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Introduction to ventilator and
pulmonary physiology
Dr.Himanshu Dave
INTRODUCTION
• A ventilator is a device used to move gas into
lungs by applying positive pressure to the
airways.
• Works on Ayre’s T piece principle.
Ventilator nicu
Parts of a ventilator
• A] Input:
• Power source
• Compressed air / compressor: It draws
atmospheric air and compresses it at 50 psi to
generate positive pressure breaths.
• Oxygen supply: piped gas supply at 50 psi
(pounds per square inch)
• B] Drive mechanism: it converts the input
power to useful ventilatory work
• Microprocessors are used.
• Programmed algorithms are used in
microprocessors.
• C] Control system: it controls either pressure
or flow ; ie pressure control or flow control.
• D] Control panel:
• FiO2 [inspired oxygen concentration]
• PIP [Peak Inspiratory Pressure]
• Tidal volume / Minute volume
• Positive End Expiratory Pressure [PEEP]
• Respiratory Rate
• Inspiratory time [Ti]
• Expiratory time [ Te]
• Flow rate
• Mode selector
• Automatically displayed parameters are MAP
and I:E ratio.
• E] Humidifier :
• The ideal humidifier should be able to deliver
saturated gas at 37 deg celcius to lower respi
tract with relative humidity of 90to 100
%without condensation in the delivery
system.
• Two types:
• 1]simple humidifier: Inspired gas is heated
and humidified without a servo control.
• Disadvantage: excessive condensation in
tubing , reduction in humidity and cooling of
gases by the time they reach the patient due
to changes in NICU temperature.
• 2] Servo controlled humidifier:
• Heated wires in the tubing
• Prevents accumulation of condensate
• Ensure adequate humidification
• F] Breathing circuit:
• Disposable circuits preferred
• Two limbs: inspiratory & expiratory
• Humidifier and temp probe connected to
inspiratory limb
• Flow sensor and capnometer attached to
breathing circuit.
PULMONARY MECHANICS
• Tidal volume : 5-8 ml/kg .Ventilator shows
both inspiratory and expiratory tidal volume
• Minute Ventilation: TV * RR [ 200-450
ml/kg/min]
Dead Space
• Part of tidal volume in proximal airways
including ET . Normal dead space without ET is
2 ml/kg
• Physiological dead space increased in case of
under perfused alveoli.
Alveolar minute ventilation
• Amount of gas that takes part in gaseous
exchange per minute.
• Determines CO2 removal.
• Its better to increase RR than tidal volume to
remove CO2.
Lung compliance
• Change in volume per unit change in pressure
• Newborn with normal lungs: 3-5 ml/kg/cm of
H2O
• Compliance in RDS : 0.1-1 ml/kg/ cm of H2O
• Decreases in : surfactant deficiency,
pneumonia , lung hypoplasia , diaphgramatic
hernia
Resistance
• Pressure required to move gas through the
airway at a constant flow rate. { pressure
/flow}
• Airway resistance : Opposing force due to
friction between air molecule and walls of
conducting airways
• Viscous resistance: Friction between tissues of
the lungs and chest wall.
• Normal value: 25-50 cm H2O /L/sec
• With ET tube it increases to 100-150 cm
H2O/L/sec.
Time constant
• Time taken by lung to inflate /deflate.
• Expiration is passive , depends on elastic recoil
of lung tissue and chest wall.
• Time constant = compliance * resistance
• One time constant = time taken by alveoli to
discharge 63% of tidal volume.
• Time constant is longer if: compliance
increased or resistance is increased { MAS
,BPD}
• When set expiratory time in ventilator is less
than 3 time constant for specific lung
condition then gas trapping occurs leading to
inadvertent PEEP.
WORK OF BREATHING
• Energy required to move the gas in and out of
the lungs by overcoming the elastic and
frictional resistance forces of the respiratory
system.
