2. Objectives
• To discuss indication of mechanical ventilation
• To discuss different modes for mechanical ventilation
2/23/2019 Department of Anesthesiology, KCH 2
3. Indications
1) Can not oxygenate (low PaO2/SpO2)- Hypoxemic respiratory failure
2) Can not ventilate (high PCO2)- Hypercarbic Respiratory failure
3) Both
4) Can not protect airway/ secure airway( Low GCS)
5) When clinician/ physician confused, either patient need or not,
needs mechanical ventilation
6) Elective ventilation for GA
2/23/2019 Department of Anesthesiology, KCH 3
4. Goals/Principles of mechanical Ventilation
1) To provide adequate ventilation and oxygenation
2) To achieve adequate lung volume and recruitment
3) To improve lung compliance
4) To reduce work of breathing
5) To limit lung injury
2/23/2019 Department of Anesthesiology, KCH 4
5. Assessment for MV
We should know
1)History and physical examination
2) Laboratory and radiological finding of patient
3) Anatomical size and structure of airway and lungs
4) Disease severity
2/23/2019 Department of Anesthesiology, KCH 5
6. Classification
Both on inferior airway invasion
1) Non- invasive : No inferior airway invasion
2) Invasive: Invasion by endotracheal tube
Based on modes
1) Controlled Mechanical Ventilation: PCV, VCV, PRVC, HFV, CMV, IMV
2) Supported spontaneous breathing: PSV, VSV
3)Mixed Respiratory Support: SIMV/ or +PS
4) Assisted spontaneous breathing: CPAP, APRV
2/23/2019 Department of Anesthesiology, KCH 6
7. VCV
Volume is independent variable
Pressure varies with compliance of lung
Expiration is passive not affected by ventilator mode, rather affected
by compliance and resistance
Not a weaning mode
Peak airway Pressure= R*F+ Vt/compliance+ PEEP
Plateau Pressure= Vt/compliance+ PEEP
2/23/2019 Department of Anesthesiology, KCH 7
8. VCV
What do we set??
Vt and RR for Minute Ventilation For PaCO2 Management
PEEP and FiO2 For Pao2 Management
Flow/ I:E ratio- for both
2/23/2019 Department of Anesthesiology, KCH 8
9. PCV
Pressure is independent variable
Volume is dependent variable Depends on: level of pressure, I-time
also it is the function of compliance and airway resistance. That’s why
volume deliver can vary breath to breath.
Ventilator adjust flow to maintain pressure.
Flow decreases throughout the inspiratory cycle.
Good mode to use if patient has large air leak, the ventilator will
increase the flow to compensate it.
Not a weaning mode
2/23/2019 Department of Anesthesiology, KCH 9
10. PCV
What do we set??
Pressure limit, T-Insp, RR,FIO2,PEEP
P and RR for Minute ventilation PaCO2 management
FiO2 and PEEP for PaO2 management
2/23/2019 Department of Anesthesiology, KCH 10
13. PRVC= Pressure Regulated Volume Control
Actually a volume control assist control mode
Target minute ventilation is set
Ventilator will adjust the flow to deliver the volume without
exceeding a target inspiratory pressure
Very useful in patient with high airway pressure.
2/23/2019 Department of Anesthesiology, KCH 13
14. PRVC
Advantage:
1)No change in MV delivery even if pulmonary condition changes
2) The desired TV will be delivered at lowest PIP, thus minimizes risk of
barotrauma.
Disadvantage:
1)Hard to use on a spontaneously breathing patient or one with air leak
2)Not a weaning mode
2/23/2019 Department of Anesthesiology, KCH 14
16. Pressure Support=PS
Supports each spontaneous breath with supplemental flow to
achieve preset pressure
All breath are triggered by patient
Preset value PIP, PEEP, FiO2
Patient determine Rate, Ti, I/E ratio, TV
2/23/2019 Department of Anesthesiology, KCH 16
17. PS
Needs intact respiratory drive
Helps to overcome airway resistance/ tube resistance, so that
spontaneous breathing will be easier
Can not be use in patient not having spontaneous breathing(i.e.
muscle relaxant)
2/23/2019 Department of Anesthesiology, KCH 17
18. SIMV= Synchronized intermittent mandatory
ventilation
Preset mechanical breath delivered within interval acc to preset and
wait for spontaneous in between, which it will use as a trigger to
deliver full breath.
If not sensed it will automatically give a breath
Vt on spontaneous breaths depends entirely upon the patient effort
and lung mechanics, can be pressure or volume controlled.
2/23/2019 Department of Anesthesiology, KCH 18
19. SIMV
Tb(time for breathing) = Tm(mandatory)+Ts(spontaneous)
If patient tries to breath during Tm, ventilator gives a fully assisted
breath
If Patient tries to breath during Ts, the ventilator will allow the
patient to take breath
2/23/2019 Department of Anesthesiology, KCH 19
24. CPAP
Provides continuous positive pressure throughout the respiratory
cycle
So gives supports to inspiration and resistance to expiration
Can be use both in invasive and non-invasive form.
Very similar to PEEP
2/23/2019 Department of Anesthesiology, KCH 24
25. PEEP
PEEP is a residual pressure above atmospheric pressure maintained
at the end of expiration.
