Weaning from mechanical ventilation
Newth C et al. Pediatr Crit Care Med 2009; 10:1–11
Peter C. RimensbergerPediatric and Neonatal ICU, Department of PediatricsUniversity Hospital of Geneva, Geneva, Switzerland
Weaning / Extubation failure: Is it a real problem in the PICU ?
Reported extubation failure rates in PICUs range from 4.1% to 19%
Baisch SD, Wheeler WB, Kurachek SC, Cornfield DN. Extubation failure in pediatric intensive care incidence and outcomes. Pediatr Crit Care Med 2005; 6:312–318.
Edmunds S, Weiss I, Harrison R. Extubation failure in a large pediatric ICU population. Chest 2001; 119:897–900.
Fontela PS, Piva JP, Garcia PC, et al. Risk factors for extubation failure inmechanically ventilated pediatric patients. Pediatr Crit Care Med 2005; 6166–170.
Adrienne G. Randolph et al. JAMA 2002;288(20):2561-2568
Effect of Mechanical Ventilator Weaning Protocols on Respiratory Outcomes in Infants
and Children: A Randomized Controlled Trial
In contrast with adult patients, the majority of children are weaned from mechanical ventilator support in 2 days or less.
Weaning protocols did not significantly shorten this brief duration of weaning.
Weaning: The key questions
1. Is the cause of respiratory failure gone or getting better ?
2. Is the patient well oxygenated and ventilated ?
3. Can the heart tolerate the increased work of breathing ?
Discontinuation of Mechanical Ventilation
To discontinue mechanical ventilation requires:
– Patient preparation
– Assessment of readinessFor independent breathing
For extubation
– A brief trial of minimally assisted breathingAn assessment of probable upper airway patency after extubation
– Either abrupt or gradual withdrawal of positive pressure, depending on the patient’s readiness
Factors that may contribute to extubation failure in pediatric patients
• young age
• duration of mechanical ventilation
• prolonged treatment with sedatives and analgesics
Fontela PS, Piva JP, Garcia PC, et al. Risk factors for extubation failure in mechanically ventilated pediatric patients. Pediatr Crit Care Med 2005; 6166–170.
Failure rate of planned extubations of patients within the first 48 hrs of arrival in the pediatric intensive care unit (PICU) is, on average, half that of the rate for patients ventilated for longer than 48 hrs.
Kurachek SC et al.Crit Care Med 2003; 31:2657–2664
Ventilation > 48 hours: contrary to common perception there is no relationship
between the duration of MV and rates of failed extubation
Kurachek SC et al.Crit Care Med 2003; 31:2657–2664
Concepts of Weaning
Classical Methods for Gradually Withdrawing Ventilator Support
The most common weaning approach: gradual reduction of ventilatory support 1) By reducing ventilatroy rate: IMV or SIMV
2) By reducing inspiratory pressure: PS
PS is often combined with IMV/SIMV during weaning
Volume support and volume-assured pressure support are special forms of PS available in certain ventilators that guarantee a minimal tidal volume per assisted breath.Weaning with volume support is semiautomatic, where the PS level required to maintain a certain tidal volume is reduced automatically as respiratory mechanics improve.
Getting ready for extubation
• Weaning– decrease the PEEP (4-5)– decrease the rate– decrease the PIP (as needed)
• What you want to do is decrease what the vent does and see if the patient can make up the difference….
Airw
ay p
ress
ure Inspiration Expiration
Controlled ventilation
Ventilator work
Trigger patient
J.J. Marini, et al Am Rev Respir Dis 1986: 134: 902-909
Assisted Ventilation
Ventilator work
Patient work
Paw = Pvent + Pmus
Pvent
Spontaneous Breathing Trialsand Extubation Readiness Tests
SBT conducted on PS of 10 cm H2O versus
SBT using a T-piece no difference
Spontanoeus Breathing Test (SBT)
Of the 323 patients (77%) who passed the SBT and were extubated, 14% were reintubated within 48 hrs.
Respiratory rate, tidal volume, rapid shallow breathing index (RSBI), and maximal negative inspiratory pressure (PImax) were all poor predictors of extubation outcome.
Farias JA et al. Intensive Care Med 2002; 28:752–757
Farias JA et al. Intensive Care Med 2001; 27:1649–1654
Rapid Shallow Breathing Index (RSBI): f/VT
The frequency to tidal volume ratio (or rapid shallow breathing index, RSBI) is a simple and useful integrative indicator of the balance between power supply and power demand.
