Transcript Slide 1

MECHANICAL
VENTILATION
• Phunsup Wongsurakiat, MD, FCCP
• Division of Respiratory Disease and TB
• Department of Medicine, Siriraj Hospital
Mechanical Ventilation
• Invasive (intubation)
• Non-invasive (other interface such as face mask):
- negative pressure
- positive pressure
Inspiratory Hold: PIP and
Plateau pressures (VC)
Peak Pressure
Plateau
Proximal
airway
pressure
Inspiratory Hold
DISTENDING PRESSURES
Plat P - Base P (PEEP) = pressure to distend resp system
(lung + chest wall)
Plat P = peak alveolar pressure
Transpulmonary pressure = Plat P – Pleural pressure
Influence of chest wall
stiffness
35 cm H2O
35 cm H2O
5 cm H2O
30 cm H2O
10 cm H2O
25 cm H2O
FLOW Resistance (R)
Peak P - PlatP = pressure for flow
R = Flow/(PeakP - Plat P)
Physiology of Respiration
O2 consumption (VO2) ≈ 250 mL/ min
CO2 production (VCO2) ≈ 200 mL/ min
Cardiac output (CO) ≈ 5 L/min
Minute ventilation = RR X VT ≈ 5 - 8 L/min
VT ≈ 5 - 8 mL / kg
RR ≈ 12 - 20 bpm
PaCO2 = 35-45 mmHg
pH = 7.35-7.45
Physiology of Respiration
PAO2 = PIO2 – PaCO2 / R
[PIO2 = FIO2 x (barometric pressure – 47)]
PaCO2 = k x VCO2 / VA
Mechanical Ventilation
Variables
Mode
Objectives
Clinical settings
Complications
Mechanical Ventilation
Variables
Tidal volume
Rate
Total time (inversely related to rate):
- inspiratory time (adjustable)
- expiratory time (total time - inspiratory
time)
Flow (tidal volume / inspiratory time)
Minute ventilation
Minute ventilation
VE = VT * f
end of inspiration-beginning of expiration
total breath duration
VT
tidal volume
f
tidal volume
VT = 500 ml
breaths/ minute
beginning of inspiration
f = 12 breaths/minute
VE = 500 ml * 12 = 6 L
Mechanical Ventilation
Variables
Trigger sensitivity
FiO2
Pressure:
- peak pressure
- plateau pressure
Compliance
Mechanical Ventilation
Modes
Limit
variables rise no higher than some preset
value and increase to preset value before
inspiration ends = limit variable
Cycle
Variable that terminate inspiration = cycle
variable
Breath characteristics
Gas Delivery
Mechanical Ventilation
Bird
Limit: pressure, flow
Cycle: pressure
Bennett 7200 (volume assist-control)
Limit: volume, flow
Cycle: volume
Pressure support
Limit: pressure
Cycle: flow
Mechanical Ventilation
Modes
Volume-targeted: Pre-set tidal volume
Pressure-targeted: Pre-set inspiratory
pressure
Mandatory breaths: Breaths that the
ventilator delivers to the patient at a set
frequency, volume/pressure, flow/time
Spontaneous breaths: Patient initiated breath
Mechanical Ventilation
Modes
Volume-targeted
Controlled mechanical ventilation (CMV)
Assist/control (A/C) mechanical
ventilation
Synchronized intermittent mandatory
ventilation (SIMV)
Modes of Ventilation
(CMV)
Background:
• Full preset tidal volume at a fixed preset rate
• Rate and minute ventilation cannot  by patient effort
• Trigger sensitivity is locked out, need sedated or paralyzed
Modes of Ventilation
(CMV)
Advantages:
Near complete resting of ventilatory muscles
Respiratory muscle rest, secured minute ventilation
Disadvantages:
“Stack" breaths (air trapping) and develop barotrauma
“AutoPEEP" with barotrauma or hypotension
Need sedated or paralyzed
Respiratory muscle atrophy
Uses:
apnea, little breathing effort, unstable
Modes of Ventilation
(Assist/Control)
Background:
• Full preset tidal volume at a minimum preset rate
