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Oxygen Therapy

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    • Oxygen therapy works by increasing the FiO2 and oxygen flow rate
    • FiO2 determined by
      • Concentration of supplemental oxygen
      • Flow rate of oxygen
      • Oxygen delivery device
      • Patient respiratory effort
    • Concentration of oxygen
      • Room air 21%
      • Oxygen tank 100%
      • Oxygen concentrator >90%

    A. RESPIRATORY FAILURE

    1. Type I
    • Pneumonia
    • Bronchial asthma
    • Bronchiolitis
    • Pertussis
    • Pulmonary oedema
    • Aspiration pneumonitis
    • Apnoea of prematurity
    • Congenital heart disease
    • Anaphylaxis
    • Shock
    2. TYPE II
    • Apnoea
    • Birth asphyxia
    • Pneumothorax
    • Hypoventilation e.g. bulbar polio
    • Muscular dystrophy

    B. DIAGNOSTIC ROLE

    Hyperoxic Test

    • Quantitating the partial oxygen pressure (PO2) or O2 saturation (e.g. by pulse oximetry) during the administration of 100% oxygen is the most useful method of distinguishing cyanosis produced primarily by heart disease or by lung disease in sick infants
    • In cyanotic heart disease, the partial arterial oxygen pressure (PaO2) increases very little when 100% oxygen is administered over the values obtained while breathing room air.
    • However, PaO2 usually increases very significantly when oxygen is administered to a patient who has lung disease.

    C. O2 AS AN ANTIDOTE

    • Antidote in Carbon monoxide poisoning
    • 100%,
    • Hyperbaric- half-life of carboxyhemoglobin is 5 hr in room air, but 1.5 hr in 100% O2 and 15โ€“30 min in 3 atmospheres hyperbaric

    Oxygen delivery devices

    • Nasal cannula
    • Nasal catheter
    • Face mask
    • Oxygen hood
    • Oxygen tent
    • Endotracheal/nasotracheal tube/tracheostomy

    O2 Cylinder

    • Parts- reservoir, pressure gauge, flow meter, humidifier, connector, rubber-tubing
    • O2 produced by cooling air until it liquefies & then distilled to separate pure O2 from it
    • Delivers stored O2 (100%),
    • Simple to maintain

    Advantages

    • No need for electricity,
    • Cheap to procure

    Disadvantages

    • Expensive to maintain (subsequent refills)
    • Heavy & difficult to transport
    • Risk of fire hazard/explosion
    Oxygen Cylinder
    Oxygen Cylinder

    O2 Concentrator

    • Parts- pressure gauge, zeolite-filled cylinder, flowmeter, humidifier, air filter, rubber tubing, start button & indicator light
    • O2 is produced when nitrogen is separated from room air
    • Delivers >90% oxygen
    • Consists of an electrically powered compressor to force compressed air through synthetic aluminum silicate (zeolite) which binds reversibly to nitrogen
    • Requires electricity
    • Portable, suitable for home use

    Advantages

    • Cheap to maintain
    • Less risk of fire hazard/explosion

    Disadvantages

    • Need expertise for repair/maintenance
    • Expensive
    • Unavailability of spare parts
    Oxygen Concentrator

    1. Nasal cannula
    2. Nasal prongs
    3. Venturi mask
    4. Nasopharyngeal catheter
    5. Face mask
    6. Simple mask
    7. Face tent
    8. Rebreathing mask
    9. Oxygen hood

    Nasal Prongs

    • Low flow device (35-40%)
    • Least expensive
    • No need for humidification
    • No gastric distension
    • Easily dislodged
    • Comfortable, easy to use
    • Risk of nasal blockage
    Nasal Prongs

    Nasal Catheter

    • Inserted into nasopharynx (equivalent of distance from side of nostril to inner margin of eyebrow)
    • Low flow device
    • FiO2 similar to nasal cannula
    • Clogged by secretions ๏ƒ  Airway obstruction
    • Less risk of gastric distension
    • Well tolerated, unlikely to be dislodged
    • Humidification not necessary
    Nasal Catheter

    Head Box

    • Used in industrialized countries
    • Well tolerated by babies
    • Requires no humidification
    • Higher flow O2
    • Risk of hypercarbia if tube kinks/disconnects or flow rate is too low
    • Interferes with feeding
    Head box

    Nasopharyngeal Catheter

    • Inserted to just beyond the soft palate in the oropharynx (equivalent of distance from side of nostril to front of ear)
    • Can deliver lowest flow rate to achieve a set concentration in the airway
    • No risk of hypercarbia if O2 is turned off/ tube disconnects
    • Less likely to be dislodged if well secured
    • Requires humidification
    • Catheter blockage & airway obstruction
    • Gastric distension, irritability
    • Requires continuous & skilled nursing care
    Nasopharyngeal Catheter