In adults: A rapid shallow breathing index < 100 generally indicates adequate power reserve. In this instance, the RSBI indicated that spontaneous breathing without pressure support was not tolerable, likely due in part to the development of gas trapping.
wide range of age groups with different respiratory rates
Limitations of RSBI in children
RR above normal age limits:
< 6 months: 20–60 breaths/min
< 2 years: 15–45 breaths/min
< 5 years: 10–35 breaths/min
or > 1,5 x normal
F. Leclerc, O. Noizet, W. Chaari, A. Sadik, Y. RiouPrinciples of mechanical ventilation weaning in paediatric intensive careAnnales Françaises d’Anestésie et de Réanimation 28 (2009) 685–687
Weaning failure: Objective Criteria
Rapid Shallow Breathing Index (RSBI): f/VT
Compliance, Resistance, Oxygenation, Pressure Index (CROP Index):(Dynamic Compliance x Maximal Negative Inspiratory Pressure x (PaO2/PAO2)/ Respiratory Rate)
Venkataraman ST et al. Crit Care Med 2000; 28:2991–2996
Rapid Shallow Breathing Index (RSBI): f/VT
Compliance, Resistance, Oxygenation, Pressure Index (CROP Index):(Dynamic Compliance x Maximal Negative Inspiratory Pressure x (PaO2/PAO2)/ Respiratory Rate)
Volumetric Capnography: physiologic dead space (VD/VT)
Phase 1: - airway deadspace
Phase 2: - mixing of airway deadspace and alveolar gas
Phase 3: - alveolar volume
Measurement of End-tidal CO2 and Dead SpaceThe Single Breath CO2 Curve
The Single Breath CO2 Curve with added PaCO2 value
Area X = volume of CO2
Area Y = wasted ventilation due to alveolar deadspaceArea Z = wasted ventilation due to airway deadspace
Physiologic VD / VT = (Y+Z) / (X+Y+Z)Physiologic Deadspace = (VD / VT) * (VT)Alveolar Deadspace = VD phys - VD airway
VD/VT ≤ 0.50 reliably predicts extubationsuccess with 75% sensitivity and 92% specificity,
whereas a VD/VT > 0.65 identified patients at risk for failure
Hubble CL, Gentile MA, Tripp DS, et al:Crit Care Med 2000; 28:2034–2040
Deadspace to tidal volume ratio predicts successful
extubation in infants and children
The Single Breath CO2 Curve and VCO2
Airway deadspace (VD airway) = area p
Volume of CO2 = area X. Adding volumes of each breath gives CO2 elimination in ml / min
MV SV not present
VCO2 Not readyto extubate
Volumetric CO2 recording
Volumetric CO2 Monitoring
• Watch VCO2 (CO2 elimination) over time as wean ventilator
• If mechanical ventilation taken over by spontaneous ventilation with VCO2 remaining stable or increasing, then probably approaching extubation point
Khan, Nadeem; Brown, Andrew; Venkataraman, Shekhar T. Critical Care Medicine 199624(9):1568-1579
Predictors of extubation success and failure inmechanically ventilated infants and children
Venkataraman STCrit Care Med 2000; 28:2991–2996
Predictors of extubation success
and failure inmechanically
ventilated infants and children
Venkataraman ST et al. Crit Care Med 2000; 28:2991–2996
Reasons for reintubation
a spontaneous tidal volume that is at least normal, a low FIO2, a low Paw,a low OI, a low PIP, a high dynamic compliance, a low FrVe (fraction of total minute ventilation provided by the
ventilator)
a normal or high Vt/Ti (mean inspiratory flow)
are associated with a low risk of failure
Preextubation variables easily obtained at the bedside can predict the relative risk of reintubation
Venkataraman ST et al. Crit Care Med 2000; 28:2991–2996
Sedation?
