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Principles of Mechanical Ventilation
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Aimes

• Ventilator settings
• Modes of ventilation
• Monitoring of the patient
• Trouble shooting

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Origins of mechanical ventilation

• Negative-pressure ventilators (iron lungs)
• Non-invasive ventilation first used in Boston
  Childrens Hospital in 1928
• Used extensively during polio outbreaks in 1940s
  1950s
• Positive-pressure ventilators
• Invasive ventilation first used at Massachusetts
  General Hospital in 1955
• Now the modern standard of mechanical ventilation

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Ventilator settings
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Ventilator settings

• Ventilator mode
• Respiratory rate
• Tidal volume or pressure settings
• Inspiratory flow
• IE ratio
• PEEP
• FiO2
• Inspiratory trigger

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Respiratory rate

• What is the pt actual rate demand?

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Inspiratory time

• Set as
• of respiratory cycle
• RR10 IE 1/2 Total respiratory time60/10
  TCT6 Sec
• IE ratio
• Expiratory time not set
• Remaining time after inspiration before next
  breath

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Tidal Volume or Pressure setting

• Maximum volume/pressure to achieve good
  ventilation and oxygenation without producing
  alveolar overdistention
• Max cc/kg? 10 cc/kg
• Some clinical exceptions

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Inspiratory flow

• Varies with the Vt, IE and RR
• Normally about 35-45 l/min

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IE Ratio

• 12
• Prolonged at 13, 14,
• Inverse ratio

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FIO2

• The usual goal is to use the minimum Fio2
  required to have a PaO2 gt 60mmhg or a sat gt90
• Start at 100
• Oxygen toxicity normally with Fio2 gt40

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Inspiratory Triger

• 2 modes
• Airway pressure
• Flow triggering

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Positive End-expiratory Pressure (PEEP)

• What is PEEP?
• What is the goal of PEEP?
• Improve oxygenation
• Diminish the work of breathing

?
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PEEP

• Barotrauma
• Diminish cardiac output
• Regional hypoperfusion
• NaCl retention
• Augmentation of I.C.P.?
• Paradoxal hypoxemia

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PEEP

• Contraindication
• No absolute CI
• Barotrauma
• Airway trauma
• Hemodynamic instability
• I.C.P.?
• Bronchospasm?

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PEEP
What PEEP do you want? Usually, 5-10 cmH2O
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Rise time (Ramp)

• determines speed of rise of flow (volume control
  mode) or pressure (pressure control and pressure
  regulated volume control modes)
• very short rise times may be more uncomfortable
  for the patient
• long rise times may result in a lower tidal
  volume being delivered (pressure control mode) or
  higher pressure being required (volume control
  and pressure regulated volume control modes)

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Rise time
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Theory

• Ventilation vs. Oxygenation
• Pressure Cycling vs. Volume Cycling

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Principles (1) Ventilation
The goal of ventilation is to facilitate CO2
release and maintain normal PaCO2

• Minute ventilation (MV)
• Total amount of gas exhaled/min.
• VE (RR) x (TV)
• VE comprised of 2 factors

V/Q Matching. Zone 1 demonstrates dead-space
ventilation (ventilation without perfusion).
Zone 2 demonstrates normal perfusion. Zone 3
demonstrates shunting (perfusion without
ventilation).
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Principles (2) Oxygenation
The primary goal of oxygenation is to maximize O2
delivery to blood (PaO2)

• Alveolar-arterial O2 gradient (PAO2 PaO2)
• Oxygenation in context of ICU
• V/Q mismatching
• Patient position (supine)
• Airway pressure, pulmonary parenchymal disease,
  small-airway disease
• Adjustments FiO2 and PEEP

V/Q Matching. Zone 1 demonstrates dead-space
ventilation (ventilation without perfusion).
Zone 2 demonstrates normal perfusion. Zone 3
demonstrates shunting (perfusion without
ventilation).
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Pressure ventilation vs. volume ventilation
Pressure-cycled modes deliver a fixed pressure at
variable volume (neonates) Volume-cycled modes
deliver a fixed volume at variable pressure
(adults)
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Pressure ventilation vs. volume ventilation

• Pressure-cycled modes
• Pressure Support Ventilation (PSV)
• Pressure Control Ventilation (PCV)
• CPAP
• BiPAP
• Volume-cycled modes
• Control
• Assist
• Assist/Control
• Intermittent Mandatory Ventilation (IMV)
• Synchronous Intermittent Mandatory Ventilation
  (SIMV)
• Volume-cycled modes have the inherent risk of
  volutrauma.

