Thermoregulation

Question 1

What are the methods of Heat Loss in a Neonate

Answer 1

Evaporation - heat loss through wet skin

Convection- heat loss from cooler air circulating around warmer skin particularly when exposed

Conduction- heat loss through direct contact with a cold surface (eg. Scales)

Radiation- heat loss from heat radiating towards a cooler surface (eg. A cold wall)

Question 2

What is the Thermoneutral Range of Temperature

Answer 2

The narrow range of environmental temperature at which the basal metabolic rate of the baby is at a minimum, oxygen consumption is at lowest and baby maintains its normal body temperature

(Essentially this means the baby is able to use the least energy possible to keep itself warm and is relaxed)

Question 3

Why should a baby be kept in the thermoneutral range of temperature?

Answer 3

This is so that their energy is utilised for growth and other vital functions

Question 4

Physiological Processes behind Neonatal Thermoregulation

Answer 4

• the heat-regulating mechanism in the neonate is inefficient and the body temperature may drop
• should be born into a temperature of 26 degrees, dried and wrapped up, ideally with skin-to-skin
• the baby is used to an intra-uterine temperature of 37.8 degrees
• wet skin at birth and high surface area-to volume ratio means that heat is lost through the skin surface
• the baby has a lack of subcutaneous fat at term; and a lack of adipose tissue & brown fat as a preterm baby
• poor energy stores and limited brown fat means there is limited thermogenesis (heat production)

Question 5

What is thermoregulation

Answer 5

The control of the generation and loss of heat activated and performed through thermal sensors, afferent pathways, an integration system in the CNS, efferent pathways and target organs

• in the first few days, neonates sweat only from their head region
• the area where heat can be lost (the head) is very small compared to the body mass that can generate heat
• neonates are unable to shiver
• if they become cold, they can decrease their surface area by adopting the fetal position

Question 6

Describe non-shivering thermogenesis

Answer 6

Heat is generated through metabolism in the brown adipose tissue

• brown adipose tissue is situated around the kidneys, mediastinum, around the nape of the neck and scapulae, along the spinal column and around the large blood vessels in the neck
• *it is for this reason that it is crucial to keep the nape of the neck warm in neonates in order to maximise heat regulation**
• brown adipocytes (fat cells) begin to proliferate at 26-30 weeks gestation. These have an extremely high propensity for metabolic activity and therefore heat production
• adrenaline and thyroxine increase the metabolic activity within the brown fat cells and heat is produced

Question 7

What is Cold Stress?

Answer 7

This is when the peripheries are cold and the trunk of the body is warm

Question 8

Cold Stress causes what change in hormones in order to heat up the neonate?

Answer 8

The activity of the sympathetic nerve fibres during cold stress causes the adrenal glands to release the necessary catecholamines, such as noradrenaline —> this stimulates the anterior pituitary gland —> releases thyroid-stimulating hormone (TSH) —> causes the thyroid gland to increase its production of thyroxine (T4)

Adrenaline and thyroxine increase the metabolic activity within the brown fat cells and heat is produced but this process requires extra oxygen and glucose

Question 9

Heat Gain Methods in a Neonate

Answer 9

• metabolic processes such as oxidative metabolism of glucose, fats and proteins
• physical activity such as crying, restlessness and hyperactivity
• non-shivering thermogenesis generated through metabolism in brown adipose tissue

Question 10

Heat Loss Methods in a Neonate

Answer 10

Evaporation
Convection
Radiation
Conduction

Question 11

Describe the physiology of the onset of breathing.

Answer 11

• the inflation of the lungs encourages the intra-alveolar fluid to move into the surrounding interstitium. It is also absorbed by the body
• the respiratory system in the medulla oblongata of the brain matches the respiratory effort to cellular metabolic needs. The medulla is influenced by chemoreceptors and stretch reflexes.

