Transcript Slide 1
D. Sara Salarian,
Improve oxygenation
Increase/maintain minute ventilation and help
CO2 clearance
Decrease work of breathing
Protect airway
Nov 2006
Kishore P.
Critical Care Conference
Mask based device
Negative pressure ventilators
“The Iron Lung”
Origins of mechanical ventilation
The era of intensive care medicine began with positive-pressure ventilation
• Negative-pressure ventilators
(“iron lungs”)
• Non-invasive ventilation first
used in Boston Children’s
Hospital in 1928
• Used extensively during polio
outbreaks in 1940s – 1950s
• Positive-pressure ventilators
The iron lung created negative pressure in abdomen
as well as the chest, decreasing cardiac output.
• Invasive ventilation first used at
Massachusetts General Hospital
in 1955
• Now the modern standard of
mechanical ventilation
Iron lung polio ward at Rancho Los Amigos Hospital
in 1953.
Spontaneous/Controlled/Dual
Controlled Mechanical Ventilation (CMV)
Assist Control (AC)/Volume Control (VC)
Intermittent Mandatory Ventilation (SIMV)
Pressure Control (PCV)
Pressure Support Ventilation (PSV)
CPAP
+PEEP
Spontaneous
IMV
Nov 2006
Controlled MV
SIMV
Kishore P.
Assist
control
Critical Care
Conference
Assisted-pressure support
Breath Types
1.Spontaneous Breath
• Inspiration is both initiated and
terminated by the patient.
2.Mandatory Breath
• Inspiration is either initiated or
terminated by the ventilator.
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Breath Patterns
1.Continuous Mandatory Ventilation
• CMV
• All breaths mandatory
2.Intermittent Mandatory Ventilation
• IMV or SIMV
• Mandatory and spontaneous breaths
3.Continuous Spontaneous Ventilation
• All breaths spontaneous
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Phase Variables
TRIGGER starts inspiration
Example: pressure drop when patient sucks in
LIMIT preset inspiratory value
Example: preset maximum inspiratory flow
CYCLE stops inspiration
Example: preset inspiratory time
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the controlled variables of tidal volume and
inspiratory flow determine airway pressure and
inspiratory time
Variations in airway resistance or lung compliance
alter airway pressures but do not affect minute
ventilation
There are three methods of initiating the inspiratory
phase in volume-cycled mechanical ventilators:
controlled, assist-control, and intermittent
mandatory ventilation (IMV)
Ventilator applies a predefined target pressure
to the airway during inspiration
Adv.
- decreased risk of barotrauma
Disadv.
- with decreasing compliance or increasing
resistance, tidal volume and minute ventilation
fall
Nov 2006
Kishore P.
Critical Care Conference
Spontaneo
us
VCV
PCV
PSV
Pressur
Volume
Flow
I-time
e
variable variable variable
variable
FIXED
variable
variable
variable
FIXED
FIXED
FIXED
variable
FIXED
FIXED
Variable variable
3 Categories of PPV
CMV
A/C Volume
A/C Pressure
SIMV
SIMV Volume
SIMV Pressure
SPONTANEOUS
CPAP w/PSV
CPAP w/o PSV
Other
minute
ventilation is completely dependent upon
the rate and tidal volume set on the ventilator.
Any respiratory efforts made by the patient do
not contribute to minute ventilation
Controlled ventilation is the required ventilatory
mode in patients who are making no respiratory
effort (eg, spinal cord injury or drug overdose
and those who have been subjected to
pharmacologic paralysis).
Advantages: rests muscles of respiration
Disadvantages: requires sedation/neuromuscular blockade, potential adverse
hemodynamic effects
Time Triggered, Pressure Limited, Time Cycled Ventilation
Time-Cycled
Flow
(L/min)
Set PC level
Press
(cm H2O)
ure
Volume
(ml)
Time (sec)
Flow
(L/min)
Set PC level
Pressure
(cm H2O)
Cl
Cl
Volume
(ml)
Time (sec)
Flow
(L/min)
Pressure
(cm H2O)
Volume
(ml)
Time (sec)
In the assist-control (A/C) mode, the ventilator
senses an inspiratory effort by the patient and
responds by delivering a preset tidal volume. Every
inspiratory effort that satisfies the ventilator's
demand valve trigger threshold initiates delivery of
the preset tidal volume
Patient work is therefore required to trigger the
ventilator and continues during inspiration
A control mode back-up rate is set on the ventilator
to prevent hypoventilation
Volume or time-cycled breaths + minimal
ventilator rate
Additional breaths delivered with inspiratory effort
Order: AC Vt 500, RR12, 100% FiO2, 5 PEEP
Advantages: reduced work of breathing; allows
patient to modify minute ventilation
Disadvantages: potential adverse hemodynamic
effects or inappropriate hyperventilation
With intermittent mandatory ventilation (IMV), the
degree of ventilatory support is determined by the
selected IMV rate. At regular intervals, the ventilator
delivers a breath based upon a preset tidal volume and
rate. In addition, the patient is allowed to breathe
spontaneously through the ventilator circuit at a tidal
volume and rate determined according to need and
capacity.
