspnoea, and this is often the body’s response to hypoxia (Booker, 2008: 18). In addition to assessing the patient’s respiratory rate and depth, use of accessory muscles and ability to speak, the nurse should also use pulse oximetry and the results of arterial blood gases to determine oxygen required. Hypoxia should always be assessed and treated early to reduce the severity of the patient’s symptoms, and to prevent further deterioration of their condition (Booker, 2008:18).

There are four types of hypoxia:
  1. Hypoxic hypoxia – occurs when there is poor gas exchange between the alveoli and the capilliary
  2. Ischaemic (Stagnant) hypoxia - Occurs when there is obstruction to blood flow servicing areas of the body
  3. Histotoxic hypoxia- the body’s cells are unable to use the oxygen even if there is sufficient oxygen circulating. This is likely to occur in some cases of poisoning
  4. Anaemic hypoxia - occurs when the ability to transport oxygen is impaired due to lack of haemoglobin or inefficient haemoglobin (Marieb & Hoehn, 2010: 832; Moore, 2007: 50).


The following reference will provide you with a greater understanding of forms of hypoxia. Whilst it is an older article, it still discusses well the types of hypoxia and what occurs at tissue level.






Pierson, D.J. 2000 Pathophysiology and clinical effects of chronic hypoxia. Respiratory Care, 45, 1, 39-50.



ExerciseAnimation.gif
Exercise
The main type of hypoxia involved in COPD is hypoxic hypoxia. The reason for this is the inefficient gas exchange at the alveoli. Next time you encounter a patient with an exacerbation of COPD, think about the reasons as to why they may have inefficient oxygenation. What does their full blood count say? What is happening with their arterial blood gases? Are they coughing up sputum? What is their history – do they have cardiac failure that may contribute to their poor oxygenation? What interventions can you provide that will improve oxygenation?



Posture or positioning your patient is one method of improving oxygenation. In the page 'what can my patient do to conserve energy and improve oxygenation', there is a discussion on positioning your patient for better oxygenation. It is important however to position your patient in such a way as to allow them to use all of their available thoracic area and accessory muscles to improve tidal volume. Where your patient has large volumes of mucous, it is worth considering a referral to a physiotherapist to provide some chest physiotherapy. Once the acute exacerbation has stabilised, they may be able to assist with diagnostic tools such as spirometry, six minute walk tests and pulmonary function testing to assess the severity of COPD (Bauldoff & Diaz, 2006: 33-34).


Your patient may require supplemental oxygen. There are many devices available to apply or administer oxygen. Let’s move on to examine oxygen therapy.


What oxygen delivery device do I use?


Oxygen is a drug. In administering oxygen, you will need to have an understanding of how to monitor your patient, as well as an understanding of individual delivery devices and how they function.

In assessing the amount of oxygen required for your patient, you should have an understanding of their arterial blood gases. To learn about interpreting arterial blood gases, see this link to a learning package by Orlando Health (2010).


http://orlandohealth.com/MediaBank/Docs/SLP/2010%20ABG%20SLP.pdf

It is important to understand your patient’s level of hypoxia, and hypercapnia to ascertain the amount of oxygen required, and also the best way to deliver it. When applying oxygen, you should continue to assess respiratory rate, depth and pattern to ensure that the patient is tolerating the oxygen applied. If you are concerned, it is important to seek early medical review to prevent your patient from deteriorating further. A combination of oxygen saturation, physical assessment, and arterial blood gases will determine the type of oxygen delivery system required. In the patient with COPD it is appropriate to maintain their oxygen saturations above 90% (Bauldoff & Diaz, 2006: 37), however this is contingent on whether the patient normally retains CO2, in which case oxygen saturations should be kept between 90-92% - see the section on what if my patient is a CO2 retainer?



We will now move to examine variable delivery oxygen devices and their application. It should be remembered that room air at sea level has a fraction of inspired air (FiO2) of 21%. Remembering this number will help to understand the impact that oxygen delivery devices have on patients.




nasal_cannula.JPG


Figure 8. Nasal cannula. Source: http://www.le-west.co.uk/medical/OXYGEN-NASAL-CANNULA_M1110.html



Nasal cannula are designed to be inserted into the nostrils and can deliver 1-6 litres of oxygen per minute. However, it is recommended that they not exceed 4 litres per minute unless attached to a humidifier to prevent drying of the nasal mucosa. According to Stich and Cassella (2009: 52), they can deliver an FiO2 of 24% at 1litre/minute ranging up to 44% at 6 litres/minute. Simple cannula are used commonly for supplemental oxygen to patients with mild hypoxia.


Advantages: Patients can talk, eat and drink without removing cannula. Patients can mouth breathe without affecting their function.



