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.
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.
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.
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
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