Pulmonary Physiology Pulmonary Physiology in Ventilated Babies in Ventilated Babies Mohamed T. Khashaba Mohamed T. Khashaba Professor of Pediatrics & Neonatology Professor of Pediatrics & Neonatology Head of NICU Head of NICU , , Mansoura faculty of Medicine Mansoura faculty of Medicine
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Pulmonary Physiology in Pulmonary Physiology in Ventilated BabiesVentilated Babies
Mohamed T. KhashabaMohamed T. Khashaba Professor of Pediatrics & NeonatologyProfessor of Pediatrics & Neonatology
Head of NICUHead of NICU,,
Mansoura faculty of MedicineMansoura faculty of Medicine
1.1. Pulmonary mechanicsPulmonary mechanics..2.2. Physiology of gas exchange:Physiology of gas exchange:
• COCO22
• OO22
3.3. V/Q mismatching.V/Q mismatching.
4.4. FiOFiO22 and its effects. and its effects.
5.5. Dead space.Dead space.
6.6. Effects of:Effects of:• Elevated intra thoracic pressure.Elevated intra thoracic pressure.• Pulm. Edema.Pulm. Edema.• High PaOHigh PaO22
ABCsABCs
Respiratory system is composed of Respiratory system is composed of millions of air exchange units connected to millions of air exchange units connected to outside by conducting airways.outside by conducting airways.
Lungs inflate by contraction of diaphragm Lungs inflate by contraction of diaphragm rendering intrapleural pressure –ve.rendering intrapleural pressure –ve.
Intercostal muscles contract mainly to Intercostal muscles contract mainly to stabilize the chest wall.stabilize the chest wall.
ABCsABCs
Lungs tend to deflate by 2 forces:Lungs tend to deflate by 2 forces:
A. elastic recoil of stretched tissues.A. elastic recoil of stretched tissues.
B. Surface tension within the air spaces.B. Surface tension within the air spaces.
Structural and Functional Limitations in Structural and Functional Limitations in NeonatesNeonates
1. Neonatal thorax is more cylindrical.1. Neonatal thorax is more cylindrical.
2. More compliant chest wall.2. More compliant chest wall.
1.1. Decrease of lung edema, water content Decrease of lung edema, water content
will improve compliance e.g by diuretics.will improve compliance e.g by diuretics.
2.2. Improvement of RDS is associated with Improvement of RDS is associated with
diuresis.diuresis.
3.3. Rapid infusions increases water flux into Rapid infusions increases water flux into
the interstitium.the interstitium.
Laplace LawLaplace Law
P = 2 ST/ rP = 2 ST/ r
pp : pressure required to counteract : pressure required to counteract tendency of air spaces to collapse.tendency of air spaces to collapse.
STST: surface tension in the air spaces.: surface tension in the air spaces.
RR : radius. : radius.
Clinical ApplicationClinical Application
With improved inflation, pressure has to With improved inflation, pressure has to decrease to avoid volutrauma.decrease to avoid volutrauma.
More pressure is needed in preterms due to More pressure is needed in preterms due to small radius and increased surface tension small radius and increased surface tension
Avoid factors leading to increased Avoid factors leading to increased metabolism e.g infections, temperature metabolism e.g infections, temperature instability, manipulations and instability, manipulations and catecholamines.catecholamines.
Gas Exchange During Assisted Gas Exchange During Assisted VentilationVentilation
OO22
• Depends on MAP “ mean airway pressure” Depends on MAP “ mean airway pressure”
• ie PAW ie PAW
What are the Factors that What are the Factors that Increase Paw ?Increase Paw ?
2.2. Positive end expiratory pressure (PEEP).Positive end expiratory pressure (PEEP).
3.3. Inspiratory: Expiratory time (I/E ratio ).Inspiratory: Expiratory time (I/E ratio ).
4.4. Inspiratory flow. Inspiratory flow.
Ventilatory Settings that augment Ventilatory Settings that augment PaWPaW
30
20
10
0
2
3
4
1
0 1 2
Air
way
Pre
ssur
e (c
m H
2O) Insp.
flow
PIP
I:E
PEEP
Seconds
How PaW affects OxygenationHow PaW affects Oxygenation??
Through augmenting QThrough augmenting Q//V matchingV matching..
V/Q mismatching V/Q mismatching
1.1. Reduction in perfusion Reduction in perfusion • Collapse of air spaceCollapse of air space. . • Over distension of air space Over distension of air space
• PPAAOO2 2 = = 150150 - - 4545 = = +100 mmHg at room air+100 mmHg at room air..
Dead Space Volume (VD)Dead Space Volume (VD)
1.1. Automatic VAutomatic VDD • Usually constantUsually constant..• Includes the apparatus dead space. Includes the apparatus dead space. • Of minor consideration, usually VD/VT is < 0.3.Of minor consideration, usually VD/VT is < 0.3.
2.2. Alveolar VD Alveolar VD • In ventilated but poorly perfused lung regions. In ventilated but poorly perfused lung regions. • AD/VT may exceed.0.6AD/VT may exceed.0.6