neonatal mechanical venilation

1. Tageldin Aly
Pediatric and neonatal mechanical ventilation
Pulmonary mechanics
Resistance and time constant
Part 4

2. Compliance vs. Resistance

3. Practical point
Optimal PEEP

4. Resistance
. The oppositional force for air flow into the lung
. Higher the resistance, greater is the pressure
required to drive the gases into the lungs
Depends on:
.Airway diameter
.Airway length
.Viscosity of gas

5. Normal range
25 -50 cmH2o /l/sec

6. POISSEUILLE LAW

7. Types of airway resistance

8. Resistance
Resistance is directly proportional to:
.Length
.Viscosity. 1/r4.
. Pressure required to drive 1L/min of gas flow
into the lungs

9. Clinical Implications
As length increases- resistance increase
Eg: long ET tube
flow sensor or capnograph
. Trim the ET tube to 2.5cm outside the
upper lip

10. Clinical Implications (cont.)
A small decrease in airway diameter causes a
large change in resistance
. Removal of airway secretions and largest diameter
ET tube that fits the glottis to be chosen
. Higher air flows increases the resistance by
causing turbulence to gas flow

11. Diseases with airway obstruction
MAS vs. BPD

12. TIME CONSTANT= CXR
Time taken to empty the gases from lung
. It nearly takes 3-5 time constants to completely
empty the lungs
. Time constant(sec)= Compliance x Resistance

13. TIME CONSTANT = CXR

14. TIME CONSTANT = CXR

15. Clinical Implications
RDS
. Low compliance, normal resistance
. Hence time constant-> less
. Time required to inflate (Ti) or deflate (Te)
the lungs ->Hence short

16. Clinical Implications MAS
Resistance is high Compliance decreases little bit
.Hence, time constant increases
. Time required to inflate (Ti) or deflate(Te) the
lungs hence is long
. A short set expiratory time on ventilator can lead
to inadequate lung emptying and hence gas
trapping

17. Clinical Implications
HMD vs.MAS

18. Key points
.optimal PEEP
. Clinical application of pulmonary mechanics
. Monitoring of pulmonary mechanics
. Short expiratory time lead to air leak

19. Thank you