Hypoxia: types & effects, Cyanosis, Hypercapnia, Dyspnea, Asphyxia By Dr. Roomi.

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Hypoxia: types & effects, Cyanosis, Hypercapnia, Dyspnea, Asphyxia By Dr. Roomi
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TYPES OF HYPOXIA: There are 4 types of hypoxia: 1.Hypoxic Hypoxia 2.Anemic Hypoxia 3.Stagnant / Ischemic Hypoxia 4.Histotoxic Hypoxia
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HYPOXIC HYPOXIA: Causes: 1.High altitude decreased PO 2 in atmospheric air. 2.Respiratory muscle paralysis. 3.Obstructive lung disease (COPD). 4.Restrictive lung disease (pulmonary fibrosis, pneumothorax). 5.Depression of respiratory centre (disease/ drug). Effect on arterial PO 2: Decreased arterial partial pressure of oxygen. MCQ In other types of hypoxia, PO 2 is normal.
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Clinical features of Hypoxic Hypoxia: Due to decrease arterial PO2 Interstitial cells in peritubular capillaries of kidney secrete Erythropoietin polycythemia Hypoxia pulmonary V.C Pulm. Hypertension Rt. Vent. Hypertrophy Rt. Vent. Failure. TREATMENT: O2 treatment is most effective in this type of hypoxia.
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ANEMIC HYPOXIA: Arterial PO2 is normal but inadequate O2 carrying capacity of blood. Causes: 1.decrease in Hb conc. 2.abnormal Hb like met-Hb or Hb-S 3.CO poisoning: binding site of Hb for oxygen is not available
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CO Poisoning CO is produced by incomplete combustion of carbon. CO is a colorless & odourless gas. Hb has 250 times more affinity to bind with CO as compared to O 2. Carbon monoxide Hb shifts the oxy-Hb curve to left O2 dissociation becomes difficult. CO also inhibits cytochrome. In CO poisoning, skin is cherry red colored. There is no stim. of resp. centre, because arterial PO 2 is normal. When there is 70% carbon monoxy Hb in blood death occurs.
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Treatment of CO Poisoning: Remove the subject from source of exposure. 100% oxygen therapy can help. Hyper-barric O 2 can help (O 2 with increased pressure = 2-3 atm)
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STAGNANT / ISCHEMIC HYPOXIA: CAUSES: Decreased cardiac output / sluggish blood flow due to: heart failure, hemorrhage, circulatory shock and venous obstruction. EFFECTS: Blood remains in tissues for longer time, so tissue extracts increased oxygen from blood more AV difference of oxygen concentration. So, PCO 2 increases, it facilitates unloading of oxygen from hemoglobin (shifts the oxy-hemoglobin association dissociation curve to right).
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HISTOTOXIC HYPOXIA: (poverty amongst plenty) DEFINITION: Inability of the tissues to utilize oxygen inspite of normal arterial PO2 and oxygen carrying capacity. CAUSES: Cyanide poisoning (it inhibits cytochrome oxidases oxidative process is inhibited). Narcotic overdosage (it inactivates the enzyme dehydrogenase inhibition of tissue oxygenation). Beri-beri (it is deficiency of thiamine co-enzyme which is required for many oxidative reactions). TREATMENT: Methylene blue or nitrites. These convert hemoglobin met- hemoglobin. Cyanide + met-hemoglobin cyn-met-hemoglobin (non-toxic compound).
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CYANOSIS: Definition: Bluish discoloration of skin & mucus membrane, when conc. of deoxy-Hb in small blood vessels like capillaries > 5 g/dl.
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Types of Cyanosis: 1. Peripheral: Seen on: exposure to moderate cold & in case of stagnant hypoxia. Seen in: fingers, outer surface of lips. Arterial PO 2 remains normal.
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Types of Cyanosis: 2. Central: Seen in : case of Congenital heart diseases & chronic lung disease. Mostly Arterial PO 2 is below normal (due to hypoxic hypoxia).
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Conditions in which Cyanosis does not occur: Severe anemia (less than 5 gram deoxy Hb/dl) CO poisoning (masked due to cherry red complexion) Met-Hemoglobinemia (chocolate brown discoloration)
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DYSPNEA = Air Hunger Dyspnea: shortness of breath (SOB), or air hunger, is the subjective symptom of breathlessness. 3 factors that cause the sensation of dyspnea: 1) Abnormality of respiratory gases in body fluids (mainly hypercapnia & partly hypoxia) 2) Increase work of breathing by respiratory muscles to breath forcefuly e.g. in asthma 3) State of Mind (neurogenic/emotional dyspnea) More enhanced in people who are claustrophobic (fear of not being able to receive a sufficient quantity of air e.g., small or crowded places).
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HYPERCAPNIA: DEFINITION: Excess CO 2 in body fluids. (Hypercapnia + Hypoxia): Only when hypoxia is caused by hypoventilation or circulatory deficiency.
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Causes of hypoxia + hypercapnia (simultaneously): In hypoxia due to hypoventilation, CO 2 transfer between alveoli & atmosphere is affected as much as is oxygen transfer. In circulatory deficiency decreased blood flow decreased removal of CO 2 from the tissues tissue hypercapnia + hypoxia. But transport capacity of blood for CO 2 is more than 3 times that for O 2, so resulting tissue hypercapnia in much less than tissue hypoxia.
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Severe hypercapnea When alveolar PCO 2 rises above about 60-75 mm Hg air hunger / dyspnea becomes severe. If PCO 2 rises to 80-100 mm Hg lethargy, +/- semicomatose If PCO 2 rises to 120 to 150 mm Hg + / - anesthesia & death At such high PCO 2 Resp. Centre is depressed rather than stimulated vicious circle
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ASPHYXIA: DEFINITION: Simultanoeus acute hypoxia & hypercapnia. CAUSES: Acute airway obstruction When a person is forced to re-breathe his own air in a confined space.
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Mechanism: During asphyxia hypoxia + hypercapnia strong stimulation of respiratory centre & violent inspiratory efforts heart rate increases, BP increases, CATS increase from adrenal medulla (increase in nor- epinephrine > epinephrine) unconsciousness, convulsions & decrease in respiratory rate death.
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O 2 THERAPY: (3 ways) O2 mask on nose Intra-nasal tube O2 tent (newborn)
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Oxygen therapy is helpful in: 1.Most helpful in hypoxic hypoxia. 2.May be helpful in cyanide or CO poisoning 3.May be helpful in case of Gas Gangrene. Note: No use in Anemic & Ischemic (stagnant) hypoxia.
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OXYGEN TOXICITY If 100% O 2 treatment is given for over 8 hours: Features of airway irritation sore throat substernal distress nasal congestion coughing If 100% O 2 treatment is given for 24-48 hrs: Toxic effects start like: lung damage, decreased ability of alveolar macrophages to kill bacteria, decrease in surfactant secretion, cyst formation in lung may occur, Retrolental fibroplasia in infants kept in O 2 tents for long.
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Cause of toxic effects of oxygen: When O 2 is given for longer period toxic effects. Formation of certain free radicals: 1.Super-oxide ions (O 2 -) 2.Hydrogen peroxide (H 2 O 2 ) Prevention of toxic effects of oxygen: By anti-oxidants like vitamin E.

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