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TRANSCRIPT
Cardiovascular System – Cardiovascular changes at birth
Dr Graeme Polglase
the Ritchie Centre
Transition at Birth
Contents
The cardiopulmonary circulatory transition. Fetal and adult physiology Mechanisms driving the transition
Stabilisation of the cardiopulmonary circulatory transition.
New insights into the benefit of delayed cord clamping.
Adult vs. Fetal circulation
Fetus: – Umbilical flow supports
LVO and RVO. – Ventricles pump in
parallel due to:
– foramen ovale – ductus arteriosus
Driven by: – umbilical circulation
Newborn/Adult:
– Ventricles pump in series
PUMP 1. Blood flows from high pressure to low pressure
P1
P2 P3
If P1 and P2 > P3 Blood will flow down P3.
Pressure
If P1 > P2 & P3 (P2 = P3) Blood will flow equally In both directions. = >
PUMP
P1
P2 P3
2. Blood flows along the path of least resistance.
R2
If R1 = R2 Blood will flow equally through both
Resistance
If R1 > R2 Blood will flow through R2 R1 = >
Right Ventricle
Fetal Circulation
Lung
Pulmonary Circulation
Systemic Circulation (Placenta)
Ductus Arteriosus
Pulmonary Circulation: High Pressure High Resistance Low Blood Flow
Systemic Circulation: Lower Pressure Low Resistance
PPA > PSA
PVR > SVR Ductus Arteriosus: Right to Left Flow
45-50 mmHg 40-45 mmHg
Pulmonary circulation
Vasoconstricted during fetal life – high resistance & low blood flow – pulmonary pressure > systemic pressure – right-to-left shunt through the ductus
arteriosus.
Causes of vasoconstriction – not known – High degree of fetal lung expansion. – Low PO2
– Release of circulating vasoconstrictors.
Right Ventricle
Newborn Circulation
Pulmonary Circulation
Systemic Circulation
Ductus Arteriosus
Pulmonary Circulation: Low Pressure Low Resistance High Blood Flow
Systemic Circulation: High Pressure Higher Resistance PPA < PSA
PVR < SVR Ductus Arteriosus: Left to Right Flow
Cardio-Pulmonary Transition at Birth
Newborn 100% of RVO enters the lung PBF is high, PVR is low Systemic arterial pressure > pulmonary arterial pressure DA flow is left to right
Need to 1) Decrease pulmonary vascular resistance 2) Reverse pulmonary-systemic pressure gradient
1) Decrease in pulmonary vascular resistance at birth
Overall mechanism unknown – ↑ blood PO2
– release of vasodilators (?) – An effect of ventilation (?) – Reduction in lung volume caused by lung
aeration
Aeration of the lung is the principal component!
Pulmonary blood flow changes at birth
2 mins
Start Ventilation Clamp cord Deliver
+ve
-ve
Instability
FETUS NEWBORN
Cardio-Pulmonary Transition at Birth
Need to 1) Decrease pulmonary vascular resistance Aerating the lung
2) Reverse pulmonary-systemic pressure gradient
Cardiovascular changes at birth
Reversing the pulmonary-systemic pressure gradient Clamp umbilical cord
– lose 1/3 of fetal blood volume • Umbilical cord “milking” (or leaving the cord open)
– lose 50% of venous return / right ventricular output. – ↑ Systemic blood pressure
Driven by removal of the placental circulation
Before Cord Occlusion
After Cord Occlusion
Start ventilation
Cardiovascular changes at birth
Venous return from umbilical circ ↓ → ↓ right atrial filling ↓ right atrial pressure (RAP)
+ aeration of the lung
Pulmonary vascular resistance ↓ → ↑pulmonary blood flow. ↓ pulmonary arterial pressure ↑ left atrial filling → ↑ left atrial pressure
Systemic arterial pressure > Pulmonary arterial pressure (left to right ductus arteriosus flow) LAP > RAP → reversal of flow through and closure of foramen ovale (FO)
All happens within the first minutes of life.
Cardio-Pulmonary Transition at Birth
Need to 1) Decrease pulmonary vascular resistance Aerating the lung
2) Reverse pulmonary-systemic pressure gradient
Remove the placental circulation
Body
FO
Placenta
Brain
Right Heart
Lungs (High PVR)
50 % of CVO
50 % of CVO
Left Heart
The cardiopulmonary transition
DA
Before Cord Occlusion
After Cord Occlusion
Start ventilation
Umbilical cord occlusion
ventilation Lungs (Low PVR)
PPA > PSA PPA < PSA
Stabilises Left and Right Ventricular Output at Birth
Contents
The cardiopulmonary circulatory transition. Fetal and adult physiology Mechanisms driving the transition
Stabilisation of the cardiopulmonary circulatory transition.
