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INVASIVE MECHANICAL VENTILATION D. Sara Salarian,
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D. Sara Salarian,. Nov 2006 Kishore P. Critical Care Conference Improve oxygenation Increase/maintain minute ventilation and help CO 2 clearance

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Page 1: D. Sara Salarian,. Nov 2006 Kishore P. Critical Care Conference  Improve oxygenation  Increase/maintain minute ventilation and help CO 2 clearance

INVASIVE MECHANICAL VENTILATION

D. Sara Salarian,

Page 2: D. Sara Salarian,. Nov 2006 Kishore P. Critical Care Conference  Improve oxygenation  Increase/maintain minute ventilation and help CO 2 clearance

Nov 2006Kishore P.

Critical Care Conference

Why ventilate?

Improve oxygenation Increase/maintain minute ventilation and

help CO2 clearance Decrease work of breathing Protect airway

Page 3: D. Sara Salarian,. Nov 2006 Kishore P. Critical Care Conference  Improve oxygenation  Increase/maintain minute ventilation and help CO 2 clearance

Mask based device

Negative pressure ventilators“The Iron Lung”

Page 4: D. Sara Salarian,. Nov 2006 Kishore P. Critical Care Conference  Improve oxygenation  Increase/maintain minute ventilation and help CO 2 clearance

Origins of mechanical ventilation

• Negative-pressure ventilators (“iron lungs”)

• Non-invasive ventilation first used in Boston Children’s Hospital in 1928

• Used extensively during polio outbreaks in 1940s – 1950s

• Positive-pressure ventilators

• Invasive ventilation first used at Massachusetts General Hospital in 1955

• Now the modern standard of mechanical ventilation

The era of intensive care medicine began with positive-pressure ventilation

The iron lung created negative pressure in abdomen as well as the chest, decreasing cardiac output.

Iron lung polio ward at Rancho Los Amigos Hospital in 1953.

Page 5: D. Sara Salarian,. Nov 2006 Kishore P. Critical Care Conference  Improve oxygenation  Increase/maintain minute ventilation and help CO 2 clearance

Modes of Mechanical Ventilation

Spontaneous/Controlled/Dual Controlled Mechanical Ventilation (CMV) Assist Control (AC)/Volume Control (VC) Intermittent Mandatory Ventilation (SIMV) Pressure Control (PCV) Pressure Support Ventilation (PSV)

Page 6: D. Sara Salarian,. Nov 2006 Kishore P. Critical Care Conference  Improve oxygenation  Increase/maintain minute ventilation and help CO 2 clearance

Nov 2006Kishore P.

Critical Care Conference

Patient system interaction

Assist control Assisted-pressure supportControlled MV

Spontaneous

SIMVIMV

+PEEP

CPAP

Page 7: D. Sara Salarian,. Nov 2006 Kishore P. Critical Care Conference  Improve oxygenation  Increase/maintain minute ventilation and help CO 2 clearance

Breath Types

1.Spontaneous Breath • Inspiration is both initiated and

terminated by the patient.

2.Mandatory Breath • Inspiration is either initiated or

terminated by the ventilator.

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Page 8: D. Sara Salarian,. Nov 2006 Kishore P. Critical Care Conference  Improve oxygenation  Increase/maintain minute ventilation and help CO 2 clearance

Breath Patterns

1.Continuous Mandatory Ventilation • CMV • All breaths mandatory

2.Intermittent Mandatory Ventilation • IMV or SIMV • Mandatory and spontaneous

breaths

3.Continuous Spontaneous Ventilation • All breaths spontaneous

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Page 9: D. Sara Salarian,. Nov 2006 Kishore P. Critical Care Conference  Improve oxygenation  Increase/maintain minute ventilation and help CO 2 clearance

Phase Variables

TRIGGER starts inspiration Example: pressure drop when patient

sucks in

LIMIT preset inspiratory value Example: preset maximum inspiratory

flow

CYCLE stops inspiration Example: preset inspiratory time

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Page 10: D. Sara Salarian,. Nov 2006 Kishore P. Critical Care Conference  Improve oxygenation  Increase/maintain minute ventilation and help CO 2 clearance

VOLUME-CYCLED VENTILATION

the controlled variables of tidal volume and inspiratory flow determine airway pressure and inspiratory time

Variations in airway resistance or lung compliance alter airway pressures but do not affect minute ventilation

There are three methods of initiating the inspiratory phase in volume-cycled mechanical ventilators: controlled, assist-control, and intermittent mandatory ventilation (IMV)

Page 11: D. Sara Salarian,. Nov 2006 Kishore P. Critical Care Conference  Improve oxygenation  Increase/maintain minute ventilation and help CO 2 clearance

Nov 2006Kishore P.

