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Shivering and Non shivering Thermogenesis/ Incubator Care/ KMC

Dr Mrs Marcia Morayo Ihekaike

MBBS, FMCPaed, LMIH

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Outline

Objectives
Overview
Pathophysiology
Mechanisms of heat loss
Consequences of hypothermia
Treatment of hypothermia

Incubator
Radiant warmer
Kangaroo Mother Care

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Objectives

At the end of this lecture, students should be able to define and classify hypothermia
Understand the physiology of temperature regulation in the newborn
Know the mechanisms of heat loss in a newborn
Understand the consequences of hypothermia
Know how to treat hypothermia

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Overview

Maintaining a neutral thermal environment is one of the key physiologic challenges that a newborn must face after delivery.
Thermal care is central to reducing morbidity and mortality in newborns.
Thermoregulation is the ability to balance heat production and heat loss in order to maintain body temperature within a certain normal range.

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Overview

The neutral thermal environment is the external temperature range within which metabolic rate and hence oxygen consumption are at a minimum while the infant maintains a normal body temperature.
The specific environmental temperature required to maintain thermoneutrality depends on whether the neonate is wet or clothed, its weight, its gestational age, and its age in hours and days.

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A normal body temperature implies only a balance between heat production and heat loss and should not be interpreted as the equivalent of an optimal and minimal metabolic rate and oxygen consumption.
The normal skin temperature in the neonate is 36.0-36.5°C.
The normal core (rectal) temperature is 36.5-37.5°C.
Axillary temperature may be 0.5-1.0°C lower.

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Hypothermia

Hypothermia is a state in which the body’s mechanism for temperature regulation is overwhelmed in the face of a cold stressor.
It is classified as accidental or intentional
Primary or secondary
Also classified by the degree of hypothermia
Hypothermia affects virtually all organ systems; the most significant effects are seen in the CVS and CNS.

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Immediately after delivery if no action is taken, the core and skin temperatures of a term neonate can decrease at a rate of approximately 0.1°C and 0.3°C per minute respectively.
The World Health Organisation defines
mild hypothermia as a core body temperature of 36°C-36.4°C,
moderate hypothermia as 35.9°C-32°C and
severe hypothermia as less than 32°C

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Pathophysiology

Body’s core temperature is tightly regulated in the thermoneutral zone between 36.5°C and 37.5°C, outside of which thermoregulatory responses are usually activated.
The body maintains a stable core temperature through balancing heat production and heat loss.
Heat production increases with striated muscle contraction; shivering increases the rate of heat production 2-5times.

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The hypothalamus controls thermoregulation via
Increased heat conservation (peripheral vasoconstriction and behaviour responses)
And heat production (shivering and increasing levels of thyroxine and epinephrine).

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Mechanisms of heat production

Mechanisms of heat production in the newborn are;

Metabolic processes
Voluntary muscle activity
Peripheral vasoconstriction
Nonshivering thermogenesis

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Metabolic processes

The brain, heart, and liver produce the most metabolic energy by oxidative metabolism of glucose, fat and protein.
The amount of heat produced varies with activity, state, health status, environmental temperature.

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Voluntary muscle activity

Increased muscle activity during restlessness and crying generate heat.
Conservation of heat by assuming a flexed position to decrease exposed surface area.

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Peripheral vasoconstriction

In response to cooling, peripheral vasoconstriction reduces blood flow to the skin and therefore decreases loss of heat from skin surfaces.

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Nonshivering thermogenesis

Heat is produced by metabolism of brown fat.
Neonates have a metabolic response to cooling that involves chemical (nonshivering) thermogenesis by sympathetic nerve discharge of norepinephrine in the brown fat.
The brown fat is a specialized tissue of the neonate.

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Norepinephrine in brown fat activates lipase, which results in lipolysis followed by oxidation or re- esterification of the fatty acids that are released.
This chemical process generates heat by releasing the energy produced instead of storing it as Adenosine-5-Triphosphate (ATP).
Brown fat constitutes approximately 1.4 percent of the body mass of newborns greater than 2kilograms

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A rich blood supply to the brown fat helps transfer of heat to the rest of the body.
This reaction increases the metabolic rate and oxygen consumption 2- to 3-fold.
Thus, in neonates with respiratory insufficiency, cold stress may also result in tissue hypoxia and neurologic damage.
Brown fat is located in nape of the neck, between the scapulae, in the mediastinum, heart, great vessels, axillary regions and around the kidneys and adrenals.

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With continued cold stress the stores of brown fat become depleted resulting in hypoxia and hypoglycaemia.
Brown adipose tissue can be identified after 26 weeks’ gestation.
Post delivery brown adipose tissue does not continue to develop, as it would have done in the intrauterine environment, so preterm neonates remain at a disadvantage.

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The preterm infant has the additional disadvantages of
decreased fat for insulation,
greater body water content
decreased glycogen stores,
immature skin which increases water loss,
altered skin blood-flow (e.g. peripheral cyanosis)
poor vascular control,

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Poorly developed metabolic mechanism for responding to thermal stress (e.g. no shivering)
a narrower range of thermal control
In addition, their hypotonic ("frog") posture limits their ability to curl up to reduce the skin area exposed to the colder environment.

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Mechanisms of heat loss in the Newborn

Radiation. Radiation is heat loss from the infant (warm object) to a colder nearby object.
Conduction. Conduction is direct heat loss from the infant to the cool surface with which he or she is in direct contact.
Convection. Convection is heat loss from the infant to the surrounding cooler air.
Evaporation. Heat may be lost by water evaporation from the skin of the infant (this is especially likely immediately after delivery).

