Managing Breathing: Oxygen Therapy

Week 3

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Oxygen Therapy is usually defined as the administration of oxygen at concentrations greater than those found in ambient air. The main goal of oxygen therapy is to treat or prevent hypoxemia thereby preventing tissue hypoxia which may result in tissue injury or even cell death (O'Driscoll et al, 2015).

 Oxygen may be administered as a medical intervention to manage acute or emergency situations or as a part of chronic or long-term patient care. Oxygen therapy may therefore be a key tool in the hospital setting to manage a medical emergency or in the home setting, as a way of managing long-standing illness. The use of oxygen should be planned, and in most circumstances should be a prescribed therapy (see Emergency Situations below).

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Terms used in this section

Hypoxaemia

 Subnormal oxygenation of arterial blood, short of anoxia. (nb. US spelling is Hypoxemia)
Hypoxia Hypoxia refers to a condition where the amount of oxygen available to the cells is not adequate to meet metabolic need.
Anoxia Anoxia is a condition characterised by an absence of oxygen supply to an organ or a tissue.
Hypercapnia Hypercapnia refers to an increased amount of carbon dioxide in the blood
PaO2 Defined as a decreased partial pressure of oxygen in arterial blood
SaO2 The saturation level of oxygen in haemoglobin, as measured by samples obtained from arterial puncture in patients breathing room air
 FiO2 Fraction of inspired oxygen

Why give Oxygen?

Oxygen is vital for metabolic processes in cells and therefore the function of tissues within the body. The atmospheric content of oxygen within room air is only 21%. Although this amount is adequate for healthy individuals, those with certain diseases or who are acutely ill, can benefit from an increased oxygen fraction in the gas they breathe, which will increase the oxygen content of their blood. In most of these situations, increasing the oxygen fraction to around 30 % to 35% is enough to make a significant difference to the blood oxygen level.

Indications for Oxygen Therapy

  • Documented hypoxaemia, defined as a PaO2 below normal range. PaO2 of < 60 mm Hg or SaO2 of < 90% in patients breathing room air, or with PaO2 and/or SaO2below desirable range for the person's specific clinical situation.
  • An acute situation in which hypoxaemia is suspected. Substantiation of hypoxemia is required within an appropriate period of time following initiation of therapy.
  • Severe trauma.
  • Short-term therapy (e.g., carbon monoxide poisoning) or surgical intervention (e.g., post-anesthesia recovery).
  • Pneumothorax absorption.

Some of the causes of hypoxaemia are: low inspired oxygen levels (e.g., at high altitude), Hypoventilation, V/Q mismatch (e.g., COPD), Anatomical Shunt (e.g., cardiac anomalies), Physiological Shunt (e.g., atelectasis), Diffusion deficit (e.g., interstitial lung disease), Haemoglobin deficiencies.

 

O’Driscoll et al. (2008) suggest the following options for stepping up or down oxygen doses:
• Venturi 24 per cent mask at 2–4 L/min or nasal cannulae at 1 L/min
• Venturi 28 per cent mask at 4–6 L/min or nasal cannulae at 2 L/min
• Venturi 35 per cent mask at 8–10 L/min or nasal cannulae at 4–6 L/min
• Venturi 40 per cent at 10–12 L/min or simple face mask at 5–6 L/min
• Venturi 60 per cent at 12–15 L/min or simple face mask at 7–10 L/min
• Non-rebreathe mask at 15 L/min

Each device will now be considered in more detail.