    Face Mask

    • Requires high flow rate
    • Interferes with feeding
    • Not tolerated by small children
    • Risk of CO2 accumulation
    • Types
      1. Simple
      2. Partial rebreathing
      3. Non-rebreathing
      4. Venturi

    Simple Face Mask

    • Must fit tightly on patient's face
    • Allows unregulated flow of room air such that FiO2 delivered 35-50%
    • Used for self-breathing patients
    • Increase flow rate to prevent rebreathing
    • Flow rate of 5-8 L/min needed to deliver FiO2 of 50-60%
    • Seals poorly hence air mixes with O2

    Partial Rebreather Mask

    • Simple mask with an attached reservoir
    • Oxygen flow rate of 6-10L required to deliver 50-70% FiO2
    • High flow needed to prevent CO2 build up
    • Lacks a 1-way valve between mask and reservoir bag

    Non-Rebreather Face Mask

    • Flow rate of 10-12 L/min needed to delivers highest FiO2 at 70-100%
    • Has an attached reservoir bag that connects to O2 tank
    • Exhaled air is directed through a 1-way valve which prevents inhalation of room air and re-inhalation of exhaled air

    Venturi Mask

    • Venturi effect is based on Bernoulli principle which states that as the speed of a moving fluid increases, the pressure within the fluid decreases
    • Air entrainment device that delivers a known O2 conc. to patients on controlled O2 therapy
    • Best method for delivering a specific and consistent FiO2.
    • Delivers FiO2 of 24-55% at flow rate of 4-10L
    • Colour coded at 24%, 28%, 31%, 35%, 40% and 50%.

    Oxygen Hood and Tent

    • Well tolerated
    • Do not need humidification.
    • Usually require much higher flows of oxygen, as well as a mixing device to ensure the correct oxygen concentration.
    • The concentration falls to nearly 21% (room air) every time the headbox is opened to give access to the child's face or head.
    • Oxygen therapy has to be discontinued whilst the child is feeding

    • Clinical- cyanosis, tachypnoea, inability to feed/drink, grunting, restlessness, chest indrawing
    • End tidal CO2 โ€“ Capnograph/Capnometer measures the absorption of infrared light by CO2. Normal range 4-6% (equivalent of 35-45mmHg)
    • Oxygen saturation (SPO2): Pulse oximetry is a non-invasive method. A sensor is placed on fingertip/earlobe or across a foot (infants). Light with red & infrared wavelengths is sequentially passed from one side to a photo-detector on the other side. Changing absorbance of each of the 2 wavelengths is measured.
    • Based on the ratio of changing absorbance of the red & infrared light caused by the difference in color between O2-bound (bright red) & O2-unbound (dark red/blue, in severe cases) blood Hb, a measure of oxygenation (% Hb bound with O2) can be made
    • Arterial blood gases: Determine the pH of blood, partial pressure of O2, CO2, HCO3 level. Others may measure lactate, Hb, oxyHb, carboxyHb, lactate. Blood sample is usually obtained from radial/femoral artery or from an arterial catheter in situ into a pre-heparinised syringe.
    • Transcutaneous PO2/PCO2(tcPO2/tcPCO2): Non-invasive measurement of PaO2&PaCO2 locally in tissue capillaries by application to the skin a special set of electrodes which contain photoelectric sensors capable of picking specific wavelengths of radiation emitted by O2 and reduced Hb

    O2 Toxicity

  1. Bronchopulmonary dysplasia- occurs in preterms on long term O2 therapy. Affects 30% of infants < 1000g. Usually characterised by inflammation and lung scarring. Poor development of antioxidant defence mechanism against hyperoxic treatment has been implicated.
  2. Retinopathy of prematurity โ€“ refers to a vasoproliferative retinal disorder seen in preterms who receive high flow O2. Retinal arteries haemorrhage and scarring cause retinal detachment and blindness.
  3. Absorption atelectasis- refers to alveolar collapse due to nitrogen washout when delivering O2 for long periods
  4. Respiratory acidosis- due to increased CO2
  5. Ventilatory depression e.g. COPD
  6. Suppression of erythropoiesis
  7. Air leakage syndrome
  8. Alveolar haemorrhage
  9. Interstitial and alveolar oedema
  10. Mucosal drying
  11. Mucociliary dysfunction

    12. Related to Procedure

    • Gastric distention and diaphragmatic splinting
    • Cannula obstruction
    • Infection
    • Explosion risk
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