1) during its descent through the birth canal, the fetus experiences a reduction in oxygen (physiological hypoxia) and an accumulation of carbon dioxide. This Hypoxia and Hypercarbia is crucial to the establishment of a new respiratory drive with the medulla oblongata and contributes to more successful pulmonary ventilation.
2) the emptying of pulmonary fluid from the lung, expansion of the pulmonary vascular bed and pulmonary tissue creates a NEGATIVE PRESSURE which assists the first breath
3) elastic recoil of the rib cage at delivery increases the capacity and the infant is stimulated to inspire (at first inspiration, the diaphragm contracts strongly and the flexible ribs and sternum are pulled concave. Subsequent breaths require much less mechanical work).

Question 12

The Factors initiating the first breath and lung expansion

Answer 12

• compression of the chest wall during delivery
• the recoil of the chest wall immediately after birth
• chemoreceptors stimulated by the reduction in oxygen and increase in carbon dioxide in the blood
• sensory stimuli on the skin, such as touch, pressure and cold
• stimulation of the senses by light and noise

Question 13

Physiological Processes involved in Resuscitation of the Newborn

Answer 13

A- airway —> ensure latency
B- breathing —> ensure oxygen enters the lungs
C- cardiac function —> ensure there is adequate heart beat and circulation
D- drugs —> ensure that the resuscitation trolley with all its components is available

• clear upper airways with suction
• intermittent positive pressure ventilation (IPPV) via face mask & bag attached to oxygen supply
• baby should become pink as oxygen supply improves and heart rate should improve
• baby breathing spontaneously - continue oxygen until condition improves and heart rate should improve
• baby kept warm- temp falls - increased demand for glucose and oxygen
• if mother had received Pethidine or morphine within the last 2/3 hours, Naloxone hydrochloride (Narcan) is advised if baby is unresponsive

Question 14

Umbilical vein becomes what ligament?

Answer 14

Ligamentum teres hepatis

Question 15

Umbilical arteries become what ligaments?

Answer 15

The medial umbilical ligaments

Question 16

The ductus venosus becomes what ligament?

Answer 16

Ligamentum venosum

Question 17

The ductus arteriosus becomes what ligament?

Answer 17

Ligamentum arteriosum

Question 18

Foramen ovale becomes what ligament?

Answer 18

Fossa ovalis

Question 19

Hypogastric arteries become what ligaments?

Answer 19

Obliterated hypogastric arteries

Question 20

Describe fetal circulation and the changes that occur following birth

Answer 20

The separation of the neonate from the placental circulation results in the collapse of the umbilical arteries and vein, ductus venosus, hypogastric arteries and ductus arteriosus (these fibrose and turn into supporting ligaments)

• This results in a reduction in flow to the right atrium, causing a fall in the right atrial pressure. As blood flow through the hypogastric arteries ceases, the volume of blood is now contained in a smaller systemic compartment —> increase in systemic vascular resistance —> increases return of blood volume to lungs
• Larger volumes of blood are now returned from lungs via pulmonary veins to the left atrium —> increase in left atrial pressure
• Initial equalising of prssures in the two atria closes the flap of the FORAMEN OVALE and the right-to-left intra-arterial shunt of blood ceases
• As baby takes their first breath, the lungs expand and oxygenated air is inspired. This displaces the pulmonary fluid further and triggers mechanisms essential to effective respiration and pulmonary gas exchange
• Oxygen content of blood increases —> vasodilation of pulmonary vascular bed —> pulmonary vascular resistance falls by 80% —> increases pulmonary blood flow
• The amount of blood being shunted by the DUCTUS ARTERIOSUS is decreased —> oxygen tension in blood rises —> fibromuscular tissue of the ductus arteriosus constricts and closes

Question 21

Discuss the effects of the combined respiratory and circulatory changes at birth

Answer 21

• when the baby takes its first breath the lungs inflate for the first time, increasing pulmonary blood flow. Blood returning from the lungs increases the pressure in the left atrium, closing the flap over the FORAMEN OVALE and preventing blood flow between the atria. Blood entering the atrium is therefore diverted into the right ventricle and into the pulmonary circulation through the pulmonary arteries. As pulmonary circulation is established, blood oxygen levels increase, causing constriction and closure of the ductus arteriosus
• if these adaptations do not occur, they are evident as congenital abnormalities