QUANDO VENTILARE?
CON COSA VENTILARE?
Andrea Vianello
S.C. Fisiopatologia Respiratoria
Ospedale-Università di Padova
RESPIRATORY FAILURE
LUNG
FAILURE
PUMP
FAILURE
GAS EXCHANGE
FAILURE
VENTILATORY
FAILURE
HYPOXEMIA
HYPERCAPNIA
What’s the point of ventilation?
– Deliver O2 to alveoli
• Hb binds O2 (small amount dissolved)
• CVS transports to tissues to make ATP - do work
– Remove CO2 from pulmonary vessels
• from tissues - metabolism
Why ventilate?- purposes
• To maintain or improve ventilation, &
tissue oxygenation.
• To decrease the work of breathing &
improve patient’s comfort.
When ventilate?- indications
• Failure of pulmonary gas exchange
– Hypoxaemia: low blood O2
• “Mechanical” failure
– Hypercarbia: high blood CO2
– Respiratory muscle fatigue
• Need to intubate eg patient unconscious
• Others eg
– need neuro-muscular paralysis to allow surgery
– cardiovascular reasons
Non-Invasive
Ventilation
“a form of
ventilatory
support that
avoids airway
invasion”
Hill et al Crit Care Med 2007; 35:2402-7
Paziente con riacutizzazione acidotica di BPCO
Terapia medica + O2 q.b. per SpO2 89-92%
Airway
narrowing &
obstruction
Airway
Inflammation
AutoPEEP
Shortened
muscles
curvature
 muscle
strength
 Frictional
WOB
 Elastic
WOB
Gas
trapping
 VT
 VA
 VE
PaCO2
pH
PaO2
 VCO2
usa i farmaci e bene !
Airway
Inflammation
Steroids
Abx
Shortened
muscles
curvature
BDs
 Frictional
WOB
AutoPEEP
 Elastic
WOB
Gas
trapping
Teophylline
 muscle
strength
Airway
narrowing &
obstruction
 VT
 VA
 VE
PaCO2
pH
PaO2
 VCO2
usa i farmaci e bene !
Airway
Inflammation
Steroids
Abx
Shortened
muscles
curvature
BDs
Teophylline
 muscle
strength
Airway
narrowing &
obstruction
MV
PEEP
AutoPEEP
 Elastic
WOB
Gas
trapping
 VT
 VE
MV
 VA
 Frictional
WOB
PaCO2
pH
PaO2
MV
 VCO2
Paziente con riacutizzazione acidotica di BPCO
Terapia medica + O2 q.b. per SpO2 89-92%
Ripetizione di EGA
pH > 7.35
NIV non indicata
>7.30 pH < 7.35
pH < 7.30
pH < 7.20
NIV consigliata
l’80% dei pazienti migliora comunque con
terapia standard
Ogni 10 pazienti trattati con NIV si evita 1 ETI;
NIV migliora la dispnea
NIV altamente consigliata
Senza NIV 1 paziente su 2 necessita di ETI
NIV migliora la sopravvivenza
NIV altamente consigliata
1 paziente su 2 fallisce NIV
Tuttavia con NIV migliora outcome
ospedaliero e sopravvivenza a 1 anno
NIV VS TRATTAMENTO STANDARD
Keenan S et al
NIV VS TRATTAMENTO STANDARD
Keenan S et al
NIV VS TRATTAMENTO STANDARD
Keenan S et al
The ICU studies
• Confirm the feasibility of NIV
• Confirm the effectiveness of NIV
• Selected patients / enthusiastic
Units
• Reduced complications particularly infectious
– 16% v 48% 1 ,18 v 60%
2
• Reduce ICU / Hospital stay
– 23 v 35 days
1
, 9 v 15 days
2
1. Brochard et al NEJM 1995; 333:817-22 2. Girou et al JAMA 2000; 284:2361-7
2005; 128
49 pazienti con IRA in BPCO dopo fallimento terapia medica, pH
7.2
• Simili durata di permanenza in ICU, durata VM, complicanze
generali, mortalità in ICU, e mortalità in ospedale
• con NIV 48% evitano ETI, sopravvivono con permanenza in
ICU inferiore vs pazienti VM invasiva (P=0.02)
• A 1 anno: NIV inferiore riospedalizzazione (65% vs 100%
P=0.016) e minor frequenza di riutilizzo supplemento di
ossigeno (0% vs 36%)
Studio caso-controllo: 64 paz. con IRA trattati con NIV pH = 7.18
• 40/64 (62%) fallimento NIV (RR con NIV - 38%)
• Simili mortalità in ICU, e mortalità in ospedale; durata di
NIVin riduce
di ETI e
permanenza
ICU e postnecessità
ICU, ma:
ospedalizzazione,
migliora
outcome
a lungo
• Inferiori complicanze (P=0.01)
e probabilità
di rimanenere
in
VM (P=0.056)
termine
• Se NIV efficace (24/64 = 38%) migliore sopravvivenza e
ridotta permanenza in ICU vs pazienti VM invasiva
Definition: What is it?