Critical Care Conference

Modes of ventilationPressure controlled

Ventilator applies a predefined target pressure to the airway during inspiration

Adv.- decreased risk of barotrauma

Disadv.- with decreasing compliance or increasing resistance, tidal volume and minute ventilation fall

Page 12: D. Sara Salarian,. Nov 2006 Kishore P. Critical Care Conference  Improve oxygenation  Increase/maintain minute ventilation and help CO 2 clearance

Comparison chart

Volume Pressure Flow I-time

Spontaneous

variable

variable

variable

variable

VCV FIXED variable FIXED FIXED

PCV variable FIXED

variable FIXED

PSVvariable FIXED

Variable

variable

Page 13: D. Sara Salarian,. Nov 2006 Kishore P. Critical Care Conference  Improve oxygenation  Increase/maintain minute ventilation and help CO 2 clearance

MODES OF PPV

C M VA /C V o lu m e

A /C P ressu re

S IM VS IM V V o lu m e

S IM V P ressu re

S P O N TA N E O U SC P A P w /P S V

C P A P w /o P S VO th er

3 C a teg ories o f P P V

Page 14: D. Sara Salarian,. Nov 2006 Kishore P. Critical Care Conference  Improve oxygenation  Increase/maintain minute ventilation and help CO 2 clearance

Controlled mechanical ventilation (CMV)

minute ventilation is completely dependent upon the rate and tidal volume set on the ventilator. Any respiratory efforts made by the patient do not contribute to minute ventilation

Controlled ventilation is the required ventilatory mode in patients who are making no respiratory effort (eg, spinal cord injury or drug overdose and those who have been subjected to pharmacologic paralysis).

Page 15: D. Sara Salarian,. Nov 2006 Kishore P. Critical Care Conference  Improve oxygenation  Increase/maintain minute ventilation and help CO 2 clearance

Controlled Mechanical Ventilation Advantages: rests muscles of respiration Disadvantages: requires sedation/neuro-

muscular blockade, potential adverse hemodynamic effects

Advantages: rests muscles of respiration Disadvantages: requires sedation/neuro-

muscular blockade, potential adverse hemodynamic effects

Page 16: D. Sara Salarian,. Nov 2006 Kishore P. Critical Care Conference  Improve oxygenation  Increase/maintain minute ventilation and help CO 2 clearance

Controlled Mode (Pressure-Targeted Ventilation)

Controlled Mode (Pressure-Targeted Ventilation)

Pressure

Flow

Volume

(L/min)

(cm H2O)

(ml)

Time (sec)

Time-Cycled

Set PC level

Time Triggered, Pressure Limited, Time Cycled Ventilation

Page 17: D. Sara Salarian,. Nov 2006 Kishore P. Critical Care Conference  Improve oxygenation  Increase/maintain minute ventilation and help CO 2 clearance

Pressure Control Ventilation C = VT / PC

Pressure Control Ventilation C = VT / PC

Flow

Pressure

VolumeCl

Cl

Set PC level

Time (sec)

(L/min)

(cm H2O)

(ml)

Page 18: D. Sara Salarian,. Nov 2006 Kishore P. Critical Care Conference  Improve oxygenation  Increase/maintain minute ventilation and help CO 2 clearance

Controlled Mode Volume TargetedControlled Mode Volume Targeted

Flow

Pressure

Volume

Time (sec)

(L/min)

(cm H2O)

(ml)

Page 19: D. Sara Salarian,. Nov 2006 Kishore P. Critical Care Conference  Improve oxygenation  Increase/maintain minute ventilation and help CO 2 clearance

ASSIST-CONTROL MECHANICAL VENTILATION

In the assist-control (A/C) mode, the ventilator senses an inspiratory effort by the patient and responds by delivering a preset tidal volume. Every inspiratory effort that satisfies the ventilator's demand valve trigger threshold initiates delivery of the preset tidal volume

Patient work is therefore required to trigger the ventilator and continues during inspiration

A control mode back-up rate is set on the ventilator to prevent hypoventilation

Page 20: D. Sara Salarian,. Nov 2006 Kishore P. Critical Care Conference  Improve oxygenation  Increase/maintain minute ventilation and help CO 2 clearance

Assist-Control Ventilation

Volume or time-cycled breaths + minimal ventilator rate

Additional breaths delivered with inspiratory effort

Order: AC Vt 500, RR12, 100% FiO2, 5 PEEP

Page 21: D. Sara Salarian,. Nov 2006 Kishore P. Critical Care Conference  Improve oxygenation  Increase/maintain minute ventilation and help CO 2 clearance