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Etiology

Decreased heat production
Increased heat loss e.g. delivery in an area with an environmental temperature below recommended levels, caesarean delivery, low Apgar scores requiring resuscitation, maternal hypertension
Impaired thermoregulation e.g. sepsis, intracranial haemorrhage, drug withdrawal

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Effects of cold stress in the newborn

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Consequences of excessive heat loss

Insufficient oxygen supply and hypoxia from increased oxygen consumption.
Hypoglycaemia secondary to depletion of glycogen stores.
Activation of glycogen stores can cause transient hyperglycaemia.
Metabolic acidosis caused by hypoxia and peripheral vasoconstriction.
Prolonged, unrecognized cold stress may divert calories to produce heat, impairing growth.
Pulmonary hypertension as a result of acidosis and hypoxia.

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Signs and symptoms of hypothermia

Acrocyanosis and cool, mottled, or pale skin
Hypoglycaemia
Transient hyperglycaemia
Bradycardia
Tachypnoea, restlessness, shallow and irregular respirations

Respiratory distress, apnoea, hypoxemia, metabolic acidosis
Decreased activity, lethargy, hypotonia
Feeble cry, poor feeding
Decreased weight gain

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Consequences of Hypothermia

Clotting disorders: Disseminated intravascular coagulation and pulmonary haemorrhage can accompany severe hypothermia.
Shock with resulting decreases in systemic arterial pressure, plasma volume, and cardiac output.
Intraventricular haemorrhage.
Severe sinus bradycardia.
Increases the risk of late onset sepsis.
Increased neonatal mortality

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Prevention and management of hypothermia

The “warm chain” is a set of interlinked procedures to be performed at birth and during the next few hours and days after birth in order to minimize heat loss in all newborns.
Failure to implement any one of these procedures will break the chain and put the newborn at risk of getting cold.
Ideally, hospitals that care for sick and low birth weight newborns should have additional equipment such as overhead heaters, heated mattresses, incubators and low-reading thermometers that read temperatures down to 25°C.

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Indications for close monitoring of newborn’s temperature

Difficulty maintaining the “warm chain” or providing an optimal thermal environment
Low birth weight and/or ill newborn
Resuscitation required at birth
Suspicion of hypothermia or hyperthermia
With rewarming or cooling down
If the newborn has been re-admitted to hospital for any reason

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Treatment of hypothermia

Rewarming may induce apnoea and hypotension; therefore, the hypothermic infant should be continuously and closely monitored regardless of the rewarming method (rapid or slow).
One recommendation is to rewarm at a rate of 1°C/h unless the infant weighs <1200 g, the gestational age is <28 weeks, or the temperature is <32.0°C and the infant can be rewarmed more slowly (with a rate not to exceed 0.6°C/h).
Another recommendation is that, during rewarming, the skin temperature should not be >1 °C warmer than the coexisting rectal temperature.

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While rewarming, neonates should be monitored and treated as needed for hypoglycaemia, hypoxaemia, and apnoea.
Underlying conditions such as sepsis, drug withdrawal, or intracranial haemorrhage may require specific treatment.

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Method of rewarming

Incubator

Radiant warmer

Kangaroo mother care (KMC)

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Infant Incubator

It provides an environment that can be adjusted to provide the ideal temperature as well as the perfect amount of oxygen, humidity, and light.
It is important in maintaining a small environment of desired temperature which minimizes the heat loss.

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It consists of the baby tray that is enclosed in a box like structure to provide a fix warm environment.
The box is generally made of fibre glass or acrylic which is transparent.
The heating mechanism is below the tray.
The heat generated is not used directly to heat the body but to warm the air mixture which is then circulated in the closed environment around the baby.

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The temperature of the air as well as the baby is indicated on panels.
Temperature control can be automatic or manual based on the incubators.
Incubators are armed with alarms to derive attention for temperature change.

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History of Incubator

In 1891 - First modern incubator invented by Dr Alexander Lyon
1898 - First American Incubator Hospital was set up at the Trans Mississippi Exposition in Omaha , Nebraska.
1907 - Pierre Constant Budin released the study of Influence of body temperature on infant mortality
In 1932 - Julius Hess in his patents for incubators proposed a mechanism for the addition of supplemental oxygen in the incubator.
1933 - Blackfan and Yaglaw released report on the improved survival for newborn infants nurtured in humidity enriched environment.

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Advantages of Incubator care

It provides the closest environment to that of the mother’s uterus.
Temperature at a uniform airflow and the humidity can be controlled to the desired level.
It protects the baby from all the disturbances and infection in the NICU.

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Disadvantages

Since the baby lies in a closed hood it is difficult to access the baby for medical procedure or care.

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Transport Incubator

A transport incubator is used when a sick or premature baby is moved from one hospital to another.
It is similar to the Infant Incubator but is battery powered

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Radiant warmer

It’s a body warming device to provide heat to the body.
Helps maintain body temperature of baby
It limits metabolism rate

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It consists of an open tray where baby is kept
The artificial heating is provided by a heating mechanism mounted overhead
The heating mechanism consists of quartz which produces the desired heat and a reflecting mechanism to divert the heat at the baby tray.

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Skin temperature is monitored by a temperature measuring knob that is kept continuously attached to the body.
A small LCD panel continuously shows the body temperature.
Radiant warmers are equipped with alarm to indicate the change in temperature and hence attract attention of medical professional attending to the baby.

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Differences

Incubator