• Mechanical Ventilation
=Machine to ventilate lungs = move air in (+ out)
– Several ways to..move air in (IPPV vs others)
Intermittent Positive Pressure Ventilation
Definition: What is it?
• Mechanical Ventilation
=Machine to ventilate lungs = move air in (+ out)
– Several ways to..move air in (IPPV vs others)
Intermittent Positive Pressure Ventilation
– Several ways to connect the ventilator to
the patient
Several ways to connect the
machine to patient
• Oro-tracheal Intubation
• Tracheostomy
• Non-Invasive
Ventilation
Normal breath
Normal breath inspiration, awake
Lung @ FRC= balance
-2cm H20
Diaphragm contracts
Chest volume
Pleural pressure
-7cm H20
Air moves down
pressure gradient
to fill lungs
Alveolar
pressure falls
La pompa diaframmatica genera P garantendo
la ventilazione polmonare, regolata da:
Equazione di moto del Sistema Respiratorio:
Pmusc = V / C + V’ x R
Normal breath
Normal breath expiration, awake
-7cm H20
Diaphragm relaxes
Pleural /
Chest volume 
Pleural pressure
rises
-2cm H20
Air moves down
pressure gradient
out of lungs
Alveolar
pressure rises
Ventilator breath
Portable ventilator
ICU ventilator
ICU ventilator
Ventilator breath
Ventilator breath inspiration
0 cm H20
 lung pressure
Air blown in
Air moves down
pressure gradient
to fill lungs
+5 to+10 cm H20
 Pleural
pressure
Il ventilatore sostituisce totalmente o
parzialmente la pompa muscolare:
Equazione di moto del Sistema Respiratorio:
Pappl (+ Pmusc) = V / C + V’ x R
Ventilator breath
Ventilator breath expiration
Similar to spontaneous…ie passive
Ventilator stops
blowing air in
Air moves out
Down gradient
Pressure gradient
Alveolus-trachea
 Lung volume
Practicalities
• Ventilator settings:
• Pressure vs volume
• ‘Assist’ vs ‘Control’
• Trigger sensitivity
• PEEP?
Details: Inspiration
Pressure or Volume?
• Do you push in..
– A gas at a set pressure? = ‘pressure…..’
– A set volume of gas? = ‘volume….’
Details: Inspiration
Pressure cm H20
Pressure or Volume?
Pressure cm H20
Time
Time
Pressure Ventilators
• The use of pressure ventilators is increasing
in critical care units.
• A typical pressure mode delivers a selected
gas pressure to the patient early in
inspiration, and sustains the pressure
throughout the inspiratory phase.
• By meeting the patient’s inspiratory flow
demand throughout inspiration, patient effort
is reduced and comfort increased.
• Although pressure is consistent with these
modes, volume is not.
• Volume will change with changes in
resistance or compliance
• Therefore, exhaled tidal volume is the
variable to monitor closely.
• With pressure modes, the pressure level to
be delivered is selected, and with some
mode options, rate and inspiratory time are
preset as well.
Details: Inspiration
Pressure or Volume?
Volume Ventilators
• The volume ventilator has been historically
used in critical care settings
• A respiratory rate, inspiratory time, and tidal
volume are selected for the mechanical
breaths.
