24- Oxygen therapy

• Indications to use O2

  • Hypoxia
  • Acute hypotension
  • Breathing inadequacy
  • Trauma (any trauma pt is put on rebreather 15L in ER)
• Mechanisms of hypoxemia

  1. VQ mismatch

  2. High altitude

  3. Right to left shunt

  4. Impaired diffusion

  5. Alveolar hypoventilation
• VQ mismatch

  • Reduced retention, normal perfusion→collapsed alveolus, fluid filled (edema)
  • Reduced perfusion, normal ventilation→PE
• Right to left shunt

  • Mixing deoxygenated blood with oxygenated blood→delivery of deoxygenated blood to organs
  • Intracardiac (ASD, VSD)
  • Intrapulmonary(AVmalformation)
• Impaired diffusion

  • Any destruction to alveolar capillary membrane. (emphysema, fibrosis, ILD)
• Alveolar hypoventilation

  • Central: stroke, MS, tumor, narcotic use
  • Peripheral: neuromuscular (Duchenne, MG), severe kyphoscoliosis, increased airway resistance (asthma, COPD, smoker bronchiectasis)
• Requirements for oxygen delivery systems

  • Oxygen supply
  • Flowmeter
  • Oxygen tubing
  • Delivery device
  • Humidifier: essential if >4L of oxygen given. Prevents drying of MM and epistaxis and formation of tenacious thick sputum
• Dangers of O2 therapy

  • Ignition hazard
  • Risk of respiratory depression (example, COPD: hypoxic drive if high O2 concentration given may result of resp depression)
  • Risk of O2 toxicity esp. if high flow on long term
• Nasal cannula

  • Simplest way of oxygen delivery
  • Very convenient to the patient (can eat and speak)
  • 1-4L/min, 24-40% FiO2 (>4L→discomfort and drying of MM with no added benefit)
  • Used for minor respiratory distress (non-acute ward use or if mildly hypoxic)
• Simple face mask (Hudson mask)

  Simple face mask with no bag; requires good fit
• Simple face mask (Hudson mask)

  • Flow rate 5-10L, delivers variable amount of O2 (40-60%)
• Venturi mask

  Simple face mask with a valve/adapter with a certain diameter that controls the flow
• Venturi mask

  • Gives a controlled way of oxygen delivery (specific volume of air and O2)
  • Useful for accurately delivering low concentration of O2; esp. in COPD pts who depend on the hypoxic drive & should only be given a controlled amount of oxygen
• Venturi mask oxygen flow rates and concentrations

  • BLUE = 2-4L/min = 24% O2
  • WHITE = 4-6L/min = 28% O2
  • YELLOW = 8-10L/min = 35% O2
  • RED = 10-12L/min = 40% O2
  • GREEN = 12-15L/min = 60% O2
• Numbers/colors may vary from one place to another so always read the valves
• Non-rebreather mask


  Simple mask with a valve: one-way exhalation port & freely expanding bag
• Non-rebreather mask

  • Oxygen fills the bag à prevents it from diluting with outside air. The patient exhales from the valve in the mask. Mask is sealed tightly à very high O2 concentration
  • Used in patients who are acutely ill and not responding to other methods. Acts as a bridge to another action (high flow NC, noninvasive ventilation)
  • Delivers >85% FiO2 and 15L O2
• High flow NC

  Huge flow of O2 (30-60L) with very good humidification, esp. for those with persistent hypoxemic (example: COVID19)
• High flow NC

  • Through wide nasal prongs, provides PEEP à prevents alveoli from collapsing
  • Heated and humidified
  • Inspiratory demands better met
  • Provides high functional residual capacity by delivery of positive end-expiratory pressure
  • Lighter and easily tolerable than non-invasive
  • Oxygen dilution minimized
  • Washout of dead space (CO2 removal)
• CPAP

  Continuous positive airway pressure = high pressure air/oxygen with a tight-fitting mask. Positive pressure all the time. Keeps airways open in OSA or HF.
• BiPAP

  Bilevel positive airway pressure = high positive pressure on inspiration and lower positive pressure on expiration. Used in COPD and atelectasis.
• Invasive ventilation


  Ventilation bag/machine is attached to an artificial airway (ETT) to ventilate lungs.
• Invasive ventilation is discussed further under "Respiratory Failure".