Ventilació MecàNica Rpetits

1997

Spontaneous Breathing

ExhalationExhalation InspirationInspiration

Spontaneous Breathing

ExhalationExhalation InspirationInspiration

Normal Blood Gas Parameters

Arterial Mixed Venous

Normal Range Normal Range

pH, units 7.40 7.35-7.45 7.36 7.31-7.41

PCO2, mmHg 40 35-45 46 41-51

PO2, mmHg 97 80-100 40 35-40

O2Sat. % 97 95-100 75 70-75

HCO3, mEq/L 24 22-26 24 22-26

BE, mEq/L 0 +2 0 +2

Respiratory Tract

Tube + Balloon model

Airways

(Tube)

Alveoli

(Balloon)

O2CO2

Respiration

Ventilation– Mechanical

movement

– Pressure difference

Diffusion– Molecular movement

– Concentrationdifference

Perfusion

Precondition of Inspiration

Pa < Pb

– Spontaneousbreath

Pb > Pa

– Mechanicalventilation

PbPb

Pa

Gas Flow

PaPa << PbPb

Inspiration

Mechanical Breath

Spontaneous Breath

Pressure

Time

Alveolar Pressure Changes

Spontaneous Inspiration

Volume Change

Gas Flow

Pressure Difference

Mechanical Ventilation

Pressure Difference

Volume Change

Gas Flow

Pressure

Flow

Time

Volume Ventilation

Constant flow rate

Guaranteed tidal volumedelivery

Not affected by lungimpedance

Variable pressure

Increased Increased InspiratoryInspiratory Pressure Pressure

Compliance Compliance

Volume

Pressure

Volume Ventilation

Guaranteed tidal volume, not affectedGuaranteed tidal volume, not affectedby the changes in pulmonary mechanicsby the changes in pulmonary mechanics

“The Feature of the Tube”

Pressure Difference =Flow Rate x Resistance of the Tube

Pressure Difference =Flow Rate x Resistance of the Tube

R = PF

Airway Resistance

Pressure Ventilation

Constant insp. pressure

Decelerating, variableinspiratory flow rate

Time cycled: (A)– Pressure Control

Flow cycled: (B)– Pressure Support

Pressure

Flow

A B

Time CycledTime Cycled

Flow Cycled

Pressure Ventilation

Guaranteed pressure,Guaranteed pressure, is is not affectednot affectedby the changes in pulmonary mechanicsby the changes in pulmonary mechanics

Decreased Tidal VolumeDecreased Tidal Volume

Compliance Compliance

Volume

Pressure

Volume

Pressure

V

P

C = V P

Compliance

Control variables

Volume Ventilation Pressure Ventilation

Pressure

Flowtime

Pressure

Flowtime

Terminology: Flow and Volume

Minute Ventilation = Tidal Volume x Breath RateMinute Ventilation = Tidal Volume x Breath Rate

Pressure

Flow

Time

Tidal Volume Tidal Volume

Continuous Mandatory Ventilation

Control: Only machine initiated mandatory breaths:

Assist: Only patient initiated mandatory breaths:

Assist/Control: machine and patient initiated breaths:

Paw

Paw

Paw

CMV

Paw

Paw

Intermittent Mandatory Ventilation

IMV: Machine initiated + Spontaneous breaths

SIMV: Mandatory (patient or machine initiated) +Spontaneous breaths

SIMV + Pressure Support

Pressure supported spontaneous + Patient, ormachine-initiated mandatory breaths

Paw

(PSV)

Continuous Positive Airway Pressure

Pressure Support Ventilation

Paw CPAP

Paw PS

Spontaneous Modes

CPAP

PSV

Terminology: PEEP, I:E Ratio

Pressure

Time

Positive EndExpiratory Pr.

T insp. T exp. I : E = 1 : 2 I : E = 1 : 2

I : E = 4 : 1 I : E = 4 : 1

PEEP

PIP

PIP

PEEPT insp.

Atrapament = PEEPi

I

IIII

IIIE

EEE

E E E

Static and Dynamic Pressures

time

Pressure

PEEP

PIP

Pplat

Alveolar Distending (recoil) Pressure difference (Pdis)

Flow-ResistivePressure difference (Pres)

High Compliance

Indicates reduced elastic resistance oninspiration and a diminished expelling forceduring exhalation

Low Compliance

Indicates increased elastic resistance oninspiration and an increased expelling forceduring expiration

Found in patients with stiff lungs (RDS,Hypoplasia, pulmonary fibrosis, pulmonaryedema, pulmonary contusions, hemothorax,ileus)

Poden presentar insuficiència respiratoria els malalts que

estàn en VM ?

• Si, s’ha d’bservar si el malalt està desadaptat.

Normal

Fatiga diafragmàtica

Moment de retirada de la VM

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