Neonatal hypothermia

Introduction to neonatal hypothermia When the skin temperature of newborns is maintained at 36-37 ° C, the oxygen consumption is the lowest, and normal metabolism can be guaranteed. The so-called hypothermia refers to the core (rectal) body temperature 35 ° C, characterized by hypothermia, cold body surface, low response. The mechanism of hypothermia is reduced heat production or increased heat dissipation, or both. Therefore, in neonatal diseases, any decrease in heat production or increased heat dissipation can be seen as a main symptom due to hypothermia. Hypothermia can not only cause hard swelling of the skin, but also damage the vital organs of the body, affect function, and even lead to death. basic knowledge The proportion of the disease: the incidence of newborns is about 0.5% -1% Susceptible people: children Mode of infection: non-infectious Complications: neonatal hypoglycemia pneumonia gastrointestinal bleeding sepsis

Neonatal hypothermia

Stimulated by the cold (20%):

Neonatal body surface area is relatively large, heat dissipation is greater than heat production, when the ambient temperature is lower than the neutral temperature, it is not effectively warm, can not maintain body temperature, often the skin temperature drops below 35 °C, forming a low body temperature.

Insufficient food intake (25%):

The amount of glycogen stored in the liver of the newborn is very small. If the food is insufficient, it can be exhausted within 18 to 24 hours after birth.

Hypoxia and nervous system dysfunction (20%):

The main part of neonatal heat production is the metabolic decomposition of fatty acids in brown fat and brown fat. It needs perfect neurological function and sufficient oxygen supply. When neonates are deficient in oxygen and nervous system dysfunction, brown fat can not be used. Chemistry The heat production process is often impossible, and the body temperature is not prone to rise.

Disease impact: (15%):

When neonates suffer from sepsis, pneumonia and other infectious diseases, due to reduced eating, caloric intake is insufficient; shock, acidosis and microcirculatory disorders affect the decomposition of brown fat, so that the body heat production is reduced, at this time, if the ambient temperature is low, Insufficient warmth, the baby is easy to cause hypothermia.

Pathogenesis

1. Heat dissipation is greater than heat production: when the body temperature is 3335°C, the body can reach equilibrium by increasing heat production and heat loss. When the body temperature is below 33°C, the body can't generate enough heat to replenish heat. At this time, heat dissipation must be reduced. To the minimum or external heating can restore the body temperature to normal, when the body temperature is lower than 22 ° C, it is impossible to recover, and the body is not reactive to the ambient temperature.

Whether the full-term or premature baby is stimulated by cold, it can produce skin vasoconstriction reaction. When the skin temperature is above 35 °C, the contraction effect is the strongest. When the temperature drops below 35 °C, the blood vessel changes from contraction to expansion. With liquid exudation, the peripheral vasoconstriction reaction caused by cold stimulation can increase the warmth of deep tissue in the body, but the warming effect of newborns is limited. When the cold stimulation is strong or the duration is long, the heat dissipation is greater than the heat production, body temperature. It will be lowered.

When the newborn's temperature drops below the neutral temperature, the body's heat production increases, but it can't increase the heat production by increasing muscle activity (chilling), mainly by increasing the oxygen consumption and increasing the metabolic rate to compensate for the heat production. This compensatory heat production is not sufficient within a day. When the cold stimulation is strong, although the metabolism is increased, the body temperature cannot be maintained, and the hypothermia is formed.

2. The amount of stored glycogen is small: the amount of glycogen stored in the liver of the newborn is very small, and if the food is insufficient, the endogenous heat is insufficient.

3. Brown fat can not be used: the main part of neonatal heat production in brown fat, brown fat, fatty acid metabolism, need to have a perfect nervous system function and adequate oxygen supply, neonatal in the absence of oxygen and nervous system dysfunction Brown fat can not be used, chemical heat production process can not be carried out often, body temperature is not easy to rise, neonatal sepsis, pneumonia and other infectious diseases, due to reduced intake of food, insufficient caloric intake; due to shock, acidosis and microcirculatory disorders It affects the decomposition of brown fat and reduces the body heat production. At this time, if the ambient temperature is low, the warmth is not enough, and the baby is easy to cause hypothermia.

4. Changes in various systems at low body temperature

(1) Cardiovascular: Within the effective response to cold stimulation (about as low as 33 ° C), the heart rate increases and enhances the sympathetic response. Below this range, the heart rate decreases, initially slows down quickly, then gradually decreases, and the heart rate changes. The slowness is due to inhibition of the myocardium, prolonged contraction time, and inhibition of normal central impulse information. Arrhythmia is not common in neonates, and changes in the nailfold microcirculation of neonates are observed with a nailfold microcirculation microscope (low body temperature). It can be seen that the nails are deformed by capillary vasospasm, the blood flow becomes slow, and the blood cells are stagnant. The blood flow velocity of the limbs is slowed from the limb blood flow diagram, indicating that the microcirculatory disorder exists in the neonatal hypothermia, and the blood pressure is progressive at low body temperature. The decline is due to a decrease in cardiac output and peripheral vasodilation.

