Mechanical Ventilation Basic Modes Lokesh Tiwari AIIMS Patna CME on Mechanical Ventilation: Bench to Bedside AIIMS RAIPUR: 22nd August 2015

What are ventilators ? A machine that generates a controlled flow of gas into a patient’s airways Supportive role to buy time

Mechanical ventilation Several models have evolved over time- Negative pressure ventilation Positive pressure ventilation Simple pneumatic system New generation microprocessor controlled systems. The basic function and applications remain common.

Basic Ventilator Parameters Tidal volume Frequency PIP Plateau Pressure PEEP Inspiratory Time Expiratory time I:E Ratio

Basic Ventilator Parameters Mode Tidal volume Frequency PIP Plateau Pressure PEEP Inspiratory Time Expiratory time I:E Ratio

Starting a ventilator: Mode Mode denotes interplay b/w patient and the ventilator Describes the style of breath support based on relationship between the various possible types of breath and inspiratory – phase variables

Where to Start ? CPAP, IPAP, EPAP, NIV Pressure control, Volume control CMV, Assist Control, IMV, SIMV, PSV, ASV, MMV, APRV PCV, PRVC, PSV, VCIRV, Volume Support, Auto Mode, BiLevel, BiPAP, HFJV, HFOV

Objective From

Objective To

Objectives Understand how ventilators control breath delivery, phase and control variables. Understand the basic modes of ventilation. Combinations, tailor-making, mix and match…

The ventilator circuit

The ventilator circuit Blender Air-O2 mixture of desired FiO2 at 50 psi 50 psi air 50 psi O2 Stepped down pressure Pressure regulating valve Flow regulator Insp limb Exp limb T-piece & ETT tube

Flow regulators / PEEP Flow in ventilator circuit- constant ETT PIP T-connection ETT Flow in ET & patient airway- keeps changing in magnitude & direction !! Flow sensor Baby’s airway

What does flow sensor do? Flow in ventilator circuit- constant T-connection Flow sensor ETT Insp flow Exp flow  RR = tidal vol - insp flow = peri-tube leak

Ventilatory Phases Inspiration: Inspiratory valve opens and expiratory valve is closed Inspiratory pause: inspiratory valve and expiratory valve closed Expiration: Inspiratory valve closed and expiratory valve open Expiratory pause: Inspiratory valve and expiratory (or PEEP) valve closed at end of expiration Ti Te Inspiration: the change from expiration to inspiration. Inspiratory valve opens and expiratory valve is closed Inspiratory pause: inspiratory valve and expiratory valve closed Expiration: Inspiratory valve closed and expiratory valve open Expiratory pause: Inspiratory valve and expiratory (or PEEP) valve closed at end of expiration

Phase Variables: Trigger, Limit and Cycling

Phase variables Trigger : ventilator (time)- triggered or patient (pressure or flow) triggered Limit: flow-limited or pressure-limited Cycling: volume, time, flow or pressure cycled.

Phase variables: Trigger What causes the breath to begin (signal to open the inspiratory valve) Machine (controlled): the ventilator will trigger regular breaths at a frequency which will depend on the set respiratory rate, ie, they will be ventilator time triggered. Patient (assisted): If the patient does make an effort to breathe and the ventilator can sense it (by either sensing a negative inspiratory pressure or an inspiratory flow) and deliver a breath, it will be called a patient-triggered breath.

Phase Variables: Trigger

Phase Variables: Trigger

Phase variables: Limit Factor which controls the inspiration inflow Flow Limited: a fixed flow rate and pattern is set and maintained throughout inspiration. An adequate tidal volume (Ti dependent) Pressure will be variable (comp and resistance dependent) Pressure limited: the pressure is not allowed to go above a preset limit. The tidal volume will be variable (comp and resistance dependent) When the inspiratory valve is opened, gas from the compressor will rush into the lung (at a compressed pressure of 60 lb/in2) unless limited by some ventilator mechanism. The term 'limit' denotes the factor which controls the inspiration inflow. It implies that the set limit cannot be overcome and yet, on reaching this The ventilator can either deliver gas at a fixedflow rate and pattern or at a fixed pressure during inspiration. In flow-limited breathing, a fixed inspiratory flow rate and pattern is set by the clinician and maintained throughout inspiration. As the flow is assured, the patient will receive an adequate tidal volume for a given inspiratory time. However, the airway pressure will rise to whatever level is required to deliver the flow and there is therefore an increased likelihood of

Phase variables: Cycling Signal that stops the inspiration and starts the expiration. Without inspiratory pause: one signal With inspiratory pause: two cycling signals (one to close inspiratory valve and the second to open the expiratory valve) Volume Time Flow Pressure : back-up form of cycling when the airway pressure reaches the set high-pressure alarm level

The ventilatory cycle PIP PEEP Ti Te 0.65 sec 0.35 sec 1 resp cycle= Ti + Te

Breath type: Spontaneous vs Mechanical vs assisted Time (sec) Spontaneous Paw (cm H2O) Inspiration Expiration Assisted

