Transcript Modes of Mechanical Ventilation

Modes of
Mechanical Ventilation
Mohamad S Ahmad, M.D.
Lecturer of Anaesthesia and
Intensive CareAin Shams
University Cairo, Egypt
2008
Introduction
Ventilation
• The goal of ventilation is to facilitate CO2
release and maintain normal PaCO2
• Minute ventilation (VE)
– Total amount of gas exhaled/min.
– VE = (RR) x (TV)
– VE comprised of 2 factors
• VA = alveolar ventilation
• VD = dead space ventilation
– VD/VT = 0.33
• VE regulated by brain stem, responding to pH
and PaCO2
Oxygenation
• The primary goal of oxygenation is to
maximize O2 delivery to blood (PaO2)
• Alveolar-arterial O2 gradient (PAO2 –
PaO2)
– A-a gradient measures efficiency of
oxygenation
• PaO2 partially depends on ventilation
but more on V/Q matching
Adjustments
• To affect
oxygenation,
adjust:
– FiO2
– PEEP
– I time
– PIP
MAP
• To affect
ventilation, adjust:
– Respiratory
Rate
– Tidal Volume
VE
COMPLIANCE =  Volume /  Pressure
If volume is set, pressure varies…..if pressure
is set, volume varies
Goals of Mechanical
Ventilation
• Achieve and maintain adequate
pulmonary gas exchange
• Minimize the risk of lung injury
• Reduce patient work of breathing
• Optimize patient comfort
Ideal Mode of Ventilation
• Synchronizes with the patient’s
spontaneous respiratory effort
• Maintains adequate and consistent tidal
volume and minute ventilation at low
airway pressures
• Responds to rapid changes in pulmonary
mechanics or patient demand
• Provides the lowest possible WOB
Ideal Ventilator Design
• Achieves all the important goals of mechanical
ventilation
• Provides a variety of modes that can ventilate
even the most challenging pulmonary diseases
• Has monitoring capabilities to adequately
assess ventilator and patient performance
• Has safety features and alarms that offer lung
protective strategies
MODES
• Ventilator mode can be defined as a set of operating
characteristics that control how the ventilator
functions
• Operating mode can be described by (1)the way a
ventilator is triggered into inspir. and cycled into
expir., (2)what variables are limited during
inspiration, (3)and whether or not the mode allows
mand., spont. breaths or both.
• spontaneous, PEEP, CPAP, BiPAP, CMV, AC, IMV,
SIMV, MMV, PSV, PCV, APRV, IRV
SPONTANEOUS
• 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 patient’s
insp. demand, and (3) provide adjunctive
modes such as PEEP to complement the spont.
effort
• Apnea ventilation is a safety feature used for
spontaneous mode
PEEP
• 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
• Two major indication for PEEP are:
- Intrapulmonary shunt
- Decreased FRC and lung compliance
• Complications assoc. with PEEP include
- Decrease venous return and C. O.
- Barotrauma
- Incr. ICP
- Alterations of renal, hepatic blood flow
CPAP
• 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 with ET tube or facemask
BiPAP
• 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
• Indications for BiPAP:
- preventing intubation of end-stage COPD
patient
- supporting patients with chronic ventilatory
failure
- patient’s with restrictive chest wall disease
- neuromuscular disease
- nocturnal hypoventilation
CMV
• 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., seizure,
complete rest for pt. for 24 hr., chest injury
Assist Control (A/C)
• Pt. always receives a mechanical breath, either
timed or assisted
• Indicated when full ventilatory support is
needed, used when pt. has a stable
respiratory drive (10-12 spont. rate)
• Advantages include a very small WOB
when sens. and flow are set properly, and
this mode allows the pt. to control the RR
• Disadvantage include alveolar hypervent.
IMV
• 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
SIMV
• 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)
• Advantages include maintaining resp.
muscle strength, reduces V/Q mismatch,
decreases mean airway press., helps wean pt
PSV
• Used to lower the WOB and augment a
patient’s spont. tidal volume
• When PSV is used with SIMV, it lowers the
O2 consumption because of the decr. WOB
• Typically used in the SIMV mode to help
weaning by (1) increasing spont. tidal volume
(2) decreasing spont. RR (3)decreasing WOB
PCV
• 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
ALTERNATIVE MODES OF
MECHANICAL VENTILATION
• Dual-control ventilation modes were
designed to combine the advantages of
volume-control ventilation with pressurecontrol ventilation
• These dual-control modes attempt to
increase the safety and comfort of
mechanical ventilation
pressure-regulated volume-control
(PRVC)
• a desired tidal volume is preset and the
ventilator delivers a pressure-limited
(controlled) breath until that preset tidal
volume is achieved
• ↑ Vt
↓ PIP & ↓ Vt
↑ PIP
• provides the opportunity to deliver
minimum minute ventilation at the lowest
peak airway pressures possible
volume support ventilation (VSV)
• The patient triggers every breath, controlling
his own respiratory frequency and inspiratory
time but the machine can guarantee minute
ventilation
• The pressure support is automatically adjusted
up or down according to patient's lung
compliance and/or resistance to deliver a
preset tidal volume
• This mode cannot be used in a patient who
lacks spontaneous breathing effort
• This mode is considered as a self-weaning
mode
Automode
PRVC
VSV
• designed for automatic weaning from pressure
control to pressure support depending on the
patient's effort
Volume-assured pressure support
ventilation (VAPSV)
PSV
VCV
• Advantages include a reduction in the work
of breathing, lowered airway resistance, and
lowered intrinsic PEEP
Automatic tube compensation(ATC)
Designed to overcome the resistance of the
endotracheal tube by means of
continuous calculations
Proportional assist
ventilation(PAV)
• This mode adjusts airway pressure in
proportion to the patient's effort
• If patient's effort and/or demand are
increased, the ventilator support is
increased, and vice versa, to always give a
set proportion of the breath
High-frequency ventilation (HFV)
• HFV is time-cycled positive pressure
ventilation that delivers a high frequency (60–
120 breathes per min) of small tidal volumes
(1.5 mL/kg) that are usually less than the
anatomic dead space
• 3 different modes: high-frequency positivepressure ventilation (HFPPV), high-frequency
jet ventilation (HFJV), and high-frequency
oscillatory ventilation (HFOV)
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 expiration
Thank
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