Most present day ventilators synchronize the
intermittent ventilator breaths with inspiratory effort by
the patient, a modality termed synchronized IMV or
SIMV. However, this modification requires a trigger
modality
Potential advantages
More comfortable for some
patients
Less hemodynamic effects
Potential disadvantages
Increased work of breathing
Flow
(L/m)
Pressure
(cm H2O)
Volume
(mL)
Spontaneous Breaths
SIMV + PS
(Pressure-Targeted Ventilation)
Time-Cycled
Flow-Cycled
Flow
(L/min)
Press
(cm H2O)
ure
Set PC level
Set PS level
Volume
(ml)
Time (sec)
PS Breath
Pressure support ventilation (PSV) is flowcycled in that, once triggered by a demand
valve, the preset pressure is sustained until the
inspiratory flow tapers, usually to 25 percent
of its maximal value [22]. PSV tends to be a
comfortable ventilatory modality because the
patient has greater control over ventilator
cycling and flow rates. Close monitoring is
required whenever PSV is used alone because
neither tidal volume nor minute ventilation is
guaranteed. PSV can be added during full or
partial support with SIMV to overcome
endotracheal tube and ventilator circuitry
resistance encountered during spontaneous
breaths
Pressure assist during spontaneous inspiration
with flow-cycled breath
Pressure assist continues until inspiratory
effort decreases
Delivered tidal volume dependent on
inspiratory effort and resistance/compliance of
lung/thorax
Order: PS 10, PEEP 0, 50%
FiO
Potential advantages
Patient comfort
Decreased work of breathing
May enhance patient-ventilator synchrony
Used with SIMV to support spontaneous
breaths
Potential disadvantages
Variable tidal volume if pulmonary
resistance/compliance changes rapidly
If sole mode of ventilation, apnea alarm mode may be
only backup
Gas leak from circuit may interfere with cycling
Flow Cycling
Flow
(L/m)
Set PS level
Pressure
(cm H2O)
CPAP level
Volume
(mL)
Time (sec)
Ventilatory support requires consideration of
trigger mode and sensitivity, respiratory rate,
tidal volume, flow rate, flow pattern, and the
fraction of inspired oxygen (FiO2).
Mode
Rate
Volume (VT)
Pressure
FIO2
PEEP
I:E
Determinants of CO2 clearance
- Ventilator factors
* Rate
* Tidal volume
* Anatomical dead space
- Patient factors
* Physiological dead space
* CO2 production
Nov 2006
Kishore P.
Critical Care Conference
Alveolar minute
ventilation
Determinants of Oxygenation
- Ventilator factors:
* FiO2 ( fraction of oxygen in inspired air)
* Mean airway pressure
* PEEP ( positive end expiratory pressure)
- Patient factors
* V/Q (ventilation/ perfusion) mismatch
* Shunt
* Diffusion defect
* Reduced mixed venous oxygen
Nov 2006
Kishore P.
Critical Care Conference
Adjust FiO2 and PEEP according to PaO2 and
SpO2
Adjust TV and rate according to PCO2 and pH
Nov 2006
Kishore P.
Critical Care Conference
PEEP: an elevation in
alveolar pressure above
atmospheric pressure at
the end of exhalation
Extrinsic PEEP
(ePEEP): applied
through a mechanical
ventilator
ACV without PEEP
ACV with PEEP
Normal
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Flow does not
return to zero
- Auto-PEEP
Inspiration
Normal
Patient
Flow (L/min)
Time (sec)
}
Air Trapping
Auto-PEEP
Expiration
Inspiration
PIFR
FRC
VT
PEFR
Expiration
Volume (ml)
Inspiration
Flow
(L/min)
Does not return
to baseline
Volume (ml)
Normal
Abnormal
Expiration
Inspiration
Flow
(L/min)
Volume (ml)
Air Leak in mL
Normal
Abnormal
Expiration
Inspiration
Flow
(L/min)
Origins
Volume (ml)
Normal
Abnormal
Expiration