Assist-Control Ventilation

Advantages: reduced work of breathing; allows patient to modify minute ventilation

Disadvantages: potential adverse hemodynamic effects or inappropriate hyperventilation

Page 22: D. Sara Salarian,. Nov 2006 Kishore P. Critical Care Conference  Improve oxygenation  Increase/maintain minute ventilation and help CO 2 clearance

INTERMITTENT MANDATORY VENTILATION

With intermittent mandatory ventilation (IMV), the degree of ventilatory support is determined by the selected IMV rate. At regular intervals, the ventilator delivers a breath based upon a preset tidal volume and rate. In addition, the patient is allowed to breathe spontaneously through the ventilator circuit at a tidal volume and rate determined according to need and capacity.

Most present day ventilators synchronize the intermittent ventilator breaths with inspiratory effort by the patient, a modality termed synchronized IMV or SIMV. However, this modification requires a trigger modality

Page 23: D. Sara Salarian,. Nov 2006 Kishore P. Critical Care Conference  Improve oxygenation  Increase/maintain minute ventilation and help CO 2 clearance

Synchronized Intermittent Mandatory Ventilation (SIMV)

Potential advantages More comfortable for some

patients Less hemodynamic effects

Potential disadvantages Increased work of breathing

Page 24: D. Sara Salarian,. Nov 2006 Kishore P. Critical Care Conference  Improve oxygenation  Increase/maintain minute ventilation and help CO 2 clearance

SIMV(Volume-Targeted Ventilation)

SIMV(Volume-Targeted Ventilation)

Spontaneous Breaths

Flow(L/m)

Pressure(cm H2O)

Volume(mL)

Page 25: D. Sara Salarian,. Nov 2006 Kishore P. Critical Care Conference  Improve oxygenation  Increase/maintain minute ventilation and help CO 2 clearance

Pressure

Flow

Volume

(L/min)

(cm H2O)

(ml)

SIMV + PS (Pressure-Targeted

Ventilation)

SIMV + PS (Pressure-Targeted

Ventilation)

PS Breath

Set PS levelSet PC level

Time (sec)

Time-Cycled Flow-Cycled

Page 26: D. Sara Salarian,. Nov 2006 Kishore P. Critical Care Conference  Improve oxygenation  Increase/maintain minute ventilation and help CO 2 clearance

PRESSURE SUPPORT VENTILATION Pressure support ventilation (PSV) is flow-

cycled in that, once triggered by a demand valve, the preset pressure is sustained until the inspiratory flow tapers, usually to 25 percent of its maximal value [22]. PSV tends to be a comfortable ventilatory modality because the patient has greater control over ventilator cycling and flow rates. Close monitoring is required whenever PSV is used alone because neither tidal volume nor minute ventilation is guaranteed. PSV can be added during full or partial support with SIMV to overcome endotracheal tube and ventilator circuitry resistance encountered during spontaneous breaths

Page 27: D. Sara Salarian,. Nov 2006 Kishore P. Critical Care Conference  Improve oxygenation  Increase/maintain minute ventilation and help CO 2 clearance

Pressure-Support Ventilation Pressure assist during spontaneous inspiration

with flow-cycled breath Pressure assist continues until inspiratory

effort decreases Delivered tidal volume dependent on

inspiratory effort and resistance/compliance of lung/thorax

Order: PS 10, PEEP 0, 50% FiO2

Page 28: D. Sara Salarian,. Nov 2006 Kishore P. Critical Care Conference  Improve oxygenation  Increase/maintain minute ventilation and help CO 2 clearance

Pressure-Support Ventilation Potential advantages

Patient comfort Decreased work of breathing May enhance patient-ventilator synchrony Used with SIMV to support spontaneous

breaths

Page 29: D. Sara Salarian,. Nov 2006 Kishore P. Critical Care Conference  Improve oxygenation  Increase/maintain minute ventilation and help CO 2 clearance

Pressure-Support Ventilation

Potential disadvantages Variable tidal volume if pulmonary

resistance/compliance changes rapidly

If sole mode of ventilation, apnea alarm mode may be only backup

Gas leak from circuit may interfere with cycling

Page 30: D. Sara Salarian,. Nov 2006 Kishore P. Critical Care Conference  Improve oxygenation  Increase/maintain minute ventilation and help CO 2 clearance

CPAP + PSV CPAP + PSV

Set PS level

CPAP level

Time (sec)

Flow(L/m)

Pressure(cm H2O)

Volume(mL)

Flow Cycling

Page 31: D. Sara Salarian,. Nov 2006 Kishore P. Critical Care Conference  Improve oxygenation  Increase/maintain minute ventilation and help CO 2 clearance
Page 32: D. Sara Salarian,. Nov 2006 Kishore P. Critical Care Conference  Improve oxygenation  Increase/maintain minute ventilation and help CO 2 clearance

VENTILATOR SETTINGS

Ventilatory support requires consideration of trigger mode and sensitivity, respiratory rate, tidal volume, flow rate, flow pattern, and the fraction of inspired oxygen (FiO2).

