Download - Ventilatory strategies in the icu
Ventilatory strategies in the ICU
Ventilatory strategies in the ICU
Need for mechanical ventilation
Modes of ventilation – VCV, PCV, DCV
Invasive vs Noninvasive ventilation
Weaning from mechanical ventilation
Extubation and failure to extubate
Ventilatory strategies in the ICU
Need for mechanical ventilation
Respiratory distress RS:
• Mouth open
• Alae nasi flaring
• Pursed lips
• Tracheal tug
• Active accessory muscles
• Breathlessness
• Tachypnoea
• Cyanosis
• Paradoxical respiration
CVS:
• Cool extremities
• Rising pulse
• Falling BP
• Anxiety
• Drowsiness
• Restlessness
• Disorientation
• Picking bedclothes
CNS
“Inability to maintain either the normal
delivery of O2 to the tissues ± removal of
CO2 from the tissues”
Type I vs Type II
Respiratory failure
INDICATIONS FOR MECHANICAL VENTILATION
• Ventilation abnormalities - Respiratory muscle dysfunction
Respiratory muscle fatigue
Chest wall abnormalities
Neuromuscular disease
Decreased ventilatory drive
Increased airway resistance
• Oxygenation abnormalities - Refractory hypoxaemia
Need for PEEP
Excessive work of breathing
INDICATIONS FOR MECHANICAL VENTILATION
• Need for anaesthesia, sedation and/or
neuromuscular blockade
• Need to decrease systemic/myocardial
oxygen consumption, e.g., low cardiac
output states
• Use of hyperventilation to reduce
intracranial pressure
Oxygen delivery
Adequate alveolar ventilation
Restore acid-base balance
Reduce work of breathing
Minimal side-effects
Goals of ventilatory support
Ventilatory strategies in the ICU
Need for mechanical ventilation
Modes of ventilation – VCV, PCV, DCV
vs
Man
Machine
Inspiration
2 3
Expiration 41
SET TRIGGER1, Trigger
3, Cycling
4, Baseline P cmH2O
2, Limit
Time
Basic Modes of Ventilation
Volu
me
Pres
sure
Flow
Insp
Exp
Volume limitedConstant flow
Time
Volu
me
Pres
sure
Flow
Insp
Exp
Volume limitedConstant flow
Pressure limitedVolume controlled Pressure controlled
Time
Volume controlled vs Pressure controlled modes
COMPARISON VCV PCV
Volume Constant Varies
Effect of low compliance
Higher pressure Lower volume
Effect of high airway resistance
Higher pressure Lower volume
Peak airway pressure
High Lower
Mean airway pressure
Lower Higher
Case scenario 1
A 30 year old man, weighing 50 kg who had
undergone laparotomy the previous day was
complaining of pain at the incision. The
postgraduate prescribed morphine 50 mg and
phenergan 12.5 mg IM. The injections were given.
Fifteen minutes later, he becomes apnoeic.
Time-triggered, flow lim
ited and
volume-cycled
Case scenario 2
He was nicely settled on ventilator but now seems
to have some respiratory efforts
Patient-triggered, flow lim
ited
and volume-cycled
Patient-triggered, flow lim
ited
and volume-cycled
Mechanical Ventilation
Volume Controlled Ventilation
Pressure Controlled Ventilation
Pressure Control Ventilation - CMV
Pressure
Flow
Volume
0
30
Time-triggered, pressure-limited
and time-cycled
Time
Pressure Control Ventilation - SIMV
Pressure
Flow
Volume
0
30
Patient-triggered, pressure-limited
and time-cycled
Time
Case scenario 3
By 4 AM, the patient seems to be stable
and breathing a lot better than before. You
want to see whether you can encourage
his spontaneous breaths and wean him by
morning. What mode would you choose?
