5 - Selecting MV Type and Mode

framework for MV selection

• indication

• pathology

• treatment goals

• patient interface (mask/tube)

• location

• duration

• staff training

two methods of noninvasive ventilation

• CPAP

• NIV

  • pressure triggered, patient limited, flow cycle

  • critical care ventilators

full ventilatory support (FVS)

ventilator provides all energy for alveolar ventilation

• RR > 8 breaths/min

• adequate V_T

• preset volume/pressure

partial ventilatory support (PVS)

patient participates in WOB

• RR < 6 breaths/min

breath delivery and modes

• type of breath

  • mandatory, spontaneous, assisted

• controlled variable

  • volume/pressure

• timing

  • continuous mandatory ventilation (CMV)

  • intermittent mandatory ventilation (IMV)

  • continuous spontaneous ventilation (CSV)

mandatory breath delivery

breath delivery that is ventilator controlled

• variables: time, V_T, and inspiratory pressure

spontaneous breath delivery

breath delivery that is patient-controlled

• variables: time, V_T

• based on patient’s demand and lung characteristics

assisted breath delivery

breath delivery that is ventilator- and patient-controlled

• all/part of breath made by ventilator

categories of MV

• volume

• pressure

• combined

volume control ventilation (VCV)

fixed volume, pressure variable

advantages of VCV

• guaranteed volume and V_E

• can maintain P_aCO₂

disadvantages of VCV

• risk of high pressure

• risk of patient-ventilator asynchrony

VCV waveforms

• pressure

• changes with changes in C_stat and R_aw

• can show P_plat with breath hold

VCV waveforms

• flow

• constant

• low mean airway pressure (MAP)

VCV waveforms

• volume

consistent waveform

pressure control ventilation (PCV)

fixed pressure, volume variable

advantages of PCV

• set max pressure

• reduces risk of alveolar overdistention

• decelerating flow pattern

disadvantages of PCV

• volume varies

• clinicians may be unfamiliar with mode

• V_T and V_E decrease when lung characteristics worsen

PCV waveforms

• pressure

• square shape

• holds for duration of i-time

• does not change with C_stat and R_aw

PCV waveforms

• flow

• variable

• will change with C_stat and R_aw

PCV waveforms

• volume

• decelerating ramp

• variable

benefits of combined volume-pressure ventilation

• fluctuates between modes to maintain minimal V_T

• allows patient to do more WOB

• aids in weaning from MV

• helps deliver minimal pressure

• decreases risk of baro-/volutrauma

continuous mandatory ventilation (CMV)

• every breath is mandatory

• time/patient triggered

intermittent mandatory ventilation (IMV)

• set number of mandatory breaths

• patient can breathe between set breaths

continuous spontaneous ventilation (CSV)

• all breaths are spontaneous

• patient triggered

control ventilation (historial mode)

MV mode

• preset intervals (time-cycled)

• patient “locked out” from any spontaneous efforts

• only effective for patients that can’t participate in WOB (transected C2 or C3 nerve)

assisted ventilation (historical mode)

MV mode

• ventilation cycles in response to patient inspiratory effort (patient triggered)

• breath raised to set V_T

• unable to wean

volume controlled CMV (VC-CMV or VC-AC)

MV mode

• all breaths mandatory

pressure controlled CMV (PC-AC)

MV mode

• time/patient triggered

• time cycled

IMV

MV mode

• volume/pressure targeted breaths at set intervals (time triggered)

• patient can breathe between set breaths

• can have pressure support for spontaneous breaths

• can’t synch with patient breaths

synchronized intermittent mandatory ventilation (SIMV)

MV mode

• mandatory breaths synch with spontaneous breaths

• may be volume/pressure controlled with or without pressure support (PS)

advantages of SIMV

• maintain muscle strength

• used for weaning

• full/partial support can be adjusted

• may reduce alkalosis

disadvantages of SIMV

• may increase WOB

• may increase wean time

• patient difficulty with lowering set rate

• no proper V_T

CPAP

MV mode

• improve oxygenation in patients with refractory hypoxemia and low FRC

pressure support ventilation (PSV)

MV mode

• constant pressure during inspiration

• patient triggered, pressure limited, flow cycled

• other settings

  • flow acceleration %

  • inspiratory rise time

  • inspiratory rise time %

  • slope adjustment

  • inspiratory cycle %

  • inspiratory flow termination

  • expiratory flow sensitivity

volume support ventilation (VSV)

MV mode

• target volume

• not commonly used

airway pressure release ventilation (APRV) / BiVent

MV mode

• patient breathes elevated baseline pressure

• possible pressure released then re-established

BiPAP

MV mode

• like CPAP but without constant pressure

• settings: IPAP, EPAP, RR, F_iO₂

volume assured PS (VAPS)

combined MV mode

• PS breath

• as flow decelerates, flow continues until volume delivered

pressure regulated volume control (PRVC) / AutoFlow

combined MV mode

• pressure changes to obtain set V_T

high frequency ventilation (HFV)

ventilation with RR > 60

mandatory minimum ventilation (MMV)

MV mode

• used for weaning

• ventilator provides part of V_E that patient can’t accomplish by increasing RR or pressure

adaptive support ventilation (ASV)

MV mode

• variation of MMV

• RT sets V_E based on patient’s IBW and estimated V_D

• can adjust targeted ventilation based on patient needs

• used for weaning

proportional assist ventilation (PAV)

MV mode

• pressure, flow, and volume proportional to patient’s spontaneous effort

• pressure depends on:

  • inspiratory flow and volume demand

  • degree of amplification chosen by RT

• positive feedback system