Nasal cannulaeoxygen masks.jpg

These may be used for people with acute or chronic respiratory disease where low levels of oxygen are required. They are well tolerated and administer oxygen directly into the nostrils. Oxygen flow is adjusted by using the oxygen flow meter. Estimated oxygen concentration achieved ranges from 25 to 40 per cent using a flow rate of 2–6 L per minute. However, flow rates of more than 4 L per minute are not recommended due to the drying effect on the nasal mucosa (Vines et al. 2000). Administration may not be very accurate, as actual oxygen intake varies according to how much the patient breathes through their mouth (Khaw et al, 2008). To make the nasal cannulae fit closely, move the ends of the tubes through the horizontal piece of tubing across the nose and also the adaptor on the tubing below the chin. With nasal cannulae, people can eat, drink and talk more easily than with masks. Procedures such as mouthcare can be carried out without disrupting oxygen administration. Zevola and Maiier (2001) found that nasal cannulae were considered comfortable and were better tolerated than masks; some patients find an oxygen mask claustrophobic. New materials like Softech ® make the cannulae easy to tolerate and comfortable to wear (see www.teleflex.com). 

 Simple face mask

These are referred to as Hudson, MC (medium concentration) or semi-rigid.  To make the mask fit comfortably, the strap should be adjusted to fit behind the ears. The oxygen amount delivered is adjusted by using the flow meter and the exact amount delivered depends on rate and depth of breathing. If a patient is breathing rapidly large amounts of room air are drawn in and dilute the concentration (Pruitt and Jacobs 2003). Oxygen can be delivered at 4–15 L per minute, achieving concentrations of 35–70 per cent (see manufacturer guidelines for the mask you are using). Rates of below 4 L per minute should not be used as, with a low flow rate, rebreathing of carbon dioxide may occur due to exhaled carbon dioxide accumulating within the mask (Khaw, et al, 2008). 

Venturi mask system                                                                                               

In the Venturi system the oxygen concentration is not significantly affected by the rate and depth of breathing and a set concentration can thus be achieved (Higgins 2005). The mask is supplied with different coloured fittings, each clearly marked with an oxygen percentage and the required flow rate. The device ensures that oxygen flow is accurately diluted with entrained air. You can thus administer the exact percentage prescribed by fitting the correct device and setting the correct flow rate.

 Non-rebreathing masks

These have a large reservoir for oxygen with valves to allow the patient to inhale only oxygen and prevent it mixing with expired gases. Oxygen concentration is determined by the flow meter. They can provide up to 85 per cent oxygen (Gwinnutt, 2006), particularly for short periods of time, for example post-operatively or in an emergency. The valve must be pressed to enable the chamber to fill with oxygen.

Hazards of oxygen therapy

The two main hazards are fire, and the delivery of oxygen to people with chronic pulmonary disease, who retain carbon dioxide.

People who retain Carbon Dioxide

Normally, rising levels of CO2 stimulate respiration. However, some patients with chronic respiratory disease may continuously have a high level of CO2 in their blood and therefore their chemo-receptors are no longer stimulated by this. For these patients, who retain CO2, the less important hypoxic drive predominates, which means that breathing is only stimulated by lack of oxygen.  However, oxygen therapy can improve the patient’s outcomes. Croxton and Bailey (2006) reported improved survival rates in people with COPD who have long-term oxygen therapy. People with chronic respiratory disease are, therefore, normally prescribed less than 28 per cent oxygen (via a venturi mask) or 2 L/min (via nasal cannulae) initially and would only be prescribed a higher amount if indicated by arterial blood gas analysis or pulse oximetry (O’Driscoll et al, 2008, NICE 2010). These patients should carry an oxygen alert card (O,Driscoll et al, 2008).

 Patients who understand how and why they need oxygen are more likely to tolerate it (Baird 2001) so clear explanations are necessary.  An adult who is confused due to hypoxia may resist oxygen therapy. Repositioning to improve ventilation, for example sitting upright in a chair or in bed, will be helpful. Nasal cannulae rather than a mask may be better tolerated. Support and explanations from a familiar relative may help. If a person with learning disabilities needs oxygen therapy, you must consider level of understanding and learning ability. Demonstration of the mask/cannulae in position on a carer or nurse, and an explanation of the associated sensations and sounds, may be reassuring.

