Physiological adaptations at birth Flashcards
What are 5 key areas of physiological adaptation at birth of the fetus?
- Respiratory system
- Cardiovascular system
- Genitourinary system
- Gastrointestinal system
- Haemtological system
How much liquid does the fetal lung contain at term?
100ml - equals the functional residual capacity, forms liquid cast of future air spaces
What must happen in the respiratory system at birth?
fluid must be cleared to make way for airway - failure to do so leads to breathlessness
What is it called when babies fail to clear the fluid in their lungs?
transient tachypnoea of the newborn (TTN)
How long does does TTN usually last?
day or two
What factor increases the risk of TTN?
elective caesarean section
What is respiratory distress syndrome (RDS)?
deficiency of surfactant, commoner in pre-term infants (0.1% at term vs 30% at 28 weeks)
What is surfactant in the lungs?
complex lipoprotein consisting largely of phosphatidyl choline, synthesised by type II pneumocytes within the alveoli, important in reducing surface tension and allowing alveoli to expand
What are 3 things that contribute to reduced surfactant production?
- Hypoxia
- Acidosis
- Hypothermia
What is the treatment to increase production of surfactant in the fetus?
antenatal steroids - increase production and reduce incidence of RDS
What are 4 presenting features of respiratory distress syndrome?
- Tachypnoea
- Grunting
- Intercostal recession commencing in first 4 h
- Low oxygen saturations requiring oxygen
What investigation may be performed in RDS and what will it show?
CXR - generalised reticulogranular appearance - ground glass
What is the management of RDS?
- some improve with supplemental oxygen or continuous positive airway pressure (CPAP)
- if worsening, intubation and administration of artificial surfactant via ET tube
When is meconium usually passed?
usually retained in colon in utero, but may be passed through sphincter under physiological conditions, particularly after 40 weeks
What can early passage of meconium lead to?
fetal hypoxic stress, irritative to neonatal lungs so may lead to pneumonitis = meconium aspiration syndrome
What are the features of meconium aspiration syndrome?
range from mild neonatal tachypnoea to severe respiratory compromise
What can cause meconium aspiration syndrome to be worse? 2 things
- more likely to be severe if associated acidosis (but this doesn’t increase incidence)
- if meconium is thick
What is the treatment of meconium aspiration syndrome?
- oxygen, mechanical ventilation, surfactant therapy (can displace or inactivate endogenous surfactant)
- if severe, extracorporeal membrane oxygenation (ECMO) ± pulmonary lavage
What maternal condition predisposes to RDS?
diabetes
What changes to the cardiovascular system occur soon after birth?
relaxation of smooth muscle in pulmonary vessels which is triggered by entry of oxygen into lung with first breath (paradoxical response to oxygen)
What can cause the relaxation of smooth muscle in pulmonary vessels not to occur after birth?
prolonged fetal hypoxia
What is the name of the condition where smooth muscle in pulmonary vessels does not relax following birth?
persistent fetal circulation
What is it difficult to distinguish persistent fetal circulation from?
congenital cyanotic heart disease
What is the role of the fetal kidney in utero?
maintaining amniotic fluid volume (negligible role in excretion of waste products)
How does the role of the kidneys change from in utero to after birth?
in utero, maintains amniotic fluid volume but little role in excreting waste products; kidney must excrete all body’s waste as well as conserve fluid
initial rise in blood urea and creatinine concentrations
What is the maximum urine osmolality that the newborn can attain?
600 mol/L (1800mmol/L in adult)
What are common complications of neonatal illness, relating to urinary system function in the neonate?
dehydration and electrolyte disturbances - as newborn can’t concentrate urine very much
What are 2 physiological changes that are common in the U+Es of a neonate?
- rise in blood urea
- rise in creatinine
What can deficiencies in swallowing result in in utero?
polyhydramnios - usually swallows amniotic fluid at same rate it is produced
What should be done if a baby has had polyhydramnios in utero and why?
- newborn should be examined for swallowing problems
- should have orogastric tube passed in order to exclude complete oesophageal atresia
What is the usual haemoglobin concentration of the term fetus?
180 g/L (high)
Why do fetuses have high haemoglobin concetration at term?
due to low arterial oxygen tension (3-4 kPa) which characterised latter part of intrauterine life
By how much does neonatal Hb fall after birth and when?
falls to around 100 g/L by about 8 weeks of age
What other aspects of the neonatal FBC is different at birth?
WCC: 12-20 x 109 /L
polymorphs predominate
How does WCC change following birth and when?
7-12 x 109 /L and mainly lymphocytic
What are 5 aspects of routine care immediately after birth?
- Assessment: apgar scores 1, 5 and 10 minutes
- Preventing hypothermia
- Examination for obvious abnormalities
- Weighing and measuring - weight, length, head circumference
- Umbilical cord
What is the purpose of the assessment with apgar scores after birth?
reasonably objective record of how baby initially responded to challenge of extrauterine life and serves as guide to need for resuscitation
Why is preventing hypothermia very important in the newborn?
newborn babies can lose heat faster than they can generate it, and hypothermia is dangerous and must be prevented
What are 5 ways of preventing hypothermia in the newborn?
- Delivery room must be warm and draughts kept to a minimum
- Baby should be immediately dried and wrapped in towels or blankets
- Put hat on head to prevent heat loss
- If resuscitation required, should be under radiant heater
- Preterm babies routinely delivered into polythene bags to minimise evaporative losses and improve temperature control
What are 4 mechamisms of heat loss in babies?
- Evaporation of water from wet skin
- Convective loss due to air currents
- Radiation to cold surfaces
- Conductive loss to col mattress
What are 4 mechanisms of heat gain in neonates?
- Oxidation of brown fat (lots in newborn)
- Muscular activity
- Radiant heater over cot or Resuscitaire
- Warm mattress
What kind of examination is done immediately after birth?
brief examination for any obvious external abnormalities - full routine examination should be deferred until later (first 2 days)
What measurements are taken of the baby at birth and why are they useful?
- weight, length, head circumference
- assessment of how well baby has grown in utero
- baseline against which to judge subsequent growth
What should be done to the umbilical cord at birth?
cord should be checked to see whether it contains usual 2 arteries and one vein
plastic cord clamp fixed to leave 2cm of cord proximally
Why is it important to check the arteries and veins in the umbilical cord at birth?
if single artery rather than 2 - 20% association with congenital abnormalities, mainly of genitourinary system
After birth what should subsequent care of the umbilical cord involve?
keep it clean and dry;
When should you alter the usual cord length at which it is clamped and why?
if likely to need intensive care, leave longer than 2cm as provides accessible route for arterial and central venous cannulation
What drug is administered to the baby shortly after birth and why
- vitamin K, 1mg IM
- (less complete protection: 2mg orally twice in first week with further oral dose at 1 month)
- preventing haemorrhagic disease of newborn as vitamin K does not cross placenta well and babies have low serum concentrations and poor stores
- do not have gut bacteria to synthesise it for them and human milk poor source
- lack of it leads to shortage of clotting factors II, VII, IX and X
When does haemorrhagic disease of the newborn classically occur?
between days 1-6 but can occur up to 12 weeks after delivery
early form if mother taking anticonvulsants
Which babies are at reduced risk of haemorrhagic disease of the newborn?
bottle fed as formula milks contain it
