weaning protocol; weaning failure ; difficult weaning

1. Weaning from Mechanical
Ventilation
Dr. Ram Gopal Maurya

2. • Weaning is the process of withdrawing
mechanical ventilatory support and
transferring the work of breathing from the
ventilator to the patient.
• The process of gradually reducing mechanical
ventilatory support must be individualized for
each patient.

3. • Weaning Success: Weaning success is defined
as absence of ventilatory support 48 hours
following the extubation.
• CLASSIFICATION OF WEANING:
1. simple weaning : patients who proceed from
initiation of weaning to successful extubation
on the first attempt.
2. difficult weaning: patients who fail initial
weaning and require up to 7 days from the
first SBT to achieve successful weaning.
3. prolonged weaning: require more than 7
days from the first SBT to achieve successful
weaning.

4. • The simple weaning group represents 60%-
70% of ventilated patients, the difficult group
includes 20%-25% of patients, and the
prolonged group includes the remaining 5%-
15% of patients.
• Weaning Failure: defined as either the
failure of spontaneous breathing trial
(SBT) or the need for reintubation
within 48 hours following extubation.

5. PATIENT CONDITION PRIOR TO
WEANING
• Before weaning, the patient should have recovered from the
acute phase of the disease leading to mechanical ventilation
and be able to assume adequate spontaneous breathing.

6. WEANING CRITERIA
• Weaning criteria are used to evaluate the
readiness of a patient for a weaning trial and
the likelihood of weaning success.
a. Clinical criteria
b. Ventilatory criteria
c. Oxygenation criteria
d. Pulmonary reserve and measurements

7. Clinical criteria
• Resolution of acute phase of disease
• Adequate cough
• Absence of excessive secretions
• Cardiovascular and hemodynamic stability

8. Ventilatory criteria

9. Oxygenation criteria

10. QS/QT
• physiologic shunt to total perfusion (QS/QT) ratio is used
to estimate how much pulmonary perfusion is wasted.
• Shunted pulmonary perfusion cannot take part in gas
exchange due to mismatch of ventilation (e.g.,
atelectasis).

11. • In clinical settings, a calculated physiologic shunt of
10% or less is considered normal. Shunt of 10% to 20%
indicates mild physiologic shunt, and shunt of 20% to
30% shows significant physiologic shunt. Greater than
30% shunt reflects critical and severe shunt.
• Since physiologic shunt in mechanical ventilation is
usually intrapulmonary in origin (inadequate
ventilation in relation to pulmonary perfusion),
weaning failure becomes likely when spontaneous
ventilation cannot keep up with the pulmonary
perfusion.

12. P(A-a)O2.
• The alveolar-arterial oxygen tension gradient
(P(A-a)O2) is used to estimate the degree of
hypoxemia and the degree of physiologic shunt.
• This gradient is directly related to the degree of
hypoxemia or shunt (a larger gradient reflects
more severe hypoxemia or shunt).
• On room air, the P(A-a)O2 should be less than 4
mm Hg for every 10 years in age.
• On 100% oxygen, every 50 mm Hg difference in
P(A-a)O2 approximates 2% physiologic shunt
(Barnes, 1994; Burton et al., 1997; Shapiro et al.,
1994).

13. • In mechanical ventilation, P(A-a)O2 of less
than 350 mm Hg while on 100% oxygen
suggests a likelihood of weaning success. P(A-
a)O2 of 350 mm Hg while on 100% oxygen
approximates 14% shunt and values of greater
than 350 mm Hg may hinder the weaning
process.

14. Pulmonary reserve

15. Pulmonary measurements

16. Combind weaning indices
• Rapid shallow breathing index ( RSBI )
• Simplified weaning index ( SWI )
• Compliance rate oxygenation and pressure (
CROP ) index

17. RAPID SHALLOW BREATHING INDEX
(RSBI)
• The rapid shallow breathing index (RSBI) or f/VT index
has been used to evaluate the effectively of the
spontaneous breathing pattern.
• The RSBI (f/VT index) is calculated by dividing the
spontaneous breathing frequency (breaths/min) by the
average spontaneous VT (L).
• When the RSBI or f/VT index is greater than 100
breaths/min/L (rounded from 105 breaths/min/L), it
correlates with weaning failure. On the other hand,
absence of rapid shallow breathing (f/VT ratio ,100
breaths/min/L), is an accurate predictor of weaning
success

20. • When SWI is less than 9/min,highly predictive
(93%) of weaning success
• And when SWI is more than 11/min, 95%
probability of weaning failure.

22. WEANING PROCEDURE
• Weaning can be done using:-
1. Spontaneous breathing trials
2. Pressure support Ventilation
3. Synchronised Mandatory Intermittent
Ventilation (SIMV)– Not Recommended alone

23. Spontaneous breathing trial (SBT)
• An evaluation of a patient’s readiness for
weaning from mechanical ventilation and
extubation.
• SBT is the major diagnostic test to determine if
patients can be successfully extubated and
weaned from mechanical ventilation.
• Spontaneous breathing may be augmented with
lowlevel (≤ 8 cm H2O) of pressure support, CPAP,
or automatic tube compensation (ATC).
• SBT may last up to 30 minutes.