• Additional full tidal volumes given if the patient initiates extra breaths
Modes of Ventilation
(Assist/Control)
Advantages:
• Near complete resting of ventilatory muscles
• Comfortable, respiratory muscle rest, secured minute ventilation
• Effectively used in awake, sedated, or paralyzed patients
Disadvantages:
• Hyperventilate and become alkalotic
• “Stack" breaths (air trapping) and develop barotrauma
• “AutoPEEP" with barotrauma or hypotension
Uses:
• apnea, little breathing effort, unstable
Modes of Ventilation
(SIMV + Pressure support)
Background:
•Preset tidal volume at a fixed preset rate
•Ventilator waits a predetermined trigger period
•Patient can take additional breaths but tidal volume of these
extra breaths is dependent on the patient's inspiratory effort
Modes of Ventilation
(SIMV + Pressure support)
Advantages:
• Improved venous return: intermittent negative pressure
(spontaneous) breaths
• More comfortable: more control over their ventilatory pattern
and minute ventilation
Disadvantages:
• Can result in chronic respiratory fatigue if set rate is too low;
Uses:
• Weaning, bronchopleural fistula
Mechanical Ventilation
Modes
Pressure-targeted
Pressure support ventilation (PSV)
Pressure-control ventilation (PCV)
Pressure-targeted assist-control (A/C-PC)
Pressure-targeted SIMV (SIMV-PC)
Pressure support Ventilation
Background:
• Patient triggers, a preset pressure support is delivered
• Terminate inspiration by flow rate
• Tidal volume and minute ventilation are dependent on the preset pressure
and patient’s lung-thorax compliance
Pressure support Ventilation
Advantages:
• Avoids patient-ventilator asynchrony
• More comfortable: full control over ventilatory pattern and minute
ventilation
• Avoids breath stacking and autoPEEP (especially in patients with COPD)
Disadvantages:
• Required patient’s triggering, cannot be used in heavily sedated, paralyzed,
or comatose patients
• Respiratory muscle fatigue if pressure support is set too low
Pressure Control Ventilation
Background:
• Ventilator control predetermined pressure in a
fixed predetermined time and rate
Pressure Control Ventilation
Advantages:
• Pressure and time are controlled
• High flow rate
Disadvantages:
• Tidal volume variable
• Produced autoPEEP if inspiratory time too long
• Uncomfortable mode for most patients
Pressure-targeted assist-control
(A/C-PC)
All breaths machine-delivered at a preset
inflation pressure
Patients can  rate by triggering additional
machine breaths if desired
Same as assist/control volume targeted mode
Pressure-targeted SIMV
(SIMV-PC)
Fixed rate of machine-delivered breaths at a
preset inflation pressure
Patients can breathe spontaneously between
machine-delivered breaths if desired
Same as SIMV volume targeted mode
Mechanical Ventilation
Objectives:
• Physiology
• Comfortable
• Least complications
Mechanical Ventilation
Usual settings
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Minute Ventilation = RR X VT ( 5 - 8 L/min)
VT = 5 - 8 mL / kg
RR = 12 - 20 bpm
PaCO2 = 35-45 mmHg
pH = 7.35-7.45
Mechanical Ventilation
Triggering: sensitivity of ventilator to patient’s
respiratory effort.
• Flow or pressure setting that allows ventilator to detect
patient’s inspiratory effort
• Allows ventilator synchronize with patient’s
spontaneous respiratory efforts
• Improving patient’s comfort during mechanical
ventilation.