Adrienne G. Randolph et al. JAMA 2002;288(20):2561-2568
The “air leak” testto predict which patients are at risk for
postextubation stridor and extubation failure
76% of the physicians routinely use the “air leak” test test prior to extubation
Foland JA, Super DM, Dahdah NS, Mhanna MJ. The use of the air leak test and corticosteroids in intubated children: a survey of pediatric critical care fellowship directors. Respir Care 2002; 47:662–666
The ‘air leak’ testto predict which patients are at risk for
postextubation stridor and extubation failure
Increased risk for post-extubation stridor or extubation failure when there is absence of a leak around the ETT or leak at a > 30 cm H2OKemper KJ et al. Crit Care Med 1991; 19:352–355Seid AB et al. Arch Otolaryngol Head Neck Surg 1991; 117:880–882
A leak around the ETT at > 20 cm H2O had a sensitivity of 83.3% in predicting post-extubation stridor in patients age > 6 yearsMhanna MJ et al. Crit Care Med 2002; 30:2639–2643
3 x higher incidence of adverse events in patients without an air leak at 25cmH2O Suominen Pet al. Paediatr Anaesth 2006; 16:641–647.
Reduced incidence of post-extubation stridor in both neonatal and pediatric patients
Trend towards decreased rates of re-intubation in the corticosteroid groups (statistically not significant)
But there was considerable variation noted in the pediatric trials examined in this meta-analysis, which the authors attributed to possible differences in risk among the populations studied.
Prophylactic systemic corticosteroids in an attempt to minimize post-extubation stridor ?
Markovitz BP, Randolph AG. Corticosteroids for the prevention of reintubation and postextubation stridor in pediatric patients: A meta analysis. Pediatr Crit Care Med 2002; 3:223–226.
In neonates: RR 0.42; 95% CI 0.07 to 2.32
Prophylactic systemic corticosteroids in an attempt to minimize post-extubation stridor ?
In children: significantly reduced in children with underlying airway abnormalities (n = 62) but not in the study that excluded these children (n = 153)
In adults RR 0.48; 95% CI 0.19 to 1.22 for reintubation(n = 1953) RR 0.47; 95% CI 0.22 to 0.99 for stridor
Markovitz BP, Randolph AG, Khemani RG:Corticosteroids for the prevention and treatment of post-extubation stridor
in neonates, children and adults. Cochrane Database Syst Rev 2008; (2):CD001000
Markovitz BP, Randolph AG, Khemani RG:Corticosteroids for the prevention and treatment of post-extubation stridor
in neonates, children and adults. Cochrane Database Syst Rev 2008; (2):CD001000
Using corticosteroids to prevent (or treat) stridor after extubation
has not proven effective for neonates, children or
adults. However, given the consistent trend toward benefit, this intervention
does merit further study
Extubation Criteria
1. Neurologic
2. Cardiovascular
3. Pulmonary
Neurologic
• Patient must be able to protect his airway, e.g, have cough, gag, and swallow reflexes.
• Level of sedation should be low enough that the patient doesn’t become apneic once the ETT is removed.
• No apnea on the ventilator.
• Must be strong enough to generate a spontaneous TV of 5-7ml/kg on 5-10 cm H2O PS or have a negative inspiratory force (NIF) of 25cm H2O or higher.
• Being able to follow commands is preferred.
Cardiovascular
• Patient must be able to increase cardiac output to meet demands of work of breathing.
• Patient should have evidence of adequate cardiac output without being on significant inotropic support.
• Patient must be hemodynamically stable.
Pulmonary
• Patient should have a patent airway.
• Pulmonary compliance and resistance should be near normal.
• Patient should have “normal” blood gas and work-of-breathing on the following settings:
– FiO2 <40%
– PEEP ±5cm H2O
– PS 5-8cm H2O
– Spontaneous TV of 5-7ml/kg
– Close to normal breath rate according to age
Conclusions:Weaning Readiness and Extubation Criteria
1. Ability to protect upper airwayEffective cough
Alertness
2. Improving clinical condition
3. Adequate lumen of trachea and larynx“Leak test” during airway pressurization
Upper airway obstruction is the single most common cause of extubation failure.
A reliable method of assessing readiness for weaning and predicting extubation success is not evident from the pediatric literature.
Weaning is often not considered early enough in the course of ventilation.
Conclusions:Weaning Readiness and Extubation Criteria
Extubation
– Control of airway reflexes
– Patent upper airway (air leak around tube?)
– Minimal oxygen requirement
– Minimize pressure support (0 - max 10) (Normal compliance = Vt 8 ml/kg with PS of 8)
– Comfortable spontaneous breathing
– “Awake ” patient