Disadvantages: Irritation to nasal mucosa both by dry oxygen and physical abrasion causing epistaxis or rhinitis. An increased risk of pressure areas to areas of face that come into contact with tubing (Smith, 2005:11).




oxysaver_reservoir_cannula.gif



Figure 9. Reservoir cannula. Source: http://www.wingsandwheels.com/page35.htm

Reservoir cannula are not as commonly used and are relatively new devices. The concept is that they can store oxygen in the reservoir and so give a higher concentration of oxygen on each breath than simple cannula. That is, when set at 2litres/minute, they are capable of delivering a similar FiO2 as a simple nasal cannula set at 4 litres/minute. This makes them perfect for home use with oxygen concentrators, as they require less flow to deliver a higher concentration (Stitch & Cassella, 2009:51). The reservoir can be located in the nasal section (a moustache type) or in a pendant area worn at neck line (not pictured).


Advantages: The same as for simple cannula, however can provide a higher concentration of oxygen with less flow. No need to humidify as the reservoir also captures moisture.


Disadvantages: The same as for simple cannula, however increased risk of pressure areas due to the extra weight of the reservoir (Stitch & Cassella, 2009:51).




hudson_mask.jpg



Figure 10. Simple face mask or Hudson mask. Source: http://gardenrain.wordpress.com/2009/10/14/methods-of-and-indications-for-oxygen-delivery/


The simple face mask or hudson mask is the next step up from nasal cannula. The mask covers the nose and mouth and delivers a variable FiO2 based on the patient’s respiratory rate. This is due to CO2 mixing with O2. The faster a person breathes, the lower FiO2 they will receive. The mask should be set at 5 litres/ minute or more, as less than 5 litres/minute will result in the patient rebreathing their own CO2 (Smith, 2005:11) . The Hudson mask will deliver an FiO2 of 35-50% based on normal breathing patterns and a wall setting of 5-10 litres/minute.


Advantages: Able to deliver a higher FiO2 than nasal prongs. Useful for patients who may be ‘mouth breathers’.

Disadvantages: Oxygen can dry mouth and skin mucosa causing pressure areas and/or discomfort. May be uncomfortable for people who experience claustrophobia. If wall setting not higher than 5 litres/minute then patient likely to rebreathe their own CO2. This may be an issue where pCO2 is concerned (see What if my patient is a CO2 retainer section). Needs to be removed or to nasal cannula to eat, talk, mobilise and attend to mouth care. Good control of nausea should be sought to prevent the patient vomiting in the mask (Stitch & Cassella, 2009:51).



non_rebreather_adult.jpg




Figure 11. Non-rebreather mask. Source: http://www.505pcga.org/projects.html


The non-rebreather mask is capable of delivering up to 15 litres/minute from the wall supplying an FiO2 of 60-80% with a minimum rate of 10 litres/minute. It has a reservoir bag at the base of the mask filled with 100% oxygen and fitted with a one way valve to prevent CO2 from being exhaled into the reservoir.


Advantages: Able to deliver a high volume of oxygen without risk of rebreathing patient’s own CO2.

Disadvantages: Same as for Hudson mask. In addition, mask needs to be adjusted to maintain close contact with skin to be most effective. Minimum amount of oxygen at the wall is 10 litres/minute, so patient needs to be closely monitored to ensure they do not receive too much oxygen (Stitch & Cassella, 2009:53).



venturi-mask.jpg




Figure 12. Venturi or percentage mask. Source http://www.topfreebiz.com

The venturi or percentage mask delivers a fixed FiO2, making it useful to provide a specific amount of oxygen. The venturi mask has several attachments that are designed to entrap or capture room air. This means that dependent on the attachment fixed on to the mask, an FiO2 of 24-50% is achievable regardless of the rate of flow from the wall.


Advantages: Able to fix a concentration of oxygen, making it useful for patients who have a chronically raised CO2 level (CO2 retainers). Design of mask means that the patient will receive a fixed concentration without risk of a flow rate from the wall that is too high.

Disadvantages: Largely the same as for a simple face mask (Stitch & Cassella, 2009:53).






Oxygen being a drug means that you should provide the minimum amount required to alleviate the effects of hypoxia. The guide below should assist you to determine which device is required. However you should always consult with the treating medical team so that they are aware of your interventions.


Smith (2005: 12) provides a useful table for the selection of oxygen delivery device based on saturation of oxygen. Please note that this table is based on a patient with normal carbon dioxide levels. A patient with hypercarbia or COPD should maintain their oxygen saturations above 90% and in the case of hypercarbia 90-92%.



Respiratory Condition
Oxygen Saturation
Treatment
%FiO2
Normal respiration
95-100%
Nil
Nil
Mild Hypoxia
91-94%
Nasal Cannula or simple mask
24-50%
Moderate Hypoxia
86-91%
Simple mask, venturi or non-rebreather
35-80%
Severe Hypoxia
85% or less
Non-rebreather or consider non-invasive ventilation or intubation
80%




This page has examined simple and variable flow oxygen delivery systems. Your patient may require non-invasive ventilation such as CPAP or BiPAP or in extreme cases invasive ventilation to correct disturbances in arterial blood gases. This page has not discussed such interventions, however you should be encouraged to explore an understanding of these devices to further your understanding of treatment options.