Pressure Support Ventilation (PSV)
Pressure Support Ventilation (PSV)P
r es s
ur e
Fl o
w
Vo
lum
e
Time
25 %
0
20
Patient triggered, pressure
controlled, flow cycled
ventilation
Time
Positive End-Expiratory Pressure (PEEP)
PEEP is not a mode of ventilation per se
0
+
PEEP with Mandatory breaths
Alv
eola
r pr
essu
re
Time
5
Baseline variable
Continuous Positive Airway Pressure (CPAP)
Appropriate for patients who have adequate
spontaneous ventilation but persistent
hypoxaemia due to physiological shunting
Pre
ssur
e (c
m H
2O
)
0
+
-Baseline
Ventilatory setting
Mode
Frequency
Tidal volume
I:E ratio
FIO2
Ventilatory strategies in the ICU
Need for mechanical ventilation
Modes of ventilation – VCV, PCV, DCV
Invasive vs Noninvasive ventilation
Mechanical Ventilation
Invasive ventilation
Noninvasive Ventilation
Noninvasive Ventilation – Advantages
Reduced need for sedation
Preservation of airway reflexes
Avoidance of upper airway trauma
Decreased ventilator associated pneumonia
Improved patient comfort
Shorter length of stay in the ICU and hospital
Improved survival
Noninvasive Ventilation – Disadvantages
Claustrophobia
Facial/nasal pressure lesions
Unprotected airway
Inability to suction deep airway
Gastric distension with face mask
Delay in intubation
Noninvasive Ventilation - Contraindications
Cardiac or respiratory arrest
Haemodynamic instability
Patients unable to co-operate
Inability to protect airway
High risk for aspiration
Active upper GI bleed
Severe hypoxaemia
Facial trauma, surgery or burns
Case scenario 4
This patient was doing fine for two days
but developed abdominal distension,
vomited and aspirated. He had to be
reintubated and ventilated. He has stiff
lungs now.
Case scenario 4
ABG
FIO2 – 1
PaO2 – 100 mm Hg
PaCO2 – 45 mm Hg
pH – 7.3
SpO2 – 98%
Mode
Frequency
Tidal volume
I:E ratio
FIO2
PaO2PvO2P50
a
v
PO2 (mm Hg)
Hae
mog
lobi
n sa
tura
tion
(%)
Oxygenation status
PaO2/FIO2 ratio
³500 – Normal
250 – Good
100 – 250: Poor
100 - Critical
10% shunt
PaO
2 (m
mH
g)
10040 60 800 20
Air
600
400
200
Assume normal QT, VO2, Hb, C(a-v)O2
20% shunt
30% shunt40% shunt50% shunt
FIO2 (%)
Nunn JF: Oxygen. In Nunn JF (ed): Applied Respiratory Physiology, 3rd ed. London: Butterworths,1987,109
Normal
NormalShunt Dead space
Case Scenario 4 Mode - PCV
Frequency - Higher
Tidal volume - Lower
I:E ratio – 1:2 to 1:1 or
even inverse ratio ventilation
FIO2 – As required
PEEP
Avoid
• Barotrauma
• Volutrauma
• Atelectrauma
• Biotrauma
• Oxygen toxicity
Mean airway pressure
Increase mean airway pressure by Increasing peak airway pressure
Increasing plateau pressure
Increase duration of inspiration (I:E ratio)
Increase PEEP
Bilevel Positive Airway Pressure
Ventilation (BiPAP)
Mechanical Ventilation
Volume Controlled Ventilation
Pressure Controlled Ventilation
Dual Controlled Ventilation
Dual control breath to breath
PRVC = Time or patient-triggered, Pressure-
limited, volume targeted and time-cycled
Case Scenario 5
A 20 year old man, known asthmatic, was
admitted to the Casualty with severe
wheeze. He is tachypnoeic, hypoxic and
restless. He was sedated and intubated but
his lungs are very stiff. What would you do?
