Temperature Flashcards
Basics of hypothermia
> It is preventable
Should be a priority regardless of if the infant is sick or well
Normal core temp for an infant
36.5 to 37.5
Aim to protect and maintain at 37
Hypothermia ranges
Mild - 36-36.4
Mod 32-35.9
Severe - less than 32
In lower weight infants under 1 kg , severe starts @ 35*c
High-risk groups for hypothermia
- pre-term low weight
- SGA
- prolonged resus
- infants with - infectious, cardiac, neurological and endocrine problems
- infants with surgical problems
- decreased activity
Physiological response to “cold stress” - Vasoconstriction
This decreases heat loss
- prevents blood from reaching the surface where heat loss occurs.
However, in prolonged cases, this also decreases blood flow and 02 to the tissues and thus risk for anaerobic metabolism and lactic acidosis
Physiological response to “cold stress”
This increases heat production
- Located around the kidneys, adrenal glands, mediastinum, subscapular and axillary regions and neck.
In response to cold stress, norepinephrine is released into the nerve endings in brown fat, directing it to be “burned”.
- brown fat cells generate more energy than any other tissue in the body
Called “non-shierving thermogenesis’
What factors can affect the ability of brown fat to be metabolised?
Needs 02 and glucose
Thus - hypoglycemia, hypoxic babies can not meet cellular demands for this to happen
Surface area and heat loss - mechanisms
Babes can’t shiver - hence they flex their arms and legs to generate some heat. thus also reducing the surface area and heat loss
A thermal neutral zone is defined as
The environmental temperature permits the infant to expend the least amount of energy to maintain normal body temperature.
What controls temperature regulation in infants?
The hypothalamus, it activates a norepinephrine release when alerted
(Hypothermia) - 1. Norrepinephrone and peripheral vasoconstriction - what happens
In response to cold stress and hypothermia, norepinephrine causes the peripheral blood vessels to constrict. this is a protective mechanism to keep blood in the core of the body and away from the skin where it dispiates.
- However - after long periods of time will change to anaerobic metabolism and Ph will drop = acidosis
(Hypothermia) - 2. Norrepinephrone and pulmonary vasoconstriction - what happens
Norepinephrine also causes the pulmonary blood vessels to constrict, which increases vascular resistance in the lungs.
> when the blood vessels in the lungs constrict, they choose the path of less resistance, often right-to-left across the ductus arteriosis into the aortia.
de-oxygentated blood will then enter the arterial circulation (instead of going to the lungs) and the infant will become hypoxemic.
“shunting”
Potential clinical signs from hypothermia
Hypoxemia + resp distress
Hypoxia
Hypoglycemia
The hypoxemia chain
Hypoxemia > hypoxia > anaerobic metabolism (cells not functioning) > increased lactic acid > decreased PH
How quickly can a baby’s temp drop?
0.2-1 degree per min
Mechanisms of heat loss (4)
Conduction
Convection
Radiation
Evaporation
Heat loss by Conduction
Involves the transfer of heat between two solid objects e.g. infant body and x-ray plate
- larger the temp. gradient the faster the heat loss
How to assist?
Insulation
Pre-warm
A chemical thermal mattress underneath
Heat loss by Convection
Occurs when the infant’s heat is swept away by air currents such as drafts/vents/aircon.
How to assist?
Keep sides closed
If less than 28 G, increase delivery room temp to 26 to 28
Cover the preterm infant with a piece of food-grade plastic (most helpful in those under 1.5 kg)
- Oxygen is cole and will stimulate cold receptors and norrepinenrphne release which will increase metabolic rate and 02 consumption. - thus when flowing directly into the lungs cools the whole body! Use warmed air
Heat loss via Evaporation
Occurs when there is moisture in the skin surface or resp. tract mucosa is converted into vapor.
How to assist?
Quickly drying
Pre warmed blankets
Heat loss via Radiation
Transfer of heat between two solid surfaces that are not in contact with one another. e.g. one part of the infant’s body to adjacent solid surfaces aka - limb of two sides of the cot
How to assist?
Cover the incubator
Thermal shades
Move infant away from cold window
Rewarming the hypothermic infant after accidental hypothermia
The best recommendation is to re-warm while closely monitoring vitals/level of consciousness/acid + base balance
- rectal temp is the gold standard (can be 0.2-0.5 lower than axilla)
Incubator should be set @ 1-1.5 *C above infants temp
Hypoxic - Ischemic Encephalopathy (HIE)
At times infants experience very stressful births with impaired placental > fetal perfusion. This results in poor cardiac output and thus poor 02 and oxygenation of all organs (including the brain).
When the metabolic acidosis is so severe that it causes brain damage it is known as HIE
Therapeutic / Neuroprotective Hypothermia + Candiates
Following the initial ischemic insult to the brain, there is a death of neurons. The recommended treatment for HIE is international body cooling.
CANDIDATES / CRITERIA
> started within 6 hours of birth
> infants must be greater or equal to 36 weeks
> greater or equal to 1.8 kg
> must have an abnormal neo. exa,
Temp’s every 15 min , must not ever drop below 33.5 *C
Criteria of a true birth asphyxia
Hypoxia
Acidemia
Metabolic acidosis
