Weaning from mechanical Ventilation

1. By M.Abdeljawad
1

2. Historical Aspects of
Mechanical Ventilation
2

3. Hippocrates
As early as in the fifth
century bc , Hippocrates,
described a
technique for the prevention
of asphyxiation. In his work,
“Treatise on Air,”
Hippocrates stated, “One
should introduce
a cannula into the trachea
along the jawbone so that air
can be
drawn into the lungs.”
Hippocrates thus provided
the first
description of endotracheal
intubation (ET).
3

4. Paracelsus
The first form of
mechanical ventilator can
probably be
credited to Paracelsus, who
in 1530 used fire-bellows
fitted
with a tube to pump air
into the patient’s mouth.
‫ديسمبر‬1493‫سويسرا‬–‫توفي‬
‫في‬24‫سبتمبر‬1541‫في‬‫زالتسبوغ‬
‫النمسا‬
4

5. Andreas Vesalius
In 1653,
Andreas Vesalius recognized that
artificial respiration could
be administered by
tracheotomising a dog.24 In his
classic,
“De Humani Corporis Fabricia,”
Vesalius stated, “But that
life may … be restored to the
animal, an opening must be
attempted in the trunk of the
trachea, in which a tube of reed
or cane should be put; you will
then blow into this so that the
lung may rise again and the animal
take in air… And also as
I do this, and take care that the
lung is inflated in intervals,
the motion of the heart and
arteries does not stop….”
‫فيزاليوس‬ ‫أندرياس‬‫عالم‬ ‫هو‬‫وطبيب‬ ‫تشريح‬
‫جراح‬‫فلمنكي‬(‫بلجيكي‬( )31‫ديسمبر‬1514-
5

6. Robert Hooke
A hundred years later, Robert Hooke
duplicated Vesalius’
experiments on dog, and while
insufflating
air into an opening made into the
animal’s trachea, observed
that “the dog… capable of being kept
alive by the reciprocal
blowing up of his lungs with Bellows,
and they suffered to
subside, for the space of an hour or more,
after his Thorax had
been so displayed, and his Aspera arteria
cut off just below the
Epiglottis and bound upon the nose of
the Bellows.”11 Hooke
also made the important observation
that it was not merely the regular
movement of the thorax that prevented
asphyxia,
but the maintenance of
phasic airflow into the
lungs
‫هوك‬ ‫روبرت‬(18‫يوليو‬1635‫وفق‬ ،‫التقويم‬‫القديم‬-3
‫مارس‬1703)‫فيلسوف‬‫وعالم‬ ‫ومعماري‬ ‫طبيعي‬
‫إنجليزي‬ ‫موسوعي‬
6

7. John Fothergill
What was possibly the
first successful instance
of human resuscitation
by mouth-to-mouth
breathing was described
in 1744 by John
Fothergill in England.
1712-1720‫بريطانيا‬ ‫فوثرجيل‬ ‫جون‬
7

8. Royal Humane Society
“Society for the
Rescue of Drowned
Persons”
The use of bellows to resuscitate
victims of near-drowning
was described by the Royal Humane
Society in the eighteenth
century.20 The society, also known as
the “Society for
the Rescue of Drowned Persons” was
constituted in 1767, but
the development of fatal
pneumothoraces produced by
vigorous
attempts at resuscitation led to
subsequent abandonment
of such techniques. John Hunter’s
innovative double-bellows
system (one bellow for blowing in
fresh air, and another for
drawing out the contaminated air)
was adapted by the Society
in 1782, and introduced a new concept
into ventilatory care
8

9. William Macewen
In 1880, William Macewen was the
first to describe and to perform
that technique. In his paper
entitled "clinical observations on
the introduction of tracheal tubes
by the mouth instead of
performing tracheotomy or
laryngotomy' he describes in
addition two cases of endotracheal
intubation lasting at least 36 h. He
can, therefore, be said also to have
performed the first long-time
intubation.
(‫مواليد‬22‫يونيو‬1848‫في‬‫اسكتلندا‬-‫الوفاة‬
22‫مارس‬1924‫في‬‫غالسكو‬)،
‫هو‬‫جراح‬‫اسكتلندي‬‫مجالجراحة‬ ‫في‬ ً‫ا‬‫رائد‬ ‫كان‬
‫الدماغ‬ ‫الحديثة‬‫جراحة‬ ‫تطوير‬ ‫في‬ ‫وساهم‬
‫العظام‬‫بالترقيع‬ . ‫والعالج‬
‫الجراحي‬‫للفتق‬ , ‫واستئصال‬‫الرئة‬(‫إزالة‬
‫الرئتين‬.)
9

