Basic mechanical ventilation

1. Basic mechanical ventilation Charles GomersallDept of Anaesthesia & Intensive CareThe Chinese University of Hong KongPrince of Wales Hospital Version 1.0 May 2003

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3. Disclaimer • Although considerable care has been taken in the preparation of this tutorial, the author, the Prince of Wales Hospital and The Chinese University of Hong Kong take no responsibility for any adverse event resulting from its use.

4. CO2 O2

5. Getting oxygen in • Depends on • PAO2 • FIO2 • PACO2 • Alveolar pressure • Ventilation • Diffusing capacity • Perfusion • Ventilation-perfusion matching     

6. Carbon dioxide out • Respiratory rate • Tidal volume • Deadspace

7. Oxygen in  FIO2  mean alveolar pressure PEEP Re-open alveoli and  shunt Carbon dioxide out  ventilation  RR  tidal volume Main determinants

8. Mean airway pressure Mean airway pressure Mean airway pressure Pressure Pressure Time Time

9. Mean airway pressure Mean airway pressure Mean airway pressure Pressure Pressure Time Time

10. Inspiratory time • Set as: • % of respiratory cycle • I:E ratio • Expiratory time not set • Remaining time after inspiration before next breath

11. Inspiratory time • Increased inspiratory time • Improved oxygenation • Unnatural pattern of breathing • Deeper sedation • Increased risk of gas trapping

12. Mean airway pressure Mean airway pressure Mean airway pressure Pressure Pressure Time Time

13. PEEP Improves oxygenation •  mean alveolar pressure •  shunting

14. Other settings • Trigger sensitivity •  sensitivity preferable • Flow triggering general more sensitive than pressure triggering •  flow or  pressure   sensitivity

15. Other settings Rise time Rise time Flow Inspiratory time Inspiratory time Pressure Time Time

16. Respiratory complications • Nosocomial pneumonia • Barotrauma • Gas trapping

17. Barotrauma • High pressures (barotrauma) • High volumes (volutrauma) • Shear injury

18. Gas trapping

19. Gas trapping

20. Gas trapping

21. Gas trapping

22. Gas trapping

23. Gas trapping

24. Gas trapping

25. Gas trapping • Predisposing factors: • asthma or COPD • long inspiratory time ( expiratory time short) • high respiratory rate ( absolute expiratory time short) • Effects • progressive hyperinflation of alveoli • progressive rise in end-expiratory pressure (intrinsic PEEP)

26. Intrinsic PEEP (PEEPi) Pressure PEEPtot PEEPe Time

27. Gas trapping • Adverse effects • Barotrauma • Cardiovascular compromise

28. Cardiovascular effects • Preload • positive intrathoracic pressure reduces venous return • exacerbated by • high inspiratory pressure • prolonged inspiratory time • PEEP

29. Cardiovascular effects • decreased afterload due to decreased LV transmural pressure

30. Cardiovascular effects • decreased afterload due to decreased LV transmural pressure

31. Cardiovascular effects • Overall effect depends on whether ventricular contractility is normal or abnormal •  contractility •  cardiac output • normal contractility •  cardiac output

32. Hypotension • Consider • Drug induced • Gas trapping • Tension pneumothorax

33. Modes • To learn about specific modes of ventilation (eg PRVC) download the appropriate lectures by clicking on the button Download