Respiratory pathway affecting carbon dioxide elimination |
Central nervous system ↓ | "Won't breathe" |
Peripheral nervous system ↓ | "Can't breathe" |
Respiratory muscles ↓ |
Chest wall and pleura ↓ |
Upper airway ↓ |
Lungs | Abnormal gas exchange: "Can't breathe enough" |
Schematic figure representing the respiratory pathway, along which a variety of diseases can affect carbon dioxide elimination and result in hypercapnia. Note that gas exchange abnormalities alone are relatively uncommon causes of hypercapnia, but gas exchange problems in the setting of reduced mechanical capability of the ventilatory pump are very common explanations for acute and chronic hypercapnia. |
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Mechanism and etiologies of hypercapnia |
Mechanism | Etiologies |
Decreased minute ventilation (global hypoventilation; extra pulmonary causes) |
Decreased central respiratory drive | - Sedative overdose (eg, narcotic or benzodiazepine, some anesthetics, tricyclic antidepressants)
- Encephalitis
- Stroke
- Central and obstructive sleep apnea
- Obesity hypoventilation
- Congenital central alveolar hypoventilation
- Brainstem disease
- Metabolic alkalosis
- Hypothyroidism*
- Hypothermia
- Starvation
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Decreased respiratory neuromuscular or thoracic cage function | Primary spinal cord/lower motor neuron/muscle disorders - Cervical spine injury or disease (eg, trauma syringomyelia)¶
- Amyotrophic lateral sclerosis
- Poliomyelitis
- Guillain-Barré syndrome
- Phrenic nerve injury
- Critical illness polymyoneuropathy
- Myasthenia gravis
- Muscular dystrophy
- Polymyositis
- Tetanus
- Transverse myelitis (eg, multiple sclerosis)
- Tick paralysis
- Acute intermittent porphyria
- Eaton Lambert syndrome
- Neuralgic amyotrophy
- Periodic paralysis
- Glycogen storage and mitochondrial diseases
- Respiratory muscle fatigue
| Thoracic cage disorders - Kyphoscoliosis
- Thoracoplasty
- Flail Chest
- Ankylosing spondylitis
- Pectus excavatum
- Fibrothorax
| Metabolic disordersΔ - Hypophosphatemia
- Hypomagnesemia
- Hypothyroidism
- Hyperthyroidism
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Toxins, poisoning, drugs - Tetanus
- Dinoflagellate poisoning
- Shellfish poisoning (red tide)
- Ciguatera poisoning
- Botulism
- Organophosphates
- Succinylcholine and neuromuscular blockade
- Procainamide
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Increased dead space (gas exchange abnormalities; pulmonary parenchymal causes or airway disorders) |
Anatomic | Short shallow breathing |
Physiologic | - Pulmonary embolism (usually severe)
- Pulmonary vascular disease (usually severe)
- Dynamic hyperinflation (eg, upper and lower airway disorders including chronic obstructive pulmonary disease, severe asthma)
- Endstage interstitial lung disease
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Increased carbon dioxide production |
| - Fever
- Thyrotoxicosis
- Increased catabolism (sepsis, steroids)
- Overfeeding
- Metabolic acidosis
- Exercise
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Multifactorial |
| Upper airway disorders◊ - Severe laryngeal or tracheal disorders (stenosis/tumors/angioedema/tracheomalacia)
- Vocal cord paralysis
- Epiglottitis
- Foreign body aspiration
- Retropharyngeal disorders
- Obstructive goiter
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