24. SBT Steps

25. SBT Failure

26. Pressure Support Ventilation
• helps to reduce the airflow resistance
imposed on the patient by the endotracheal
tube and ventilator circuit.

27. Weaning using SIMV
• Based on the results of the sixth International Consensus
Conference on Intensive Care Medicine, synchronized intermittent
mandatory ventilation (SIMV) should be avoided as a stand-alone
weaning modality (Boles et al., 2007). However, SIMV remains an
effective tool in providing partial ventilatory support during
continuous mechanical ventilation.

28. • Automatic Tube Compensation.
Automatic tube compensation (ATC) is a mode
in the Evita 4 ventilator (Dräger Medical) that
reduces the airflow resistance imposed by the
artificial airway (endotracheal or
tracheostomy tube). It allows the patient to
have a breathing pattern as if breathing
spontaneously without an artificial airway.
This type of compensation may facilitate
breathing efficacy and reduce the work of
breathing throughout the weaning process.

29. WEANING PROTOCOL

30. Termination criteria:
• Spontaneous frequency >35/min for 5 min;
• SpO2 < 90%,
• Heart rate >140/min or 120% of baseline;
• Systolic pressure >180 mm Hg or ,< 90 mm
Hg;
• Signs of anxiety or use of accessory muscles.

32. WEANING FAILURE

34. CAUSES OF WEANING FAILURE
• Aside from the pathological conditions that
lead to the need for mechanical ventilation,
weaning failure may occur when the work of
spontaneous breathing becomes too great for
the patient to sustain.
• Weaning failure is generally related to (1)
increase of airflow resistance, (2) decrease of
compliance, or (3) respiratory muscle fatigue.

35. Increase of Airflow Resistance
• Normal subjects using an endotracheal (ET)
tube have an increase of 54% to 240% in the
work of breathing, depending on the size of
the ET tube and ventilator flow rate.
• To minimize this ET tubes of larger size should
be used when it is appropriate to the patient’s
size & the ET tube may be cut to about an inch
from the patient’s lips.

36. Other strategies for decreasing airway
resistance
• periodic monitoring of the ET tube for kinking or
obstructions by secretions, or other devices attached
to the ET tube such as a continuous suction catheter,
heat and moisture exchanger, or end-tidal CO2
monitor probe.
• Endotracheal suctioning to remove retained
secretions and use of bronchodilators to relieve
bronchospasm have also been used successfully to
reduce the airflow resistance.

37. Decrease of Compliance

38. Respiratory Muscle Fatigue

39. • following topics should be evaluated in a diffi
cult-towean patient:
1. Airway And Lung Dysfunction,
2. Brain Dysfunction,
3. Cardiac Dysfunction,
4. Diaphragm Dysfunction, And
5. Endocrine Dysfunction.

40. Airway and lung dysfunction
• Elevated airway resistance, reduced respiratory
system com pliance, and impaired gas exchange
increase the work of breathing

41. Brain dysfunction
• Brain dysfunction in diffi cult-to-wean patients
is related mostly to delirium.
• Other psychological disturbances, such as
anxiety and depression, may interfere with
successful weaning.

42. Cardiac dysfunction
• Th e transition from mechanical ventilation to
spon taneous breathing imposes an additional
load on the cardiovascular system because of
intrathoracic pressure changes, which aff ect
ventricular preload and afterload and increased
oxygen consumption by the respiratory muscles.
• In patients with COPD but without cardiac
disease, weaning was associated with a signifi
cant reduction in left ventricle ejection fraction
and this reduction was probably due to increased
left ventricular afterload.

43. • Diagnostic approach
1. electrocardiography at the fi nal stages of the
weaning trial to detect ischemia
2. SvO2 could be used as a screening tool for
cardiac dysfunction in difficult weaning. Th e
decrease in SvO2 resulted from the inability
to improve cardiac output and therefore
oxygen transport.
3. BNP
4. Echocardiography.

44. Treatment strategies
• In diffi cult-to-wean patients with evidence of
cardiac failure, afterload reduction and
ultimately the use of inotropes must be
considered.

45. Diaphragm/respiratory muscle
function
• Diaphragm/respiratory muscle weakness can be
one of the cause of weaning failure.
• It should be kept in mind that dysfunction of the
respiratory muscle may result from a lesion
anywhere between the aff erent chemo-
receptors of the respiratory centers and the
contractile proteins.
• Some commom etiology: disuse atrophy; Critical
illness polyneuropathy and myopathy;
malnutrition; electrolyte imbalance; etc

46. • Diaphragmatic strength is obtained by
stimulation of the phrenic nerves and recording
the resulting transdiaphragmatic pressure (Pdi).
Weaning-failure patients have twitch Pdi values
below 10cm H2O, whereas values of 35 to 39cm
H2O are observed in healthy subjects.
• Diaphragmatic rapid shallow breathing index/
diaphragmatic excursion can also be used for
weaning.

47. Treatment strategies
• Mechanical ventilation is a double-edged
sword for the respiratory muscles.
• Antioxidants: Antioxidant supplementation
was associated with a reduction in ventilator-
dependent days

48. Endocrine and metabolic dysfunction
• adrenal insuffi ciency.
• Hypothyroidism.
• Malnutrition.
• Electrolyte abnormalities, including very low
plasma levels of phosphate and magnesium,
have been shown to aff ect skeletal muscle
function.