Neonatal hypothermia

Introduction The neonatal skin temperature is maintained at 36-37 ° C, the lowest oxygen consumption, and can ensure normal metabolism. The so-called hypothermia refers to the core (rectal) body temperature 35 ° C, the body temperature is too low, the body surface is cold, the reaction is low. The mechanism of hypothermia is the reduction of heat production or 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.

Cause

The body surface area of the newborn is relatively large. The skin is very thin and the blood vessels are more likely to dissipate heat, and the body temperature regulation center is not perfected, so that the regulation function is incomplete. Hypothermia is prone to occur when the ambient temperature is lowered, the warming measures are insufficient, or the calorie intake is insufficient.

Irritated by cold

The body surface area of the newborn is relatively large, and the heat dissipation is greater than the heat production. When the ambient temperature is lower than the neutral temperature, it is not effectively warmed, and the body temperature cannot be maintained. The skin temperature is often lowered below 35 °C to form a low body temperature.

2. Insufficient food intake

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

3. Hypoxia and nervous system dysfunction

The main part of neonatal heat production in brown fat, brown fat, the metabolic decomposition of fatty acids needs a perfect nervous system function and sufficient oxygen supply, the newborn can not use brown fat in the absence of oxygen and nervous system dysfunction, chemical heat production The process often cannot be carried out, and the body temperature is not prone to rise.

4. Disease effects

When a newborn suffers from an infectious disease such as sepsis pneumonia, the calorie intake is reduced due to eating; the brown fat is decomposed by shock, acidosis and microcirculation disorders, which reduces the body heat production. At this time, if the ambient temperature is low, the baby is not warm enough. It is easy to cause hypothermia.

Pathogenesis:

1. Heat dissipation is greater than heat production

When the body temperature is 33 ~ 35 ° C, the body can increase the heat and heat to reach the equilibrium temperature below 33 ° C, the body can not produce enough heat to supplement the heat, at this time must reduce the heat to the minimum or external heating When the body temperature returns to normal body temperature below 22 °C, it is impossible to recover, and the body is in an unresponsive state to the ambient temperature.

Skin vasoconstriction can occur in both full-term or premature infants with cold stimulation. When the skin temperature is above 35 °C, the contraction is the strongest to fall below 35 °C, the blood vessels change from contraction to expansion, and the peripheral vasoconstriction reaction caused by liquid exudation cold stimulation can increase the warmth of deep tissue in the body. This kind of warming effect of newborns is limited. When the cold stimulation is strong or the duration is long, the heat dissipation is lower than that of the thermogenic body.

When the newborn's temperature drops below the neutral temperature, the body's heat production increases but the increase in heat production by increasing muscle activity (chilling) is mainly to increase the oxygen consumption and increase the metabolic rate to compensate for the heat production. Within the first few days after birth. This compensatory heat production is not sufficient. When the cold stimulation is strong, although the metabolic increase is still unable to maintain body temperature, it will form a hypothermia.

2. Store less glycogen

The amount of glycogen stored in the liver of the newborn is small. If the food is insufficient, the endogenous heat is insufficient.

3. Brown fat can not be used

The main part of neonatal heat production is the metabolic decomposition of fatty acids in brown fat brown fat. It needs perfect neurological function and sufficient oxygen supply. In the case of hypoxia and nervous system dysfunction, brown fat can not be used, chemical heat production The process often fails to occur and the body temperature does not rise. Neonatal septic pneumonia and other infectious diseases reduce the caloric intake due to eating; due to shock, acidosis and microcirculatory disorders affecting the brown fat decomposition, the body heat production is reduced. At this time, if the ambient temperature is low, the warmth is not enough, the baby is very Easy to cause hypothermia.

4. Changes in various systems at low body temperature

(1) Cardiovascular: In the range of effective response to cold stimuli (about as low as 33 ° C), the heart rate increases and the sympathetic response increases below this range. The heart rate decreases initially, and then gradually decreases. Arrhythmias, which are inhibited, prolonged during contraction, and suppressed by normal central impulse information, are not common in newborns. Observation of the microcirculation microcirculation in neonates with a wrinkle microcirculation microscope (low body temperature) showed that the nail folds were deformed, the blood flow became slow, and the blood cells were stagnant. From the limb blood flow map, it can be seen that the slower blood flow velocity of the limb indicates that there is a microcirculatory disorder in the neonatal hypothermia. The progressive decrease in blood pressure at hypothermia is due to a decrease in cardiac output and peripheral vasodilation.

(2) Breathing: When the baby is stimulated by cold, the breathing will increase rapidly at the beginning, and the body temperature will gradually decrease. As the respiratory center is restrained, the breathing gradually slows down. If the respiration rate does not decrease with the decrease of body temperature, it may be combined with lung lesions such as pneumonia and pulmonary hemorrhage.