• WOB= Pressure[force]*volume [displacement]
• In a healthy newborn at rest ; 1% of total
metabolic rate [energy] is required for work of
breathing.
• When work of breathing is increased ,
respiratory failure occurs due to muscle
fatigue.
Gaseous exchange in lungs
• Po2 in dry air = atm pressure * 0.21
= 760 * 0.21
= 160 mm Hg
• Po2 In humidified air = [760-47] * 0.21
= 150 mm Hg
• In alveoli : p Ao2 = 100 mm Hg
p ACO2 = 40 mm Hg
• In alveolar capillaries: paO2 = 40 mm Hg
paCO2= 45 mm Hg
• Gaseous exchange occurs along pressure gradient
• Gas exchange depends on:
1] Alveolar ventilation
2] Alveolar perfusion
3] Pressure gradient
• CO2 diffuse 20 times faster than O2.
Ventilation of lungs
• Dependent on position of each area of lung on
compliance curve.
• Bases are on favourable area on compliance
curve than the apices , thus receives
favourable ventilation.
Ventilator nicu
Perfusion of lungs
• The blood that reaches the alveoli via the
capillaries.
• In hypoxia , pulmonary vascular constriction
occurs and resistance increases , thus
decreasing blood flow to low ventilated areas
V/Q mismatch
• In diseased lungs , some alveoli are over
ventilated while some are over perfused.
• Partially obstructed pulmonary arteriole leads
to relatively over ventilation
Hypoxemia
• It may arise due to five mechanism:
• 1) Alveolar hypoventilation
• 2) low FiO2
• 3) V/Q mismatch
• 4) Shunt
• 5) Diffusion through alveolo- capillary
membrane is affected
How to assess cause of hypoxemia
paCO2 AaDO2 Response in paO2
to Increase in Fio2
[upto 100%]
Hypoventilation Increased Not affected increases
Decreased FiO2 Decreased due to
hyperventilation
Not affected Increases
V/Q mismatch Normal Increases Increases
Shunt Normal Increases No improvement
Diffusion defect Normal Normal. Increased increases
Oxygenation during assisted
ventilation
• It depends on MAP [Mean Airway Pressure]
• MAP is the measure of the average pressure
to which lungs are exposed during the
respiratory cycle.
• It determine oxygenation [other than FiO2]
• It is calculated by ventilator.
• MAP = [PIP*Ti+ PEEP*Te]
Ti + Te
Ventilator nicu
• Pressure control mode : MAP can be increased
by increasing PIP, PEEP, I:E ratio and flow rate
• In diseases with decreased compliance [
pneumonia ,RDS ] MAP is preferred over FiO2
for increasing oxygenation
• In obstructive conditions [MAS] and in
conditions with air leak [ pulmonary
interstitial emphysema , pneumothorax] FiO2
is preferred over MAP.
CO2 elimination
• It depends on alveolar minute ventilation
[ rate * ( TV – Dead space) ]
• In a pressure control mode , TV depends on
difference between PIP and PEEP.
• CO2 can be eliminated by:
1) Increasing PIP
2) Increasing Rate
3) Decreasing the dead space
4) Decreasing PEEP in hyperinflated lung.
When to ventilate a newborn?
Goals of mechanical ventilation
1] To provide adequate oxygenation and
ventilation with minimal intervention.
2] With the minimum risk of lung injury.
3] Decrease the work of breathing.
4] Maintaining the neonate comfortness.
Indications of mechanical ventilation
• Most common indication for assisted
ventilation is : Respiratory failure.
• Respiratory distress [chest retractions and
increased respiratory rate ] is the early
warning sign.
Scoring system to predict
respiratory failure in new born
Silverman Anderson Scoring
• Useful to predict respiratory failure in new
born pre term babies.
