11 Dec

The Management of Chronic Hypoventilation (1)

The Management of Chronic Hypoventilation (1)Chronic alveolar hypoventilation, defined as a sustained increase in Pco2 exceeding 45 mm Hg, is a condition commonly encountered by the chest physician. Most cases are related to chronic airway obstruction, but a substantial minority of cases have other contributing factors such as ventilatory control defects, respiratory muscle weakness, or a combination of factors. Effective therapy requires that each of these factors be identified and addressed. The purpose of this review is to describe an approach to these patients that will consistently identify these other factors and to discuss the treatment of such patients with particular attention to the noninvasive modes of ventilatory assistance currently available. The pathophysiology of chronic alveolar hypoventilation has recently been reviewed in this journal, and will be considered only briefly. buy antibiotics online
Pathophysiology of Chronic Hypoventilation
As shown in Table 1, chronic hypoventilation can arise from a defect involving virtually any aspect of the respiratory apparatus. In essence, hypoventilation occurs when the respiratory system fails to meet the demand for ventilatory work either because the ability to supply ventilatory work has become limited, such as in the case of decreased respiratory drive or respiratory muscle weakness, or when the demand for ventilatory work becomes excessive, such as in the case of severe airway obstruction.

Table 1—Causes of Chronic Hypoventilation Syndrome

Causes
(1) Impaired ventilatory control
Functional
Obesity-hypoventilation syndrome
Myxedema
Drugs (narcotics, sedatives)
Metabolic abnormalities (hypokalemia, hypophosphatemia, hypomagnesemia, metabolic alkalosis)
Structural
Brain-stem infarction or neoplasm
Idiopathic
Primary alveolar hypoventilation
(2) Neuromuscular disorders
Myopathies
Muscular dystrophy
Neuropathies
Bilateral diaphragm paralysis
Poliomyelitis
Amyotrophic lateral sclerosis
Cervical spinal cord injury
Guillain-Barr£ syndrome
Disorders of neuromuscular junction
Myasthenia gravis
(3) Chest wall abnormalities
Kyphoscoliosis
Thoracoplasty
(4) Airway obstruction
Upper airway
Tracheal stenosis
Obstructive sleep apnea
Laryngeal or nasal polyps
Tonsillar hypertrophy
Lower airway
Chronic obstructive pulmonary disease
(5) Parenchymal lung disease
Interstitial lung disease
Surgical resection

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