hypoxia: types & effects, cyanosis, hypercapnia, dyspnea, asphyxia by dr. roomi
TRANSCRIPT
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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 Hypoxia2. Anemic Hypoxia3. Stagnant / Ischemic Hypoxia4. Histotoxic Hypoxia
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HYPOXIC HYPOXIA:
Causes:1. High altitude decreased PO2 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 PO2:
– Decreased arterial partial pressure of oxygen. MCQ– In other types of hypoxia, PO2 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 O2.• 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 PO2 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 O2 can help (O2 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, PCO2 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 PO2 remains normal.
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Types of Cyanosis:
2. Central:• Seen in :– case of Congenital heart
diseases & – chronic lung disease.
• Mostly Arterial PO2 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 CO2 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, CO2 transfer between alveoli & atmosphere is affected as much as is oxygen transfer.
• In circulatory deficiency decreased blood flow decreased removal of CO2 from the tissues tissue hypercapnia + hypoxia.
• But transport capacity of blood for CO2 is more than 3 times that for O2, so resulting tissue hypercapnia in much less than tissue hypoxia.
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Severe hypercapnea
• When alveolar PCO2 rises above about 60-75 mm Hg air hunger / dyspnea becomes severe.
• If PCO2 rises to 80-100 mm Hg lethargy, +/- semicomatose
• If PCO2 rises to 120 to 150 mm Hg + / - anesthesia & death
• At such high PCO2 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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O2 THERAPY: (3 ways)
O2 mask on noseIntra-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 poisoning3. May be helpful in case of Gas Gangrene.• Note: No use in Anemic & Ischemic (stagnant)
hypoxia.
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OXYGEN TOXICITYIf 100% O2 treatment is given for over 8 hours:
Features of airway irritation– sore throat– substernal distress– nasal congestion– coughing
If 100% O2 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 O2 tents for long.
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Cause of toxic effects of oxygen:
• When O2 is given for longer period toxic effects.• Formation of certain free radicals:
1. Super-oxide ions (O2-)2. Hydrogen peroxide (H2O2)
• Prevention of toxic effects of oxygen:– By anti-oxidants like vitamin E.