Oxygen Therapy Definition etc

• Oxygen Therapy - Principles:

  • What is the fraction of inspired oxygen (FiO2 ) of room air? - 0.21
  • Oxygen therapy will increase FiO2, therefore increase PAO2(partial pressure of alveolar oxygen), therefore increase SaO2 (saturation of oxygen in arterial blood - amount of haemoglobin saturated with oxygen) and increase PaO2 (partial pressure of arterial oxygen - amount of oxygen dissolved in blood)
• What are the indications for O2 therapy?

  • hypoxaemia - low oxygen in the blood, PaO2 of 7 or below
  • Breathlessness alone is NOT an indication for oxygen therapy
  • Breathlessness and hypoxaemia may well co-exist but their relationship is limited (e.g. someone with dysfunctional breathing will be breathless but have normal o2 levels)
• Oxygen Therapy:

  • Oxygen is an expensive drug
  • Oxygen should be medically prescribed
  • flowrate
  • concentration
  • duration
  • the delivery device
  • All this should be documented on the patient’s drug chart
  • BUT in an emergency administer O2 first and then document
• Oxygen Flowmeter

  • goes from 0.5 - 15 l/m
• FiO2 can be prescribed at these levels:

  • 24%
  • 28%
  • 35%
  • 40%
  • 60%
  • You can only state the exact FiO2 when using a fixed performance delivery device
• O2 Therapy and Chronic Hypercapnia:

  • loss of hypoxic drive
  • reversal of HPVC (worsened V/Q mismatch) - high o2 levels cause pulmonary vasculature to dilate - more blood goes to lungs, but ventilation stays the same
  • Haldane effect - low o2 -> less o2 bound to haemoglobin, so co2 binds to haemoglobin, but when o2 is provided -> haemoglobin pushes off co2 into blood, to pick up o2, due to having higher affinity for o2 -> increases PaCO2
• Monitoring:

  • Oxygen therapy must be monitored with
  • oxygen saturation recordings (dose must also be recorded)
  • arterial blood gas measurements where appropriate
• Haldane effect:

  1. low o2 -> less o2 bound to haemoglobin, so co2 binds to haemoglobin
  2. but when o2 is provided -> haemoglobin pushes off co2 into blood to pick up o2 (due to haemoglobin having higher affinity for o2)
  3. increases PaCO2