10. Appreciation of the fact
that life could be sustained by
supporting the function of the
lungs (and indeed the circulation)
by external means led to
the development of machines
devised for this purpose.
- In 1838, Scottish physician John
Dalziez described the first tank
ventilator.
-In 1864 a body-tank ventilator was
developed by Alfred Jones of
Kentucky.
10

11. the iron lung
-In 1929, Philip Drinker, Louis
Shaw, and Charles McKhann saw
the
development of what was dubbed
“the iron lung.
11

12. 12

13. positive-pressure
mechanical ventilation
Intensive use of positive-pressure
mechanical ventilation gained
momentum during the polio epidemic in
Scandinavia and the United States in the
early 1950s. In Copenhagen, the patient
with polio and respiratory paralysis who
was supported by manually forcing 50%
oxygen through a tracheostomy had a
reduced mortality rate.
However, this heroic intervention
required the continuous activity of 1400
medical students recruited from the
universities. The overwhelming
manpower needed, coupled with a
decrease in mortality rate from 80% to
25%, led to the adaptation of the
positive-pressure machines used in the
operating room for use in the ICU.
Positive-pressure ventilation means that
airway pressure is applied at the patient's
airway through an endotracheal or
tracheostomy tube. The positive nature
of the pressure causes the gas to flow
into the lungs until the ventilator breath
is terminated. As the airway pressure
drops to zero, elastic recoil of the chest
accomplishes passive exhalation by
pushing the tidal volume out.
13

14. 14

15. A-To Maintain Adequate Oxygenation
(Sao2<95%) with a Fio2 >0.5
(Hypoxia)
 Mechanical ventilation is often electively instituted when it is
not possible to maintain an adequate oxygen saturation of
hemoglobin
 Arterial oxygenation is controlled by one of the following
mechanisms:
 1- Fi02: Initially it is adjusted at 40% (may be at 50% in severe
hypoxic patients). Avoid higher concentrations > 50-60% to
avoid the risk of 02 toxicity. Then after 10 min, arterial blood
gases are repeated to readjust the FiOi.
 2- Positive end-expiratory pressure (PEEP).
 3- Inverse ratio ventilation (IRV).
 4- Pressure Support.
 In addition to the prone ventilation and inhaled nitric oxide that
are used to improve oxygenation.
15

16. B-To Maintain he PaCo2 at Satisfactory level
(Hypoventilation)
 A major indication for mechanical ventilation is when
the alveolar ventilation falls short of the patient’s
requirements.
 Conditions that depress the respiratory center produce
a decline in alveolar ventilation with a rise in arterial
CO2 tension.
 A rising PaCO2 can also result from the
hypoventilation that results when fatiguing respiratory
muscles are unable to sustain ventilation, as in a
patient who is expending considerable effort in
moving air into stiffened or obstructed lungs.
16

17.  Under such circumstances, mechanical ventilation
may be used to support gas exchange until the
patient’s respiratory drive has been restored, or tired
respiratory muscles rejuvenated, and the inciting
pathology significantly resolved
17

18. Causes of Hypoventilation.
CNS
depression
Spinal cord
or
peripheral
nerve
disorders
Neuro-
muscular
disorders
Disorders
affecting the
thoracic cage
(extra
pulmonary
airway)
obstruction
Sedative
agents
Spinal trauma Respiratory
muscle fatigue
Kyphoscoliosis Tracheal
obstruction by
stenosis,
tumor
Cerebrovascul
ar accidents
Botulism Poor nutrition Flail chest Epiglottitis
Central sleep
apnea
Guillian Barre
syndrome
Muscular
dystrophies
Ankylosing
spondylosis
Obstructive
sleep apnea
Metabolic
alkalosis
Multiple
sclerosis
Myasthenia
gravis
Myxedema Polio Steroid 18

19. -The aim is to produce gradual changes in the PaC02 until an
adequate satisfactory level is reached. C02 tension is controlled
by:
1- The dead space: A reduction of dead space such as cutting of
the endotracheal tube or the use of a tracheostomy tube
decreases the PaC02.
2- The minute ventilation= respiratory rate x tidal volume.
Increasing the tidal volume usually decreases the PaC02 more
than increasing the respiratory rate. The latter may also cause
respiratory alkalosis.
-CO2 tension should be adjusted as follows:
• In patients with a normal PaC02 before mechanical ventilation,
minute ventilation should be adjusted to produce a PaCO2
between 30-35 mm Hg.
19

