Administration of Oxygen

Oxygen is administered when there is a deficiency of oxygen in the blood or tissues - hypoxaemia à hypoxia

Causes of hypoxia

1. Inadequate oxygenation of lungs for extrinsic reasons, (extrinsic hypoxia)

2. Pulmonary Disease, (hypoxic hypoxia)

3. Venous - to - arterial shunts

4. Inadequate circulation of oxygen, (stagnant hypoxia)

5. Inadequate transport of oxygen, (anaemic hypoxia)

6. Inadequate tissue capability to use oxygen, (histotic hypoxia)

All of the above may be indications for oxygen therapy.

Hypoxia can cause death.

It is important to ensure there is adequate oxygenation of the tissues including vital organs such as the brain, heart, kidney and liver.

Hypoxia may cause serious or irreversible damage to tissues.

Equipment

Supply

Always use the correct cylinder/wall supply

Black cylinders with white on top - Oxygen

Grey cylinders which have black and white on top - Air

Blue cylinder with a blue and white top - Entonox

Flowmeter

Allow settings in litres per minute

Tubing

Green bubble tubing is fine for short term therapy

Use wider tubing 2 - 2.5 cm for longer term humidified therapy

Masks / nasal cannular / bags

Some "ventimasks" masks allow air to mix with the oxygen to control the percentage accurately, from 24 - 50%.

With simple (Hudson or MC masks) the concentration of O₂ is not so well quantified.

Nasal cannulae allow patients more freedom of movement but cannot deliver more than 40%

Partial rebreather bags without valves can also be used to deliver 50 - 75%

Reservoir bags with valves may be used to give high concentrations, up to 100%

Manual resuscitation bag are for patients with insufficient inspiratory effort

Tents and incubators may be used for young children

Other administration systems

Non-invasive positive pressure ventilation (NIPPV), such as continuous positive airway pressure (CPAP)

Mechanical ventilators for IPPV

Hyperbaric oxygen chambers

T-piece for spontaneous breathing via a tracheotomy

Humidifier

O₂ bubbles through these to allow water to humidify the dry supplied oxygen. Water may be warmed. Use sterile water for irrigation.

Humidification prevents mucous membranes from drying out and prevents mucus becoming viscous. This allows easy expectoration.

Nursing aspects

Appropriate explanation.

Gain co-operation, take time to communicate.

Normally nurse sitting up to maximise the efficiency of the respiratory muscles, help to drain lung fields and to dilate the bronchial passages.

Remember ill patients are more prone to opportunistic infection - make sure the delivery system is not infected.

Water particles in the air may transport bacteria in humidified O₂ therapy - observe for infection, encourage sitting up and expectoration, chest physio, use new or sterilised equipment for each patient.

Mouth care, (tooth brush and paste).

Assessment / indications

Observation of patients condition; spirometry, peak flows, level of reported dyspnoea, orthopnoea.

Look for the clinical features of hypoxia

* Tachypnoea

* Oxygen saturation <88%

* Tachycardia and increased stroke volume

* Dysrhythmias such as PVCs (Ventricular ectopics)

* Cerebral hypoxia - reduced level of consciousness, irritability, confusion, lethargy and eventually coma

* Cyanosis is a late sign indicating a low PaO₂

Administration

The aim of oxygen therapy is to give enough to maintain tissue oxygenation and therefore internal respiration.

Normal air contains 20.84% oxygen.

Oxygen should be medically prescribed where possible and prescribed rate of oxygen should not normally be exceeded.

In an emergency situation or if you suspect hypoxia give plenty of oxygen in the short term while help is coming.

It is important that patients on longer term therapy receive the correct concentration of oxygen (this is measured in %)

High oxygen concentrations (>30%) are used post-anaesthetic, in emergencies, acute conditions such as asthma and in carbon monoxide poisoning.

Low oxygen concentrations (24 - 28%) are used in patients who retain CO₂.

Oxygen percentages are titrated with oximetry, clinical features and arterial blood gases.

The percentage concentration is achieved by controlling the flow rate in litres per minute and by the type of mask.

Oxygen should be humidified if given for longer time periods.

A written record of times and levels of administration should be kept.

Long term oxygen therapy may be given at home for chronic conditions.

Oxygen toxicity

The lungs may be damaged if high concentrations are given over several days.

This may increase the permeability of pulmonary capillaries leading to fluid and blood accumulation in the alveoli.

Severe cases may progress to pneumonia, fibrosis, pulmonary hypertension and RVF.

This will not be a problem over shorter time periods.

(High levels of oxygen may cause retinopathy in premature babies and neonates.)

Respiratory control

Respiration is controlled by the respiratory centre in the medulla oblongata of the brain stem. This is sensitive to the level of carbon dioxide present in the blood. If the level of carbon dioxide rises, the respiratory centre sends impulses to the respiratory muscles to increase rate and volume of breathing.

The respiratory centre also receives stimuli via nerves from the chemoreceptors in the carotid and aortic bodies. When blood oxygen levels fall, impulses are sent to the respiratory centre which in turn increases the rate and depth of breathing.

In health it is the increase in CO₂ rather than the lack of O₂ which stimulates breathing.

Some patients with chronic obstructive airway disease retain CO₂ so have a constantly high level in the blood. This overwhelms the respiratory centre which therefore becomes unresponsive to these high levels.

These patients are kept breathing only by the low oxygen levels detected by the chemoreceptors. If this hypoxic drive is lost by giving too high a concentration of oxygen, respiration will be depressed or even cease.

Carbon dioxide narcosis

Hypoventilation caused by suppression of the hypoxic drive will result in the accumulation of even more CO₂ leading to drowsiness and eventual death. This is known as carbon dioxide narcosis.

Patients with chronic bronchitis should not normally be given more than 24% oxygen. Theoretically this problem only effects the `blue bloated` type of COPD not the `pink puffers`.

If a patient did stop breathing we could IPPV them until their natural drive is restored.

Safety aspects

Oxygen is not flammable, it does not burn

Oxygen is odourless, colourless and aids combustion

Oxygen aids combustion so is especially dangerous when mixed with a flammable gas

Do not use antiseptic tinctures, alcohol and ether in immediate proximity to oxygen environment

Ensure a no smoking policy in vicinity of oxygen

Ensure no naked flames

Do not use electrical equipment close to oxygen tents

Do not allow mechanical toys inside an oxygen tent

Have fire extinguishers available

Ward oxygen cylinders should be stored upright and secured to the wall

Flow meters and cylinders may blow back during changing