1. Patho-Physiology of Respiratory Failure. John KOLBE Respiratory Services Green Lane Hospital, & Faculty of Health Sciences University of Auckland.

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

5. Relationship of PaCO 2 and (Alveolar) Ventilation VT = VA + VD

7. Respiratory Drive Neuromuscular Transmission Load

8. HYPOVENTILATION   Drive   Neuromuscular Transmission  Muscle weakness/ (fatigue = reversible) + LOAD.

9. HYPERCAPNIA  Hypoventilation -  Respiratory Drive - Neuro-muscular (in)competence (-  Drive) -  Neuromuscular Transmission - Muscle weakness/fatigue - Abnormal load  V/Q mismatch (Multi-factorial)

14. Alveolar-Arterial Oxygen Gradient. ie, at sea level, breathing air; PAO2 = 20 - PaCO2/0.8 A-a Gradient = 20 - PaCO2/0.8 -PaO2 (Normal A-a gradient = 1-2 kPa)

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)

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)

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

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