Mechanical_Ventilation解读

Can attempt to recruit (PEEP) lung regions to participate in gas exchange Attempts to optimize perfusion to ventilated regions

Ventilation

Minute ventilation = MV = VT x RR


RR – respiratory rate
Mechanical ventilation

A way to deliver gas to lungs using positive
pressure ...

at a given rate ... sensitive to either time- and/or patientbased triggers ...
Autoflow (PRVC)

In classic volume-control SIMV, a constant flow is delivered until a preset VT is reached (or for a specified Ti); this overall results in higher PIPs delivered than in pressure-control, where a decelerating flow is used until the preset PIP is achieved Autoflow calculates compliance and delivers the minimal “PIP” (pressure-regulated) required to achieve the preset VT (volume control) using a decelerating flow pattern

pressure – preset PIP

If volume is preset, pressure (PIP) varies; if pressure is preset, VT varies, per lung compliance: Compliance = Δ Volume/Δ Pressure
Or ... MV = VT/Ti x Ti/Ttot

Alveolar ventilation = (VTotal – VDead) x RR

MV = 500 mL x 12 bpm = 6000 mL/min

MV = 150 mL x 40 bpm = 6000 mL/min
Dead space

at pre-defined volumes or pressures
Modes of control – old school

Controlled mechanical ventilation (CMV) – pt UNable to breath above vent breaths
Flow

Intermittent mandatory ventilation (IMV) – pt able to breathe above vent, but breaths were unsupported, and vent breaths did not sync with patient effort
Pressure-volume relationship
Volume
Compliance = Δ Volume/ Δ Pressure
FRC 0 Transpulmonary pressure
Oxygenation

PAO2 = (Patm – PH2O)(FiO2) – (PaCO2/R)
Optimize V/Q matching (ie, = 1)
Mechanical Ventilation
Nadir Yehya, MD PICU Fellow
Overview

Basic physiology Terminology Modes of ventilation Settings


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Complications
Weaning

Nonconventional modes
Flow

Synchronized IMV (SIMV) – pt able to trigger vent, and vent breaths sync with pt effort; extra breaths UN-supported; back-up rate provided
Flow
Modes of control - modern

Pressure support (PS) – pt triggers every breath with NO mandatory back-up rate
Flow

COMBINED MODES – SIMV + PS
Flow
Modes

Whatever mode of control, the amount of support is limited by either volume – preset VT
Flow
Modes of control - modern

Assist control (AC) – pt able to trigger vent, but EVERY breath is a fully-supported vent breath; back-up rate provided
Terminology

PIP – peak inspiratory pressure Plateau pressure (Pplat) – alveolar pressure at no flow PEEP – positive end-expiratory pressure MAP – mean airway pressure (area under pressure curve) PS – pressure support Ti - inspiratory time I:E ratio – inspiratory/expiratory ratio VT – tidal volume