Oxygenation Failure and Oxygen Therapy

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Oxygenation Failure and Oxygen Therapy
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Respiratory Failure

• Occurs because of inadequate gas exchange
• Type I oxygenation failure
• Blood bypasses or is not fully oxygenated in the
  lungs causing hypoxemia
• PaCO2 is normal or low because ventilation is
  unchanged or increased due to breathlessness
• Causes V/Q mismatch, right ? left shunt, low
  inspired oxygen
• Oxygenation is improved by re-expanding collapsed
  alveoli, oxygen therapy, and reduction of V/Q
  mismatch

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Respiratory Failure, cont

• Type II ventilatory failure
• Hypoventilation reduces CO2 clearance causing
  hypercapnia with or without hypoxemia
• Causes resp muscle weakness, chest wall
  deformity (kyphoscoliosis), impaired resp drive,
  excessive WOB
• Ventilation is improved and WOB decreased by
  decreasing airway resistance, ventilatory
  support, and increasing compliance

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Tissue Hypoxia

• Tissue hypoxia occurs within 4 minutes of
  cardiorespiratory arrest because oxygen reserves
  are small
• Causes of tissue hypoxia
• Hypoxemia
• Failure of oxygen transport
• Decreased CO/perfusion
• Anemia
• hemoglobinopathy
• Failure of tissue oxygen utilization
• Sepsis
• Poisoning (cyanide)

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Monitoring Oxygenation

• Arterial saturation
• Saturation of Hb is determined by partial
  pressure of oxygen in the plasma (PO2)
• Pulse oximetry and ABG analysis measure SpO2,
  SaO2, and PaO2
• These can be normal with tissue hypoxia if its
  caused by failure of oxygen transport or
  utilizationin these cases, mixed venous sat is a
  better indicator of tissue oxygenation
• PaO2/FiO2 ratio is a good index of gas exchange
  that adjusts for FiO2 changes
• PA-aO2 determines efficiency of gas exchange
• Detection of single-organ ischemia is difficult

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Acute Oxygen Therapy

• Indications for instituting oxygen
• Cardiorespiratory arrest
• Hypoxemia
• Hypotension
• Low cardiac output
• Metabolic acidosis
• Respiratory distress

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Oxygen Dosage

• Inadequate O2 therapy causes more deaths and
  disability than can be justified by the risks of
  oxygen
• The risk of hypoxia is usually greater than the
  risk of hypercapnia ? dont withhold oxygen for
  that reason!!
• Use whatever it takes to get the SaO2 to
  90-93...if the person has COPD, a venturi mask
  is a better option so the FiO2 can be controlled

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Efficacy of Oxygen Therapy

• Hypoxemic patients
• Get the most benefit from O2 therapy
• A true shunt causes persistent hypoxemia despite
  increases in FiO2improved oxygenation requires
  reduction of the shunt condition
• In alveolar hypoventilation, O2 therapy relieves
  the hypoxemia but not the hypercarbia

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Efficacy of Oxygen Therapy, cont

• Patients without hypoxemia
• In low CO states, high FiO2 only marginally
  improves oxygenation because Hb is fully
  saturated and O2 solubility is low
• These patients require restoration of blood flow
• In CO poisoning, high dose O2 is essential
  despite a normal PaO2 to reduce the CO half-life