Control variables Pressure: Pressure signal is the feedback signal (Pressure Preset) Volume: Volume signal is the feedback signal. usually measure the flow and turn it into volume signal electronically. (volume preset) Time Flow Combinations

Volume Control Ventilation Preset Peak Flow Flow Dependent on Cl & Raw Pressure Preset Vt Volume Time (sec)

Pressure Control Ventilation Flow Set PC level Pressure Cl Cl Volume Time (sec)

Basic Modes of Ventilation Controlled Mechanical Ventilation Assist Control Ventilation Intermittent Mandatory Ventilation Synchronized Intermittent Mandatory Ventilation Pressure Support Combinations

Controlled mandatory ventilation (CMV) The ventilator delivers Preset tidal volume (or pressure) at a time triggered (preset) respiratory rate. As the ventilator controls both tidal volume (pressure) and respiratory rate, the ventilator “controls” the patients minute volume. Pressure The ventilator delivers the preset tidal volume at a time triggered (preset) respiratory rate. As the ventilator controls both tidal volume and respiratory rate, the ventilator “controls” the patients minute volume. The patient can not change the ventilator respiratory rate or breath spontaneously. Thus this mode should be applied only when patient has no breathing efforts either due to disease or under heavy sedation and muscle relaxants otherwise it will lead to asynchrony and increased work of breathing.

Controlled mandatory ventilation (CMV) Volume controlled Pressure controlled

Controlled mandatory ventilation (Volume-Targeted) Time triggered, Flow limited, Volume cycled Ventilation Preset Peak Flow Flow (L/m) Dependent on CL & Raw Pressure (cm H2O) Preset VT Volume Cycling Volume (mL) Time (sec)

Controlled mandatory ventilation (Pressure-Targeted) Time Triggered, Pressure Limited, Time Cycled Ventilation Time-Cycled Pressure Flow Volume (L/min) (cm H2O) (ml) Set PC level Time (sec)

Controlled mandatory ventilation (CMV) Patient can not breath spontaneously Patient can not change the ventilator respiratory rate Suitable only when patient has no breathing efforts Disease or Under heavy sedation and muscle relaxants

Controlled mandatory ventilation (CMV) Asynchrony and increased work of breathing. Not suitable for patient who is awake or has own respiratory efforts Can not be used during weaning

Assist Control Ventilation

Assist Control Ventilation Time (sec) Control ventilation (CMV) Assist / control ventilation Pressure Control Control Assisted

Assist Control Ventilation A set tidal volume (volume control) or a set pressure and time (pressure control) is delivered at a minimum rate Additional ventilator breaths are given if triggered by the patient Mandatory breaths: Ventilator delivers preset volume and preset flow rate at a set back-up rate Spontaneous breaths: Additional cycles can be triggered by the patient but otherwise are identical to the mandatory breath. Control ventilation (CMV) Assist / control ventilation Pressure

Assist Control Ventilation Tidal volume (VT) of each delivered breath is the same, whether it is assisted breath or controlled breath Minimum breath rate is guaranteed (controlled breaths with set VT) Control ventilation (CMV) Assist / control ventilation Pressure Tidal volume (VT) of each delivered breath is the same, whether it is patient triggered (assist) or ventilator triggered (control) If the patient does not initiate a breath before a requisite period of time determined by the set respiratory rate (RR), the ventilator will deliver the set VT Regardless of whether the breath is patient-triggered or time-triggered, the exhalation valve closes and the ventilator generates inspiratory flow at a set rate and pattern (flow limited). Inspiratory flow lasts until the set VT is delivered at which time the breath is cycled-off (volume-cycled). Thus, the AC mode is patient- or time-triggered, flow-limited, and volume-cycled. The airway pressures generated by chosen ventilator settings are determined by the compliance of the respiratory system and the resistance of the airways.

Assist Control Ventilation (volume) Assist Control Ventilation (Pressure) Assist Control Ventilation

Assist Control Ventilation (Pressure) Patient / TimeTriggered, Pressure Limited, Time Cycled Ventilation Pressure Flow Volume Set PC level Time-Cycled Pt triggered Time triggered Time (sec)

Assist Control Ventilation (Volume) Patient / Time triggered, Flow limited, Volume cycled Ventilation Time (sec) Flow Pressure Volume Preset VT Volume Cycling

Assist Control Ventilation Asynchrony taken care of to some extent Low work of breathing, as every breath is supported and tidal volume is guaranteed. Hyperventilation Respiratory alkalosis. Natural breaths are not allowed Breath stacking High volumes and pressures Control ventilation (CMV) Assist / control ventilation Pressure tachypnea could lead to hyperventilation and respiratory alkalosis. Breath stacking can occur when the patient initiates a second breath before exhaling the first. The results are high volumes and pressures in the system.

