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BASICS OFNEONATAL VENTILATION      Dr Abid Ali Rizvi
Why do we ventilate neonates?   Oxygenation   CO2 elimination   Overwhelming Work of Breathing   Poor respiratory driv...
Applied Mechanics   Flow of gas                   Generates the inflating pressure.   PIP minus PEEP                Crea...
Start here:   A pressure gradient between the airway opening    (mouth) and the alveoli must be present to drive the    f...
Components of the inflating pressure                 Mean Airway Pressure =                 area under the Pressure Time C...
PIP wave form is shaped by the gas flowrate during inspiration.
Compliance   Compliance describes the elasticity or distensibility    of the respiratory structures (alveoli, chest wall,...
Elastance [E] :Recoil Tendency   Elastance is reciprocal of compliance [C].   It measures the ease with which a distende...
Compliance
Airway resistance   Airway resistance is the opposition to gas flow.   Ratio of driving pressure to the rate of air flow...
Airway resistance
ET resistance increases with flow
Time Constant [Kt] = C x Raw   One time constant of a respiratory system is    defined as the time required by the alveol...
% filling and emptying of alveoli afterevery Time Constant.
Time Constant [Kt] = C x Raw   Stiff alveoli (eg HMD) have very short [Kt ], so small Ti is    sufficient to fill them, a...
Anatomic Dead Space   Anatomic dead space:     The  total volume of the conducting airways from the      nose or mouth d...
Intrapulmonary RL shunting [ V/Q ]   Alveolar Dead Space [Collapsed alveoli]
Instrumental dead spaceIn babies <1000 g, the extradead space may slightlyincrease PaCO2 levels.The advantages of using fl...
Work of Breathing                                       Work = Pressure x Volume                                       W...
2 Components of WOB:Elastic and Resistive – Resp. Rate Dependency
Imposed work of breathing [WOB]   ET, circuit tubing, ventilator exhalation valve, all    increase the resistance against...
Techniques to counter the Imposed WOB:  Avoid  narrow ET if possible.                   [Poiseuilles equation R   . L ...
Mean Airway Pressure [MAP/Paw]Contributing parameters {PIP, PEEP, Ti, Flow, Rate}Important for the:       MAP= (PIP-PEEP) ...
Mean Airway Pressure [MAP/Paw]               Safety & Efficiency of               ventilation is best in               thi...
Importance of PEEP   Presence of ET in the glottis disables the braking    action of the vocal cords during expiration, w...
Modes of Neonatal Ventilation -Classified by three factors:   Breath initiation:     Controlledor     Synchronized with...
CMV & IMV: by definition…   Continuous Mandatory Ventilation: Used most often    in the paralyzed or apneic patients. The...
Poor Synchronization causes:   Baby fighting with the ventilator.   Increased WOB   Abnormally high intra-thoracic and ...
Synchronized ventilation modes    Nomenclature is a mess.    Heart of synchronized ventilation is the breath     sensor ...
Limitations of flow sensors   ET leak: expiratory TV may be underestimated.   Less than the expected expiratory tidal vo...
Assist Control [A/C]    Patient Triggered Ventilation [PTV]   Every breath of baby that the flow sensor detects is    sup...
A/C: Green parts at beginning of flowcurve is the patient`s effort
Synchronized Intermittent Mandatory Vent.    [SIMV]   SIMV was developed as a result of the problem of    high respirator...
SIMV breaths:Green spontaneous;   Blue ventilator
Volume Targeted Ventilation [VTV]Targeted Tidal Volume [TTV] VentilationVolume Guarantee [VG]  Physician selects a desired...
Pressure Support Ventilation [PSV]                            Peak Expiratory Flow
PSV with SIMV
Effect of various parameters onoxygenation and ventilation.
In brief: Always Check:   Chest movement, air entry, presence of retractions,    hyper-inflated chest, wheezing etc.   L...
Basics of neonatal ventilation 1
Basics of neonatal ventilation 1
Basics of neonatal ventilation 1
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Basics of neonatal ventilation 1

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Basics of neonatal ventilation 1

  1. 1. BASICS OFNEONATAL VENTILATION Dr Abid Ali Rizvi
  2. 2. Why do we ventilate neonates? Oxygenation CO2 elimination Overwhelming Work of Breathing Poor respiratory drive Others: Transport of sick baby, pre-op etc.
  3. 3. Applied Mechanics Flow of gas Generates the inflating pressure. PIP minus PEEP Creates a pressure gradient [DP]. Compliance [C] and Airway Resistance [Raw] Dictate the PIP and PEEP required. Tidal Volume [TV] Is proportional to the DP size. TV x Rate = Minute volume Quantifies the CO2 removal. Mean Airway Pressure [Paw] Quantifies the adequacy of alveolar recruitment & oxygenation. Time Constant = [C] x [Raw] Decides optimum Ti and Te Dead Space [VD] Right to Left Shunting Work of Breathing [WOB] Endotracheal Leak
  4. 4. Start here: A pressure gradient between the airway opening (mouth) and the alveoli must be present to drive the flow of gases during both inspiration and expiration. Peak Inspiratory Pressure [PIP]: Opens the alveoli. Positive End Expiratory Pressure [PEEP]: Prevents the alveoli from collapsing during exhalation; thereby maintains adequate Functional Residual Capacity [FRC].
