Oxygen Therapy

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Description

Oxygen therapy has been in use for centuries. Oxygen is gas used as a drug/medication and a such should be prescribed and administered in the right manner with regards to presenting indications for it's use; which is always in hypoxaemia. It has side effects and specific risks, but, with objective monitoring and administration, it is a potent therapy for the patient with respiratory condition.

Indications For Oxygen Therapy

Oxygen is rarely indicated for any other reason than Hypoxaemia.

• Hypoxaemia: Oxygen can be given in high or low concentration in all the conditions associated with hypoxaemia. Hypoxaemia occurs frequently in diseases like lower respiratory tract infection (severe pneumonia or bronchiolitis), upper airway obstruction, severe asthma, common neonatal conditions like birth asphyxia and in respiratory distress syndrome, severe sepsis, heart failure, cardiac arrest, trauma, carbon monoxide poisoning, and obstetric and perioperative emergencies.

Other indications include:

• Increased work of breathing

• Increased myocardial work and/or Myocardial infarction

• Pulmonary hypertension

• Pre-oxygenation in induction and difficult intubation.

• Pre and post suctioning

• Postoperative oxygenation especially in abdominal and chest surgeries

• Hyperbaric oxygen therapy indicated in decompression sickness, gas embolism, gas gangrene and carbon monoxide poisoning.

• Anaemic Hypoxia : it’s benefits is limited due circulatory deficit.

• In aerosol drug delivery.

Risks Of Oxygen Therapy

1. Depression of ventilation:

It is seen in COPD patients with chronic CO₂ retention who have hypoxic respiratory drive to breath. Increased arterial tension to normal can lose the hypercapnoeic stimulus to maintain ventilation resulting in hypoventilation in these patients.

2. Hyperbaric oxygen toxicity:

Long term hyperbaric O2 therapy can lead to pulmonary, optic and central nervous system toxicity.

3. Fire hazard:

Oxygen supports combustion of other fuels. Least level of supplemental oxygen (FIO2 greater than the 21% oxygen in ambient air)  should be administratered during laser bronchoscopy to avoid intratracheal ignition.

4. Absorption atelectasis:

Given only pure oxygen results in the collapse of the dependent part of the lungs as it quickly taken up from the alveoli. It is also a risk in general anaesthesia induction

5. Retinopathy of prematurity (ROP):

It usually occur in  low birth weight, very premature infant. That is why in preterm infants, 50-80 mmHg PaO₂ is recommended in  infants receiving oxygen

6. Bacterial contamination associated with certain nebulization and humidification systems is a possible hazard.

7. Oxygen therapy is contrindicated in patients suffering from paraquat poisoning

8. Pulmonary toxicity:

Patients exposed to high oxygen levels for a prolonged period of time have lung damage. The extent of lung damage is dependent on FiO₂ and duration of exposure. It is due to intracellular free radicals (such as superoxide, activated hydroxyl ions, singlet O₂ and hydrogen peroxide) formed which can damage alveolar-capillary membrane. It starts with increased permeability of the capillaries with resultant edema, thickened membranes and finally to pulmonary fibrosis.

Care should be taken in the use of oxygen in patients receiving bleomycin or have previously used it.

Delivery Devices for Oxygen Therapy

The oxygen delivery devices are grouped into 2:

Low flow oxygen delivery system

High flow oxygen delivery system

Low flow oxygen delivery systems are those that the exact fraction of oxygen in the inspired air (FiO²) will be based on the patient's anatomic reservoir and minute ventilation. They are:

• Nasal Cannula: It can carry upto 1 – 6Litres of O² Per Minute with FIO² 0.24 – 0.44 (approx 4% per liter flow) and FIO2 decreases as Ventilation rate increases. It is the recommended device for oxygen delivery in children less than 5years of age. It is ideal for long term oxygen therapy. It does not increase dead space and there is no rebreathing

Simple Mask: It can carry upto5 – 10Litres of O² per Minute with FIO² 0.35 – 0.55 (approx flowrate of 40%)  Flowrates should be set at 5 L/min or more to avoid rebreathing expired CO2 retained in the mask. It slightly increases dead space and there is little rebreathing. It is usually uncomfortable for patients, obstruct eating and drinking and also, muffles speech.

Partial Rebreather is a simple mask with a reservoir bag. Oxygen flow should always be supplied to

maintain the reservior bag on inspiration thus avoiding reservoir bag deflation. At a flow of 6-10 L/min the system can provide 50-70% oxygen. It is considered

Nonrebreather The non-rebreathing mask is similar to the partial rebreathing mask except it has a series of one-way valves. One valve is placed between the bag and the mask to prevent exhaled air from returning to the bag. There should be a minimum flow of 10 L/min. The delivered FIO2 of this system is 7-10%.

High-flow systems deliver a prescribed gas mixture (either high or low) at flowrates that exceed patient demand.

23,24,31

Venturi Mask : the flowrate is at about FIO2 0.24 – 0.50 with variable LPM. Flow and corresponding FIO2 varies by manufacturer

If air-entrainment masks is available it can be used to accurately deliver preset oxygen concentration to the trachea up to 40% but the inspiratory flowrates is usually inadequate for adults in respiratory distress.7,24,31,32

 Aerosol masks, tracheostomy collars, T-tube adapters, and face tents can be used with high-flow supplemental oxygen systems but not all aerosol generators can deliver high oxygen concentration at the needed flows rate.