Case scenario 5
Mode - PCV
Frequency - Slower
Tidal volume – 7 ml/kg
I:E ratio – Longer I:E
FIO2
ABG
FIO2 – 1
PaO2 – 250 mm Hg
PaCO2 – 50 mm Hg
pH – 7.3
Auto-PEEP Detection F
LO
W
INCREASED RESISTANCE NORMAL
TIME
LINEAR DECAY
EXPONENTIAL DECAY
Flow –time graph
Auto-PEEP Reduction
Low respiratory rate
Lower tidal volume
Large endotracheal tube
Higher inspiratory flow rate
Longer expiratory time
Permissive hypercapnia
Watch • Gas exchange
• Lung mechanics – Volumes,
pressures
• CVS
• The complete picture!
Ventilatory strategies in the ICU
Need for mechanical ventilation
Modes of ventilation – VCV, PCV, DCV
Noninvasive ventilation
Weaning from mechanical ventilation
“Weaning” is …
gradual discontinuation
of ventilatory support
When to wean?
Early withdrawal Vs
Premature discontinuation
Has there been a
significant improvement
or reversal
in the primary pathology ?
Step 1
Assessment of patients
Are they ready for weaning?
Step 2
Is the respiratory
function adequate?
FIO2 < 0.4 – 0.5
PaO2 (mmHg) > 60
SaO2 (%) > 90
SvO2 (%) > 60
PaO2/PAO2 ratio > 0.35
PaO2/FIO2 ratio > 350
Oxygenation
PaCO2 < 50 mmHg
pH > 7.35
Ventilation
Respiratory rate < 35.min-1
Minute volume < 10 L.min-1
Maximum inspiratory pressure
> - 20 cmH2O
Vital capacity > 10 ml.kg-1
VD / VT < 0.6
Rapid shallow breathing index (RSBI) *
* Yang KL, Tobin MJ. N Engl J Med 1991,324:1445-50
f / VT < 105 (b.min-1L-1)
Where,
f = Respiratory rate in breaths.min-1
VT = Tidal volume in Litres
Are his other systems
functioning adequately?
Spontaneous
Breathing Trial
(SBT)
Low levels of CPAP (e.g., 5 cmH2O)
Low levels of pressure support
(e.g., 5 – 7 cmH2O) or
Simply as “T-piece breathing”
Screening phase (5 min)
Assessment phase (30 – 120 min)Ref: MacIntyre NR. Chest 120, December 2001 375S – 395S
Monitoring during weaning
Monitors do not
substitute for an ever
vigilant clinician !
The patient
Oxygenation
Ventilation
Cardiovascular status
Failed Spontaneous
Breathing Trial (SBT)
Why ?
What next ?
The most common cause of
failure to wean is an
imbalance between
ventilatory capability and
ventilatory demand.
Patients who fail an SBT should
receive a stable, nonfatiguing,
comfortable form of ventilation
Attempts at weaning can continue
with once daily SBTs.
Twice daily SBTs offer no
advantage over once daily SBT.
Ventilatory strategies in the ICU
Need for mechanical ventilation
Modes of ventilation – VCV, PCV, DCV
Noninvasive ventilation
Weaning from mechanical ventilation
Extubation and failure to extubate
The decision to discontinue
ventilatory support
must be distinct from the
decision to extubate !
Those who will be successfully extubated will have
i) the resolution of the disease
ii) haemodynamic stability
iii) absence of sepsis
iv) adequate oxygenation status
v) adequate ventilatory status…. etc, etc
and also will have….
the ability to maintain
patency of the airway
? Upper airway obstruction
? Excess respiratory secretions
? Inability to protect airway
? Cardiac failure or ischaemia
? Encephalopathy
? Respiratory failure
? GI bleeding, sepsis, seizures
Causes of
failure to
extubate
Maziak DE, Meade MO, Todd RJ. Chest 1998;114:605-9
Insufficient evidence exists to support the
idea that the timing of tracheotomy alters
the duration of mechanical ventilation in
critically ill patients.
ROLE OF TRACHEOSTOMY IN
WEANING
Ventilatory strategies in the ICU
Need for mechanical ventilation
Modes of ventilation – VCV, PCV, DCV
Noninvasive ventilation
Weaning from mechanical ventilation
Extubation and failure to extubate
Thank you