PEEP can be added to any mode
PEEP helps to recruit alveoli, increase FRC , Redistribute pulmonary
edema, Decrease intrapulmonary shunt, Increase PaO2.(GOOD)
PEEP , decreases venous return/CO, increase ICP/intensify cerebral
ischemia/ risk of barotrauma(Bad)
2/23/2019 Department of Anesthesiology, KCH 25
26. NASAL CPAP FOR NEONATE/INFANT
Nasal prong/Nasopharyngral tube/ET tube can be use for nasal cpap2/23/2019 Department of Anesthesiology, KCH 26
27. Indication
Disease condition;
1)Retained lung fluid
2)Post-extubation (if risk of airway collapse)
3)Atelectasis
4)Respiratory distress syndrome
5) For administration of controlled concentration of nitric oxide
2/23/2019 Department of Anesthesiology, KCH 27
28. CONTD
Physical findings:
1)Increase WOB ,indicated by increase RR by 30-40%
2)Sub-sternal/suprasternal retraction
3)Grunting and nasal flaring
4)Pale or cyanotic skin color
5)Agitation
2/23/2019 Department of Anesthesiology, KCH 28
29. Contraindication/ Should 'Not Try
C/I:
Choanal atresia
Untreated diaphragmatic hernia
Cleft palate
TEF
Should 'not try:
Cardiovascular instability
Severe ventilatory impairment
Severe hypoxemia
Frequent apnea
High level of sedation
2/23/2019 Department of Anesthesiology, KCH 29
30. How it Helps??
Reduces grunting and tachypnea
Increases FRC and PaO2
Decreases intrapulmonary shunting
Improves lung compliance
Aids in stabilization of floppy infant chest wall
2/23/2019 Department of Anesthesiology, KCH 30
31. CONTD
Improves distribution of ventilation
Reduce WOB
Reduces central and obstructive sleep apnea by mechanically
splinting the upper airway.
Better recruitment and oxygenation
Stimulation of infant/neonate for breathing
2/23/2019 Department of Anesthesiology, KCH 31
32. APRV= Airway Pressure Release Ventilation
It is a form of CPAP with release of pressure in between
It is a inverse ration ventilation
Uses lower PIP to maintain oxygenation and ventilation without
compromising venous return
Improves V/Q matching
2/23/2019 Department of Anesthesiology, KCH 32
33. APRV
Improves renal perfusion and urine output
Maintaining normal cyclic decrease in pleural pressure augmenting
venous return and improving CO
Need for sedation less
Chance of respiratory muscle atrophy and atelectasis less(as
spontaneous breath is present)
C/I Increase ICP, brocho-pleural fistula and Obstructive Lung Disease
2/23/2019 Department of Anesthesiology, KCH 33
34. APRV Settings
• P High= Inspiratory Pressure
• T high= time for inspiration
• P low/PEEP= expiratory pressure
• T low/PEEP= time spent in exp. Phase = allows
High mean airway pressure maintained
2/23/2019 Department of Anesthesiology, KCH 34
37. Initial setting for APRV
P high:
20-25 cm H2O- mean airway
pressure
30cmh2o if pplat is >=30cmh2o
Higher setting may be required
for morbid obesity and if thoracic
and abdominal compliance
decrease(ascites)
T high: minimum 2-3 seconds,
progressively increase to 10-15 sec
Helps in oxygenation
P low: Peep set at zero, provides
high Pressure difference for
unimpeded expiratory flow
T low/PEEP: 50-70% of peak
expiratory flow.
0.2 to 0.6 sec
2/23/2019 Department of Anesthesiology, KCH 37
39. NAVA= Neurally Adjusted Ventilatory Assistance
• It is a spontaneous or supported mode
• Patient initiated synchronized breathing mode
• Breathing support is triggered by the electrical activity of the
diaphragm(EADi)
• NAVA setting(1-4 cm H2o/uv) multiplies measures EADi to provide
pressure, which is proportional and synchronized to patient effort
• It avoids over/under assistance
• Lung protective mode in spontaneous breath
• Avoids asynchrony, so less sedation required and better sleep.
2/23/2019 Department of Anesthesiology, KCH 39
43. Summary
We should know
When to start mechanical ventilation
Which mode would be better for particular patient
Setting should be appropriate according to patient to minimize injury
to lung
Steps of changing modes for weaning
2/23/2019 Department of Anesthesiology, KCH 43
44. References
• Clinical Application of Mechanical Ventilation(Chang)
• Miller Anesthesia- 8th edition
• Barash anesthesia- 8th edition
2/23/2019 Department of Anesthesiology, KCH 44
Editor's Notes
Symptom; dyspnea, orthopnea, increased cough/ wheez,somnolence
Signs: stridor, tachypnea, use of accessory muscle of respiration, retraction, prolonged expiratory phase, Paradoxical abdominal motion on inspiration, cyanosis
Lab: Arterial blood gas measurement, pulse oxymetric study
Others; chest radiograph, measurement of pulmonary compliance
RDS= TTN, MAS, Pulmonary hemorrhage, paralysis of hemodiaphragm, following repair of diaphragm, congenital cardiac anomalies, RSV, apnea of prematurity, (VLBW baby, premature infant risk for RDS)