Oxygen Therapy

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Oxygen Therapy
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Introduction

• The transport and delivery of oxygen to body
  tissues is the essence of resp. care
• Foundation for the rational use of oxygen is
  knowledge of its pharmacokinetics and
  appreciation of the biomedical changes induced by
  too much tissue oxygen (hyperoxia) and too little
  (hypoxia). Need optimal level
• PaO2 is arterial blood oxygen pressure

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Indications for O2 Therapy

• Primary indication is to prevent or relieve
  hypoxemia .
• Hypoxemia can be caused by hypoventilation,
  right-to-left shunts, diffusion impairments, and
  ventilation-perfusion mismatch.
• Alveolar-arterial oxygen gradient P(A-a)O2
  can help determine need for O2 therapy

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Hypoxemia (contd)

• A normal A-a O2 in hypoxemia usually indicates
  the hypoxia is caused by hypoventilation and that
  oxygen therapy alone will not help
• Alveolar Air Equation PAO2
  (PB - 47) x FIO2 - PaCO2/.8
• Normal PaO2 80 - 100 mmHg
• P(A-a)O2 on room air 5-10 mmHg
• P(A-a)O2 on 100 O2 30-60 mmHg

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Indications for Acute O2 Therapy

• Blood gas values PaO2 lt
  60 mmHg SaO2 lt 90
• Clinical signs and symptoms of mild-moderate
  hypoxia tachycardia disorientation tachypne
  a dyspnea cyanosis hypertension restlessnes
  s

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Indications (contd.)

• Clinical signs and symptoms of moderate-severe
  hypoxia cardiac arrhythmias labored
  breathing slow bounding pulse lethargy
  coma

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General Criteria for Long-Term O2 Therapy

• PaO2 lt 55 mmHg at rest on room air
• Evidence of tissue hypoxia pulmonary
  hypertension compensatory polycythemia cor
  pulmonale
• Evidence of central cyanosis
• Severe arterial hypoxemia on exercise
• Improvement with low-flow O2 therapy

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Indications (contd.)

• High-risk patients myocardial
  infarction hemorrhagic shock anaphylactic
  shock burn patients

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Contraindications for O2 Therapy

• primarily a concern over too much O2 leading to
  oxygen toxicity
• in an infant too much O2 can lead to retrolental
  fibroplasia
• Early symptoms of O2 toxicity retrosternal
  discomfort restlessness lethargy vomiting
  cough dyspnea

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Contraindications (contd.)

• Late signs of O2 toxicity respiratory
  insufficicency cyanosis frothy or bloody
  sputum asphyxia
• symptoms develop after 4-12 hours of breathing
  100 O2

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Mechanism of O2 Toxicity

• O2 is used at the cellular level to produce ATP.
  O2 molecule is reduced by cytochrome oxidase and
  forms OH. and H2O2 (free radicals)
• increases in free radicals lead to cell damage,
  wherein leakage from these cells leads to an
  inflammation process
• glutathione, peroxidase, Vitamins C E protect
  against free radicals