New insights into the benefit of delayed cord clamping.
A Role for Neuroprotection?
~50 mmHg 90-150 mmHg
“developmental immaturity can render the preterm neonate particularly susceptible to cerebral hemodynamic consequences in response to systemic disturbances”
Impaired Cerebral Autoregulation
Circulation Stabilisation – Delayed Cord Clamping
Does the timing of ventilation onset relative to umbilical cord clamping improve the stability of the circulatory transition at birth in a baby which is apnoeic?
Flow probes: • Left pulmonary artery • Ductus arteriosus • Carotid artery
Catheters: • Main pulmonary artery • Main Carotid Artery • Jugular Vein
Surgical Methods
Experimental timeline
(Clamp 1st Vent 2nd)
-1h 0 5 10 20 30 min
(Vent 1st Clamp 2nd)
-1h 0 5 10 20 30 min
Cardiovascular effects of cord clamping prior to ventilation.
Fetus
the RITCHIE CENTRE
Placenta
Right Heart
Left Heart
Upper body
Lower body
Ductus arteriosus
Pre-ductal arteries
Foramen Ovale
X X
Lungs
Low resistance 50% of CO
What are the cardiovascular consequences of cord clamping prior to ventilation?
20
70
20
70
-200
600
-400
900
0
200
CA
P
(mm
Hg)
P
AP
(m
mH
g)
PB
F (m
L/m
in)
DA
BF
(mL/
min
) C
AB
F (m
L/m
in)
Cord clamp
What are the cardiovascular consequences of cord clamping prior to ventilation?
20
70
20
70
-200
600
-400
900
0
200
CA
P
(mm
Hg)
P
AP
(m
mH
g)
PB
F (m
L/m
in)
DA
BF
(mL/
min
) C
AB
F (m
L/m
in)
Cord clamp
Changes over the first 10 heart beats
Placenta
Right Heart
Left Heart
Upper body
Lungs
Lower body
Ductus arteriosus
Foramen Ovale
X X
Cord clamp
Lung
Left Ventricular Output Critically Dependent Upon Increasing Pulmonary Blood flow
Effect of cord clamping followed by ventilation
Clamp Vent Clamp Vent
Placenta
Right Heart
Left Heart
Upper body
Lungs
Lower body
Ductus arteriosus
Foramen Ovale
X X
Effect of cord clamping followed by ventilation
Clamp Vent Clamp Vent
Delaying Cord Clamping until Ventilation Initiated
Lungs aerate
Placenta
Right Heart
Left Heart
Upper body
Lungs
Lower body
Ductus arteriosus
Foramen Ovale
X X 50% Venous Return
the RITCHIE CENTRE
20
70
20
70
-200
600
-400
900
0
200
CA
P
(mm
Hg)
P
AP
(m
mH
g)
PB
F (m
L/m
in)
DA
BF
(mL/
min
) C
AB
F (m
L/m
in)
Unventilated (Clamp 1st) Ventilated (Vent 1st)
Cardiovascular consequences of ventilating before cord clamping
Cord clamp Cord clamp
Changes over the first 10 heart beats
Clamp First Ventilate First
Ventilation before cord clamping stabilises the cardiovascular transition at birth
Clamp First Ventilate First
Improves Stability!
Benefits of delayed cord clamping until ventilation onset
• Decrease PVR and hence increase PBF before the cord is clamped
• PBF can immediately replace umbilical venous return as the primary source of preload for the LV – Stabilises LV output after birth – Potentially reduces risk of IVH
Acknowledgements
The Ritchie Centre Stuart Hooper Sasmira Bhatt Euan Wallace Kelly Crossley Beth Allison Valerie Zahra and the entire lab
Royal North Shore Hospital Martin Kluckow
King Edward Memorial Hospital Andrew Gill
Leiden University Medical Centre Arjan te Pas
Beyond Retirement Colin Morley
Spark of Life Neonatal Satellite
2013
The magic minutes after birth – making the most of them Transition from placenta to air breathing
Prof Stuart Hooper
Using oxygen wisely in the delivery room
Dr Jennifer Dawson
Transitional Circulation Dr Graeme Polglase Sustained inflations at birth Prof Stuart Hooper Monitoring in the delivery room Prof Peter Davis
Role of a sustained inflation
at birth
Stuart Hooper
the RITCHIE CENTRE
Should a liquid-filled lung be ventilated in the same way as an air-filled lung? Will they behave the same?
