Fetal/neonatal

Question 1

Describe the changes that occur to the circulatory and respiratory system at birth

Answer 1

1) At birth pulmonary vascular resistance falls as a result of the increased PAO2.
2) At birth circulation changes from a parallel to a series system
3) At birth there is a fall in cardiac right and left end diastolic pressure.
4) The initial breath afterbirth generates a pressure of 70-100cmH2O
5) FRC rises to 30ml/kg in the hour after birth
6) 4-6 weeks after birth the foramen ovale is expected to close.

Question 2

Describe the anatomical differences of a neonatal airway and the implications that this has on airway management.

Answer 2

Bones-
Small mandible- less anterior excursion and small mouth opening.
Prominent occiput- neck is flexed in supine position

Nasopharynx-
Infants are obligate nasal breathers

Oropharynx-
Larger tonsils and adenoids- can cause obstruction, nasopharyngeal airways can cause abrasion and bleeding.
Infants have a proportionally larger tongue in comparison to the oropharynx- can cause obstruction and interferes with laryngoscopy.

Laryngopharynx-
Anatomic subglottic narrowing- effective anatomic seal can be achieved without the use of a cuffed ETT, also can cause foreign bodies to lodge below the cords.
Large floppy epiglottis- projects further into the airway.

Trachea
Superior laryngeal position- located opposite C3/4 vs C4/5 in adults.
Short Trachea- risk of R main bronchus intubation or extubation.
Soft trachea- cricoid pressure may cause airway collapse.
Narrow Trachea- via hagen-poiseuille equation can cause far greater resistance with only a small change in radius. Target for needle/surgical cricothyroidostomy is smaller. Risk of stenosis in prolonged intubation/tracheostomy.

Under/over extension of the neck can cause airway obstruction in the neonate.

Question 3

What are the differences in body fluid composition in the neonate vs adults

Answer 3

Neonates have a lower percentage of body water
Lower percentage of total body fat
Have a lower serum albumin
Gastric pH in neonates is alkalotic at birth
Serum glucose levels in neonates are higher than that of older children and are more prone to hypoglycaemia.

Question 4

Describe the agents and doses that can be considered for pre medication in children.

Answer 4

Midazolam- oral 0.1-0.5mg/kg (up to 20mg)
Ketamine- 3mg/kg oral
For a deeper sedated child a combination of the 2 can be considered.
Clonidine- low oral bioavailability, 4mcg/kg

Question 5

Describe the foetal circulation

Answer 5

Blood flow-
Right to left cardiac shunting is physiologically normal in foetal circulation.
Contradictory to out of utero circulation, there is high systemic vascular resistance and low pulmonary vascular resistance.
The majority of blood passing down the descending aorta comes from the ductus arteriosus/right ventricle.

(Anatomical diagram)

Oxygenation-
Foetal blood leaving the placenta has an O2 sat of about 80%, cerebral blood circualation has a O2 %sat of around 62%. The Lower body receives blood with %sat of approx 58%. Blood returning to the placenta has a %sat of approx 58%.

Question 6

What is the thermoneutral zone, what is the range for adults and neonates?

Answer 6

The thermoneutral zone is the range across which the basal rate of heat production is balanced by heat loss.
I.e. it is the body heat loss and production are equal.
In adults this is between 21 and 31 degrees celcius.
In neonates this is higher- between 32 and 34 degrees.