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Introduction to Mechanical Ventilation Spontaneous Breathing.

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Presentation on theme: "Introduction to Mechanical Ventilation Spontaneous Breathing."— Presentation transcript:


2 Introduction to Mechanical Ventilation

3 Spontaneous Breathing

4 Positive Pressure Breath

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

6 Indications for Mechanical Ventilation Apnea Acute Ventilatory Failure – Ph 7.30 or – Clinical Signs Impending Ventilatory Failure Acute Respiratory Failure

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

8 Positive Pressure Flow Pattern Considerations Flow = Pressure divided by resistance

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

10 Positive Pressure Flow Patterns Accelerating/decelerat ing or sine wave Peak flow occurs at mid-inspiration Mimics spontaneous breathing

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

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

13 Compare & Contrast

14 Cycling Cycling refers to how the ventilator ends the inspiratory phase of the breath

15 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

16 Triggering The mechanism that starts the inspiratory phase

17 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

18 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

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

20 Ventilator “Modes”

21 Control Mode

22 Assist Mode

23 Assist/Control

24 IMV – Intermittent Mandatory Ventilation



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

28 Some Practical Applications

29 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!

30 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

31 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

32 Resistance and Pressure Vary Directly Resistance and Pressure Vary Inversely With Compliance

33 Initial Values – Peak = 28 cmH2O – Plateau = 23 cmH2O 2 Hours later -peak = 32 cmH2O -plateau = 27 cmH2O

34 Initial Values – Peak = 31 cmH2O – Plateau = 25 cmH2O 2 Hours Later – Peak = 40 cmH2O – Plateau = 25 cmH2O

35 Initial Values – Peak = 49 cmH20 – Plateau = 30 cmH2O 2 Hours Later – Peak = 49 cmH2O – Plateau = 26 cmH2O

36 Initial Values – Peak = 36 cmH2O – Plateau = 29 cmH2O 2 Hours Later – Peak = 32 cmH2O – Plateau = 29 cmH20

37 Initial Values – Peak = 29 cmH2O – Plateau = 22 cmH2O 2 Hours Later – Peak = 41 cmH2O – Plateau = 28 cmH2O

38 Initial Values – Peak = 33 cmH2O – Plateau = 21 cmH2O 2 Hours Later – Peak = 34 cmH2O – Plateau = 19 cmH2O

39 Now lets have some Fun with more math!

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