Upper chest
retractions
Lower chest
retractions
Xiphoid
retractions
Nasal flaring Respiraorty
grunt
Grade 0 synchronised No
retractions
none None none
Grade 1 Lag on
inspiration
Just visible Just visible minimal On
auscultation
Grade 2 See-saw Marked marked marked Naked ear
• Score of [0-3] : mild distress
• Score of [4-6]: moderate distress
• Score of [>7]: impending respiratory failure
Downe’s Score
• Useful to predict respiratory failure in term
babies
Score 0 1 2
Respiratory
rate
< 60 60-80 >80 / apnoea
Cyanosis None In room air In 40% oxygen
Retractions None Mild Mod – severe
Grunting None Audible with
stethoscope
Audible
without steth
Air entry Clear Decreased Barely audible
• Score > 4 : indicates respiratory distress
• Score > 8 : impending respiratory failure
ABGA Score
Parameters 0 1 2 3
PaO2 > 60 50-60 < 50 <50
pH > 7.3 7.2-7.29 7.1-7.19 < 7.1
PaCO2 < 50 50-60 61-70 >70
A score of > 3 indicates the need for CPAP or
mechanical ventilation.
Causes of respiratory failure in
neonates which may require
ventilation
• Apnoea of prematurity non responsive to drugs .
• Respiratory Distress Syndrome
• Meconium Aspiration Syndrome
• Pneumonia
• Broncho Pulmonary Dysplasia
• Persistent pulmonary hypertension of newborn
• Pulmonary hemorrhage
• Congenital neuro muscular disorder
• Congenital diaphragmatic hernia
• Post operative ventilatory support
• Sepsis
• Shock
• ICH
• CPAP failure
Presence of 2 or more of these
parameters helps in deciding initiation
of mechanical ventilation
• Moderate to severe retractions
• Respiratory rate > 70 / min
• Cyanosis with FiO2 > 40%
• Intractable apnoea
• Shock
• PaO2 < 50 mm Hg even with FiO 2 100%
• PaCO2 > 60 mm Hg
• Ph<7.25
Reference
• Approach to neonatal ventilation : Rajib
Kumar
• Manual of neonatal care : Cloherty
THANK YOU

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Ventilator nicu

  • 1. Introduction to ventilator and pulmonary physiology Dr.Himanshu Dave
  • 2. INTRODUCTION • A ventilator is a device used to move gas into lungs by applying positive pressure to the airways. • Works on Ayre’s T piece principle.
  • 4. Parts of a ventilator • A] Input: • Power source • Compressed air / compressor: It draws atmospheric air and compresses it at 50 psi to generate positive pressure breaths. • Oxygen supply: piped gas supply at 50 psi (pounds per square inch)
  • 5. • B] Drive mechanism: it converts the input power to useful ventilatory work • Microprocessors are used. • Programmed algorithms are used in microprocessors.
  • 6. • C] Control system: it controls either pressure or flow ; ie pressure control or flow control.
  • 7. • D] Control panel: • FiO2 [inspired oxygen concentration] • PIP [Peak Inspiratory Pressure] • Tidal volume / Minute volume • Positive End Expiratory Pressure [PEEP] • Respiratory Rate • Inspiratory time [Ti] • Expiratory time [ Te] • Flow rate • Mode selector
  • 8. • Automatically displayed parameters are MAP and I:E ratio.
  • 9. • E] Humidifier : • The ideal humidifier should be able to deliver saturated gas at 37 deg celcius to lower respi tract with relative humidity of 90to 100 %without condensation in the delivery system.
  • 10. • Two types: • 1]simple humidifier: Inspired gas is heated and humidified without a servo control. • Disadvantage: excessive condensation in tubing , reduction in humidity and cooling of gases by the time they reach the patient due to changes in NICU temperature.
  • 11. • 2] Servo controlled humidifier: • Heated wires in the tubing • Prevents accumulation of condensate • Ensure adequate humidification
  • 12. • F] Breathing circuit: • Disposable circuits preferred • Two limbs: inspiratory & expiratory • Humidifier and temp probe connected to inspiratory limb • Flow sensor and capnometer attached to breathing circuit.
