INITIATION AND WEANING
OF MECHANICAL
VENTILATION
BY
AHMED MOHAMED HASSAN
OUTLINE
Definition.
 Indications
 Ventilator Settings
 Modes of Ventilation
 Weaning
 Summary

DEFINITION

Use of a mechanical apparatus to provide the
requirements of a patient’s breathing.

Use of positive pressure to physically transport
gases into and out of lungs
(earlier ventilators used negative pressure)

Usually performed via ETT but not always
(noninvasive ventilation)
MECHANICAL VENTILATION ( MV )

A supportive measure – not a therapy

Must diagnose and treat underlying cause

Used to support &/or rest patient until
underlying disorder improved
INDICATIONS FOR MV

Acute resp failure:
ARDS
 Heart failure.
 Pneumonia
 Sepsis.
 Complication of surgery.
 Trauma

Acute exacerbations COPD.
 Neuromuscular diseases.

VENTILATOR SETTINGS
FIO2
 Volume (VT)
 Rate
 Pressure
 PEEP
 I:E
 Flow rate

VENTILATOR SETTINGS

Fraction of inspired oxygen (FiO2):



Target Sao2 90 % & Pao2< 60mmHg.
Atempt to keep FiO2 <50% to avoid O2 toxicty.
Tidal volume (Vt):



Is constant in volume-cycled modes and variable with in
pressure-limited modes.
In patients without lung disease Vt of 8 - 10 mL/kg .
Lower Vt 6 ml/kg are recommended for ARDS, &
Vt 8
mL/kg is recommended in patients with asthma, COPD(as
long as no increase in plateau presure).
VENTILATOR SETTINGS

Respiratory rate (RR):
12 and 20 breaths per minute is reasonable.
 Determine minute ventilation.


Minute ventilation (VE):
Is the product of the Vt and RR.
 V is based on PaCO2 as a marker of ventilatory
requirements.
 V of approximately 5 L/min maintain normocapnea.
 Permissive hypercapnia is allowed in ARDS and status
asthmaticus.

E
E
VENTILATOR SETTINGS

Inflation pressure limit:



High inflation pressures cause barotruama. Increased Pplat,
is most injurious, reflecting alveolar overdistention and not
airway resistance.
Pplat > 30 cm H2O is recommended.
Inspiratory Sensitivity :


It is the drop in airway pressure that is required before the
ventilator senses the patient's effort.
0.5 to 1 cm H2O allow very weak patients to initiate a
breath, Higher values make triggering more difficult.
VENTILATOR SETTINGS

Inspiratory flow rate:





The ratio of Vt to inspiratory flow rate determines inspiratory time (Ti).
inspir flow rate
Ti
time for expiration
auto PEEP.
inspir flow rate
PIP & not Pplat.
COPD & asthma the expiratory time should be increased to allow
exhalation of trapped gas.
Positive end-expiratory pressure (PEEP):



PEEP is the maintenance of positive pressure after expiratory flow is
completed.
Useful to treat refractory hypoxemia
Complication:
 Hypotension
 Diastolic dysfunctions
 Barotrauma
MODES OF MV

MV may be:

Invasive, delivered
through an endotracheal
tube (ETT) or
tracheostomy tube.

Noninvasive positive
pressure ventilation
(NIPPV) interfaces the
ventilator with the patient
through a full-face or
nasal mask.
MOODS OF MECHANICAL VENTILATION

Volume cycled MV:

Pressure-limited MV:

Delivers a preset (Vt) specified by the
operator.

Delivers a flow until a preset pressure
limit that is set by the operator is
reached.

(PIP) are, depending on the patient's
compliance.

PIP is always the same but Vt is
variable, according to the patient's
compliance.

Examples:
• Pressure Support Ventilation (PSV)
• Pressure Control Ventilation (PCV)
• CPAP
• BiPAP

Examples:
• Assist/Control
• Intermittent Mandatory Ventilation
(IMV)
• Synchronous Intermittent
Mandatory Ventilation (SIMV)
PRESSURE SUPPORT VENTILATION(PSV)




Every breath is an assisted breath.
The patient determines the inspiratory flow
rate and the RR.
Advantages:
 Better patient synchrony
 Limits Peak inspiratory Pressure.
Disadvantages:
 Inadequate volumes if the ETT is blocked
or decreased lung compliance.
 Apnea backup is less supportive than that
of AC
PRESSURE CONTROL VENTILATION (PCV)




Controlled breaths are delivered
at a preset time interval.
RR, maximal pressure limit are
both controlled.
Spontaneous breaths is allowed
between the mandatory breaths.
Advantades:



Decrease risk of barotrauma
Used in inverse ratio ventilation.
Disadvantages:

Cannot ensure minimal VE
CONTINUOUS POSITIVE AIRWAY PRESSURE (CPAP):
Used for oxygenation and as a mode of
weaning.
 patient assumes most of the work of breathing
& determine RR, Vt & VE.

BIPAP

Ventilator delivers two levels of positive airway
pressure for preset periods of time.

Advantages:
 Decreased
requirement for sedation.
 Used in Obstructive Sleep Apnea.

