physiologic principles of neonatal ventilation

1. Neonatal ventilation basics
Amitava Sur

2. Tidal volume ventilation & dead space…
• Minute ventilation(MV)= VT X RR
• Conventionally - ventilation indicates exchange of
gases in the physiological lung space (alveoli) and
not the conducting system (anatomical dead space)
• Anatomical vs alveolar dead space?

3. Vd- Dead space
Neonatal Vd= 2.5-3ml/kg

4. By a ventilator we mean positive pressure ventilator !!

5. Respiratory motion equation…
muscle pressure + ventilator pressure (forces delivering breath) = elastic load + resistive
load (forces opposing)

6. Time constant (kT)…
• 1 TC = Time taken for 63% of the lung volume to deflate/ 33% of volume
to inflate
• 3 TCs = time taken for equilibration of lung pressure with outside
• kT = Compliance X Resistance
• Most neonatal ACUTE lung pathologies have reduced lung
compliance (RDS, TTN, pneumonia) except MAS
• Chronic neonatal ventilation - issue of increased resistance (TCs will
vary)
• When choosing i Time consider the TC of the lung

7. Understanding preterm perspective
Gestations of
borderline
viability

9. Basic principle of mechanical ventilation
Any ventilator / mode of
ventilation will operate on the
following principles :
• Breathing pattern /Breath
control variable
• Breath sequence
• Control strategy
A. Pressure control
B. Volume control
C. Dual control
A. Continuous Mandatory Ventilation
B. Intermittent Mandatory Ventilation
C. Continuous Spontaneous Ventilation
A. Trigger
B. Limit
C. Cycle

10. Commonly used modes (Drager)
• PC AC VG— Patient triggered (Assist control) Pressure Limited
Time cycled Volume controlled mode
• PC AC—- Patient triggered (Assist control) Pressure Limited Time
cycled
• PSV(PC/VG) - Patient triggered (AC) Patient/ Flow cycled
Volume/Pressure controlled Time limited mode

11. HFOV

12. HFOV- principles
• CO2 elimination (DCO2)= VT2 X f
• Oxygenation= MAP & FiO2
• Ventilation= Hz , Amp/Del P, I:E (normally set at 1:2)
• But…they are not mutually exclusive

14. Practical points about HFOV…
Switching to HFOV:
• MAP? Choose at least 2 above the Pmean/MAP on conventional
• Radiological confirmation (NOT ABSOLUTE) - 8-9 ribs expansion
• Amplitude- Good shake !!! Titrate with Pco2 on BG
Monitoring :
• CXR (preferably 1 hr after switch), PaO2
• DCO2
• Vthf ( 1.5-2.5ml/kg)

15. Practical points of HFOV(Vn500)…
• May need frequent blood gases initially to find sweet spot
• Trends of DCO2 very effective - sudden precipitous drop -?
Pneumothorax, ET blockage
• MAP/FiO2- Rule of thumb, decrease FiO2 <40% before weaning MAP
except when air trapping is a consideration
• Complex relation b/w Amplitude and Hz. If desiring del P> 40 Hz needs
to be <8 because of oscillator mechanism and flexible circuit
• Optimize sedation (specially preterm ) when oscillating

16. HFO-VG & HFO-Sigh

17. NIV - Bipap & HFNC
• Bipap/ Biphasic (Viasys)- based on APRV
• Dont set Phigh & Plow too close - air trap
• HFNC- dead space CO2 washout + PEEP ??