Page 33: D. Sara Salarian,. Nov 2006 Kishore P. Critical Care Conference  Improve oxygenation  Increase/maintain minute ventilation and help CO 2 clearance

Ventilator Settings

Mode Rate Volume (VT) Pressure FIO2 PEEP I:E

Page 34: D. Sara Salarian,. Nov 2006 Kishore P. Critical Care Conference  Improve oxygenation  Increase/maintain minute ventilation and help CO 2 clearance

Nov 2006Kishore P.

Critical Care Conference

Key concepts

Determinants of CO2 clearance

- Ventilator factors* Rate* Tidal volume* Anatomical dead space

- Patient factors* Physiological dead space* CO2 production

Alveolar minute ventilation

Page 35: D. Sara Salarian,. Nov 2006 Kishore P. Critical Care Conference  Improve oxygenation  Increase/maintain minute ventilation and help CO 2 clearance

Nov 2006Kishore P.

Critical Care Conference

Key concepts Determinants of Oxygenation

- Ventilator factors:* FiO2 ( fraction of oxygen in inspired air)

* Mean airway pressure* PEEP ( positive end expiratory pressure)

- Patient factors* V/Q (ventilation/ perfusion) mismatch* Shunt* Diffusion defect* Reduced mixed venous oxygen

Page 36: D. Sara Salarian,. Nov 2006 Kishore P. Critical Care Conference  Improve oxygenation  Increase/maintain minute ventilation and help CO 2 clearance

Nov 2006Kishore P.

Critical Care Conference

Adjust FiO2 and PEEP according to PaO2 and SpO2

Adjust TV and rate according to PCO2 and pH

Page 37: D. Sara Salarian,. Nov 2006 Kishore P. Critical Care Conference  Improve oxygenation  Increase/maintain minute ventilation and help CO 2 clearance

POSITIVE END-EXPIRATORY PRESSURE

PEEP: an elevation in alveolar pressure above atmospheric pressure at the end of exhalation

Extrinsic PEEP (ePEEP): applied through a mechanical ventilator

ACV without PEEP

ACV with PEEP

Page 38: D. Sara Salarian,. Nov 2006 Kishore P. Critical Care Conference  Improve oxygenation  Increase/maintain minute ventilation and help CO 2 clearance

Auto-PEEP Detection viathe Flow Waveform

Auto-PEEP Detection viathe Flow Waveform

Normal

--------------------------------------------------------

Flow does not return

to zero- Auto-PEEP

Page 39: D. Sara Salarian,. Nov 2006 Kishore P. Critical Care Conference  Improve oxygenation  Increase/maintain minute ventilation and help CO 2 clearance

Air TrappingAir Trapping

Inspiration

Expiration

NormalPatient

Time (sec)

Flo

w (

L/m

in)

Air TrappingAuto-PEEP

}

Page 40: D. Sara Salarian,. Nov 2006 Kishore P. Critical Care Conference  Improve oxygenation  Increase/maintain minute ventilation and help CO 2 clearance

Flow-Volume LoopFlow-Volume Loop

Volume (ml)

PEFR

FRC

Inspiration

Expiration

Flo

w (

L/m

in)

PIFR

VT

Page 41: D. Sara Salarian,. Nov 2006 Kishore P. Critical Care Conference  Improve oxygenation  Increase/maintain minute ventilation and help CO 2 clearance

Air TrappingAir TrappingInspiration

Expiration

Volume (ml)

Flow (L/min)

Does not returnto baseline

NormalAbnormal

Page 42: D. Sara Salarian,. Nov 2006 Kishore P. Critical Care Conference  Improve oxygenation  Increase/maintain minute ventilation and help CO 2 clearance

Air LeakAir

LeakInspiration

Expiration

Volume (ml)

Flow (L/min)

Air Leak in mL

NormalAbnormal

Page 43: D. Sara Salarian,. Nov 2006 Kishore P. Critical Care Conference  Improve oxygenation  Increase/maintain minute ventilation and help CO 2 clearance

Airway Secretions/Water in the CircuitAirway Secretions/Water in the Circuit

Inspiration

Expiration

Volume (ml)

Flow (L/min)

NormalAbnormal

Origins