1 Operating Modes of Mechanical Ventilation 2 Introduction
Ventilator mode can be defined as a set of operating characteristics that control how the ventilator functions
Operating mode can be described by the way a ventilator is triggered into inspir. and cycled into exhalation what variables are limited during inspiration and whether or not the mode allows mand. spont. breaths or both.
Not an actual mode since rate and tidal volume during spont. breathing are determined by patient
Role of ventilator during spont. vent. is to provide the (1) flow to the pt. in a timely manner (2) flow adequate to fulfill a patients insp. demand and (3) provide adjunctive modes such as PEEP to complement the spont. effort
5 SPONTANEOUS (contd.)
Apnea ventilation is a safety feature used for spontaneous mode
PEEP increases the end-expiratory or baseline airway press. to a value greater than atmos. and is often used to improve the pt.s O2 status esp. if refractory
PEEP is not a stand-alone mode but is used in conjunction with other modes
When PEEP is applied to spont. breathing pt. then called CPAP
7 PEEP (contd.)
Two major indication for PEEP are - intrapulmonary shunt leading to refractory hypoxemia - decreased functional residual capacity and lung compliance
Complications assoc. with PEEP include - decrease venous return and C. O. - barotrauma - incr. ICP - alterations of renal hepatic et.al.
Is PEEP applied to a spont. breathing pt.
Indications are same as PEEP but in addition pt. must have adequate lung function to sustain eucapnic ventilation
Can use in adult with ET tube or facemask and in neonates with ET or nasal
Allows one to apply IPAP and EPAP
IPAP provides positive pressure breaths and it improves hypoxemia and/or hypercapnia
EPAP (essentially PEEP) improves oxygenation by increasing the FRC and enhancing alveolar recruitment
10 BiPAP (contd.)
Indications for BiPAP - preventing intubation of end-stage COPD patient - supporting patients with chronic ventilatory failure - patients with restrictive chest wall disease - neuromuscular disease - nocturnal hypoventilation
11 BiPAP (contd)
Three modes include - spontaneous - timed - spontaneous/timed
Initial settings - if pt. breathing spont. set at 8 and 3 - use spont./timed as backup and set 2-5 breaths below pt.s spont.
IPAP levels are determined by monitoring pt.s clinical physiologic response notTV
12 BiPAP (contd)
EPAP should be increased by 2 cmH2O increments to increase FRC and oxygenation
not possible to increase EPAP higher than IPAP
Ventilator delivers the preset tidal volume at a set time interval
should only be used when the pt. is properly medicated with a combination of sedatives respiratory depressants and neuromuscular blockers
Indicated if pt. fights the vent. tetanus or other seizure complete rest for pt. for 24 hr. crushed chest where spont. paradoxical mvmt.
14 Assist Control
Pt. always receives a mechanical breath either by timed or by assist
Indicated when full ventilatory support is needed used when pt. has a stable respiratory drive (10-12 spont. rate)
The generally accepted set minimum rate is 2-4 breaths less than the pt.s assist rate or a minimum of 8 - 10 breaths
15 AC (contd)
Advantages include a very small WOB when sens. and flow is set properly and this mode allows the pt. to control the RR
Disadvantage include alveolar hypervent.
Pt. breaths spont. at any tidal volume between the mechanical breaths
Primary disadvantage is chance for breath stacking therefore care should be taken to set high press. limit properly to reduce risk of barotrauma
A mode in which the vent. delivers mandatory breaths to the pt. at or near the beginning of a spont. breath mandatory breaths are synchronized with the pt.s spont. efforts to avoid breath stacking
synchronized window refers to the time just prior to time triggering in which the vent. is responsive to the pt.s effort (0.5 sec is typical)
18 SIMV (contd)
gas source for spontaneous breathing is usually a demand valve that allows pt. to determine their tidal volume
Indications include providing partial vent. support usually after 24 hr. of full vent. support
Advantages include maintaining resp. muscle strength reduces V/Q mismatch decreases mean airway press. helps wean pt
19 SIMV (contd)
disadvantage usually has to do with trying to wean pt. too rapidly leading to incr. WOB and muscle fatique
20 MMV (Mandatory Minute Ventilation)
also called minimum minute ventilation
Provides a predetermined minute ventilation when the patients spontaneous breathing effort becomes inadequate
Useful for preventing hypoventilation and respiratory acidosis in the final stages of weaning with SIMV
Need to keep watch spontaneous minute volume (distressed pt. may increase RR with lower tidal volume)
Used to lower the WOB and augment a patients spont. tidal volume
When PSV is used with SIMV it lowers the O2 consumption because of the decr. WOB
PSV applies a preset pressure plateau to the pt. during a spont. breath
PSV breaths are patient triggered pressure limited and flow cycled
22 PSV (contd)
Typically used in the SIMV mode to help weaning by (1) increasing spont. tidal volume (2) decreasing spont. RR (3)decreasing WOB
May see M.D. adjust press. to get a desired spont. tidal volume or may see M.D. adjust press. to get a target RR i.e.
The pressure controlled breaths are time triggered by a preset resp. rate
Once inspir. begins a pressure plateau is created and maintained for a preset inspir. time
Typically used in ARDS where it takes excessive press. in volume cycled modes to ventilate a pt. leading to barotrauma
24 APRV (airway pressure release ventilation)
Is similar to CPAP in that the pt. is allowed to breathe spont. without restriction
Combines two separate levels of CPAP and the pt. may breathe spont. from both levels
Periodically pressure is dropped to the lower level reducing mean airway press.
During spont. expir. the CPAP is dropped (released) to a lower level which simulates an effective exhalation
25 APRV (contd)
See this mode used like PCV in ARDS
26 IRV (inverse ratio ventilation)
The inverse IE ratio used is 21 - 41 and often used in conjunction with PCV
IRV improves oxygenation by (1) reducing intrapulmonary shunting (2) improvement of V/Q matching and (3) decreasing deadspace ventilation
See increase of mean airway pressure and presence of auto PEEP and may worsen pulmonary edema
Similar to the add-on IMV systems used on other ventilators
set sensitivity flow and base flow
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