Respiratory depression

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See also Postoperative respiratory depression

  1. May be caused by drugs, injury, or disease
    1. a number of drugs including aminoglycosides, hypnotics, opiates, polymyxins, trimethaphan, opioids
    2. injury to the medullary or pontine respiratory centers, or failure from birth of central nervous system control over breathing while asleep ( Ondine's curse).
    3. neuromuscular diseases such as Guillan Barre, chronic illness polyneuropathy, myopathy, myelopathy
  2. rhythmic pattern of breathing is controlled by neurons located in the pons and medulla
    1. reticular formation of the medulla is a primary center containing cells associated with inspiration and expiration
    2. reticular formation is influenced by impulses from the pons, hypothalamus, reticular activating system, CN 9 and 10
    3. the apneustic center is located in the pons at the vestibular nuclei level and provides for some inspiration drive; in the upper pons the pneumotaxic center inhibits inspiratory activity either through the apneustic center or by directly affecting the inspiratory component of the medullary center
  3. most important input to the control of ventilation is the PaCO2 of the arterial blood which stimulates chemoreceptor on the ventral surface of the medulla
    1. peripheral chemoreceptors at the carotid bifurcation also affect respiration but do so through a drop in PaO2 more than PaCO2
      1. in patients with severe COPD, the hypoxic drive becomes dominant thus if a patient with COPD is given an inspired high O2 mixture to relieve hypoxemia, ventilatory drive may be severely depressed; in these patients ventilatory adequacy is best measured by end-tidal PCO2
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