20. • In patients with an initial high PaC02 before mechanical
ventilation, the PaC02 should be reduced at a rate < 7.6
mm Hg (lkpa(/hour, because rapid reduction produces a
marked fall in the cardiac output and arterial blood
pressure.
• In patients with an initial chronically high PaC02 (e.g.,
chronic bronchitis), the PaC02 should be reduced at the
same rate and should not be reduced below 40-45 mm Hg.
• In patients with a low PaC02 < 30 mm Hg before
mechanical ventilation, minute ventilation should be
adjusted to increase the PaC02 slowly by controlling the
respiratory rate. Further adjustment should be done after
one hour.
20

21. C-To Decrease the Work of
Breathing
 Another major category where assisted ventilation is used
is in those situations in which excessive work of breathing
results in hemodynamic compromise. Here, even though
gas exchange may not be actually impaired, the increased
work of breathing because of either high airway resistance
or poor lung compliance may impose a substantial burden
on, for example, a compromised myocardium
 When oxygen delivery to the tissues is compromised on
account of impaired myocardial function, mechanical
ventilation by resting the respiratory muscles can reduce
the work of breathing. This reduces the oxygen
consumption of the respiratory muscles and results in
better perfusion of the myocardium itself
21

22.  The work of breathing can be reduced by:
1- Increasing Vt and respiratory rate.
2- Increasing inspiratory flow rate (IFR).
3- Trying pressure support ventilation.
4- Using flow triggering.
5-In addition to:
• Decreasing pain, anxiety, and discomfort.
• Decreasing C02 production e.g., reducing carbohydrate
diets.
• Using sedation and paralysis.
• Reassurance.
22

23. D-Need to secure airway
(Airway stability)
23

24. IndicIndicaIndicationstionsations
Indications for intubation Indications for ventilation
Need to secure airway Hypoxia: acute hypoxemic
respiratory failure
Depressed sensorium Hypoventilation
Depressed airway reflexes Unacceptably high work of
breathing
Upper airway instability after
trauma
Hemodynamic compromise
Decreased airway patency Cardiorespiratory arrest
Need for sedation in the
setting of poor airway control
Raised intracranial pressure
Imaging (CT, MRT) and
transportation of an unstable patient
Flail chest
24

25. 25

26. Criteria for Intubation and
Ventilation
The most important is the clinical judgment
. The following criteria are guide:
1- Respiratory Gas Tension:
a- Direct Indices:
• Pa02 < 50 mm Hg in room air or Pa02 < 60 mm Hg with FI02 > 50%.
 • PaCO2 > 55 mm Hg in absence of chronic hypercarbia or metabolic
alkalosis i.e., pH is < 7.25 (would likewise imply the onset of respiratory
 muscle fatigue.)
. b- Derived Indices:
• Pa02f FI02 ratio < 200.
• Alveolar- arterial 02 tension gradient (PA-a02gradient) > 300 mm Hg
with FI02 1.0.
Dead space/tidal volume (Vd/Vt) >0.6
. • Shunt equation (Qs/Qt) > 20%
26

27. 2- Clinical Indices:
• Respiratory rate > 35 breath/ min (unacceptably high work of
breathing and a substantial degree of respiratory distress.)
• Respiratory muscle paradox.
3- Mechanical Indices:
• Tidal volume < 5 mL/kg.
• Vital capacity< 10-15 mL/kg.
• Maximum inspiratory force> - 25 cm H20. i.e., - 20 or -15 ... etc.
• Rapid shallow breathing index (respiratory rate/Vt)> 200
breaths/min/L.
• Minute ventilation < 4 L/ min or > 10 L/ min
27

28.  a forced expiratory volume in the first second (FEV1) of
less than 10 mL/kg
 forced vital capacity (FVC) of less than 15 mL/kg body
weight (both of which indicate a poor ventilatory
capability.)
28

29.  It is important to emphasize that the criteria for
intubation and ventilation are meant to serve as a
guide to the physician who must view them in the
context of the clinical situation
 Conversely, the patient does not necessarily have to
satisfy every criterion for intubation and ventilation in
order to be a candidate for invasive ventilatory
management
29

30. 30

31. 31

32. 32

33.  The ease of weaning a patient from a ventilator is
generally inversely related to the duration of the
mechanical ventilation
 Weaning should be considered as soon as the patient
has recovered sufficiently from his illness to be able to
endure the responsibility of sustained spontaneous
breathing
 The condition for which the patient was ventilated
should have improved significantly, although
incomplete resolution does not preclude successful
weaning
33

