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Patho Physiology Of Respiratory Failure
1. Patho-Physiology of Respiratory Failure. John KOLBE Respiratory Services Green Lane Hospital, & Faculty of Health Sciences University of Auckland.
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3. RESPIRATORY FAILURE Def: When the lungs fail to adequately oxygenate the arterial blood and/or fail to prevent undue CO 2 retention. In practical Terms; PaO 2 < 8kPa (60 mmHg) (Hypoxic,TypeI) PaCo 2 > 6.6 kPa (50mmHg) (Hypercapnic, Type II)
4. Relationship of PaCO 2 and (Alveolar) Ventilation PaCO 2 = Vco 2 k VA i.e. PaCO 2 1 VA
15. ALVEOLAR GAS EQUATION PaO 2 = (P b - PH 2 O) F I O 2 - PaCo 2 + k R 20 kPa - PaCo 2 0.8 (Normal A-a gradient = 1-2 kPa)
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18. V/Q = 00 V/Q = 1 V/Q = 0 V/Q mismatch - most important cause - 3 compartment model of Lung Dead Space “Ideal” Shunt
19. V/Q = V/Q = 1 V/Q = 0 Co2 - N Cco2 - N N Compensatory Hyperventilation (of V/Q = 1)
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21. Worsening Disease Unable to Undertake compensatory Hyperventilation Pa CO 2 (pH is normalised by rental (and other) mechanisms) Dangers: - High inspired O 2 - Monitoring O 2 saturations only
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23. Relationship of PaCO 2 and (Alveolar) Ventilation Ve = Va + Vd Ve = k Vco 2 PaCo 2 (1 - Vd/Vt)
24. RIGHT TO LEFT SHUNTS - distinguish from V/Q mismatch by administration of 100% O 2 - normally Pao 2 rises to >600 mmHg - role of - absorption atelectasis - relaxation of hypoxic vasoconstriction