Disadvantages:
 Theoretical
risk of over-distension of lungs.
ASSIST CONTROL (AC):



Pt RR < preset rate so all breath
will be assisted.
Pt RR > preset rate so all breath
will be controlled.
Advantages:



Ensures a minimum VE.
Better patient synchrony.
Disadvantages:

Induce respiratory alkalosis if high
respiratory drive (i.e., liver failure).
INTERMITENT MANDATORY VENTILATION (IMV)
Ventilator
will deliver a preset volume at a specific time
intervals.
Different from Controlled mode: pt can initiate spontaneous
breaths.
Different from Assisted mode: spontaneous breaths are not
supported by machine.
Advantages:
 Assures a VE
 Disadvantages:
 Patient asynchrony.
SYNCHRONIZED INTERMITTENT MANDATORY
VENTILATION (SIMV):




Delivered spontaneous, assisted,
and mandatory breath.
Most commonly used mode.
Advantages:
 Ensures a minimum VE.
Disadvantages:
 The worst mode of weaning.
NONINVASIVE VENTILATION



Avoids intubation and complications.
Can deliver various modes of ventilation
Indications:




Hypercapneic respiratory failure (COPD exac).
Cardiogenic pulmonary edema.
Hypoxic respiratory failure.
Contraindications:




Inability to cooperate (i.e. Confusion).
Inability to clear secretions.
Hemodynamic instability.
Frature skull base as it may cause pneumoencephaly.
NEW MODES OF MV
Volume Support.
 Pressure-Regulated Volume Control (PRVC).
 Volume-Assured Pressure Support.
 Automode.
 Adaptive support ventilation (ASV).
 Proportional Assist Ventilation(PAV).
 Mandatory Minute Ventilation.
 Airway Pressure Release Ventilation (APRV).

WEANING

When:



The underlying pathology improves.
Hemodynamically stable.
Oxygenation:




PaO2/FiO2 >200,
PEEP<7.5 cm H2O,
FiO2<0.5
Indices:

Rapid shallow breathing:



RR/Vt > 105 positive predictive value of 78%.
RR/Vt < 105 negative predictive value of 95 %.
Maximal Inspiratory Pressure(Pmax)

Excellent negative predictive value if less than –20 cm H2O .
WEANING

Methods:

Spontaneous breathing trials:


complete withdrawal of MV
Only one trial every 24-hour

CPAP:

Allow monitoring of RR, Vt & VE
Pressure support ventilation (PSV)



SIMV:


Gradual reduction in the level of PSV
The worst mode of weaning.
Duration:


Short-term MV (<21 days)
prolonged MV (>21 days)
30 to 120 minutes
at least 24 hours.
CAUSES OF WEANING FAILURE

Auto-PEEP.

Poor nutritional status.

Overfeeding.

Left heart failure.

Decreased magnesium and phosphate levels.

Infection/fever.

Major organ failure.
SIGNS OF WEANING FAILURE


Clinical criteria :
 Diaphoresis .
 Increased respiratory effort .
 Paradoxical breathing & use of accessory respiratory.
Cardiac:
 HR < 30 beats/min over baseline.
 Profound bradycardia.
 Ventricular ectopy.
 Supraventricular tachyarrhythmias.
 Mean arterial blood pressure equal to or greater than 15
mm Hg or equal to or less than 30 mm Hg from baseline.
SIGNS OF WEANING FAILURE

Respiratory:





RR < 35 breaths/min .
SaO2> 90%.
PaCO2 50 mmHg or increase >8 mmHg.
pH<7.33 or decrease >0.07.
PaO2 60 mm Hg with FiO2 of 0.5.
Ventilator management algorithim
Modified from Sena et al, ACS Surgery:
Principles and Practice (2005).
Initial intubation
• FiO2 = 50%
• RR = 12 – 15
• PEEP = 5
• VT = 8 – 10 ml/kg
SaO2 < 90%
SaO2 < 90%
•
•
•
•
Increase FiO2 (keep SaO2>90%)
Increase PEEP to max 20
Identify possible acute lung injury
Identify respiratory failure causes
No injury
Acute lung injury
• Low TV (lung-protective) settings
• Reduce TV to 6 ml/kg
• Increase RR up to 35 to keep
pH > 7.2, PaCO2 < 50
• Adjust PEEP to keep FiO2 < 60%
SaO2 < 90%
• Associated
conditions
(PTX,
hemothorax, hydrothorax)
• Consider
adjunct
measures
(prone positioning, HFOV, IRV)
SaO2 > 90%
•
•
•
•
Adjust RR to maintain PaCO2 = 40
Reduce FiO2 < 50% as tolerated
Reduce PEEP < 8 as tolerated
Assess criteria for SBT daily
Fail SBT
Acute lung injury
SaO2 < 90%
SaO2 > 90%
SaO2 > 90%
SaO2 > 90%
• Continue lung-protective
ventilation until:
• PaO2/FiO2 > 300
• Criteria met for SBT
Persistently fail SBT
• Consider tracheostomy
• Resume daily SBTs with CPAP or
tracheostomy collar
Pass SBT
Airway stable
Airway stable
Pass SBT
Intubated > 2 wks
Prolonged ventilator
dependence
• Consider PSV wean (gradual
reduction of pressure support)
• Consider gradual increases in SBT
duration until endurance improves
Pass SBT
Extubate
SUMMARY

Mechanical ventilation used to:
1.
2.
3.
4.
5.

Improve oxygenation.
Improve ventilation (CO2 removal).
Unload respiratory muscles.
Neuromuscular diseases.
Decrease intracranial tension.
A support until patients condition improves
SUMMARY

Different modes for ventilation
 Differ in how breaths are initiated, ended and assisted.
 No proven advantage of one mode over the other.
 Use ventilator strategies to avoid volutrauma
and other adverse effects.

Numerous trials performed to develop criteria for success
weaning, however, not very useful to predict when to begin the
weaning and physicians should rely on clinical judgement also.
SUMMARY



Daily screening may reduce the duration of MV and
ICU cost.
The removal of the artificial airway from a patient who
has successfully been discontinued from ventilatory
support should be based on assessment of airway
patency and the ability of the patient to protect the
airway.
Patients receiving MV who fail an SBT should have the
cause determined.
SUMMARY

Tracheostomy should be considered after it becomes
apparent that the patient will require prolonged MV.
Thank you