(2) Breathing: When the baby is stimulated by cold, the breathing will increase at the beginning, and the body temperature will gradually decrease. As the respiratory center is restrained, the breathing gradually slows down. For example, the respiratory rate does not slow down with the decrease of body temperature, suggesting that the lung lesion may be combined. Pneumonia, pulmonary hemorrhage, etc.

(3) Blood: Due to vasodilation, plasma is extravasated to the tissue from the surrounding circulation, blood is concentrated, and hematocrit is increased. At low body temperature, the number of platelets in peripheral blood is significantly reduced, often as low as 100,000 or less, and thrombocytopenia caused by cold. The pathogenesis may be: prostaglandin (PGI2) is a potent inhibitor of platelet aggregation, its production is reduced at low body temperature, and the ability of formed prostaglandins to inhibit platelet aggregation is also weakened, adenosine diphosphate (ADP) is one. Important physiological platelet condensate, under the influence of cold, the activity of enzymes that decompose ADP is reduced, the effect of preventing platelet aggregation is weakened, neonatal platelets react weakly to adrenaline, and at lower body temperature, plasma catecholamines are elevated to To a certain extent, platelets can produce a second condensed wave, a large number of platelets are depleted. When the body temperature is low, the oxygen ion curve is biased to the left side, oxygen is released to the tissue, and the blood pH is decreased. This is due to tissue hypoxia and lactic acid accumulation to produce metabolic acid. Poisoning and CO2 retention.

(4) Renal function: cold reduces the activity of distal renal tubular enzymes, so that the renal tubular reabsorption function, especially the reabsorption of glucose, is reduced, resulting in "cold diuretic". As the body temperature drops, blood pressure also decreases, and blood flow becomes slower. The glomerular filtration rate is reduced, resulting in less or no urine, and severe hypothermia often has azotemia.

(5) Digestive system: gastrointestinal motility is weakened at low body temperature, gastrointestinal digestive juice secretion is reduced, digestive dysfunction is poor, due to weak reaction, swallowing action is not coordinated, vomiting and aspiration are easy to occur during feeding, so the body temperature does not return to normal In the past, it was best not to feed it.

(6) nervous system: when the body temperature is lower than 35 °C, the reaction is slow, when it is lower than 33 °C, it is in a semi-coma state, the pupil begins to expand, when the temperature is lower than 30 °C, the external reaction disappears, the limb is stiff, and the respiratory heartbeat becomes slower than 26 °C. It is close to death.

(7) Metabolism: When the body temperature drops, the body's metabolic rate also decreases. When the body temperature decreases by 1 °C, the metabolic rate decreases by 5%. Because the insulin and hexokinase activities are inhibited, the process of cellular uptake and utilization of glucose is reduced, and glucose is administered at low body temperature. The body can not be fully utilized, and it is more serious when the body temperature is lower than 33 °C. At this time, the blood sugar can be increased, for example, the glucose supplement tends to remain in the extracellular fluid, and the water is extracted from the cells to dilute the extracellular fluid, so the body temperature is low. It is still controversial whether it is reasonable to give a large amount of glucose.

(8) Infection: When the body temperature is low, the body's immune function is reduced, and it is easy to be infected. After the newborn's hypothermia lasts for 24 hours, most of the infections are combined. After the death, the blood culture can often obtain positive results.

Neonatal hypothermia prevention

1. Do a good job in perinatal health: do a good job in perinatal care (especially in rural areas) and education, strengthen prenatal checkups, prevent pregnancy complications, avoid premature birth, low birth weight infants and birth injuries.

2. Keep warm: In the cold season and the area, warm equipment should be assembled for the delivery room. Once the newborn is delivered, it should be wrapped with pre-warmed towels to keep warm, so that the newborn's body temperature is stable, especially for high-risk children. Enough heat.

3. Active treatment of infection: Active treatment of underlying diseases that cause scleredema, such as infection, intracranial hemorrhage, deformity, asphyxia, birth injury and so on.

Neonatal hypothermia complications Complications neonatal hypoglycemia pneumonia gastrointestinal bleeding sepsis

Hypothermia easily induce neonatal hypoglycemia, acidemia; combined with pulmonary lesions such as pneumonia, pulmonary hemorrhage; combined with gastrointestinal bleeding; severe DIC can occur; often associated with infection such as sepsis, brain and pneumonia.

Neonatal hypothermia symptoms Common symptoms Bipolar type body temperature blood pressure drop heart rate increase response slow convulsion coma arrhythmia hypocalcemia azotemia sepsis

The clinical characteristic manifestations are: low body temperature and low response, low response, low crying, low milk absorption, low muscle tension, cold hands and feet, prolonged capillary refilling time (>5s), and acidosis After correction, hypocalcemia occurs with convulsions, if not accompanied by other organ damage (intracranial hemorrhage, aspiration pneumonia, myocardial or kidney damage, etc.), can be rewarmed after heat preservation.

