Respiratory failure - Pathophysiology of hypercapnic and...

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Unformatted text preview: Pathophysiology of hypercapnic and hypoxic respiratory failure and V/Q relationships Dr.Alok Nath Department of Pulmonary Medicine PGIMER Chandigarh Jan 2006 Respiratory Failure inadequate blood oxygenation or CO 2 removal A syndrome rather than a disease Hypoxemic Hypoxemic Hypercapnic Hypercapnic PaCO2 > 45 mmHg These two types of respiratory failure always coexist PaO2 < 60 mmHg Acute Chronic Two main categories Ventilation Removal of waste CO 2 Transfer of O 2 from air in blood Respiratory function Oxygenation Ventilation CNS Efferents PNS Respiratory Muscles Chest Wall Airways Alveoli Minute Ventilation Alveolar Ventilation PaO2 PaCO2 Chemoreceptors CNS Afferents/ Integration Dysfunction of any of the component leads to ventilatory failure Chemical Stimuli Peripheral chemoreceptors Carotid bodies, Aortic bodies Stimulus: PaO2, Acidemia (pH), PaCO2 Central chemoreceptors Near the ventrolateral surface of the medulla Stimulus: H + of brain ECF (pH), PaCO2 Chemical Stimuli Hypoxia peripheral receptors Hypercapnia central receptors Response to respiratory acidosis is always greater than metabolic acidosis Hypercapnic Respiratory Failure Partial pressures of CO 2 in blood depends on: Co 2 production Dead space Minute ventilation CO2 Production Dead Space Ratio Minute Ventilation Hypercapnic Respiratory Failure VA = VCO2 / PACO2 x K Hypercapnic respiratory failure Decreased minute ventilation V T = V D + V A (multiplying by respiratory frequency) V E = V D + V A OR V A = V E V D Acc. To alveolar ventilation equation: V A x F a CO 2 = V A So V CO2 = V A x P A CO 2 x K Now, V A = V CO2 / P A CO 2 x K Paco 2 is inversely proportional to minute ventilation Hypercapnic respiratory failure Decreased minute ventilation CNS disorders Stroke, brain tumor, spinal cord lesions, drug overdose Peripheral nerve disease Guillain-Barre syndrome, botulism, myasthenia gravis Muscle disorders Muscular dystrophy, respiratory muscles fatigue Hypercapnic respiratory failure Chest wall abnormalities Scoliosis, kyphosis, obesity Metabolic abnormalities Myxedema, hypokalemia Airway obstruction Upper airway obstruction, Asthma, COPD Pathophsiology in Asthma and COPD more complex Hypercapnic respiratory failure...
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Respiratory failure - Pathophysiology of hypercapnic and...

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