  • 13. PULMONARY MECHANICS • Tidal volume : 5-8 ml/kg .Ventilator shows both inspiratory and expiratory tidal volume • Minute Ventilation: TV * RR [ 200-450 ml/kg/min]
  • 14. Dead Space • Part of tidal volume in proximal airways including ET . Normal dead space without ET is 2 ml/kg • Physiological dead space increased in case of under perfused alveoli.
  • 15. Alveolar minute ventilation • Amount of gas that takes part in gaseous exchange per minute. • Determines CO2 removal. • Its better to increase RR than tidal volume to remove CO2.
  • 16. Lung compliance • Change in volume per unit change in pressure • Newborn with normal lungs: 3-5 ml/kg/cm of H2O • Compliance in RDS : 0.1-1 ml/kg/ cm of H2O • Decreases in : surfactant deficiency, pneumonia , lung hypoplasia , diaphgramatic hernia
  • 17. Resistance • Pressure required to move gas through the airway at a constant flow rate. { pressure /flow} • Airway resistance : Opposing force due to friction between air molecule and walls of conducting airways • Viscous resistance: Friction between tissues of the lungs and chest wall.
  • 18. • Normal value: 25-50 cm H2O /L/sec • With ET tube it increases to 100-150 cm H2O/L/sec.
  • 19. Time constant • Time taken by lung to inflate /deflate. • Expiration is passive , depends on elastic recoil of lung tissue and chest wall. • Time constant = compliance * resistance • One time constant = time taken by alveoli to discharge 63% of tidal volume.
  • 20. • Time constant is longer if: compliance increased or resistance is increased { MAS ,BPD} • When set expiratory time in ventilator is less than 3 time constant for specific lung condition then gas trapping occurs leading to inadvertent PEEP.
  • 21. WORK OF BREATHING • Energy required to move the gas in and out of the lungs by overcoming the elastic and frictional resistance forces of the respiratory system. • WOB= Pressure[force]*volume [displacement]
  • 22. • In a healthy newborn at rest ; 1% of total metabolic rate [energy] is required for work of breathing. • When work of breathing is increased , respiratory failure occurs due to muscle fatigue.
  • 23. Gaseous exchange in lungs • Po2 in dry air = atm pressure * 0.21 = 760 * 0.21 = 160 mm Hg • Po2 In humidified air = [760-47] * 0.21 = 150 mm Hg
  • 24. • In alveoli : p Ao2 = 100 mm Hg p ACO2 = 40 mm Hg • In alveolar capillaries: paO2 = 40 mm Hg paCO2= 45 mm Hg • Gaseous exchange occurs along pressure gradient
  • 25. • Gas exchange depends on: 1] Alveolar ventilation 2] Alveolar perfusion 3] Pressure gradient • CO2 diffuse 20 times faster than O2.
  • 26. Ventilation of lungs • Dependent on position of each area of lung on compliance curve. • Bases are on favourable area on compliance curve than the apices , thus receives favourable ventilation.
  • 28. Perfusion of lungs • The blood that reaches the alveoli via the capillaries. • In hypoxia , pulmonary vascular constriction occurs and resistance increases , thus decreasing blood flow to low ventilated areas
  • 29. V/Q mismatch • In diseased lungs , some alveoli are over ventilated while some are over perfused. • Partially obstructed pulmonary arteriole leads to relatively over ventilation
  • 30. Hypoxemia • It may arise due to five mechanism: • 1) Alveolar hypoventilation • 2) low FiO2 • 3) V/Q mismatch • 4) Shunt • 5) Diffusion through alveolo- capillary membrane is affected
  • 31. How to assess cause of hypoxemia paCO2 AaDO2 Response in paO2 to Increase in Fio2 [upto 100%] Hypoventilation Increased Not affected increases Decreased FiO2 Decreased due to hyperventilation Not affected Increases V/Q mismatch Normal Increases Increases Shunt Normal Increases No improvement Diffusion defect Normal Normal. Increased increases
  • 32. Oxygenation during assisted ventilation • It depends on MAP [Mean Airway Pressure] • MAP is the measure of the average pressure to which lungs are exposed during the respiratory cycle. • It determine oxygenation [other than FiO2] • It is calculated by ventilator. • MAP = [PIP*Ti+ PEEP*Te] Ti + Te
  • 34. • Pressure control mode : MAP can be increased by increasing PIP, PEEP, I:E ratio and flow rate • In diseases with decreased compliance [ pneumonia ,RDS ] MAP is preferred over FiO2 for increasing oxygenation
  • 35. • In obstructive conditions [MAS] and in conditions with air leak [ pulmonary interstitial emphysema , pneumothorax] FiO2 is preferred over MAP.