34. Criteria of Successful Weaning:
Before weaning, the following criteria should be considered:
1- The process that necessitated mechanical ventilation must be reversed or under
control before weaning is attempted i.e., patients no longer meet indications
for mechanical ventilation and must have the following criteria
- criteria for prediction of outcome
- . a- Respiratory Gas Tension:
- • Direct Indices:
- PaOi > 60 mm Hg (or SaOi > 90%) with FIOi < 0.5 with< 5 cm H20 PEEP.
- PaC02 < 50 mm Hg except if the patient has chronic hypercarbia.
- • Derived Indices:
- PaOi/Fi02 ratio > 200 mm Hg
- . Alveolar-arterial 02 tension gradient (PA- a Oagradient) < 300-350 mm Hg at
FIOi 1.0 or < 200 mm Hg at FIOi 0.5.
- Dead space/tidal volume ratio (Vd/Vt) < 0.6.
- Shunt equation Qs/Qr < 15%
34

35. b- Respiratory Rate: < 30-35 breath/ min in adults.
Both the arterial blood gases and respiratory rate are the
most useful criteria.
c- Respiratory Mechanics:
-Tidal volume> 5 mL/kg.
- Vital capacity > 10 mL/kg.
- Minute ventilation 4-10 L/min.
35

36.  Maximum inspiratory pressure (force) < - 15 to -30 cm
HzO i.e., -35, -40 ... etc is considered the threshold for
weaning. This can be detected by allowing the patient
to exhale to residual lung volume and then inhale as
forcefully as possible against a closed valve. Healthy
adults can generate a pressure of -90 to -120 cm HzO
36

37.  Rapid shallow breathing index=Respitory
rate(beath/min)/tidal volume(L)
-Its normal value is 40-50 breath/ min/ L.
- If it is< 100 breath/min/L, this indicates weaning
success.
- If it is> 100 breath/min/L, this indicates weaning
failure.
 Work of breathing: It is defined as the 02
consumption of the respiratory muscles calculated
from the metabolic gas monitor. If it is< 1.6 kg.m/min,
it indicates successful weaning.
37

38.  2- Correction of reversible factors that may complicate
weaning such as:
• Bronchospasm. • Malnutrition. • Anemia.
• Infection. • Acid-base disturbances. • Sleep
deprivation.
• Increased C02 production (high carbohydrate).
• Hypothermia or hyperthermia
38

39. 3- Good status of other systems such as:
• Glasgow coma scale should be more than 13. The patient should
be alert and conscious.
• Gag and cough reflexes should be intact.
• Hemodynamic stability should be present with minimal or no
vasopressor support except in postsurgical cardiac patients that
can be weaned in spite of high vasopressor support because the
effect of cardiopulmonary bypass and peripheral vasodilatation
usually resolve quickly.
• Underlying lung disease and respiratory muscle wasting should
be absent
39

40. General Precautions during
Weaning:
• The sedation level should be reduced.
• The FI02 is usually y 0.4 to allow successful weaning.
• Continuous pulse oximetry.
• Arterial blood gases should be checked every 20-30 min.
• In the early stages of weaning, mechanical ventilation is often
continued at night to encourage sleep, avoid fatigue, and rest
respiratory muscles.
• After short-term ventilation (< 1week), if arterial blood gases,
respiratory pattern, and cough reflex are satisfactory, the patient can be
extubated.
• After long-term ventilation (> 1week), the patient should generally be
allowed to breathe spontaneously for at least 24 hours before
extubation.
40

41. Techniques of Weaning:
 Weaning can be through a ventilator or through a T-
piece. There is no evidence that any method is
superior to others for allowing weaning from
mechanical ventilation permanently
41

42. A-Through a Ventilator
1-Synchronized lnterrnittent lJnd.itory
Ventilation (SIMVJ:
• The number of mechanical breaths is progressively decreased by
1-2 breath/min as long as the PaC02 and spontaneous respiratory
rate remain acceptable i.e., < 45 mm Hg and < 30 breath/ min
respectively, allowing the patient to slowly take over spontaneous
ventilation. When SIMV of 1-2 breaths/min is reached,
mechanical ventilation is discontinued.
• It is the least efficient mode of weaning because it promotes
dependence on the ventilator and can be confusing to the
respiratory center.
42

