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Oxygen therapy has been in use for centuries. Oxygen) (O2) 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 the case of 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. Oxygen is an expensive medication; thus, it's indication must be met before use.

INDICATIONS FOR OXYGEN THERAPY:

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 syndromesevere sepsisheart 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.

DELIVERY DEVICES FOR OXYGEN THERAPY:

The oxygen delivery devices are grouped into two:

  • 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 (approximate 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 (level 1 evidence). It is ideal for long term oxygen therapy. It does not increase dead space and there is no rebreathing
  • Simple Mask: It can carry upto 5 – 10Litres of O2 per Minute with FIO2 0.35 – 0.55 (approximate 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.
  • 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 oxygen delivery systems  deliver a prescribed gas mixture (either high or low) at flow rates that exceed patient demand.

  • 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.
  •  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.

OXYGEN STORAGE AND SOURCE:

Vacuum insulated evaporator (VIE): When a gas becomes liquid form, it occupies a much smaller volume. Therefore, a large amount of oxygen can be stored in the form of liquid. A VIE is a container designed to store liquid oxygen.The VIE system is used in large hospitals which have a pipeline system. It is the most economical way to store and supply oxygen.
Oxygen cylinders: It is expensive, cumbersome, and often unreliable. It usually serve as a backup in large hospitals and used mainly in out of hospital settings.
Oxygen concentrators: It draws air from the atmosphere and extracts nitrogen leaving upto 90-96% concentration of oxygen using zeolite molecular sieve. It is safe, reliable, and cost efficient source of oxygen, and more convenient than oxygen cylinder. It is important to have a backup  source of oxygen(Oxygen cylinder), as it needs continuous power source and regular maintenance.
Central piped oxygen: oxygen is distributed via copper pipes circulating from a central source, that is situated  outside the building. The source may be liquid oxygen, high-pressure gaseous oxygen cylinders, a large oxygen concentrator or a combination. It has the advantage of reduced  risk of fire and obviates handling and transporting heavy cylinders between hospital wards. The high installment and maintenance cost is it’s daunting factor.