Inspiration
P
+P
Inflation Pressures drives airway liquid movement
the RITCHIE CENTRE
Inspiration
P
Pressures generated by Inspiration drives airway liquid movement
the RITCHIE CENTRE
+P
Inspiration
+P
P
Pressures generated by Inspiration drives airway liquid movement
the RITCHIE CENTRE
P P P
Pressures generated by Inspiration drives airway liquid movement
the RITCHIE CENTRE
Inspiration
Partial airway liquid retention non-uniform ventilation
P = pressure
P
P
P P
P P
P
Should a liquid-filled lung be ventilated in the same way as an air-filled lung? Will they behave the same?
Ventilation: the basics
O2 CO2
Inspiration
Exhalation
When the lung is liquid-filled: Inspiration - needed for airway liquid clearance Expiration - superfluous as no gas exchange
the RITCHIE CENTRE
Uniform Lung aeration
Sustained Inflations What are the Unknowns??
How long should the sustained inflation be?
What Inflation pressure?
Physics of lung aeration
viscosity x length tube (radius tube)4
R1
Smaller very preterm infants:
Smaller airways + lower surface area = Resistance
R2 determine by epithelial barrier properties and surface area
R1 R2
RT = R1 + R2
R1 = resistance to moving liquid through a tube R2 = resistance to moving liquid across alveolar wall
2010 ILCOR Guidelines
Recommend inflation pressures of:
30 cmH2O in term infants and
20 to 25 cm H2O in preterm infants “occasionally higher pressures are required”.
Duration & Inflation pressure for a SI
0
15
30
45
0
10
20
Lung
air
volu
me
(mL/
kg)
Airw
ay p
resu
re
(cm
H2O
)
RT = P x T/ΔV
Time
ΔV
Effect of age on SI starting pressure
P1 P2 >>
Effect of age SI duration and airway resistance
P1 P2 >>
Sustained Inflations: where are we?
Inflation Pressure and duration will differ between infants: Airway size Maturity of the distal airways The volume of airway liquid present at birth
Solution?? Target an inflation volume of 20mL/kg
American NRP text book
Cardiopulmonary resuscitation
What do the guidelines say?
HR <60bpm (apneic, non-responsive infants) Start chest compressions IV epinephrine
Respiratory support ILCOR - No consensus
“initiation of intermittent positive-pressure ventilation at birth can be accomplished with either shorter or longer inspiratory times”
European - 5x 3 sec inflations
Cardiopulmonary resuscitation
“Establishing pulmonary ventilation is the key”
How???
Conventional 60 breaths/min 5x 3 sec inflations ????? 30 sec sustained inflation
Protocol
Deliver & Clamp cord
Start resuscitation BP = 20-25 mmHg
Finish 30 min after Resuscitation start
Groups 1. Conventional 60 breaths/min 2. 5x 3 sec inflations 3. 30 sec sustained inflation
Outcomes 1. Restoration of HR >120 bpm 2. Restoration of BP > 40 mmHg 3. Respiratory mechanics
HR Changes
Resuscitation start
Restoring cardiac function
Why is a SI so effective?
Better at aerating the lung To increase O2 uptake
To increase PBF and increase preload
But is this a good thing?? Could the higher BP cause brain
haemorrhage
Blood brain barrier
Extravasation of serum indicates disruption to the blood brain barrier.
the RITCHIE CENTRE
No extravasation Extravasation (Immunoreactive blood vessel)
Sheep serum extravasation- blood brain barrier disruption
the RITCHIE CENTRE
Blood brain barrier disruption
the RITCHIE CENTRE
Data presented as median (IQR)
Total blood vessel profile scores
There were more animals showing BBB disruption after a 30 sec SI
a
b
ab
Summary
Sustained inflation is fantastic at increasing HR in severely asphyxic newborns
But!! the return in circulation may be too quick and should be tempered to prevent brain haemorrhage
Spark of Life Neonatal Satellite
2013
The magic minutes after birth – making the most of them Transition from placenta to air breathing
Prof Stuart Hooper
Using oxygen wisely in the delivery room
Dr Jennifer Dawson
Transitional Circulation Dr Graeme Polglase Sustained inflations at birth Prof Stuart Hooper Monitoring in the delivery room Prof Peter Davis
Monitoring of the newborn infant in delivery room
Peter Davis Melbourne
Australian Resuscitation Council Neonatal Satellite Meeting
Evaluate respirations, heart rate and colour
ILCOR 2005
Assessment in the DR
• Colour • Heart rate • Chest rise • (tone and reflex irritability)
Can we use clinical assessment of colour?
