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hypoxia

Inadequate oxygenation of tissues, short of anoxia. Etiology: 1) pulmomary ischemia - pulmonary embolism - cardiac arrest 2) loss of oxygen carrying capacity of blood a) inadequate supply of oxygen - carboxyhemoglobin due to carbon monoxide - methemoglobinemia - respiratory hypoxia - COPD, asthma - hypoventilation: narcotic overdose - right to left pulmonary shunting - heart failure - ARDS - collapsed lung b) anemia 3) increased oxygen requirements a) in patients with fixed cardiac output - thyrotoxicosis - fever b) anaerobic exercise 4) inhibition of oxygen utilization - cyanide poisoning - diphtheria toxin 5) low atmospheric oxygen content - high altitude Pathology: 1) with reduced paO2, cerebrovascular resistance decreases & cerebral blood flow increases 2) chemoreptors in the brainstem, carotid & aortic bodies increase ventilation 3) when hypoxia is accompanied by hyperventilation & decreased pCO2, cerebrovascular resistance increases,cerebral blood flow is diminished & hypoxia is intensified 4) compared with the brain, the spinal cord & peripheral nerves are relatively resistant to hypoxia (cortex is most sensitive) 5) hypoxia causes pulmonary arterial constriction which shunts blood away from poorly ventilated lung regions but increases pulmonary vascular resistance & right ventricular afterload 6) diminished paO2 results in vasodilation & increased cardiac output 7) congestive heart failure a) causes hypoxia via pulmonary edema with collapse of alveolar space b) may be exacerbated by increased cardiac output 8) ischemia may exacerbate coronary artery disease 9) loss of aerobic metabolism -> formation of lactic acid - metabolic acidosis 10) depletion of high-energy phosphate stores (ATP & creatine phosphate) 11) brainstem centers, liver & kidney affected with more severe hypoxia 12) death usually results from respiratory failure Clinical manifestations: 1) acute effects - impaired judgement - motor incoordination - similar to alcohol intoxication 2) chronic effects - fatigue - drowsiness - apathy - inattentiveness - delayed reaction time Special laboratory: - pulse oximetry - SaO2 <= 88 mm Hg at rest or with exercise Management: 1) supplemental oxygen a) SaO2 <= 88 mm Hg at rest or with exercise b) high-flow oxygen delivered by nasal cannula for hypoxemic acute respiratory failure with lower mortality at 90 days, more ventilator- free days, & less respiratory discomfort than BiPAP [4,6] c) endotracheal intubation & mechanical ventilation rate similar for BiPAP vs high-flow oxygen [4] 2) hypoxia due to pulmonary shunts will not correct with supplemental oxygen (heart failure, ARDS) [3] a) positive pressure ventilation (CPAP, BiPAP) b) diuresis for heart failure

Related

hypoxia induced genes

Specific

anoxia anoxic/hypoxic encephalopathy asphyxia (suffocation) high-altitude cerebral edema (HACE) ischemia

General

pathologic process

References

  1. Cotran et al Robbins Pathologic Basis of Disease, 5th ed. W.B. Saunders Co, Philadelphia, PA 1994 pg 3
  2. Harrison's Principles of Internal Medicine, 14th ed. Fauci et al (eds), McGraw-Hill Inc. NY, 1998, pg 205-206
  3. Medical Knowledge Self Assessment Program (MKSAP) 15, American College of Physicians, Philadelphia 2009
  4. Frat J-P et al. High-flow oxygen through nasal cannula in acute hypoxemic respiratory failure. N Engl J Med 2015 Jun 4; 372:2185. PMID: 25981908 - Stephan F et al. High-flow nasal oxygen vs noninvasive positive airway pressure in hypoxemic patients after cardiothoracic surgery: A randomized clinical trial. JAMA 2015 Jun 16; 313:2331. PMID: 25980660
  5. Rodriguez-Roisin R, Roca J. Mechanisms of hypoxemia. Intensive Care Med. 2005 Aug;31(8):1017-9. Epub 2005 Jun 14. PMID: 16052273
  6. Qaseem A et al. Appropriate use of high-flow nasal oxygen in hospitalized patients for initial or postextubation management of acute respiratory failure: A clinical guideline from the American College of Physicians. Ann Intern Med 2021 Apr 27; [e-pub]. PMID: 33900796 https://www.acpjournals.org/doi/10.7326/M20-7533 - Baldomero AK et al. Effectiveness and harms of high-flow nasal oxygen for acute respiratory failure: An evidence report for a clinical guideline by the American College of Physicians. Ann Intern Med 2021 Apr 27; [e-pub]. PMID: 33900793 https://www.acpjournals.org/doi/10.7326/M20-4675 - Baldomero AK, et al Effectiveness and harms of high-flow nasal oxygen (HFNO) for acute respiratory failure: a systematic review protocol. BMJ Open. 2020. PMID: 32051320 Free PMC article.
  7. National Institute of Neurological Disorders and Stroke (NINDS) NINDS Cerebral Hypoxia Information Page https://www.ninds.nih.gov/Disorders/All-Disorders/Cerebral-Hypoxia-Information-Page