1. Introduction to Mechanical Ventilation

2. Spontaneous Breathing

3. Positive Pressure Breath

4. Goals of Mechanical Ventilation
Maintain ABG’s
Optimize V/Q
Decrease Myocardial Workload

5. Indications for Mechanical Ventilation
Apnea
Acute Ventilatory Failure
Ph 7.30 or <, with PaCO2 50 or >
Clinical Signs
Impending Ventilatory Failure
Acute Respiratory Failure

6. Two Ways to Achieve Continuous Mechanical Ventilation, ie CMV
Negative pressure
Positive pressure

7. Positive Pressure Flow Pattern Considerations
Flow = Pressure divided by resistance

8. Positive Pressure Flow Patterns
Constant flow or Square Wave
Flow stays constant as resistance varies
Thus pressure and resistance vary directly

9. Positive Pressure Flow Patterns
Accelerating/decelerating or sine wave
Peak flow occurs at mid-inspiration
Mimics spontaneous breathing

10. Positive Pressure Flow Patterns
Constant Pressure or tapered flow
Flow (and hence tidal volume) vary with resistance

11. Flow Patterns Summary Constant flow or square wave Sine Wave
Constant Pressure or tapered wave

12. Compare & Contrast

13. Cycling
Cycling refers to how the ventilator ends the inspiratory phase of the breath

14. Cycling Mechanisms
Volume cycling – inspiration ends when a preset tidal volume is delivered
Pressure cycling – inspiration ends when a preset pressure is reached on the airway
Time cycling – inspiration ends when a preset inspiratory time has elapsed
Flow cycling – inspiration ends when a preset flow has been reached

15. The mechanism that starts the inspiratory phase
Triggering
The mechanism that starts the inspiratory phase

16. Trigger Mechanisms
Pressure triggered – a drop in airway pressure triggers the ventilator
Flow triggered – a constant (bias) flow of gas passes through the ventilator circuit. When the patient starts to inhale the ventilator detects the drop in bias flow and triggers
Types of triggered breaths: patient = assisted; ventilator = controlled, operator = manual

17. Hazards – Positive Pressure CMV
Increased mean intrathoracic pressure
Decreased venous return
Increased intracranial pressure
Pulmonary Volu/Barotrauma
Fluid retention
Gastric Ulcers
Muscle Atrophy & Patient Dependence
Mechanical Failure
Mismanagement
Contamination/Infection

18. Preventing Hazards Maintain good I:E ratio
Make sure flow meets patient’s demand
Attention to patient and ventilator
FREQUENT HANDWASHING!

19. Ventilator “Modes”

20. Control Mode

21. Assist Mode

22. Assist/Control

23. IMV – Intermittent Mandatory Ventilation

24. PEEP

25. CPAP

26. Other Modes High Frequency Ventilation (HFV)
Pressure Control ( time cycling)
Pressure Support (flow cycling)
Airway Pressure Release Ventilation (APRV)

27. Some Practical Applications

28. Peak Pressure
Pressure on manometer immediately at end of inspiratory phase
Represents pressure needed to overcome both elastic and airway resistance
Used to calculate dynamic compliance
Cdyn = VT/Peak pressure
PEAK PRESSURE WILL CHANGE WHEN EITHER ELASTIC OR AIRWAY RESISTANCE CHANGES!

29. Plateau Pressure
Pressure on manometer after inspiration has ended but before expiration has started
Represents pressure needed to overcome elastic resistance only
Used to calculate static compliance
Cstat = VT/plateau pressure
PLATEAU PRESSURE CHANGES ONLY WHEN ELASTIC RESISTANCE CHANGES

30. Clinical Analysis By Comparing Peak and Plateau Pressure Changes
Remember – a change in elastic resistance will affect both peak and plateau pressure
Remember – a change in airway resistance only affects the peak pressure
Compare the change in plateau pressures first, then compare the changes in peak pressure

31. Resistance and Pressure Vary Directly
Resistance and Pressure Vary Inversely With Compliance

32. Initial Values 2 Hours later Peak = 28 cmH2O Plateau = 23 cmH2O

33. Initial Values 2 Hours Later Peak = 31 cmH2O Plateau = 25 cmH2O

34. Initial Values 2 Hours Later Peak = 49 cmH20 Plateau = 30 cmH2O
Peak = 49 cmH2O
Plateau = 26 cmH2O

35. Initial Values 2 Hours Later Peak = 36 cmH2O Plateau = 29 cmH2O

36. Initial Values 2 Hours Later Peak = 29 cmH2O Plateau = 22 cmH2O

37. Initial Values 2 Hours Later Peak = 33 cmH2O Plateau = 21 cmH2O

38. Now lets have some
Fun with more math!