  • 36. CO2 elimination • It depends on alveolar minute ventilation [ rate * ( TV – Dead space) ] • In a pressure control mode , TV depends on difference between PIP and PEEP. • CO2 can be eliminated by: 1) Increasing PIP 2) Increasing Rate 3) Decreasing the dead space 4) Decreasing PEEP in hyperinflated lung.
  • 37. When to ventilate a newborn?
  • 38. Goals of mechanical ventilation 1] To provide adequate oxygenation and ventilation with minimal intervention. 2] With the minimum risk of lung injury. 3] Decrease the work of breathing. 4] Maintaining the neonate comfortness.
  • 39. Indications of mechanical ventilation • Most common indication for assisted ventilation is : Respiratory failure. • Respiratory distress [chest retractions and increased respiratory rate ] is the early warning sign.
  • 40. Scoring system to predict respiratory failure in new born
  • 41. Silverman Anderson Scoring • Useful to predict respiratory failure in new born pre term babies. Upper chest retractions Lower chest retractions Xiphoid retractions Nasal flaring Respiraorty grunt Grade 0 synchronised No retractions none None none Grade 1 Lag on inspiration Just visible Just visible minimal On auscultation Grade 2 See-saw Marked marked marked Naked ear
  • 42. • Score of [0-3] : mild distress • Score of [4-6]: moderate distress • Score of [>7]: impending respiratory failure
  • 43. Downe’s Score • Useful to predict respiratory failure in term babies Score 0 1 2 Respiratory rate < 60 60-80 >80 / apnoea Cyanosis None In room air In 40% oxygen Retractions None Mild Mod – severe Grunting None Audible with stethoscope Audible without steth Air entry Clear Decreased Barely audible
  • 44. • Score > 4 : indicates respiratory distress • Score > 8 : impending respiratory failure
  • 45. ABGA Score Parameters 0 1 2 3 PaO2 > 60 50-60 < 50 <50 pH > 7.3 7.2-7.29 7.1-7.19 < 7.1 PaCO2 < 50 50-60 61-70 >70
  • 46. A score of > 3 indicates the need for CPAP or mechanical ventilation.
  • 47. Causes of respiratory failure in neonates which may require ventilation • Apnoea of prematurity non responsive to drugs . • Respiratory Distress Syndrome • Meconium Aspiration Syndrome • Pneumonia • Broncho Pulmonary Dysplasia • Persistent pulmonary hypertension of newborn • Pulmonary hemorrhage
  • 48. • Congenital neuro muscular disorder • Congenital diaphragmatic hernia • Post operative ventilatory support • Sepsis • Shock • ICH • CPAP failure
  • 49. Presence of 2 or more of these parameters helps in deciding initiation of mechanical ventilation • Moderate to severe retractions • Respiratory rate > 70 / min • Cyanosis with FiO2 > 40% • Intractable apnoea • Shock • PaO2 < 50 mm Hg even with FiO 2 100% • PaCO2 > 60 mm Hg • Ph<7.25
  • 50. Reference • Approach to neonatal ventilation : Rajib Kumar • Manual of neonatal care : Cloherty