Objectives Types and causes of hypoxia Oxygen therapy and toxicity Definition, causes and factors affecting cyanosis Hypoxia
Definition: O2 deficiency at the tissue level . Anoxia: absence of O2 (is not possible in the body during life) Types of hypoxia 1) Hypoxic hypoxia
. PaO2 2) Anemic hypoxia
. Normal PaO2, Hb. 3) Stagnant or ischemic hypoxia
. Normal PaO2 & Hb, blood flow 4) Histotoxic hypoxia
. Normal PaO2 , Hb & blood flow, oxidative enzymes
Causes: Hypoxic hypoxia (most common case of hypoxia)
1) PO2 of inspired air . High altitude. 2) Hypoventilation . Respiratory center (depression) . Nerves (myesthenia gravis) . Muscles (myopathy) . Thoracic cage (kyphosis, scoliosis) . Lung (obstructive & restrictive lung diseases) 3) Alveolo-capillary block . Pulmonary congestion, fibrosis, and edema 4) Disturbed V/Q ratio . Collapse, pneumonia, embolism 5) Shunting venous to arterial blood Anemic hypoxia 1) Quantitative: . Anemia 2) Qualitative: . CO & metHb Stagnant hypoxia 1) Generalized: . CCF . Shock. . Polycythemia. 2) Localized: . Thrombosis, embolism. . Vascular spasm Histotoxic hypoxia 1) Cytochrome oxidase . Cyanide 2) Dehydrogease . Alcohol, narcotics Hypoxia & cyanosis
Normal Hypoxic Anemic Stagnant Histotoxic All N PO 100 2 N N N O2 19.8 N N arterial % 97% N N N
PO2 40 ↑ O2 15.2 ↑ % 75% Venous ↑
No Cyanosis No red hypoxia Chemical Chemical Chemical Chemical O2 therapy ↑ Physical ↑ Physical ↑ Physical ↑ Physical ↑ CO poisoning red hypoxia
1) HbO2 HbCO (same site of O2 binding) 2) Shift O2-Hb dissociation curve to the left. 3) Affinity of Hb to CO is 230 times that of O2 4) Dissociate slowly from Hb. Symptoms 1. Red (HbCO-red cherry color) 2. Respiration is not stimulated 3. Death (70% carboxy-Hb) headache, nausea & judgment. Treatment 1. Terminatation of exposure. 2. Artificial respiration. 3. 95% O2 + % CO2 4. Exchange blood transfusion
Met-Hb (bluish) Another cause of anemic hypoxia Caused by oxidizing agents Sulph-Hb (bluish) Another cause of anemic hypoxia (rare) Caused by exposure to sulfur compounds (drugs or occupational)
Oxygen therapy Highly useful . Hypoxic hypoxia (except venous to arterial shunt) . CO poisoning Less useful anemic and stagnant hypoxia Not useful histotoxic hypoxia Oxygen toxicity
Free O2 radicals damage (oxidative enzymes & nervous symptoms)
Pure O2 . 8 hours: irritation of upper respiratory tract . 24-48 hours: damage to the lung . 48 hours: CNS symptoms In premature infant may cause blindness (↑ O2 in eye vessels vasoconstriction of retinal blood vessels) retinal fibrosis
Hyperbaric O2 accelerate onset of toxicity . Useful in CO poisoning and gas gangarene (anerobic bacteria)
Cyanosis Definition: bluish discoloration of skin and mucous membrane due to reduced Hb in capillary (5g/100ml) Cause:
. Hypoxic hypoxia and stagnant hypoxia (PO2) . Asphyxia (PO2, PCO2 & acidosis) Relation to hypoxia . Absent in anemic hypoxia & histotoxic hypoxia Types of cyanosis . Generalized . Localized (peripheral) Factors affecting cyanosis . Skin: thickness (clear in thin skin e.g. lips) and pigmentation (less clear in dark skin individual) . Capillary: direct proportional to blood flow . Hb: total (polycythemia, anemia), reduced (metHb, sulf-Hb), abnormal (lipemia)
Asphyxia In asphyxia (occlusion of the airway), acute hypercapnia and hypoxia develop together → pH drop. Pronounced stimulation of respiration, with violent respiratory effort. ↑Catecholamine secretion → ↑Blood pr & HR. Eventually the respiratory efforts cease, the blood pr and HR (asphyxiated animals can be revived at this point by artificial respiration). If artificial respiration is not started, cardiac arrest occurs in 4- 5minutes. Drowning Drowning is suffocation by immersion (water). In 10% of drowning, the first gasp of water after losing struggle not to breathe triggers laryngospasm, and death result from asphyxia without any water in the lungs. In 90% the glottic muscles eventually relax and fluid enters the lungs.