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Pressure Support Ventilation (PSV) (Assist
spontaneous breathing) ASB
Patient determines RR, VE, inspiratory time a
purely spontaneous mode

• Parameters
• Triggered by pts own breath
• Limited by pressure
• Affects inspiration only
• Uses
• Complement volume-cycled modes (i.e., SIMV)
• PSV alone
• Used alone for recovering intubated pts who are
  not quite ready for extubation
• Augments inflation volumes during spontaneous
  breaths
• BiPAP (CPAP plus PS)

PSV is most often used together with other
volume-cycled modes. PSV provides sufficient
pressure to overcome the resistance of the
ventilator tubing, and acts during inspiration
only.
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Pressure Control Ventilation (PCV)
Ventilator determines inspiratory time no
patient participation

• Parameters
• Triggered by time
• Limited by pressure
• Affects inspiration only
• Disadvantages
• Requires frequent adjustments to maintain
  adequate VE
• Pt with noncompliant lungs may require
  alterations in inspiratory times to achieve
  adequate TV

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CPAP and BiPAP
CPAP is essentially constant PEEP BiPAP is CPAP
plus PS

• Parameters
• CPAP PEEP set at 5-10 cm H2O
• BiPAP CPAP with Pressure Support (5-20 cm H2O)
• Shown to reduce need for intubation and mortality
  in COPD pts
• Indications
• When medical therapy fails (tachypnea, hypoxemia,
  respiratory acidosis)
• Use in conjunction with bronchodilators,
  steroids, oral/parenteral steroids, antibiotics
  to prevent/delay intubation
• Weaning protocols
• Obstructive Sleep Apnea

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Assist/Control Mode
Ventilator delivers a fixed volume

• Control Mode
• Pt receives a set number of breaths and cannot
  breathe between ventilator breaths
• Similar to Pressure Control
• Assist Mode
• Pt initiates all breaths, but ventilator cycles
  in at initiation to give a preset tidal volume
• Pt controls rate but always receives a full
  machine breath
• Assist/Control Mode
• Assist mode unless pts respiratory rate falls
  below preset value
• Ventilator then switches to control mode

• Rapidly breathing pts can overventilate and
  induce severe respiratory alkalosis and
  hyperinflation (auto-PEEP)

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IMV and SIMV

• IMV
• Pt receives a set number of ventilator breaths
• Different from Control pt can initiate own
  (spontaneous) breaths
• Different from Assist spontaneous breaths are
  not supported by machine with fixed TV
• Ventilator always delivers breath, even if pt
  exhaling
• SIMV
• Most commonly used mode
• Spontaneous breaths and mandatory breaths
• If pt has respiratory drive, the mandatory
  breaths are synchronized with the pts
  inspiratory effort

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       FIGURE 7-10 Synchronized
intermittent mandatory ventilation (SIMV) with
pressure support (PS) ventilation. In SIMV and
PS, mandatory breaths of a preset tidal volume
are administered in the fashion of SIMV. In this
figure the square waveform is applied to the
mandatory breaths. Only spontaneous breaths are
pressure supported ,and not the mandatory
breaths.
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Vent settings to improve ltoxygenationgt

• PEEP
• Increases FRC
• Prevents progressive atelectasis and
  intrapulmonary shunting
• Prevents repetitive opening/closing (injury)
• Recruits collapsed alveoli and improves V/Q
  matching
• Resolves intrapulmonary shunting
• Improves compliance
• Enables maintenance of adequate PaO2 at a safe
  FiO2 level
• Disadvantages
• Increases intrathoracic pressure.
• May lead to ARDS.
• Rupture PTX, pulmonary edema.

Oxygen delivery (DO2), not PaO2, should be used
to assess optimal PEEP.
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Vent settings to improve ltventilationgt
RR and TV are adjusted to maintain VE and PaCO2

• Respiratory rate
• Max RR at 35 breaths/min
• Efficiency of ventilation decreases with
  increasing RR
• Decreased time for alveolar emptying
• TV
• Goal of 10 ml/kg
• Risk of volutrauma

• IE ratio
• Increasing inspiration time will increase TV, but
  may lead to auto-PEEP
• PIP
• Elevated PIP suggests need for switch from
  volume-cycled to pressure-cycled mode
• Maintained at lt45cm H2O to minimize barotrauma
• Plateau pressures
• Pressure measured at the end of inspiratory phase
• Maintained at lt30-35cm H2O to minimize barotrauma

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CMV
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A /CV
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SIMV
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PSV(pressure support ventilation)

• Spontaneous inspiratory efforts trigger the
  ventilator to provide a variable flow of gas in
  order to attain a preset airway pressure.
• Can be used in adjunct with SIMV.

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Monitoring of the patient
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Airway pressure
Pressure
Pressure
Time
Time
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Trouble Shooting

• which pressure is going up
• Ppeak is up
• Look at your Pplat

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Trouble Shooting

• If your Pplat is high, you are faced with a
  COMPLIANCE problem
• If your Pplat is N, you are faced with a
  RESISTIVE problem

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Trouble Shooting

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Trouble Shooting

• Remove pt from ventilator
• Initiate manual ventilation
• Perform P/E and assess monitoring indices
• Check patency of airway

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Conclusion

• Ventilator settings
• Monitoring of the patient
• Trouble shooting

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reference

• Critical care nursing patricia gonce morton
  2009.
• Aaccn essential of critical care nursing marian
  chaly 2006.
• The icu book marino 2007.
• Critical care nursing jaya 2007.
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• Chronic Obstructive Pulmonary Disease and Weaning
  of Difficult-to-wean Patients from Mechanical
  Ventilation Randomized Prospective Study .Croat
  Med J 20074851-58

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Thanks For Your Atention