• The basic principle of this ventilator is that a
designated volume of air is delivered with
each breath.
• The amount of pressure required to deliver
the set volume depends on :
- Patient’s lung compliance
- Patient–ventilator resistance factors
Peak Inspiratory Pressure (PIP ) must be
monitored in volume modes because it
varies from breath to breath
30
Peak Inspiratory Pressure
Paw
cmH2O
1
-10
2
Time (s)
3
Details: Pressure vs Volume
in the Acute Setting
Secretions
hypoventilation
partial compensation
sensitive
Vt preserved
hypoventilation
insensitive
Schönhofer ERS Monograph 2001; 16: 259-73, mod
Details: leak compensation
without leakage
with leakage
small leak
huge leak
Pre-set
Pressure
Vol
Pressure
Vol
Mehta et al. Eur Respir J 2001; 17: 259-267
Interaction
Respiratory
muscle
pump
Ventilator
Ventilator
Respiratory muscle pump
.
.
work of breathing
spontaneous
assisted
controlled
Oxygen consumption mL x min
-1
Noninvasive mechanical ventilation in acute exacerbation of
restrictive thoracic disease
250
200
CMV
PSV
SB
SBT
150
100
50
0
1
2
Patient
Eur Respir Mon 2001; 6:70-73
4 Phases
Pressure
1. Inspiratory
triggering
2. Inspiration
Flow
3. Termination
of inspiration
Volume
4. Expiration
Time
Nilsestuen et al. Respir Care 2005; 50:202-232
Details: trigger sensitivity
trigger
asynchrony
insensitive
trigger
• trigger sensitivity to low
• high level of PSV
• hypercapnic encephalopathy
• sedation
• sleep
• intrinsic PEEP (COPD)
• tubing obstruction
sensitive
trigger
autotriggering
• trigger sensitivity to high
• resistance changes
• tubing leakage
• cardiac oscillation
Trigger poco sensibile: allo sforzo inspiratorio
non segue l’atto meccanico del respiratore
Trigger troppo sensibile: l’atto meccanico si
innesca spontaneamente
Pao
patient 1
patient 2
patient 3
Pes
Asynchrony between patient and ventilator
Problems:
• Increased work of breathing
• Need for sedation
• „Fighting the ventilator“
• Ventilation-Perfusion-Mismatch
• Dynamic hyperinflation
Consequences:
• Insufficient ventilation
• Withdrawal from NIV
• Weaning failure
• Prolonged ICU stay
• Costs
Prognosis !
PSV
L’operatore
imposta:

- pressione inspiratoria
- sensibilità trigger
- eventuale “rampa” (tempo di
raggiungimento PS)
- pressure-controlled
- flow-cycled
- patient-triggered
Caratteristiche: - > sincronismo paziente-ventilatore
 > comfort
- possibile graduazione sforzo
inspiratorio
lenta
media
rapida
Diversi tipi di rampa
PSV
Problemi: - difficoltà di impostazione
-
livello PS  VT: 6-8ml/Kg; RR: 20-35b/min
P0.1: 2-4 cm H2O
abolizione dissincronismi toracoaddominali
- possibile sovrassistenza
A-CV
L’operatore
imposta:

Caratteristiche:
Problemi:
-volume corrente
-frequenza respiratoria
-rapporto I/E
-sensibilità del trigger
-volume-controlled
-time-cycled
-machine e/o patient-triggered
(assistito)
-pressure-limited (eventuale)
- volume corrente insufflato
garantito
- rapporto I/E variabile
- possibile sovrassistenza 
alcalosi respiratoria
- insorgenza di PEEP intrinseca
A-CV
Hybrid modes
combine the advantages of pressure pre-set and volume pre-set
VAPS
Volume Assured Pressure Support
• Automatic adjustment of inspiratory pressure (range setting)
• Target volume set
• Measurement of inspiratory pressure and expiratory volume
• Calculation of missing inspiratory volume
• Increase of inspiratory pressure
Assurance of tidal volume + comfort of pressure pre-set
VAPS
Volume Assured Pressure Support
VAPS
Volume Assured Pressure Support
Storre et al. Chest 2006;130: 815-821
