OXYGEN THERAPY

Purpose - to relieve hypoxia and provide adequate tissue oxygenation.
Clinical indications:
1. Any patient who is likely to have significant shunt from:
  1. Fluid in the alveoli.
    1. Pulmonary edema.
    2. Pneumonia.
    3. Near-drowning.
    4. Chest trauma.
  2. Collapsed alveoli (atelectasis).
    1. Airway obstruction.
      1. Any unconscious patient.
      2. Choking.
    2. Failure to take deep breaths.
      1. Pain (rib fracture).
      2. Paralysis of the respiratory muscles (spine injury).
      3. Depression of the respiratory center (head injury, drug overdose).
    3. Collapse of an entire lung (pneumothorax).
  3. Other gases in the alveoli.
    1. Smoke inhalation.
    2. Toxic inhalations.
    3. Carbon monoxide poisoning.
  4. Respiratory arrest.
2. Cardiac arrest.
3. Shock.
4. Shortness of breath.
5. Signs of respiratory insufficiency.
6. Breathing fewer than 10 times per minute.
7. Chest pain.
8. Stroke.
9. Anemia.
10. Fetal decelerations during labor.
Precautions:
1. Patients with COPD should receive oxygen at low flow rates (usually 1-3 L/min), to prevent inhibition of hypoxic respiratory drive.
2. Excessive amounts of oxygen for prolonged periods of time will cause retrolental fibroplasia and blindness in premature infants.
3. Oxygen delivered without humidification will result in drying and irritation of respiratory mucosa, decreased ciliary action, and thickening of respiratory secretions.
4. Oxygen supports combustion, and fire is a potential hazard during its administration.
  1. Ground electrical equipment.
  2. Prohibit smoking.
  3. Institute measures to decrease static electricity.
5. High flow rates of oxygen delivered by ventilator or cuffed tracheostomy and endotracheal tubes can produce signs of oxygen toxicity in 24-48 hr:
  1. Cough, sore throat, decreased vital capacity, and substernal discomfort.
  2. Pulmonary manifestations due to:
    1. Atelectasis.
    2. Exudation of protein fluids into alveoli,
    3. Damage to pulmonary capillaries.
    4. Interstitial hemorrhage.
Oxygen administration:
1. Oxygen is dispensed from cylinder or piped-in system.
2. Methods of delivering oxygen:
  1. Nasal prongs/cannula.
    1. Comfortable and simple, and allows patient to move about in bed.
    2. Delivers 25-40% oxygen at flow rates of 4-6 L/min.
    3. Difficult to keep in position unless patient is alert and cooperative.
  2. Jet mixing Venturi mask.
    1. Allows for accurate delivery of prescribed concentration of oxygen.
    2. Delivers 24-50% oxygen at flow rates of 4-8 L/min.
    3. Useful in long-term treatment of COPD.
  3. Simple O₂ face mask.
    1. Poorly tolerated - used for short periods of time; feeling of “suffocation.”
    2. Delivers 50-60% oxygen at flow rates of 8-12 L/min.
    3. Significant rebreathing of carbon dioxide at low oxygen flow rates.
    4. Hot - may produce pressure sores around nose and mouth.
  4. Continuous positive airway pressure (CPAP) mask.
    1. Increases pulmonary volume; opens alveoli; may improve V/Q mismatch.
    2. Used with sleep apnea with or without O₂source.
  5. Nonrebreather reservoir mask.
    1. Reservoir bag has one-way valve preventing the patient from exhaling back into the bag.
    2. Oxygen flow rate prevents collapse of bag during inhalation.
    3. Delivers 90-95% oxygen at flow rates of 10-12 L/min.
    4. Ideal for severe hypoxia, but patient may complain of feelings of suffocation.
  6. T-tube.
    1. Provides humidification and enriched oxygen mixtures to tracheostomy or endotracheal tube.
    2. Delivers up to 100% oxygen at flow rates at least two times minute ventilation.
Intubation and mechanical ventilation:
1. Indications:
  1. Apnea.
  2. Inadequate upper airway or inability to clear secretions.
  3. Worsening respiratory acidosis (Paco₂ > 50 mm Hg) and hypoventilation.
  4. PaO₂ < 55 mm Hg.
  5. Absent gag reflex.
  6. Heavy sedation or paralysis.
  7. Imminent respiratory failure (respiratory rate <8-10 breaths/min or >30-40 breaths/min).
  8. Chest wall trauma.
  9. Profound shock.
  10. Controlled hyperventilation (e.g., increased ICP).
2. Types of positive pressure ventilators:
  1. Pressure cycled - gas flows into the patient until a predetermined airway pressure is reached. Tidal volume is not constant.
  2. Time cycled - gas flows for a certain percentage of time during ventilatory cycle.
  3. Volume cycled - most common ventilators used; tidal volume is determined, and a fixed volume is delivered with each breath.
3. Ventilator modes:
  1. Controlled - machine delivers a breath at a fixed rate regardless of patient’s effort or demands.
  2. Assist-controlled - machine senses a patient’s efforts to breathe and delivers a fixed tidal volume with each effort.
  3. Intermittent mandatory ventilation (IMV) - breaths are delivered by the machine, but the patient may also breathe spontaneously without machine assistance.
  4. Pressure support - patient breathes spontaneously and determines ventilator rate. Tidal volume determined by inflation pressure and patient’s lung-thorax compliance.
4. Minute ventilation - determined by the respiratory rate and the tidal volume. A respiratory rate of 10-15 breaths per minute is considered appropriate. Close monitoring is required to achieve desired (not necessarily normal) Paco,.
5. Positive end-expiratory pressure - maintenance of positive airway pressure at the end of expiration. Applied in the form of continuous positive airway pressure (CPAP) for the patient breathing spontaneously or continuous positive pressure ventilation (CPPV) for the patient receiving mechanical breaths. Applied in 3-5 cm H₂O increments. Levels |>10 - 15 cm H₂O| are associated with cardiovascular dysfunction and hemodynamic compromise.