Download Weaning from Mechanical Ventilation

Weaning from
Mechanical Ventilation
Ghamartaj Khanbabaee,MD
Pediatric Pulmonologist
Mofid Children’s Hospital
SBMU
Definition of Weaning
The transition process from
total ventilatory support
to spontaneous breathing.
This period may take many forms
ranging from abrupt withdrawal to
gradual withdrawal from ventilatory
support.
Weaning and Extubation
• Mechanical ventilation is a life-saving
intervention
• Risk of complications increases with
duration
• Short periods of mechanical ventilation,
weaning and extubation can often be
accomplished 2%and 4% of the total
duration of mechanical ventilation
• Longterm MV 60% to 70% of total duration
Weaning
Discontinuation of IPPV is achieved in most
patients without difficulty
Up to 20% of patients experience difficulty
requires more gradual process so that they
can progressively assume spontaneous
respiration
weaning
– Is the cause of respiratory failure gone or
getting better ?
– Is the patient well oxygenated and
ventilated ?
– Can the heart tolerate the increased work
of breathing ?
Extubation
• Extubation
– Control of airway reflexes
– Patent upper airway (air leak around tube?)
– Minimal oxygen requirement
– Minimal rate
– Minimize pressure support (0-10)
– “Awake ” patient
Clinical criteria used to determine readiness for trials
of spontaneous breathing
Required criteria
1. The cause of the respiratory failure has
improved
2. PaO2/FiO2≥150* or SpO2≥90 percent on
FiO2≤o.4 percent and positive end-expiratory
pressure (PEEP) ≤5 cmH2O
3. pH >7.25
4. Hemodynamic stability (no or low dose
vasopressor medications)
5. Able to initiate an inspiratory effort
Clinical criteria used to determine readiness for trials
of spontaneous breathing
Additional criteria (optional criteria)
1. Hemoglobin ≥8 to 10 mg/dL
2. Core temperature ≤38 to 38.5 degrees
Centigrade
3. Mental status awake and alert or easily
arousable
* A threshold of PaO2/FiO2≥120 can be used for patients with
chronic hypoxemia. Some patients require higher levels of PEEP
to avoid atelectasis during mechanical ventilation.
(1) The resolution of the etiology of respiratory
failure and attainment of stable respiratory status
(decreased FIO2 and PEEP level); absence of
tachypnea with a respiratory rate <60 for infants
younger than 12 months, <40 for the preschool
and school-aged child, and <30 for adolescents;
absence of acidosis [pH <7.35]; or hypercapnia
[PCO2 >60 mm Hg]; the parameters to indirectly
assess oxygenation and compliance include
PaO2:FIO2 ratio >267 [PaO2 >80 mm Hg on an
FIO2 of 0.3] and oxygen saturation [SpO2] >94%
on an FIO2 < 0.5, PIP <20 cm H2O, and PEEP < 5
cm H2O) and adequate respiratory muscle
function
(2) Hemodynamic stability, including no evidence
of shock this criterion includes good perfusion
(capillary refill <3 seconds), age-appropriate
blood pressure, and good cardiac function
(3) Neurologic stability Pediatric Glasgow Coma
Score > 11
(4) Metabolic factors serum potassium,
magnesium, and phosphorus
RCP blood gas analyses, pulse oximetry, end-tidal
CO2 measurements, and airway function screenings
Adjuncts to Weaning
Pharmacologic Agents: corticosteroid
 Heliox: Helium-oxygen (HeO2) mixture
has a low density and a high kinematic
viscosity, allowing for a reduction in airway
resistance
 Epinephrin
 Noninvasive Mechanical Ventilatory
Support
Weaning
The best approach for all patients is to
question (perhaps several times) every day:
 Why are they receiving mechanical
ventilation?
Do they require the current levels of
support?
Do they actually still need to be ventilated?
Methods of Weaning
1- T tube trials
- 30 minute T tube trial is sufficient
-Attention to increased effort ( nasal flaring,
accessory muscle recruitment, suprasternal and
intercostal retraction, or paradoxic motion of the
rib cage and abdomen).