1. Body temperature: below 35 °C.

2. Cardiovascular: mild heart rate increases, heart rate decreases when the condition worsens, initially slows down quickly, then gradually declines, a few neonates have arrhythmia, such as atrial ectopic excitability, ventricular premature contraction, atrial fibrillation and ventricular fibrillation Etc., blood pressure progressively decreases at low body temperature.

3. Breathing: The breathing increases at the beginning, and the breathing gradually slows down later.

4. Blood: The blood is concentrated, the hematocrit is increased, and the number of platelets in the peripheral blood is significantly reduced, often as low as 100,000 or less, and the blood pH is lowered, resulting in metabolic acidosis and CO2 retention.

5. Renal function: produce "cold diuretic", with lower blood pressure, less urine or no urine, severe cases often have azotemia.

6. Digestive system: prone to vomiting, aspiration.

7. Nervous system: The reaction is sluggish, the severe one is in a semi-conscious state, the pupil is enlarged, the external reaction disappears, the limb is stiff, the respiratory heartbeat is slow, and it is close to death when it is lower than 26 °C.

8. Metabolism: The metabolic rate of the body is reduced. When the body temperature is lowered by 1 °C, the metabolic rate is reduced by 5%. When the body temperature is lower than 33 °C, the blood sugar can be increased.

9. Infection: The body's immune function is reduced, and it is easy to be infected. After the newborn's hypothermia lasts for 24 hours, most of the infections include sepsis, brain and pneumonia. After death, the blood culture can often get positive results.

Neonatal hypothermia examination

Blood gas analysis, blood routine and platelets, blood urea nitrogen and electrolyte determination, blood glucose and blood culture, and DIC screening tests, etc., some neonates must measure thyroid function.

1. Blood: The hematocrit is increased, the number of platelets is significantly reduced, often as low as 100,000 or less. The decrease in platelet count is often parallel with the severity of the disease, but cyanosis rarely occurs.

2. Blood gas analysis: due to tissue hypoxia, lactic acid accumulation, blood pH decreased, metabolic acidosis and CO2 retention, obvious metabolic acidosis indicates that the tissue is hypoxic, the organs are dysfunctional, and the condition is heavier.

3. Renal failure: obvious oliguria or no urine, azotemia, increased serum creatinine and non-urea nitrogen, suggesting acute renal failure, children often die of arrhythmias caused by hyperkalemia.

4. Others: Once there is bleeding tendency or DIC test positive, the prognosis is dangerous, and blood culture or post-mortem blood culture can often get positive results.

X-ray films and electrocardiograms should be routinely reviewed and reviewed later if necessary.

1. X-ray chest X-ray: low-temperature infants without pulmonary complications X-ray films show clear lung fields, caused by pulmonary vasoconstriction, such as thickening of blood vessels, patchy or mass-like shadows, should be alert The possibility of pulmonary bleeding.

2. Electrocardiogram: It can be seen that the QRS time is prolonged, the ST segment is prolonged and decreased, the T wave can be inverted, and the heart rate is slowed down due to inhibition of the myocardium, prolonged contraction time, and inhibition of normal central impulse information. Arrhythmia can occur. Atrial ectopic excitability, ventricular premature contraction, atrial fibrillation and ventricular fibrillation, etc., may have high potassium performance.

3. Microcirculatory dysfunction: Observing the changes of the nail fold microcirculation in neonates with a wrinkle microcirculation microscope (low body temperature), it can be seen that the nail wrinkles are deformed, the blood flow becomes slow, and the blood cells are stagnant, which can be seen from the limb blood flow chart. The slower blood flow velocity of the limbs indicates that there is a microcirculatory disorder in the neonatal hypothermia.

Diagnosis of neonatal hypothermia

diagnosis

1. History and clinical features: should be asked in detail about childbirth, whether there is intrauterine distress and primary asphyxia, post-natal milking and feeding, environmental temperature and heat preservation conditions, and other disease symptoms, the reason for distinguishing hypothermia is cold stimulation Mainly based on disease, it is important to guide treatment and evaluate prognosis. It should be noted that hypothermia is often the late manifestation of certain diseases in neonates. Under reasonable environmental temperature and sufficient heat preservation conditions, if the body temperature does not rise, It is suggested that the child has serious condition, clinical heart rate, respiration, blood pressure, deep and body surface temperature and changes in fluid volume.

2. Laboratory and auxiliary examination: The laboratory and auxiliary examination of neonates with hypothermia have corresponding changes.

Differential diagnosis

1. Congenital hypothyroidism: low body temperature 1 to 3 weeks after birth, low metabolic rate, hypothermia due to low heat production, special facial features and other clinical features, abnormal thyroid function, iodine absorption rate Normally lower than 10%, T4 decreases, TSH increases, if TSH is low, TRH load test can be done. If there is also a lack of secretin in the pituitary, TSH does not rise, otherwise it rises, it is effective with thyroxine treatment, X-ray examination of distal femur An osteogenesis center appears.

2. Severe infection caused by hypothermia: physical examination can find infected lesions, there are corresponding lesion symptoms and signs, the general condition is serious, low body temperature lasts for a long time, can be found in the history of infection.

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