(3) Blood: Due to vasodilation, plasma is extravasated from the surrounding circulation to the tissue, and the blood is concentrated. The hematocrit is increased and the body temperature is significantly reduced. The number of platelets in the peripheral blood is significantly reduced, often as low as 100,000 or less. The pathogenesis of thrombocytopenia caused by cold may be: prostaglandin (PGI2) is a potent platelet aggregation inhibitor. Its hypothermia produces less prostaglandins that inhibit the formation of platelet aggregation and also attenuates adenosine diphosphate (ADP). As an important physiological platelet condensate, the activity of enzymes that decompose ADP under the influence of cold is reduced, and the effect of preventing platelet aggregation weakens the response of neonatal platelets to adrenaline, which is more obvious at low body temperature, and plasma catecholamines are elevated. To a certain extent, the platelets can produce a second condensed wave. When a large number of platelets are depleted at low body temperature, the oxygen detachment curve is biased to the left side. The release of oxygen to the tissue reduces the decrease of blood pH. This is due to the accumulation of metabolic acidosis caused by tissue hypoxic lactic acid accumulation. Caused by 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", blood pressure also decreases with body temperature, blood flow becomes slow, and the kidney is small. The ball filtration rate is reduced, resulting in low or no urine, severe hypothermia and often azotemia.

(5) Digestive system: gastrointestinal motility is weakened at low body temperature, digestive juice secretion of gastrointestinal tract is reduced, digestive dysfunction is weakened, reaction is weakened, swallowing action is uncoordinated, vomiting is easy to occur when feeding, so it is best not to return to normal before body temperature Oral feeding.

(6) Nervous system: When the body temperature is lower than 35 °C, the reaction is slower than 33 °C, and the pupil is in a semi-coma state. The pupil begins to expand. When the temperature is lower than 30 °C, the external reaction disappears. The limbs are stiff and the heartbeat slows down. When the temperature is lower than 26 °C, it is close. 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 reduces the hypothermia and the glucose body is insufficient. Use, when the body temperature is lower than 33 °C, it is more serious. At this time, the blood sugar can be increased. If the glucose is added, the glucose tends to remain in the extracellular fluid and the water is taken out from the cell to dilute the extracellular fluid. Therefore, it is reasonable to give a large amount of glucose at low body temperature. There is still controversy.

(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 blood cultures after the infection are often positive.

an examination

Related inspection

Body temperature measurement amniotic fluid general examination obstetrics B super amniotic fluid alpha fetoprotein determination (AFP) amniotic fluid bilirubin

1. History and clinical features: It should be asked in detail whether there is intrauterine distress and primary asphyxia after childbirth, after birth and feeding, environmental temperature and heat preservation conditions, and other disease symptoms to distinguish low body temperature is mainly caused by cold stimulation It is still based on disease, which is of great significance for guiding treatment and evaluating prognosis. It should be noted that hypothermia is often the late manifestation of certain diseases in neonates. Under reasonable environmental temperature and adequate heat preservation conditions, if the body temperature does not rise, the patient's condition is severe. Clinical heart rate breathing, blood pressure, deep and body surface temperature and fluid volume Change, etc.

2. Laboratory and auxiliary examinations have a corresponding change in laboratory and auxiliary examinations for neonates with hypothermia.

Laboratory inspection:

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

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

2. Blood gas analysis: due to the decrease of pH value of tissue hypoxic lactic acid accumulation blood, metabolic acidosis and CO2 retention have obvious metabolic acidosis, suggesting that the tissue is hypoxic and serious, and the dysfunction of each organ is serious.

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

4. Others: Once there is a tendency to hemorrhage or a positive DIC test, the prognosis is sinister. Blood cultures or post-mortem blood cultures often yield positive results.

Other auxiliary inspections:

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 chest radiograph shows clear lung field, caused by pulmonary vasoconstriction, such as thickening of vascular texture, patchy or mass-like shadow should be alert to pulmonary hemorrhage may.

2. Electrocardiogram: It can be seen that the QRS time is prolonged and the ST segment is extended and decreased, and the T wave can sometimes be inverted. Slow heart rate is due to myocardial inhibition, prolonged contraction time and inhibition of normal central impulse information. Arrhythmias such as atrial ectopic ventricular premature ventricular contraction and ventricular fibrillation may have high potassium manifestations.

3. Microcirculatory dysfunction: The changes of the nail wrinkle microcirculation in neonates were observed with a nailfold microcirculation microscope (low body temperature), and the blood flow of the nail wrinkles was observed to be slow and the blood cells were stagnant. From the limb blood flow map, the blood flow velocity of the limbs is slow, indicating that there is a microcirculatory disorder in the neonatal hypothermia.

Differential diagnosis

1. Congenital hypothyroidism: low body temperature 1 to 3 weeks after birth, low metabolic rate, hypothermia due to low heat production. There are special facial features and other clinical manifestations. The thyroid function is abnormal. The iodine absorption rate is 10% lower than normal. T4 decreases TSH. If the TSH is low, the TRH load test can be performed. If the gastrointestinal hormone is also lacking, the TSH does not rise, otherwise it rises. It is effective with thyroxine treatment. X-ray examination showed the osteogenesis center at the distal end of the femur.

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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