  5. 5. Components of the inflating pressure Mean Airway Pressure = area under the Pressure Time Curve Pressure PIP (cm of H2O) PEEP
  6. 6. PIP wave form is shaped by the gas flowrate during inspiration.
  7. 7. Compliance Compliance describes the elasticity or distensibility of the respiratory structures (alveoli, chest wall, and pulmonary parenchyma). A measure of the ease of expansion of the lungs and thorax. Compliance = Δvolume  Δpressure Low Compliance means Stiff lungs [as in Hyaline Membrane Disease]. It will need higher pressure gradient for pushing air inside.
  8. 8. Elastance [E] :Recoil Tendency Elastance is reciprocal of compliance [C]. It measures the ease with which a distended structure return back to its original size. E=1/C Alveoli with low compliance are difficult to inflate, but their elastance is high, so they deflate easily. Such alveolar units are prone to atelectasis during expiration.
  9. 9. Compliance
  10. 10. Airway resistance Airway resistance is the opposition to gas flow. Ratio of driving pressure to the rate of air flow. ET is the most important contributor of Raw Airway resistance depends on:  Radii of the airways (total cross-sectional area)  Lengths of the airways  Flow Type: Laminar or Turbulent  Density and viscosity of gas
  11. 11. Airway resistance
  12. 12. ET resistance increases with flow
  13. 13. Time Constant [Kt] = C x Raw One time constant of a respiratory system is defined as the time required by the alveoli to empty 63% of its tidal volume through the airways into the mouth/ventilator circuit. At the end of three [Kt ] 95% of the tidal volume is emptied. Airway diameter during inspiration: Raw . Therefore inspiratory [Kt ] are ~ half of the expiratory [Kt ].
  14. 14. % filling and emptying of alveoli afterevery Time Constant.
  15. 15. Time Constant [Kt] = C x Raw Stiff alveoli (eg HMD) have very short [Kt ], so small Ti is sufficient to fill them, and they will empty quickly also. Conditions with high Raw ( eg MAS, BPD) have long expiratory time constant, so they will empty adequately with longer Te, and will be slow to fill too. It is also dependent on the patient`s size. Every thing being equal, larger infants have longer time constant than the extremely premature ones. Therefore premature neonate will have normal breathing faster than a term AGA newborn.
  16. 16. Anatomic Dead Space Anatomic dead space:  The total volume of the conducting airways from the nose or mouth down to the level of the terminal bronchioles.  This volume does not participate in the gas exchange.  Extrathoracic : 2-2.5 ml/kg in neonates.  Intrathoracic : 1.03 ml/kg, age independent.
  17. 17. Intrapulmonary RL shunting [ V/Q ] Alveolar Dead Space [Collapsed alveoli]
  18. 18. Instrumental dead spaceIn babies <1000 g, the extradead space may slightlyincrease PaCO2 levels.The advantages of using flowsensors for monitoring, volumetargeting and flow triggering,outweigh the small effect onPaCO2.Instrumental dead spaceimposes a ventilatory burdenduring SIMV weaning in smallpreterm infants.
  19. 19. Work of Breathing  Work = Pressure x Volume  Work against Elastic Recoil  Work against Resistance  Airway resistance: Mainly the narrow ET  Tissue resistance Viscous forces within tissuesMetabolic cost of WOB in spont. as they slide over each other.breathing in normal lungs is 1-2%of total O2 consumption, but canincrease to >30% in ventilatedbaby with premature lungs.
  20. 20. 2 Components of WOB:Elastic and Resistive – Resp. Rate Dependency
  21. 21. Imposed work of breathing [WOB] ET, circuit tubing, ventilator exhalation valve, all increase the resistance against which the baby must breathe while on ventilator. This leads to increased O2 consumption and exhaustion of respiratory muscles.
  22. 22. Techniques to counter the Imposed WOB:  Avoid narrow ET if possible. [Poiseuilles equation R   . L  (Radius)4]  ‘Pressure Support’ for the spontaneous breaths.  Adequate PEEP in expiration: [Maximum WOB is for re-opening a collapsed alveoli]  Optimize the lung volume:  Lowlung volume: Airway resistance is high, so WOB .  Over-distended Lungs: Compliance is low, so WOB .  Synchronization of ventilator and baby`s cycling.  Good nutrition.  Early extubation ASAP.
  23. 23. Mean Airway Pressure [MAP/Paw]Contributing parameters {PIP, PEEP, Ti, Flow, Rate}Important for the: MAP= (PIP-PEEP) x [Ti (Ti+Te)] + PEEP Recruitment of alveolar units:  Oxygenation is directly proportional to MAP.  Surfactant preservation. Optimization of Lung volume:  Airway resistance is high at low lung volumes.  Compliance is poor at high (over-distended) lung volume.  Pulmonary vascular resistance is high at low lung volume Venous return and Cardiac output is compromised when MAP is abnormally high.