- New wheezing or crackles
- Dyspnea and changes of mental status, blood
pressure, heart rate, or cardiac rhythm
Failing a T tube trial is a significant stress
on the respiratory muscles
Methods of Weaning
2-Intermittent Mandatory Ventilation(IMV)
 Gradual reduction in the amount of support
 Progressive increase in the amount of respiratory
work
 The IMV rate is reduced, usually in steps of one to three
breaths per minute
 An arterial blood gas is measured approximately 30
minutes after the IMV rate was reduced
 The IMV rate is further reduced as long as the pH remains
above 7.30 or 7.35
 IMV may contribute to the development of
respiratory muscle fatigue or prevent recovery
from it, which could delay weaning
Methods of Weaning
3-Pressure Support Ventilation (PSV)
PSV is an attractive weaning method

Patient has control over the respiratory frequency and
the depth, length, and flow of each breath
 PSV can compensate for the increased work imposed by
the resistance of the endotracheal tube and the ventilator
circuit
 Dyspnea is the same in PSV or IMV
 Resistance posed by an endotracheal tube varies as a result of
diameter, flow rates, tube deformation, and
adherent secretions, which makes it difficult to determine
the level of PSV that overcomes the resistance of the endotracheal tube
and ventilator circuit without assisting ventilation
 The gradual withdrawal of PSV is a poor predictor of a patient's
ability to sustain ventilation after extubation (asynchrony in COPD)
Methods of Weaning
4-Noninvasive ventilation
 Noninvasive positive pressure ventilation (NPPV)
has been investigated as weaning method for
patients with COPD and acute hypercapnic
respiratory failure
 NIPPV was well tolerated


Nasal abrasions and gastric distension.
Exclusion : postoperative, altered neurologic
status, hemodynamic instability, severe
concomitant diseases
•
Recognition of Weaning Failure
1-Increased respiratory load: increased elastic load
(unresolved lung disease, secondary pneumonia,abdominal
distension, and hyperinflated lungs), increased resistive
load (thickened airway secretions, partially occluded
endotracheal tube, and upper airway obstruction), or
increased minute ventilation (pain and irritability, sepsis
/hyperthermia, and metabolic acidosis)
2- Decreased respiratory capacity: is represented by
decreased respiratory drive (sedation, CNS infection, traumatic brain
injury, and hypocapnia/alkalosis), muscular dysfunction (muscular
catabolism and weakness ,malnutrition, and severe electrolyte
disturbances), and neuromuscular disorder (diaphragmatic
dysfunction, prolonged neuromuscular blockade, and cervical spinal
injury)
Weaning
 A trial of spontaneous breathing with assessment of the
gas exchange and pattern of breathing with minimal
pressure support(~10 cm H2O) or T-tube without pressure
support appears to be equally useful approaches in order to
evaluate readiness for extubation
 Levels of PaO2 <60 mm Hg, where FiO2 >0.4 constitutes
a relative contraindication to extubation
Increased respiratory rate or reduction in tidal
volume(or particularly a combination of both)
during spontaneous breathing strongly suggests
that the patient is not ready for extubation.
Difficult to wean :
chronic pulmonary disease, neurologic disease,
malnutrition
Causes of extubation failure
 upper airway obstruction
 poor airway protection
 excess secretions
 pulmonary atelectasis
 young age (i.e., <3 years),
 duration of ventilation, severity of underline lung disease
 oxygenation impairment (i.e., oxygenation index >5)
 intravenous sedation.
Extubation
• Prerequisites to extubation include:
1) A good cough/gag (to allow the child to
protect their airway).
2) NPO about 4 hours prior to extubation (in
case the trial of extubation fails and reintubation is
required).
3) Minimize sedation.
4) Adequate oxygenation on 40% FiO2 with
CPAP (or PEEP) = 4.
