Ghamartaj Khanbabaee,MD

Pediatric Pulmonologist

Mofid Children’s Hospital

SBMU

Weaning from Weaning from Mechanical VentilationMechanical Ventilation

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

– 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 ?

weaning

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

WeaningThe 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 Weaning1- 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 rhythmFailing a T tube trial is a significant stress

on the respiratory muscles

 

Methods of Weaning2-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 Weaning3-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 Protocol1. Is patient is a candidate for weaning?

i) PaO2 > 60mmHgii) FiO2 <0.5iii) PEEP < 8 cm H2O

2. Screen for readiness—RSB Triali) SBT for one minute to calculate RSBI

3. Ensure intact airway reflexesi) Coughing during suctioning

4. Patient can now be subject to SBTsi) PS, CPAP, or T-pieceii) Up to 120 minutes

5. SBT can be terminated if patient:i) Successfully tolerates the SBT from 30-120

minutesii) Shows s/sx of failure

RSBIFirst 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 WeaningIndicators of deterioration are:

1. respiratory rate >35/mt.

2. falling tidal volume <5ml/kg

3. PaO2 <55mm Hg; Rising PaCO2

4. fall in blood pressure

5. 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. pH >7.25

3. Hemodynamic stablility

4. Ability to Initiate an Inspiratory Effort

5. Sedation (esp. with resp-depressing drugs) has itself been weaned

ConclusionType of patient Tidal Volume RR PEEP FIO2 Ins. Flow I:E Note Note

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 PH>7.2PCO2 <80 mmhgTrigger to consider

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. Trigger to consider