  24. 24. Mean Airway Pressure [MAP/Paw] Safety & Efficiency of ventilation is best in this Lung Volume & Paw range. Lung Volume Mean Airway Pressure
  25. 25. Importance of PEEP Presence of ET in the glottis disables the braking action of the vocal cords during expiration, which would normally prevent the collapse of alveoli. It is easy to expand an already open alveoli, rather than opening a fully collapsed one. FRV provides a means of oxygenation of pulmonary blood flow during expiration. PEEP split opens the floppy airways of preterm neonate, thereby preventing their collapse during expiration; so helps in reducing the airway resistance in expiration.
  26. 26. Modes of Neonatal Ventilation -Classified by three factors: Breath initiation:  Controlledor  Synchronized with the patient`s effort. Gas flow control during the breath delivery:  Pressure limited or  Volume limited Breath is termination:  Time cycled (fixed inspiratory time) or  Flow cycled (matching with the patient`s own Ti) Hybrid modes mix multiple techniques from above.
  27. 27. CMV & IMV: by definition… Continuous Mandatory Ventilation: Used most often in the paralyzed or apneic patients. The ventilator rate is set faster than the patients own breathing rate. Intermittent Mandatory Ventilation: The ventilator rate is lower (less than 30 bpm), therefore the patient gets chance to breathe spontaneously between two controlled breaths. In both CMV and IMV, breaths are delivered regardless of the patients effort. Synchronization is not intended in both.
  28. 28. Poor Synchronization causes: Baby fighting with the ventilator. Increased WOB Abnormally high intra-thoracic and intra-pulmonary pressure surges. Decreased venous return. Increased intracranial pressure. Barotrauma Sub-optimal training of muscles in weaning.
  29. 29. Synchronized ventilation modes Nomenclature is a mess. Heart of synchronized ventilation is the breath sensor attached between the ventilator tubing & ET.1. Pressure sensor2. Flow sensor 1. Pneumotachograph 2. Hot wire anemometer3. Hybrid
  30. 30. Limitations of flow sensors ET leak: expiratory TV may be underestimated. Less than the expected expiratory tidal volume due to ET leak is registered as a negative flow ( same as baby`s breath initiation). This artifact falsely triggers a ventilator breath in the middle of the baby`s expiration: [AUTOCYCLING], ventilator can end up with very high auto triggered rate. Imposing 1 mL of dead space, may increase the work of breathing in very tiny preterm.
  31. 31. Assist Control [A/C] Patient Triggered Ventilation [PTV] Every breath of baby that the flow sensor detects is supported with PIP/PEEP Ventilator rate therefore belongs to baby. Ti is fixed by the physician. Backup rate [20-30/min] is set by physician in case of apnea or flow sensor failure. Weaning is done by decreasing the PIP. If baby is excessively tachypneic, the A/C mode may deliver abnormally high ventilator breaths, causing hypocapnea.
  32. 32. A/C: Green parts at beginning of flowcurve is the patient`s effort
  33. 33. Synchronized Intermittent Mandatory Vent. [SIMV] SIMV was developed as a result of the problem of high respiratory rates associated with PTV. SIMV delivers the preset pressure and rate while allowing the patient to breathe spontaneously in between ventilator breaths. Each ventilator breath is delivered in synchrony with the patient’s breaths, yet the patient is allowed to completely control the spontaneous breaths. Work of breathing and respiratory muscle fatigue increase with low parameter SIMV.
  34. 34. SIMV breaths:Green spontaneous; Blue ventilator
  35. 35. Volume Targeted Ventilation [VTV]Targeted Tidal Volume [TTV] VentilationVolume Guarantee [VG] Physician selects a desired tidal volume (app. 5-6 mL/kg) for the baby. The ventilator then delivers the desired tidal volume at the lowest feasible PIP and Ti according to changes in Raw, C and baby`s effort. Main benefits of TTV: Reduction in volutrauma and barotrauma. A stable Tidal Volume avoiding swings in pCO2. Ventilation is at the lowest possible parameters. Ability to self wean.
  36. 36. Pressure Support Ventilation [PSV] Peak Expiratory Flow
  37. 37. PSV with SIMV
  38. 38. Effect of various parameters onoxygenation and ventilation.
  39. 39. In brief: Always Check: Chest movement, air entry, presence of retractions, hyper-inflated chest, wheezing etc. Level of ET at lips, visible secretions in ET, any kinking or disconnection, any warning alarms on the ventilator. Assess baby`s own respiratory drive: depth & rate. Signs of baby fighting the ventilator: air hunger, asynchrony, gross difference between ventilator and baby`s breathing rate. Signs of pain, agitation, abnormal posturing. Abnormal heart rate, BP, temperature. Signs of excessive sedation.

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