5) The availability of someone who can
reintubate the patient, if necessary.
6) Equipment available to reintubate the
patient, if necessary.
Extubation failure
decreasing tidal volume indexed to body weight
of a spontaneous breath
 increasing FiO2
 increasing MAP
 increasing oxygenation index
 increasing fraction of total minute ventilation
provided by the ventilator
 increasing peak ventilatory inspiratory pressure
 decreasing mean inspiratory flow

Weaning Protocol
1.
2.
3.
4.
5.
Is patient is a candidate for weaning?
i) PaO2 > 60mmHg
ii) FiO2 <0.5
iii) PEEP < 8 cm H2O
Screen for readiness—RSB Trial
i) SBT for one minute to calculate RSBI
Ensure intact airway reflexes
i) Coughing during suctioning
Patient can now be subject to SBTs
i) PS, CPAP, or T-piece
ii) Up to 120 minutes
SBT can be terminated if patient:
i) Successfully tolerates the SBT from 30-120
minutes
ii) Shows s/sx of failure
RSBI
First described by Yang and Tobin in 1991
 Rapid Shallow Breathing Index (RSBI) is the ratio of
respiratory frequency to tidal volume (f/VT)
A patient who has a RR of 25 breaths/min and a VT of 250
mL/breath has an RSBI of (25 breaths/min)/(.25 L) = 100
breaths/min/L.
 Patients who cannot tolerate independent breathing tend to
breathe rapidly (high frequency) and shallowly (low tidal
volume), they generally have a high RSBI.
 RSBI, the respiratory frequency (f) and tidal volume (VT)
were measured using a hand-held spirometer attached to
the endotracheal tube while a patient breathed room air for
one minute without any ventilator assistance
 Causes of increased RSBI :
narrow endotracheal tube, female gender, sepsis, fever,
supine position, anxiety, suctioning, and chronic restrictive
lung disease.
Failure of Weaning
Indicators of deterioration are:
1.
2.
3.
4.
5.
respiratory rate >35/mt.
falling tidal volume <5ml/kg
PaO2 <55mm Hg; Rising PaCO2
fall in blood pressure
tachycardia, cardiac arrythmias, sweating increased sympathetic activity
6. altered mental status - restlessness, anxiety,
confusion
Dependence/Failure to Wean
• Additional Features
– Cardiovascular Function
– Ischemia
– Heart Failure
– Metabolic Derangements
–
–
–
–
Hypophosphatemia
Hypocalcemia
Hypomagnesemia
Hypothyroidism (severe)
– Nutrition
– Poor—protein catabolism
– Overfeeding—excess CO2
– Deconditioning
Predictions of the outcome
of weaning
Variables used to predict weaning
success: Gas exchange
• PaO2 of > 60 mmHg with FiO2 of <
0.35
• A-a PaO2 gradient of < 350 mmHg
• PaO2/FiO2 ratio of > 200
Initiate Weaning
•
When there is:
1. Adequate Oxygenation
A) PaO2/FiO2 >150-200
B) Vent Settings: PEEP <8 and FiO2 <0.5
2.
3.
4.
5.
pH >7.25
Hemodynamic stablility
Ability to Initiate an Inspiratory Effort
Sedation (esp. with resp-depressing drugs)
has itself been weaned
Conclusion
Type of patient
Tidal Volume
RR
PEEP
FIO2
Ins. Flow
I:E
Normal
10 cc/kg
10 to 12
0 to 5
100%.
60 l/min
1:2.
ARDS
6 cc/kg
10 to 12
5 to 15
100%.
60 l/min
1:2.
COPD
6 cc/kg
10 to 12
5 to 10
100%.
100 to 120 1:3 to 1:4
Trauma
10 cc/kg
10 to 12
0.
100%.
60 l/min
1:2.
Pediatric
8-10 cc/kg Varies age 3 to 5
100%.
60 l/min
1:2.
Note
Note
PH>7.2
PCO2 <80 mmhg
Trigger to consider
Trigger to consider