Humidification of oxygen devices

Oxygen can be drying to the mucous membranes of the upper airway (Pilkington 2004). The National heart, lung and blood institute (2012) reports how oxygen therapy can cause dryness, bloody nose, skin irritation and mucus dryness. Dryness of nostrils and mouth can be prevented through good oral hygiene, application of E45 cream and adequate fluid intake. Never use petroleum jelly near oxygen, however, because of its potentially flammable nature (NHS 2011). Oxygen administered for more than a short period can be humidified, particularly if the concentration administered is high, for example, over 35 per cent, or at a rate of 4 L per minute or above (O’Driscoll et al, 2008).

 Oxygen Therapy in emergency situations

In an emergency situation an oxygen prescription is not required. The British Thoracic Society Guidelines (2008) and 2015 ( public consultation) state that the recommended target saturation range for acutely ill patients, not at risk of hypercapnic respiratory failure is 94-98%. Most non-hypoxaemic breathless patients do not benefit from oxygen therapy, so administration of oxygen must be decided based on clinical need when oxygen saturations are lower than the recommended target. For patients with known chronic respiratory disease (COPD) or other risk factors for  hypercapnic respiratory failure, the recommended taget saturation is 88 -92%.  Any deteriorating patient should be administered high concentration oxygen immediately (15l oxygen via a non-rebreath (reservoir) mask), according to British Thoracic Society guidelines (2017). 

Monitoring Oxygen Therapy

All patients receiving oxygen therapy should be monitored. Oxygen therapy can be monitored non-invasively by pulse oximetry and also by blood gas measurements (see Arterial Blood Gasses (ABGs) (Advanced)).  Oximetry provides continuous monitoring of the state of oxygenation. Blood gas analysis provides accurate information on the pH, PaO2, and PaCO2. Oxygen saturation and the inspired oxygen concentration should be recorded on the patients monitoring chart, such as the NEWS chart.

The frequency of oximetry measurements will depend on the condition being treated and the stability of the patient. Critically ill patients should have their oxygen saturations monitored continuously and recorded with a frequency appropriate to their physiological condition. Patients with mild breathlessness due to a stable condition will need less frequent monitoring. Oxygen therapy should be titrated to the saturations in order to meet the target range.

 

 tab_thumb.png References and Further Reading

Special thanks to Sue Maddex and Tracey Valler Jones for use of materials

British Thoracic Society (2017 )Guideline for emergency oxygen use in adult patients [WWW]  https://www.brit-thoracic.org.uk/document-library/clinical-information/oxygen/emergency-oxygen-use-in-adult-patients-guideline/emergency-oxygen-use-in-adult-patients-guideline Links to an external site.

Maddex. S, Valler Jones, T. (2014) Assessing and responding to physical deterioration of health IN Baillie, L. Developing practical nursing skills 4ed. CRC Press: London

National Committee of Enquiry into Patient Outcome and Death. (2005). An Acute Problem. NCEPOD

National Heart, Lung and Blood Institute (2012) Explore Oxygen administration. [WWW] http://www.nhlbi.nih.gov/ Links to an external site.

O’Driscoll, B.R., Howard, L.S. and Davison, A.G (2008) BTS guideline for emergency oxygen use in adult patients. Thorax 43(Suppl vi): vi1–vi68.

O'Driscoll, BR. Howard, LS. & Davison, AG. (2011) Emergency oxygen use in adult patients: concise guidance. London: Royal College of Physicians

Pilkington, F. (2004) Humidification for oxygen therapy in non-ventilated patients. British Journal of Nursing 13(2): 111–15.

Porter-Jones, G. (2002) Short-term oxygen therapy. Nursing Times Plus 98(40): 53–6.

Pruitt, W.C. and Jacobs, M. (2003) Breathing lessons: basics of Oxygen Therapy.  Nursing 33(10): 43-45.

Sheppard, M. and Davis, S. (2000) Oxygen therapy – 1. Nursing Times 96(29): 43–4.

Vines, D.L., Shelledy, D.C. and Peters, J. (2000) Current respiratory care. Pt 1: Oxygen therapy, oximetry, bronchial hygiene. Journal of Critical Illness 15: 507–10, 513–15.