Week 4

Context

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, 2011).

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).

Introduction

This week runs from 13th October - 19th October 2014. You will need to:

Work through this section on Oxygen Therapy
Watch the Assessing Breathing video
If appropriate work through Arterial Blood Gasses (ABGs) (Advanced) section and do the Arterial Blood Gasses (ABGs) Analysis Test (Advanced)
Watch Second Chance: Episode 3: Recovery
Complete the exercise that follows the video

Content

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.

Oxygen supplies

In hospital, oxygen is obtained either from a cylinder (black with white shoulders) or a wall-mounted piped oxygen supply. If cylinders are used the dial showing the remaining oxygen must be inspected regularly as they can run out quite quickly. It is also imperative that equipment is checked and in good working order. Between 2004-2009, there were 103 incidents of risk or harm caused to patients by faulty oxygen equipment in acute hospitals, a further four from community hospitals and two from mental health or learning disability care settings (NPSA 2009). In the home, in England and Wales, oxygen is supplied by the NHS on a regional tendering service (review due 2014). These companies supply the equipment and oxygen as part of an integrated service. In Scotland and Northern Ireland supply is by local contractors. It is usually administered from an oxygen concentrator (McLauchlan 2002), which takes in room air and removes nitrogen through filtration but without depleting the surrounding air. The concentrator runs off electricity (an emergency cylinder is supplied in case of power failure), can deliver up to 4 litres per minute, and is supplied with up to 15 m of tubing, allowing movement around the home (Baird 2001).

Delivering Oxygen

Different concentrations of oxygen are administered according to clinical need, which affects oxygen administration devices used. For example, for someone who is very breathless and mouth breathing, a mask must be used. Nurses must record details of oxygen concentration, delivery device and commencement and termination of therapy, and sign for oxygen administration on the drug chart at each drug round (O’Driscoll et al. 2008).

Choice of oxygen delivery system

Oxygen therapy can be delivered at varying concentrations, often measured in percentages (e.g. 24%, 28 %, 35%, 40%); please refer to O’Driscoll et al. (2008) for further information. The oxygen flow is measured in litres per minute using a flow meter. Devices include simple oxygen masks, Venturi masks, nasal cannulae and non-rebreathing masks (Figure 11.2). These are disposable and packaged separately and each individual has their own equipment. Masks should be cleaned regularly especially if the patient has a productive cough (please refer to manufacturer guidelines for cleaning instructions and recommended length of use). If a mask or nasal cannulae are worn for any period of time there is a risk of pressure ulcer development, particularly on the bridge of the nose or behind the ears. Therefore masks and cannulae must be correctly applied, a good fit and replaced regularly.

Oxygen Cylinders

When a patient is on oxygen therapy it is important not to suddenly discontinue it. If you need to move a patient having oxygen, then you will need to use an oxygen cylinder. It is possible to work out if you have sufficient oxygen using a formula:

Duration of Oxygen Flow =	Oxygen Cylinder Conversion Factor X Remaining Tank Pressure (psi)
	_____________________________________________________________
	Prescribed Continuous Flow Rate (lpm)

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 cannulae oxygen 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) 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 (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/).

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.

References and Further Reading

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

British Thoracic Society 2008 Guideline for emergency oxygen use in adult patients 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/

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. Available at: http://www.nhlbi.nih.gov/

National Heart, Lung and Blood Institute 2012. Explore Oxygen administration. Available at: http://www.nhlbi.nih.gov/

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.