• 3-5 minute clips from 20 videos of varying gestation requiring varying degrees of resuscitation (including none)
• 27 medical and nursing observers noted the time at which the infant turned pink
• Corresponding oxygen saturation from a masked oximeter noted
How well do 27 observers agree about colour?
How well do 27 observers agree about colour?
• Median saturation at which babies thought to become pink was 69
• Range extended from 10 to 100!
Colour and oxygen • Improvement in colour may take several minutes
to achieve, even in uncompromised babies. Exposure of the newly born to hyperoxia is detrimental to many organs at cellular and functional level.
• Therefore, colour has been removed as an indicator of oxygenation or resuscitation efficacy
ILCOR guidelines
Pediatrics, 2010, 126 (5), p. e 1321.
Can we use the colour of an infant’s tongue?
• The Giraffe study
Infant characteristics Characteristics: Study group:
n= 68
Gestational age, mean (SD), week 38 (2)
Birth weight, mean (SD), g 3214 (545)
Apgar score at 1 min, median (IQR) 9 (8-9)
Apgar score at 5 min, median (IQR) 9 (9-9)
Type of anaesthesia, n (%)
Spinal/epidural 66 (97)
General anaesthesia 2 (3)
Time to first data, median (IQR), sec 76 (67-91)
Assessor characteristics
Characteristics: n (%): Midwives 38 (84)
Paediatricians 7 (16)
≤1 year of experience 14 (31)
>1 year of experience 31 (69)
Results
• When the colour is pink, the baby has a saturation >70% and probably does not need supplemental oxygen
0.0
00.2
50.5
00.7
51.0
0S
en
sitiv
ity
0.00 0.25 0.50 0.75 1.001 - Specificity
Area under ROC curve = 0.8642
Measurement of Heart Rate (HR) in the delivery room
• Guidelines recommend auscultation or umbilical cord palpation (count for 6 seconds and multiply by 10)
• HR is an (the most?) important sign in determining need for and response to resuscitation
• How precise and accurate are clinical measurements?
Assessment of heart rate: Auscultation & palpation v ECG
-----------------------------------------------
Kamlin CO, O'Donnell CP, Everest NJ, Davis PG, Morley CJ. Resuscitation. 2006
Assessment of heart rate • Auscultation of the heart rate is more accurate than palpation
of the cord. However, both are relatively insensitive.
• Auscultation of the heart rate should remain the primary means of assessing heart rate. There is a high likelihood of underestimating the heart rate with palpation of the umbilical pulse, but this is preferable to other palpation locations.
ILCOR guidelines
Pediatrics, 2010, 126 (5), p. e 1321.
How should we judge ventilation?
• Chest movement? • Manometer?
ILCOR guidelines: Initial breaths
• Avoid excessive chest wall movement during ventilation of preterm infants
• Monitoring of inflation pressures may help provide consistent inflations and avoid unnecessarily high pressures
Pediatrics, 2010;126(5):e1323.
Displayed PIP vs Expired tidal volume
Schmölzer et al, Arch Dis Child Fetal Neonatal Ed. 2010;95(6):F393-7.
Peak inflation pressure in cm H2O
Expi
red
tidal
vol
ume
in m
l/kg
Chest wall movement?
• Infants < 32 weeks gestation who received face mask PPV immediately after birth
• Estimate tidal volume (quantitative and qualitative) – head view – side view – experienced and inexperienced operators
• Hot-wire anemometer flow sensor to measure gas flow and tidal volume
Poulton et al, Resuscitation 2011;82:175-179.
Tidal volume 0
10
20
30
4 8
10 13 2 9 16 14 5 6 11 18 19 20 15 17 7 1 3 4 8 12
expi
red
tidal
vol
ume
(VTe
) in
mL/
kg fo
r eac
h op
erat
or
measured VTe estimated VTe
Tidal volume 0
1020
304
8ex
pire
d tid
al v
olum
e (V
Te) i
n m
L/kg
for e
ach
oper
ator
measured VTe estimated VTe
1
3 4
12
18 19 20
10
13
8 9
2
16
5 6
11
17
15
7
14
8
Tidal volume 0
1020
304
8ex
pire
d tid
al v
olum
e (V
Te) i
n m
L/kg
for e
ach
oper
ator
measured VTe estimated VTe
1
3 4
12
18 19 20
10
13
8 9
2
16
5 6
11
17
15
7
14
8
Chest movement vs Expired tidal volume
0
2
4
6
8
10
12
14
Not at all Too low Appropriate Too much Not sure
Expi
red
Tida
l Vol
ume
(ml/
kg)
Clinical signs of effective ventilation are imperfect
• Displayed PIP is a poor surrogate for tidal volume delivered
• Chest rise is an inaccurate, unreliable measure of adequacy of ventilation
Why might this be important?