• AVAPS provides elegant adjustments of inspiratory pressures
according to a pre-set target volume
• AVAPS improves quality of ventilation
• Improvements of sleep quality and quality of life are comparable to
BiPAP-S/T
• However: Sleep quality is not completely normalized
• Further studies are needed
Storre et al. Chest 2006; 130: 815-821
Efficacy and comfort of Volume-Guaranteed Pressure
Support (PSV-VTG) in patients with chronic ventilatory
failure of neuromuscular origin
Efficacy and comfort of Volume-Guaranteed Pressure
Support (PSV-VTG) in patients with chronic ventilatory
failure of neuromuscular origin
Efficacy
andof
comfort
of Volume-Guaranteed Pressure
Four types
asynchronies:
Support
(PSV-VTG)
in patients
ventilatory
• Ineffective
inspiratory
effortwith
(IE):chronic
thoracofailure of neuromuscular origin
abdominal displacements not assisted by the
ventilator positive pressure boost;
• Inspiratory trigger delay: a time lag between the
initiation of the patent’s IE and the onset of
inspiratory support;
• Prolonged inspiration or late expiratory cycling
(hang-up): prolongation of mechanical insufflation
beyond the end of patient inspiration;
• Autotriggering: rapid succession of at least
three pressurizations at a RR of >40 br/min.
Efficacy and comfort of Volume-Guaranteed Pressure
Support (PSV-VTG) in patients with chronic ventilatory
failure of neuromuscular origin
Pressure cm H20
Details: PEEP?
PEEP
Time
Positive End Expiratory Pressure
Effects of PEEP
Normal, Awake
–
–
in expiration alveoli do not close (closing capacity)
change size
Lying down / Paralysis / +- pathology
–
–
–
Lungs smaller, compressed
Harder to distend, starting from a smaller volume
In expiration alveoli close (closing capacity)
PEEP
–
–
–
Keeps alveoli open in expiration
Danger: applied to all alveoli
Start at higher point on ‘compliance curve’
Effects of PEEP
‘over-distended’ alveoli
Compliance=
Volume
Volume
 Pressure
energy needed to open alveoli
?damaged during open/closing
Pressure
- abnormal forces
Effects of PEEP
Compliance=
Volume
Volume
 Pressure
PEEP: start inspiration from a higher
pressure
Pressure
Raised ‘PEEP’
↓?damage during open/closing
Regional ventilation: PEEP
Spontaneous, standing
‘over-distended’ alveoli
Compliance=
Volume
Volume
 Pressure
Pressure
Regional ventilation: PEEP
Mechanical Ventilation
Compliance=
Volume
Volume
 Pressure
Pressure
Details: Cardiovascular effects
• Compresses Pulmonary vessels
• Reduced RV outflow
• Reduced LV inflow
Details: Cardiovascular effects
• Compresses Pulmonary vessels
• Reduced LV inflow
–  Cardiac Output: Stroke Volume
– Blood Pressure = CO x resistance –
 Blood Pressure
– Neurohormonal
• Reduced RV outflow- backtracks to body
– Head-  Intracranial Pressure
– Others -  venous pressure
Vent settings to improve <oxygenation>
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
require pulmonary a. catheter)
• Rupture: PTX, pulmonary edema
PEEP: Indications
Clinical
•
•
•
•
•
Auto-PEEP
Cardiogenic pulmonary edema (↑ LV preload)
Hypoxemia with FIO2 > 0.5
Collapsing alveoli (ARDS, postop atelectasis)
Chest wall instability (chest trauma)
Physiological
•
•
•
•
PaO2 < 60 mm Hg on FIO2 0.8
PaO2 ↑ < 10 mm Hg with FIO2 F of 0.2
PA-aO2 > 300 on FIO2 1.0
Shunt > 30%
NIV treatment: summary
• The ventilator management of NIV is
continuously evolving;
• New ventilators are introduced, offering
novel features;
• Clinical applications have been expanding;
• Clinicians must make selections that best
match the ventilator with the patient’s
requirements.