Advanced Modes of CMV

RC 270

Pressure Support = mode that supports spontaneous

breathing

A preset pressure is applied to the airway with each spontaneous

inspiration

Pressure Support

Pure assist mode Patient determines rate, Vt, and

inspiratory time Inspiration is flow cycled

Most ventilators flow cycle a pressure support breath when inspiratory flow drops to 25% of the peak flow for that inspiration

PB 7200 flow cycles when pressure support flow drops to 5-10 lpm

Indications/Advantages: Pressure Support Initially used to overcome the increased

W.O.B. when breathing spontaneously through an E-T tube

Also may be used during spontaneous breaths during IMV

Weaning Assisted ventilation (instead of A/C)

PSVmax

Initial Settings and Adjustments: Pressure Support

To overcome resistance of E-T tube, start at 5-10 cmH2O

For PSVMax, set pressure to level that gives an exhaled Vt of 10-12 ml/kg

Advantages: Pressure Support

Supports spontaneous breathing with decreased W.O.B.(with or without an E-T tube)

Can be done with a face mask Usually less barotrauma and

hemodynamic compromise Patients like it!

Disadvantage: Pressure Support

A leak in the system prevents flow cycling Will cause a CPAP effect

Pressure Controlled Ventilation (PCV)

A set pressure is applied to the airway during inspiration and the

breath time cycles

Pressure Controlled Ventilation Can be used in A/C or control Flow tapers – if it drops to zero before

time cycling occurs, the pressure plateaus

Besides pressure, RCP also sets rate and either inspiratory time or I:E ratio

Vt may vary from breath to breath

Pressure Controlled Ventilation Indications are same as for any type of CMV:

Apnea Acute ventilatory failure Impending ventilatory failure Acute respiratory failure (Oxygenation failure)

Often used when volume cycling (volume control) is causing high airway pressures

Has been used to ventilate neonates since the 60s

PCV: Initial Settings and Adjustments

Initially choose a pressure (PIP) that gives desired exhaled Vt

If switching from volume cycling (volume control), use a PIP that is less than PIP during volume cycling

Adjustment in rate, PIP, and I:E (or inspiratory time based on ABGs, oximetry, and capnography

A change in PIP or I:E/insp time will change Vt

PC-IRV: Pressure Control with Inverse I:E Ratio

Control mode only

Patient is paralyzed

Settings like PCV except for inverse I:E (gives long insp time)

PC-IRV used in diseases with high elastic resistance, eg

ARDS

Prolonged insp time helps O2

To increase PaO2: increase rate, PIP or insp time

To decrease PaCO2: decrease rate or PIP

Airway Pressure Release Ventilation (APRV)

Alternating levels of CPAP in a spontaneously breathing patient

APRV

Like PC-IRV but patient is breathing spontaneously and is not paralyzed

Also used for high elastic resistance High CPAP level is applied longer than

low CPAP level Is NOT synchronized with inspiration and

expiration

APRV: Settings and Adjustments

Low CPAP usually between 2-10 cmH2O

High CPAP usually between 10-30 cmH2O

RCP also sets the time for each CPAP level Low CPAP is usually only for 1-2 seconds

Bilevel Positive Airway Pressure (BIPAP)

IPAP + EPAP

Differs from APRV – IPAP only during inspiration, EPAP only

during expiration

Rate and I:E ratio can also be set

Indications : BIPAP

Sleep apnea Ventilatory Assist without intubation

Can be done via face mask Often used to keep COPDers from being

tubed and put on A/C

Popular mode for NIPPV (Non-invasive Positive Pressure Ventilation)

High Frequency Ventilation (HFV)

A form of ventilation utilizing high rates and small Vt that seems to enhance diffusion of gases into

and out of the lung

History of CMV

HFV should not work based on classical respiratory physiology!

HFV: High Frequency Jet Ventilation (HFJV) Vt usually 20-150 ml Frequency (rate) 60-400 breaths per

minute Usually a catheter is inserted via ET

tube or transnasally to apply jet bursts to airway

Adjust rate, driving pressure, and insp time, and FIO2

HFV: High Frequency Oscillation (HFO) Vt between 5-50ml Frequency between 400-3000

Frequency expressed in Hertz (Hz) 10 Hz equals 600 breaths per minute

HFO Techniques

HFV (both HFJV and HFO)

Strict FIO2 and humidification can be variable

Both appear to cause diffusion to occur from proximal airway to alveoli How does

spontaneous breathing work?

Coaxial flow Inspiration and

expiration may be occurring simultaneously

HFV seems to stimulate mucociliary clearance

Enough already!