2. History of Assisted Ventilation
Negative pressure :
Spirophore
developed in 1876
with manual
device to create
negative pressure
chamber
3. History of Assisted Ventilation
Negative pressure :
Dr. Philips
Drinker used this
idea to develop
“Iron lung” in
1929, So many
survived “Polio
out break” Some
to date.
4. Woman in iron lung celebrates 60th birthday
After contracting polio, Dianne Odell has spent
most of her life in machine
Updated: 3:37 p.m. CT Feb 21, 2007
Associated Press Report
JACKSON, Tenn. - A Jackson woman who contracted polio 57
years ago and continues to rely on an iron lung to breathe
recently celebrated her 60th birthday, defying doctors'
expectations that she could live so long and so fully. Dianne
Odell, who turned 60 last week, is among only 30 to 40
people in the U.S. who depend on the devices.
5. History of Assisted Ventilation
Positive Pressure :
“Respirator Kit”
used to revive
apparently dead
by blowing air
into the lungs or
rectum in 1770s in
London
6. History of Assisted Ventilation
Positive pressure :
The Aerophore pulmonaire :-
developed by French Obstetrician for short term
ventilation of newborns in 1879
7. History of Assisted Ventilation
Positive pressure :
The Fell-O’Dwyre
apparatus developed in
New York for
intermittent positive
pressure ventilation,
1896
8. Neonatal Assisted Ventilation
1. Applied Pulmonary Mechanics
2. Gas Exchange During Assisted Ventilation
3. Ventilator Management
4. Practical Hints For Assisted ventilation
9. Applied Pulmonary Mechanics
Pressure Gradient is Required to Overcome
1.Elastic Properties of Lungs and Chest Wall
(Compliance)
2. Resistance to Airflow by Airway and Lung
Tissue (Resistance)
10. Applied Pulmonary Mechanics
Δ Volume (L)
Compliance =
Δ Pressure (cm H2O)
In neonate chest wall is very distensible
so does not contribute substantial elastic
load when compared to lungs.
Total compliance ∞ Lung compliance
In RDS most striking abnormality is
DECREASED LUNG COMPLIANCE
11. Applied Pulmonary Mechanics
Pressure Gradient is Required to Overcome
1.Elastic Properties of Lungs and Chest Wall
(Compliance)
2. Resistance to Airflow by Airway and Lung
Tissue (Resistance)
12. Applied Pulmonary Mechanics
Resistance is inherent property of lungs to resist airflow
Δ Pressure(cm H2O)
Resistance = Δ Flow (L/Sec)
Airway resistance ∞ length of airway
∞ 1/radius of airway
Viscous resistance ∞ lung tissue
RDS does not contribute to resistance but ET tube does
13. Applied Pulmonary Mechanics
Relationship of Compliance and Resistance :
Time Constant (sec)= Resistance × Compliance
Time Constant(sec)
= Resistance(30cm H2O/L/sec)
× Compliance(0.004L/cm H2O)
= 0.12sec × 5
= 0.6 seconds
14. Gas Exchange During
Assisted Ventilation
1. Carbon Dioxide (CO2) Elimination
2. Oxygen (O2) Uptake
15. Gas Exchange During
Assisted Ventilation
CO2 Elimination :
Alveolar Ventilation =
(Tidal volume – Dead space)(Frequency)
With a pressure ventilator TV determined by
(PIP – PEEP)
16. Gas Exchange During
Assisted Ventilation
O2 Uptake : Mean Airway Pressure(Paw)
linear direct relations
↑Paw = ↑ PaO2
Regardless of change in FiO2
Paw optimizes lung volume and
ventilation-perfusion matching
17. Gas Exchange During
Assisted Ventilation
Paw is augmented by :
1. Inspiratory flow (K)
2. Peak Inspiratory Pressure (PIP)
3. I:E Ratio(TI, TE)
4. Positive End Expiratory Pressure
(PEEP)
1 2 3 4
Paw=K(PIP-PEEP)[TI/(TI+TE)]+PEEP
18. Ventilator Management
1. Flow :
Increase in flow will give square wave ventilation, will
Increase Paw and therefore oxygenation.
Higher flow is crucial, when TI is shorter
20. Ventilator Management
3. I:E Ratio :
Reversed I:E Ratio = ↑Paw = ↑Oxygenation
No change in TV= No change in AV=No change in PaCO2
21. Ventilator Management
Frequency (Rate) :
Rate= AV= CO2 elimination= PaCO2
Short TI= TV= MV
Short TE=gas trapping= FRC= compliance with over
distention= inadverant PEEP=Pneumothorax
22. Ventilator Management
4. PEEP :
↑ PEEP(at lower range)= Better recruitment of lungs = ↑ PaO2
↑ PEEP(at higher range)=Over distention=↓Cardiac Output=↓PaO2, ↑PaCO2
PEEP just above Critical closing Pressure prevents atelectesis
23. Gas Exchange During
Assisted Ventilation
Relative effectiveness of Paw on Pao2 :
1.↑ PIP &PEEP more than ↑ I:E ratio
2.↑ PEEP at higher range is ineffective
3.↑Paw=↑Over distention=↑RL Shunt
4.↑ Paw = ↓Cardiac output
24. Ventilator Management
Inspired Oxygen Concentration (FIO2) :
When increasing vent. support first increase FIO2 to
.60 to .70 before increasing pressure which may
prevent BPD
When weaning vent. support first decrease FIO2 to .40
to.50 before decreasing pressure. Pressure should be
weaned before weaning FIO2 further to prevent PTX.
27. Practical Hints for Assisted Ventilation
Indications for Assisted Ventilation :
1. Respiratory acidosis with pH < 7.20 to 7.25
2. Severe hypoxemia, PaO2 < 50 torr. With FIO2 > 0.70
3. Apnea complicating RDS
4. Persistent Fetal Circulation
28. Practical Hints for Assisted Ventilation
Initial Ventilator Settings :
Normal RDS
PIP 12-18 cm H2O 20-25 cmH2O
PEEP 2-3 cmH2O 4-5 cmH2O
Rate 10-20 per minute 20-40 per minute
I:E Ratio 1:2 to 1:10 1:1 to 1:3
29. Practical Hints for Assisted Ventilation
Acceptable Blood Gas Values :
pH 7.25 – 7.45
PaO2 50 – 80 torr
PaCO2 35 – 50 torr
With more maturity even higher PaCO2 are tolerated
as long as pH is maintained above 7.25
30. Practical Hints for Assisted Ventilation
Weaning Strategy :
1. First decrease pressure <18
2. FIO2 <0.40
3.Rate <15
4. CPAP of 3 to 4 to overcome ET resistance
