Download History of Physiology Lecture

Lecture 1: Physiology Lecture
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Title
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What differences?
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Adults cardiac
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Differences at birth
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Lung fluid
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Stimuli for 1st
breath and
importance of first
breaths
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Lung fluid diagram
(repeat)
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Physiology
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Physiology
(simplified 1)
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Physiology
(simplified 2)
Emphasise the importance of understanding this. It is
important to understand why we do what we do.
Ask “what are the differences in arrest situations between
adults and children / babies?” Size/heat loss, anatomy,
physiology. Aetiology of arrest.
Adults and children arrest for different reasons, true also for
babies.
Draw out from the audience. If not already mentioned: size/heat loss, they come out wet, anatomy, physiology, lungs
unexpanded and contain fetal lung fluid, have never yet
breathed air. At no other time of life is lung fluid a major
problem.
Anatomical and physiological adaptations to extrauterine life do not usually affect resuscitation.
Emphasise lungs full of fluid are difficult to inflate.
Babies need to get to the position on the right where lungs
are aerated. Not all the fluid is removed; some fluid is
essential to normal respiration.
But babies with excess retained fetal lung fluid may be
tachypnoeic, grunt, require oxygen +/- ventilation etc.,
Reiterating the normal to explain the needs in resuscitation.
Establishing an adequate resting lung volume is extremely
important. Either the baby does it itself or you do it for the
baby. The newborn baby clears its own lungs by crying. Big
breaths and raised pressure on expirations. Mention the
physiology of lung fluid and its absorption.
Reiterate. Emphasise most babies do this without problems
but there are some that need help. It is this situation that this
course is addressing.
As a result of animal models we have some understanding of
the physiology of acute perinatal asphyxia. This complicated
graphical representation is commonly shown in medical and
midwifery textbooks but is difficult to understand and contains
several bits of information that are not routinely available to
us trying to resuscitate the baby (such as PaO2, PaCO2, pH
and blood pressure)
This is the same diagram made slightly simpler but more
importantly showing only the things that we can see /
measure in the clinical setting.
These are visible chest wall movements (breathing), the
colour of the baby (reflecting oxygen levels in blood) and the
heart rate. These are all plotted against time along the X-axis.
Time zero is when the cord blood supply is interrupted
© Scottish Multiprofessional Maternity Development Programme, Revised 2007
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When presenting animated slides do not talk while slide is developing
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Breathing and
Oxygenation
(colour)
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Apnoea
terminology
Heart rate
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The problem (1)!
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The problem (2)!
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The problem (3)!
Highlight these two aspects as these are the most important
things to get right in resuscitation of the newborn infant (Click
on first slide – rest will then build until gasping reached).
Babies are already relatively hypoxic in utero compared to
adults and rapidly becomes even more so. As a result the
respiratory centre begins to cause deeper and faster
respirations. After a while however the respiratory centre
ceases to function as this too depends on oxygen to work and
the baby begins a period of apnoea.
(Click on next slide – rest will then build until terminal apnoea
reached).
After a variable length of time of apnoea the baby starts to
gasp. This is a more primitive spinal breathing reflex that is
normally suppressed by the respiratory centre. The gasps
continue for a variable length of time before this stops and no
further breathing activity will occur.
Throughout the sequence the ‘colour’ of the baby will change
from ‘purple’ (relatively hypoxic in-utero levels), through blue
then eventually white as vasoconstriction occurs.
These two periods of no respiratory activity are known as
‘primary’ and ‘terminal’ (or secondary) apnoea
(Click on first slide – rest will then build until heart rate falls to
zero at end).
Heart rate may initially climb (can be seen in fetal distress)
but then falls to about 60-80 beats per minute in primary
apnoea. The initial very rapid fall is probably vagally mediated
but then lack of oxygen results in a switch to anaerobic
metabolism, which is much less efficient. The heart can no
longer pump at 140/min. Glycogen that is laid down during
the third trimester is metabolised anaerobically to provide
energy but the heart must run at a slower rate.
Eventually diminishing glycogen stores, increasing acidosis
and continued hypoxia cause the heart to fail.
It is difficult to tell where babies are on this diagram when
they are first born. A baby born at this point in primary
apnoea will be:
 Not breathing
 Blue +/- white, and
 Have a slow heart rate
Likewise a baby born at this point in the gasping phase will,
before he/she takes that first gasp, be:
 Not breathing
 Blue +/- white, and
 Have a slow heart rate
Even a baby born in terminal apnoea will look the same.
Again the baby born at this point will be:
 Not breathing
 Blue +/- white (although almost certainly white), and
 Have a slow heart rate
Thus we need an approach that will deal with all three
situations (and others in between) without over-treating the
first baby and yet ensuring that the third gets adequate help.
© Scottish Multiprofessional Maternity Development Programme, Revised 2007
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Self resuscitating
baby (primary
apnoea)
This slide shows a baby recovering from primary apnoea
without help – i.e. from the point of the arrow in slide 95..
(Click on first slide – rest will then build until sequence
finishes).
The baby continues to be apnoeic until the first gasp. Then
with gasping and an open airway the baby can get oxygen
(air) to the lungs. Because the circulation is still working
(albeit slower than normal) the oxygen is transported to the
coronary arteries and myocardium where it acts to rapidly
‘bump start’ the heart.
