Physiology of transition period with regard to Cardiovascular System in a Neonate and administration for anesthesia in such a circumstance.

1. PHYSIOLOGY OF TRANSITION PERIOD
IN NEONATES WITH RESPECT
TO CARDIOVASCULAR SYSTEM
Speaker: Dr Bhagirath.S.N
Moderator: Dr Sarika

2. Understanding Foetal Circulation
• Parallel system pumping into the
systemic circulation
• Three shunts are active before birth
Placenta
Foramen ovale
Ductus arteriosus
• Upper body receives better
oxygenated blood compared to the
lower body

3. What happens at birth….?
•Three shunts begin to close one by
one
•Closure of placenta causes increase
in systemic vascular resistance
•Onset of breathing causes the
foramen ovale to close
•Increasing O2 tension prompts the
closure of ductus arteriosus
•Functional closure: 1st hour of
life
•Anatomical closure: 1st year of
life
•Functional closure: 24-48 hours
•Anatomical closure:

4. A saturation schematic at different points of time
Foetal saturation
values
Saturation values at
day 1
Saturation values in
a neonate

6. Changes in the myocardium
Foetal myocardium differs from the adult heart
•In having fewer myofibril elements
•Less organised contractile elements
•Non-parallel arrangement of myofibrils sacrificing efficiency
•Immature sarcoplasmic reticulum
•Reduced Ca2+ATP activity-reduced contractility.
Implications
•Lesser cardiac reserve
•Poor tolerance to even mildest of hemodynamic insults
Response
•Increase in size of myocytes
•Increase in number of myocytes.
(changes being more pronounced in left ventricle).

7. Adaptive Mechanisms
Normal
mechanisms
in the adult
•Sympathetic
nervous system
•Parasympathetic
nervous system
•Frank-starling
mechanism
•Sufficient
contractile
force conferring
ample cardiac
reserve
•Mature
baroreceptors
•Reduced sensitivity
What is lacking in the
neonate.?
•underdeveloped
•Well developed
•Ineffective due to non-
compliant myocardium
•Lacks contractile force
(SV)
•Immature baroreceptors
•increased sensitivity
to anesthesia in
Baroreceptors
Adaptation seen
•Increase
d
glycogen
stores
•Increase
d rate of
anaerobic
glycolysis
•Advantag
e being
relative
resistance
to hypoxia
•Increased heart rate as
CO=HR X SV
•No adaptation.
Implication is that even
mild hypotension is poorly
tolerated.
•Increased depression
even at lighter planes of
anesthesia

8. In summary:
• Resting heart rate is much higher compared to body weight because of higher
O2 consumption per kg/body weight.
•Even mild bradycardia compromises the cardiac output as stroke volume is
limited owing to immature myocardial musculature.
•Cardiac reserve is greatly limited (30%-40%)
•Limited inotropic and chronotropic support from sympathetic nervous system