Introduction to Mechanical Introduction to Mechanical VentilationVentilation

Spontaneous BreathingSpontaneous Breathing

Positive Pressure BreathPositive Pressure Breath

Goals of Mechanical Goals of Mechanical VentilationVentilation

Maintain ABG’s

Optimize V/Q

Decrease Myocardial Workload

Indications for Mechanical Indications for Mechanical VentilationVentilation

ApneaAcute Ventilatory Failure

– Ph 7.30 or <, with PaCO2 50 or >– Clinical Signs

Impending Ventilatory FailureAcute Respiratory Failure

Two Ways to Achieve Two Ways to Achieve Continuous Mechanical Continuous Mechanical

Ventilation, ie CMVVentilation, ie CMV

Negative pressure

Positive pressure

Positive Pressure Flow Positive Pressure Flow Pattern ConsiderationsPattern Considerations

Flow = Pressure divided by resistance

Positive Pressure Flow Positive Pressure Flow PatternsPatterns

Constant flow or Square Wave

Flow stays constant as resistance varies

Thus pressure and resistance vary directly

Positive Pressure Flow Positive Pressure Flow PatternsPatterns

Accelerating/decelerating or sine wave

Peak flow occurs at mid-inspiration

Mimics spontaneous breathing

Positive Pressure Flow Positive Pressure Flow PatternsPatterns

Constant Pressure or tapered flow

Flow (and hence tidal volume) vary with resistance

Flow Patterns SummaryFlow Patterns Summary

Constant flow or square wave

Sine Wave Constant Pressure or

tapered wave

Compare & ContrastCompare & Contrast

Cycling Cycling

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

breath

Cycling MechanismsCycling 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

TriggeringTriggering

The mechanism that starts the inspiratory phase

Trigger MechanismsTrigger MechanismsPressure triggered – a drop in airway

pressure triggers the ventilatorFlow 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

Hazards – Positive Pressure Hazards – Positive Pressure CMVCMV

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

Preventing HazardsPreventing Hazards

Maintain good I:E ratioMake sure flow meets patient’s demandAttention to patient and ventilatorFREQUENT HANDWASHING!

Ventilator “Modes”Ventilator “Modes”

Control ModeControl Mode

Assist ModeAssist Mode

Assist/ControlAssist/Control

IMV – Intermittent Mandatory IMV – Intermittent Mandatory VentilationVentilation

PEEPPEEP

CPAPCPAP

Other ModesOther Modes

High Frequency Ventilation (HFV)Pressure Control ( time cycling)Pressure Support (flow cycling)Airway Pressure Release Ventilation

(APRV)

Some Practical ApplicationsSome Practical Applications

Peak PressurePeak 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!

Plateau PressurePlateau 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

Clinical Analysis By Clinical Analysis By Comparing Peak and Plateau Comparing Peak and Plateau

Pressure ChangesPressure ChangesRemember – a change in elastic resistance

will affect both peak and plateau pressureRemember – a change in airway resistance

only affects the peak pressureCompare the change in plateau pressures

first, then compare the changes in peak pressure

Resistance and Pressure Vary Resistance and Pressure Vary DirectlyDirectly

Resistance and Pressure Vary Inversely With Compliance

Initial Values– Peak = 28 cmH2O– Plateau = 23 cmH2O

2 Hours later-peak = 32 cmH2O

-plateau = 27 cmH2O

Initial Values– Peak = 31 cmH2O– Plateau = 25 cmH2O

2 Hours Later– Peak = 40 cmH2O– Plateau = 25 cmH2O

Initial Values– Peak = 49 cmH20– Plateau = 30 cmH2O

2 Hours Later– Peak = 49 cmH2O– Plateau = 26 cmH2O

Initial Values– Peak = 36 cmH2O– Plateau = 29 cmH2O

2 Hours Later– Peak = 32 cmH2O– Plateau = 29 cmH20

Initial Values– Peak = 29 cmH2O– Plateau = 22 cmH2O

2 Hours Later– Peak = 41 cmH2O– Plateau = 28 cmH2O

Initial Values– Peak = 33 cmH2O– Plateau = 21 cmH2O

2 Hours Later– Peak = 34 cmH2O– Plateau = 19 cmH2O

Now lets have someFun with more math!