Restoration of the normal heart rate and air in the lungs leads
to greater oxygenation and the baby begins to ‘pink up’. With
increasing amounts of oxygen in the blood the respiratory
centre begins to function again, normal respiratory activity
resumes and the gasps are once again suppressed.
Emphasise the key to this recovery is that the airway
needs to be open.
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Resuscitation of
baby in primary
apnoea
This slide shows what happens to the previous baby when it
is actively resuscitated – i.e. in primary apnoea from the point
of the arrow in slide 16.
(Click on first slide – rest will then build until sequence
finishes).
The baby continues to be apnoeic however inflation breaths
through an open airway replace the gasps of the previous
baby. This allows oxygen to get into the lungs. Again,
because the circulation is still working (albeit slower than
normal) the oxygen is transported to the coronary arteries
and myocardium where it acts to rapidly ‘bump start’ the
heart.
Restoration of the normal heart rate and air in the lungs leads
to greater oxygenation and the baby begins to ‘pink up’. With
increasing amounts of oxygen in the blood the respiratory
centre begins to function again, normal respiratory activity
resumes and the gasps are once again suppressed.
Points to emphasise:
1. Airway must be opened
2. This baby cannot be distinguished from the
baby in terminal apnoea.
3. Response of baby in primary apnoea to
resuscitation is respirations rather than gasps
occur
© Scottish Multiprofessional Maternity Development Programme, Revised 2007
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Resuscitation of
baby in gasping
phase
The response of this baby is similar to the previous except
that the baby continues gasping for some time despite the
instigation of inflation breaths.
(Click on first slide – rest will then build until sequence
finishes).
Oxygen gets into the lungs with gasps and the inflation
breaths. Again, because the circulation is still working (albeit
slower than normal) the oxygen is transported to the coronary
arteries and myocardium where it acts to rapidly ‘bump start’
the heart.
Restoration of the normal heart rate and air in the lungs leads
to greater oxygenation and the baby begins to ‘pink up’. With
increasing amounts of oxygen in the blood the respiratory
centre begins to function again, normal respiratory activity
resumes and the gasps are once again suppressed.
Points to emphasise:
1. Airway must be opened
2. Gasping alone is not enough to support the
baby and if this persists then ‘ventilation’
breaths may be necessary until regular
respirations occur
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The baby in
terminal apnoea
This slide shows a baby resuscitated from terminal apnoea –
i.e. from the point of the arrow in slide 18.
Emphasise that this baby will not resuscitate itself.
(Click on first slide – rest will then build until sequence
finishes).
Having dried and wrapped this baby the priority is to open up
the airway and get oxygen (air) into the lungs by inflating
them (how this is done will be covered in the next lecture and
in the practical parts of the course). If oxygen can enter the
lungs it will be transported to the coronary arteries and
myocardium where it acts to rapidly ‘bump start’ the heart.
Restoration of the normal heart rate and air in the lungs leads
to greater oxygenation and the baby begins to ‘pink up’.
Unlike our two previous babies the apnoea and gasping
continue beyond the initial lung inflation. Because gasps are
not efficient we must continue to provide ventilation until
normal breathing is restored. Eventually increasing the
amounts of oxygen in the blood the respiratory centre begins
to function again, normal respiratory activity resumes, the
gasps are once again suppressed and ventilation can be
halted.
Emphasise that even babies in terminal apnoea can
respond to simple resuscitation measures without the
need for drugs.
© Scottish Multiprofessional Maternity Development Programme, Revised 2007
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The baby in
terminal apnoea
(no response to
lung inflation)
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Any questions
Understanding is
important
This slide shows a baby resuscitated from terminal apnoea
when initial inflation of the lung does not bring about any
response.
Emphasise that again this baby will not resuscitate itself.
(Click on first slide – rest will then build until sequence
finishes).
Having dried and wrapped this baby the priority is to open up
the airway and get oxygen (air) into the lungs by inflating
them (how this is done will be covered in the next lecture and
in the practical parts of the course). Unlike the previous baby
the heart rate remains low. Therefore in this case we have to
do the job of the heart and pump oxygenated blood to the
lungs. We provide ventilation breaths and cardiac massage
(this is covered in the next lecture and in the practical
stations).
Like before if oxygen can enter the lungs it will be transported
to the coronary arteries and myocardium where it acts to
rapidly ‘bump start’ the heart.
Restoration of the normal heart rate and air in the lungs leads
to greater oxygenation and the baby begins to ‘pink up’.
Again the apnoea and gasping continue beyond the initial
lung inflation. Because gasps are not efficient we must
continue to provide ventilation until normal breathing is
restored. Eventually increasing the amounts of oxygen in the
blood the respiratory centre begins to function again, normal
respiratory activity resumes, the gasps are once again
suppressed and ventilation can be halted.
Re-emphasise that even babies in terminal apnoea can
respond to simple resuscitation measures without the
need for drugs. The only difference this time way the
need for the ‘next step’ of cardiac massage.
© Scottish Multiprofessional Maternity Development Programme, Revised 2007
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