Assist Control Ventilation Hyperventilation and breath stacking can usually be overcome by choosing optimal ventilator settings and appropriate sedation. Control ventilation (CMV) Assist / control ventilation Pressure

Intermittent Mandatory Ventilation (IMV) Pressure Machine breaths are delivered at a set rate (volume or pressure limit) Time (sec)

Intermittent Mandatory Ventilation (IMV) Pressure Machine breaths are delivered at a set rate (volume or pressure limit) Patient is allowed to breath spontaneously from either a demand valve or a continuous flow of gases but not offering any inspiratory assistance. Time (sec)

Intermittent Mandatory Ventilation (IMV) Pressure Patient’s capability determines Tidal volume of spontaneously breaths Some freedom to breath naturally even on mechanical ventilator Time (sec)

Intermittent Mandatory Ventilation (IMV) Pressure Random chance of breath stacking and asynchrony: Increased WOB Uncomfortable feeling Time (sec)

Intermittent Mandatory Ventilation (IMV) Pressure controlled IMV Volume controlled IMV

Intermittent Mandatory Ventilation (IMV) Pros: Cons: Freedom for natural spontaneous breaths even on machine Lesser chances of hyperventilation Asynchrony Random chance of breath stacking. Increase work of breathing Random high airway pressure (barotrauma) and lung volume (volutrauma) Setting appropriate pressure limit is important to reduce the risk of barotrauma

Can we synchronize it?

Synchronized Intermittent Mandatory Ventilation Ventilator delivers either patient triggered assisted breaths or time triggered mandatory breath in a synchronized fashion so as to avoid breath stacking If the patient breathes between mandatory breaths, the ventilator will allow the patient to breathe a normal breath by opening the demand (inspiratory) valve but not offering any inspiratory assistance.

Synchronization window Pressure Time interval just prior to time triggering in which the ventilator is responsive to the patient’s inspiratory effort. Time trigerring Time (sec)

SIMV If the patient makes a spontaneous inspiratory effort that falls in sync window, the ventilator is patient triggered to deliver an assisted breath and will count it as mandatory breath Pressure Patient trigerred synchronized breath Time trigerred mandatory breath

SIMV if patient does not make an inspiratory effort then ventilator will deliver a time triggered mandatory breath. Pressure Patient trigerred synchronized breath Time trigerred mandatory breath

SIMV if patient does not make an inspiratory effort then ventilator will deliver a time triggered mandatory breath. Pressure Patient trigerred synchronized breath Time trigerred mandatory breath If the pt triggers outside this window, vent will allow this spontaneous breath to occur by opening the demand (inspiratory) valve but does not offer any inspiratory assistance.

Synchronized Intermittent Mandatory Ventilation Pressure 3 types of breathing: Patient initiated assisted ventilation, Ventilator generated controlled ventilation, Unassisted spontaneous breath.

Synchronized Intermittent Mandatory Ventilation P-SIMV V-SIMV

Synchronized Intermittent Mandatory Ventilation (SIMV) It allows patients to assume a portion of their ventilatory drive: Weaning is possible Greater work of breathing than AC ventilation and therefore some may not consider it as the initial ventilator mode Friendly cardiopulmonary interaction: Negative inspiratory pressure generated by spontaneous breathing leads to increased venous return, which theoretically may help cardiac output and function

Pressure Support Ventilation Pressure (or Pressure above PEEP) is the setting variable No mandatory breaths Applicable on Spontaneous breaths: a preset pressure assist, Flow cycling: terminates when flow drops to a specified fraction (typically 25%) of its maximum. Patient effort determines size of breath and flow rate.

Pressure Support Ventilation Pressure (or Pressure above PEEP) is the setting variable No mandatory breaths Applicable on Spontaneous breaths: a preset pressure assist, Flow cycling: terminates when flow drops to a specified fraction (typically 25%) of its maximum. Patient effort determines size of breath and flow rate

Pressure Support Ventilation Pressure (or Pressure above PEEP) is the setting variable No mandatory breaths Applicable on Spontaneous breaths: a preset pressure assist, Flow cycling: terminates when flow drops to a specified fraction (typically 25%) of its maximum. Patient effort determines size of breath and flow rate.

Pressure Support Ventilation It augments spontaneous VT decreases spontaneous rates and WOB Used in conjunction with spontaneous breaths in any mode of ventilation. No guarantee of tidal volume with changing respiratory mechanics, No back up ventilation in the event of apnea.

Pressure Support Ventilation Provides pressure support to overcome the increased work of breathing imposed by the disease process, the endotracheal tube, the inspiratory valves and other mechanical aspects of ventilatory support Allows for titration of patient effort during weaning. Helpful in assessing extubation readiness

SIMV + PS Ventilation Pressure Spontaneous breath with PS

Summary

Control ventilation (CMV) Assist / control ventilation Time (sec) Control ventilation (CMV) Assist / control ventilation Pressure Control Control Assisted Pressure Pressure

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