Too much ventilation
• Björklund (Pediatric Research 1997) – 5 pairs of 127-128 day lambs (~28 weeks’)
• Six large manual inflations – reduced compliance – worse gas exchange – widespread lung injury
Excessive bagging
Standard resuscitation
What can help us?
• Pulse oximetry – How to apply – How accurate? – Limitations
• Respiratory function monitoring – An introduction
PO Sensor
Pulse Oximeter
Patient Cable
Conclusion: Apply the sensor to the right hand and then to the patient cable
Feasibility of oximetry in the DR
Using optimal technique: • 90% of infants have oximetry data in < 92 sec • preterm infants are easier to monitor than term
O’Donnell, Kamlin, Davis and Morley, J Pediatr 2005;147:698-9
How accurate is PO measurement of heart rate?
Pulse oximetry vs ECG Heart Rate
Ability of PO to detect HR <100 •Sensitivity 89% •Specificity 99% •PPV 83% •NPV 99%
40 60 80 100 120 140 160 180 200
Heart rate from ECG
40
60
80
100
120
140
160
180
200
Hea
rt ra
te fr
om M
asim
o Pu
lse
Oxi
met
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n=206 (4%) n=42 (1%)
n=4871 (94.5%) n=26 (0.5%)
Accuracy of pulse oximetry measurement of heart rate of newly born infants in the delivery room. Kamlin, Dawson, Singh, Morley, Donath, Davis. Journal of Pediatrics 2008;152(6):756-60.
10.1
-11.6
-100
-50
050
HR
from
EC
G m
inus
HR
from
Nel
lcor
PO
(bpm
)
50 100 150 200Average of HR from ECG and HR from Nellcor PO (bpm)
-0.8
Agreement between HR measurements
B A
Bland-Altman plots showing the level of agreement between HRECG and HRNellcor (A) and between HRECG and HRMasimo (B)
HRECG – HRNellcor
Mean Difference -0.8 bpm
95% Limit of Agreement ± 10.9 bpm
-100
-50
050
HR
from
EC
G m
inus
HR
from
Mas
imo
PO
(bpm
)
50 100 150 200Average of HR from ECG and HR from Masimo PO (bpm)
9.6
0.2
-9.3
10.1
-11.6
-100
-50
050
HR
from
EC
G m
inus
HR
from
Nel
lcor
PO
(bpm
)
50 100 150 200Average of HR from ECG and HR from Nellcor PO (bpm)
-0.8
Agreement between HR measurements
B A
Bland-Altman plots showing the level of agreement between HRECG and HRNellcor (A) and between HRECG and HRMasimo (B)
HRECG – HRNellcor HRECG – HRMasimo
Mean Difference -0.8 bpm 0.2 bpm
95% Limit of Agreement ± 10.9 bpm ± 9.4 bpm
Heart rate in the delivery room: What is normal?
Heart rate in healthy term babies (no interventions)
Oxygen saturations in the delivery room: What is normal?
O2 saturations in the first 10 mins 0
1020
3040
5060
7080
9010
0O
xyge
n sa
tura
tion
(%)
0 1 2 3 4 5 6 7 8 9 10Minutes after birth
10th 25th 50th 75th 90th
All babies no interventions in the delivery room
Defining the Reference Range for Oxygen Saturation for Infants After Birth. Pediatrics. 2010.
Don’t forget to look at the baby!
Measuring pressure and volume
Florian traces (200Hz) using Spectra software during ventilation
Pressure
Flow
Volume
Summary (1)
• “Colour” is no longer recommended as a useful sign in the DR
• Clinical assessment systematically underestimates true heart rate
Summary (2)
• Pulse oximetry is a useful guide to assessment of oxygenation and heart rate in the DR but: – Know what is normal – Look at the baby
• Signs of effective ventilation are imperfect – Respiratory function monitoring helps us
understand the problems
Spark of Life Neonatal Satellite
2013
The magic minutes after birth – making the most of them Transition from placenta to air breathing
Prof Stuart Hooper
Using oxygen wisely in the delivery room
Dr Jennifer Dawson
Transitional Circulation Dr Graeme Polglase Sustained inflations at birth Prof Stuart Hooper Monitoring in the delivery room Prof Peter Davis