Hypoxia
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Contents |
More Specific Terms
Introduction
- Inadequate oxygenation of tissues, short of anoxia.
Etiology
- inadequate supply of oxygen
- carboxyhemoglobin due to carbon monoxide
- respiratory hypoxia
- increased oxygen requirements
- in patients with fixed cardiac output
- thyrotoxicosis
- fever
- anaerobic exercise
- inhibition of oxygen utilization
- low atmospheric oxygen content
- high altitude
Pathology
- with reduced paO2, cerebrovascular resistance decreases & cerebral blood flow increases
- chemoreptors in the brainstem, carotid & aortic bodies increase ventilation
- when hypoxia is accompanied by hyperventilation & decreased pCO2, cerebrovascular resistance increases, cerebral blood flow is diminished & hypoxia is intensified
- compared with the brain, the spinal cord & peripheral nerves are relatively resistant to hypoxia ( cortex is most sensitive)
- hypoxia causes pulmonary arterial constriction which shunts blood away from poorly ventilated lung regions but increases pulmonary vascular resistance & right ventricular afterload
- diminished paO2 results in vasodilation & increased cardiac output
- congestive heart failure
- causes hypoxia via pulmonary edema with collapse of alveolar space
- may be exacerbated by increased cardiac output
- ischemia may exacerbate coronary artery disease
- loss of aerobic metabolism -> formation of lactic acid
- depletion of high- energy phosphate stores ( ATP & creatine phosphate)
- brainstem centers, liver & kidney affected with more severe hypoxia
- death usually results from respiratory failure
Clinical-manifestations
- acute effects
- impaired judgement
- motor incoordination
- similar to alcohol intoxication
- chronic effects
- fatigue
- drowsiness
- apathy
- inattentiveness
- delayed reaction time
Management
- supplemental oxygen
- hypoxia due to pulmonary shunts will not correct with supplemental oxygen ( heart failure, ARDS) [3]
- positive pressure ventilation ( CPAP, BiPAP)
- diuresis for heart failure
More General Terms
Additional Terms
References
- Cotran et al Robbins Pathologic Basis of Disease, 5th ed. W.B. Saunders Co, Philadelphia, PA 1994 pg 3
- Harrison's Principles of Internal Medicine, 14th ed. Fauci et al (eds), McGraw-Hill Inc. NY, 1998, pg 205-206
- Medical Knowledge Self Assessment Program (MKSAP) 15, American College of Physicians, Philadelphia 2009
- NINDS Cerebral Hypoxia Information Page [1]