Setting: lowest but not self cycling
Less work in flow triggering
Mechanical Ventilation
Flow rate:
• adjust to patient’s comfort
• Usually > 60 L/min
Pressure:
• Plateau pressure < 30 cmH2O
Positive End Expiratory Pressure
(PEEP)
•  Functional residual capacity
• Move fluid from alveoli into interstitial space
• Improve oxygenation
PEEP
In COPD : To offset auto-PEEP
To improve oxygenation in acute lung injury
To improve oxygenation, preload, afterload
in cardiogenic pulmonary edema
PEEP Titration
-  PaO2
-  FiO2 (< 0.5)
- No adverse effect:
cardiac output
lung compliance from
overdistension
( plateau pressure)
Goal:
• Obtained baseline respiratory & hemodynamic
• Change (PEEP) only , keep other parameter
constant
•  PEEP 5 cmH2O q 15 – 20 min
 O2 delivery
O2 delivery
SaO2
SaO2
No adverse effect
Compliance
SaO2
SaO2
BP or co
Volume +
vasopressor
Indequate
Adequate
Use current PEEP
PEEP more
 FiO2
Tidal
volume
PEEP to
previous level
Contraindication
Absolute: none
Relative: unilateral lung disease,
bronchopleural fistulae, intracranial
pressure, high plateau pressure, pulmonary
embolism
Ventilator Alarms
Setting
Alarm
Setting
High minute ventilation
10-15% > set or target minute volume
Low minute ventilation
10-15% < set or target minute volume
High Vt
10-15% > set or target Vt
Low Vt
10-15% < set or target Vt
High-system pressure
10 cmH20 > average peak airway
pressure
Low-system pressure
5-10 cmH20 < average peak airway
pressure
Alarms & Troubleshooting
High Peak Inspiratory Pressure:
• Secretions
• Patient biting ETT
• Patient coughing
• Changing patient’s clinical status
Low Pressure Alarm or low PEEP alarm:
• Disconnect (check all connections)
• Apnea
Mechanical Ventilation
Complications
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Disconnection
Malfunction
Patient-ventilator asynchrony
hemodynamic effects:
Barotrauma
Ventilator-induced lung injury
Oxygen toxicity
Infection
- ventilator-associated pneumonia
- sinusitis
Mechanical Ventilation
Complications
Hemodynamic effects:
Impaired venous return, increased
pulmonary vascular resistance  
cardiac output
AutoPEEP
Mean lung volume or mean alveolar
pressure correlate best with
hemodynamic effects
AutoPEEP
Exhalation is not complete by the time the next
breath is given:
- expiratory airflow obstruction
- high minute ventilation (> 15-20 l/min)
Alveolar pressure & volume remain increased
at end-expiration
AutoPEEP
Adverse Effect
Same effect as externally applied PEEP:
- Hyperinflation
-  cardiac output
Difficult to trigger ventilator → ↑ work of
breathing
AUTOPEEP
Auscultation: persistent exhalation (specific
but not sensitive)
Untriggering
Flow-time graphs
End-expiratory hold
Steps for Reducing
Dynamic Hyperinflation & AutoPEEP
Eliminate unnecessary ventilation:
Weaning
Minute ventilation
Permissive hypercapnia
Expiratory airflow obstruction:
Rx bronchospasm
Keep airways free of secretions
Maximize expiratory time:
peak inspiratory flow rate to 70 – 100 l/min
Mechanical Ventilation
Complications
Oxygen toxicity
• High FiO2 is potentially injurious
• Tissue injury depends on FiO2 and duration of
exposure and some diseases/conditions
• No evidence that sustained exposure to FiO2 < 0.5
causes tissue injury
• Lowest FiO2 with adequate tissue oxygenation
• Measurements to keep FiO2 < 0.5
Hemoglobin and 02 Transport
280 million
hemoglobin/RBC.
Each hemoglobin
has 4 polypeptide
chains and 4
hemes.
In the center of
each heme group
is 1 atom of iron
that can combine
with 1 molecule
02.
Insert fig. 16.32
Oxyhemoglobin Dissociation Curve
Insert fig.16.34
Mechanical Ventilation
Respiratory Distress
• Patient
• Ventilator (malfunction)
• Patient-ventilator asynchrony
- flow rate
- trigger
- autoPEEP
Ventilator-Induced
Lung Injury (VILI)
• Barotrauma : extraalveolar air,
pneumothorax
• Diffuse alveolar damage, pulmonary edema
Overdistention
Overdistention may be regional
Even a “normal” VT can create regional
overdistention
Ventilator Management of ARDS
INITIAL VENTILATOR TIDAL VOLUME AND
RATE ADJUSTMENTS
Calculate predicted body weight (PBW)
• Male= 50 + 2.3 [height (inches) - 60]
• Female= 45.5 + 2.3 [height (inches) - 60]
Mode: Volume Assist-Control