By Dr Bikash Shrestha

1. VENTILATION
FUNDAMENTALS
Dr Bikash Shrestha
Fellow Neonatology (NNF, India)
MD Paediatrics (AFMC, Pune, India)

2. OVERVIEW
 REPSIRATORY PHYSIOLOGY
 VENTILATOR BASICS

3. RESPIRATORY PHYSIOLOGY
 Basic characteristics
 Oxygenation
 Ventilation
 Lung volumes
 Lung mechanics

4. BASIC CHARACTERISTICS-1
 Higher respiratory rate

5. BASIC CHARACTERISTICS-2
 Higher propensity to respiratory failure
– More cylindrical thorax of newborns
– Horizontal placing of ribs
– Compliant chest wall-lower propensity to
spring out
– Closing volume almost equal to FRC

6. BASIC CHARACTERISTICS-3
 Higher propensity to respiratory failure
– Diaphragmatic attachment more horizontal
– Low muscle mass and less type I muscle fibers
– Liver is relatively larger organ
– Dramatic increase in airway resistance (Narrow
airway)
– Lung growth takes place in centripetal direction
with relatively larger anatomic dead space

7. OXYGENATION-1
 Extraction of oxygen from the atmosphere
and delivery into the mitochondria
 Directly correlated with the partial pressure
of oxygen in the alveoli (PAO2)
 Partial pressure of oxygen in artery (PaO2)
 Alveolar arterial oxygen gradient (PAO2 –
PaO2) = 5 - 15 mm Hg

8. ALEVOLAR GAS EQUATION

9. HYPOXEMIA-1
 Hypoxic gas mixture (Low FIO2)
 High altitude (Low PB)
 Hypoventilation (High PACO2)

10. HYPOXEMIA-2
 Increased alveolar arterial oxygen
gradient (PAO2 – PaO2)
 Ventilation perfusion mismatch (shunts)

11. HYPOXEMIA-3
Ventilation perfusion mismatch (shunts)

12. VENTILATION-1
 Elimination of CO2 from the blood through the
alveolus
 PaCO2 is proportional to minute ventilation
(VE)
 PaCO2 is accurately correlated to mean
alveolar minute ventilation

13. VENTILATION-2
Problem in ventilation (PaCO2)
–Reduced RR
–Reduced tidal volume
–Increased dead space

14. LUNG VOLUMES

15. LUNG MECHANICS
 Elastic recoil
 Compliance
 Resistance
 Time constant

16. ELASTIC RECOIL-1
The tendency of stretched objects
to return to their original state

17. ELASTIC RECOIL-2
 The forces tending
and resisting to
collapse are equal
at a point close to
FRC or resting state

18. ELASTIC RECOIL-3
 Surface tension is correlated with elastic
recoil
 Surface tension follows Laplace law
P = 2T
R

19. ELASTIC RECOIL-4

20. ELASTIC RECOIL-5

21. COMPLIANCE-1
Change in volume resulting from a
given change in pressure

22. COMPLIANCE-2

23. RESISTANCE
 Resistance is resulted due to friction
 Viscous resistance and airway resistance
 VR-Generated by tissue elements moving
past one another
 AR-Generated within the respiratory tract
against the gas flow
R = P1-P2
V(Flow)

24. TIME CONSTANT-1
 Time necessary for the alveoli to discharge
63% of TV

25. TIME CONSTANT-2
 Pressure changes at alveoli lag behind at the
proximal airway
 Inspiratory and expiratory time constants

26. TIME CONSTANT-3

27. TIME CONSTANT-4
 3 time constants lead to 95% equilibrium
of alveolar and proximal airway
 R (Resistance) X C (Compliance)=0.15 secs
 3 time constants = 0.45 secs

28. VENTILATOR
BREAKTHROUGHS

29. KENNEDY TRAGEDY
 1963-Patrick Bouvier Kennedy (34 wks POG/2.1 kg)
 RDS-succumbed at 39 hrs

30. VENTILATOR
BASICS

31. VENTILATOR BASICS
 Introduction
 Basic terminologies
 Oxygenation-MAP
 Modes of ventilation
 Pulmonary graphics

32. INTRODUCTION
 Movement of gas into and out of lungs by
an external source connected directly to
the patient
 Supportive, non therapeutic technology
 Most neonatal ventilators based on
Ayer’s T-piece

33. AYER’S T-PIECE

34. BASIC PARTS
 Pressurized source
 Blending chamber
 Flow control
 Exhalation valve

35. BASIC TERMINOLOGIES
 PIP – Peak inspiratory pressure
 PEEP – Positive end expiratory pressure
 Rate - Frequency
 Ti – Time allowed for inspiration
 Te – Time allowed for expiration
 IE ratio – 1:1 to 1:3

36. MEAN AIRWAY PRESSURE-1
 Average airway pressure over a given interval of
time (PAW)
 Area under the curve of pressure time curve for
one breath divided by total cycle time

37. MEAN AIRWAY PRESSURE-2

38. MODES OF VENTILATION-1
 Three factors
– How each breath is initiated
– How gas flow is controlled during delivery
– How the breath is terminated

39. MODES OF VENTILATION-2
 Breath initiation
– Controlled
– Synchronized or patient triggered
 Gas flow control
– Pressure
– Volume
 Flow termination (Cycling)
– Volume cycling -Time cycling
– Pressure cycling -Flow cycling

40. MODES OF VENTILATION-3

41. PULMONARY GRAPHICS-1
 Introduction
– Relatively new (1980’s)
– Microprocessor development (1990’s)
 Basis
– Sensor with tungsten wire at the proximal airway
– Heated wire anemometer technology
– Gas flow results in cooling of the wire
– Electricity required to bring it back to original temperature is
converted to signals

42. PULMONARY GRAPHICS-2
 Colors
– Inspiration (Red-machine) (Yellow-patient)
– Expiration (Blue)
– Auto calibrating (Green)
 Common signals
– Pressure (cm of H2O)
– Volume (mL)
– Flow (mL/sec)

43. PULMONARY GRAPHICS-3

44. PULMONARY GRAPHICS-4
 Cyclic phases
– A -Initiation of inspiration
– B -Peak inspiration
– C -End inspiration
– D -End expiration

45. “Primum non nocere”
(First do no harm)
The first tenet of Hippocratic oath

46. REFERENCES
 M Keszler. Update on mechanical ventilator strategies. Neoreviews.
2013;14:e237.
 AK Ghuman, RG Khemani, CJL Newth. Pediatric applied respiratory
physiology-the essentials. Pediatrics and Child Health. 2013;23:7.
 PD Sly, RA Collins. Physiological basis of rspiratory signs and
symptoms. Pediatric Respiratory Reviews. 2006;7:84-88.
 PC Rimensberger. Pediatric and Neonatal Mechanical Ventilation-
From Basics to Clinical Practice. Berlin. Springer-Verlag. 2015.
 JP Goldmsith, EH Karotkin. Assisted Ventilation of the Neonate. 5th ed.
USA. Saunders-Elsevier Imprint. 2015.
 SM Donn, MC Mammel. Neonatal Pulmonary Graphics-A Pocket
Atlas. New York. Sprigner. 2015.

47. DESIRABLE CME’S
 Basics of neonatal ventilation
 Pulmonary waveforms fundamentals
 Non invasive neonatal ventilation
 Newer modes of ventilation
 CPAP-Essential tool in NICU’s

48. THANK YOU