43. • In patients with acid-base disturbances or chronic C02
retention, arterial blood pH (> 7.35) is more useful
than C02 tension monitoring. Blood gas
measurements should be checked after a minimum of
10-20minutes at each setting.
• If pressure support is concomitantly used with SIMV.it
should be reduced
43

44. 2-Pressure Support Ventilation
(PSV)
• The PS level should be decreased by 2-3cm H20 (with the
same criteria of PaC02 and respiratory rate as with
SIMV).When a PSlevel of< 5-8cm H20 is reached, the
patient can be extubated.
- A PaO2 < 60mm Hg or a Sa02 < 90%require a return to
previous levels of respiratory support.
- A PaO2 of 60-70mm Hg or a Sa02 of 90%require a hold at
the current level of respiratory support. a A PaO2> 70mm
Hg or a Sa02 > 92%allow progression to weaning.
• It can be combined with SIMVor with CPAP.
44

45. 3-Continuous Positive Airway
Pressure
(CPAP)
• Low levels of CPAP (5 cm H20) while the patient
breathes spontaneously (instead of the T-piece)
because:
- It maintains the functional residual capacity (FRC).
-It prevents basal atelectasis which can occur during
prolonged T- piece trials due lo absence of a nor-mal
physiologic PEEP when the larynx is bypassed by an
endotracheal tube
 The patient is also observed clinically for signs of
fatigue and respiratory distress and arterial blood
gases are done as with the T-piece.
45

46. 4-Biphasic Positive Airway
Ventilation
(BiPAP)
• Weaning is done by decreasing the ventilation pressure
until the difference between the Phigh and Plow is
5cmH20.
46

47. B-Through a T-Piece
47

48.  Device:
AT-piece is a T-shaped circuit that is attached to the endotracheal
tube or tracheostomy tube.
It has corrugated tubing on the other two limbs.
The inhaled gas is delivered after humidification at a high flow
rate (greater than the patient's inspiratory flow rate) through
one of the upper arms of the apparatus with or without Venturi
arrangement.
The high flow rate serves two purposes:
“1-It creates a suction effect that carries the exhaled gas out of the
apparatus and prevents rebreathing of exhaled gas. “
2- It prevents the patient from inhaling room air from the
exhalation side of the apparatus. The exhaled gas exits through
the other limb of the T-circuit
48

49. Technique:
• When the patient meets the criteria for weaning, a T-piece adaptor and
heated nebulizer are connected to the patient's endotracheal tube. The
patient should be in a semi-sitting position. FIOzis set at a level 5-
10%higher than that during mechanical ventilation.
• 3-8 trials/day is performed. In them, allow the patient to breathe
spontaneously without any mechanical breaths. The patient is
observed closely during this period (usually 20-30 min) for signs of
failure of weaning
• If the above criteria of failure of weaning are present, weaning should be
discontinued.
• If the patient has been intubated for a prolonged period, or has a severe
underlying lung disease, Tpiece trials are done in periods of 10-20min
which progressively increase by 5-10minutes/hour until the patient
appears comfortable and shows acceptable arterial blood gases (SaO2>
90%,end-tidal Co2>znormal or constant throughout the trial).
49

50.  Advantages of T-piece: Less work of breathing is
needed during weaning.
 Disadvantages of T-piece: inability to monitor the
patient's spontaneous tidal volume and respiratory
rate.
50

51. Sign of Weaning Failure:
 • Discoordinate labored spontaneous breathing.
 • Exhaustion, agitation, and diaphoresis.
 • The respiratory and arterial blood gas values such as
tachypnea (> 30/min), tachycardia(> 100/min),
respiratory acidosis (pH< 7.2),rising PaCOz,and
hypoxemia (SaOi< 90%).
51

52. • Abdominal paradox:
Normally, when the diaphragm contracts, it descends into the abdomen
increasing intra-abdominal pressure.
This pushes the anterior wall of the abdomen outward. When the
diaphragm is weak or during labored breathing (i.e., contracting
diaphragm but distressed breathing),
the negative intrathoracic pressure created by accessory muscles of
respiration pulls the diaphragm upward into the thorax during
inspiration because the accessory muscles can overcome the contractile
force of the diaphragm.
This decreases intra-abdominal pressure and causes a paradoxical inward
displacement of the abdomen during inspiration (i.e., abdominal
paradox).
Therefore, abdominal paradox indicates either weak diaphragm or
labored breathing which are signs of failure of weaning.
52

53. 53

54. 54