Disorders of thermoregulation derive from the readjustment of the hypothalamic thermoregulatory center or failure of the thermoregulatory physiological mechanisms to meet the environmental challenges. As a result the normal body temperature may decrease (hypothermic state) or increase (hyperthermic state). Either of these states may take several forms.
Hypothermic states | Hyperthermic states |
Hypothermic reaction | Hyperthermic reaction |
Hypothermia | Hyperthermia |
| Fever |
HYPOTHERMIA
Hypothermia is arbitrarily defined as a core body temperature of 35 °C or below.
Causes of hypothermia:
• decreased heat loss, and
• inadequate heat production. Decreased heat loss may be the result of:
• extreme environmental conditions;
• enhanced blood flow to the skin (burns, psoriasis). Inadequate heat production may result from:
• decreased metabolism;
• altered thermoregulation;
• ingestion of certain drugs.
Patterns of fever
On the basis of the extent of temperature elevation:
• subfebrile (<38 °C during axillary measuring);
• febrile (from 38 to 39 °C);
• pyretic (from 39 to 41 °C);
• hyperpyretic (more than 41 °C).
On the basis of temperature fluctuation:
• sustained (circadian fluctuation <10 °C);
• remittent (fluctuation 1-2 °C);
• hectic (fluctuation 3 °C and more);
• intermittent (great fluctuations with falls in the morning up to normal values);
• relapsing (febrile episodes are separated by intervals of normal temperature).
Biological significance of fever:
Positive aspects: | Negative aspects: |
the growth and virulence of several bacterial species are impaired | caloric and fluid requirements are increased |
the phagocytic and bactericidal activity of neutrophils is increased | increased muscle catabolism leading to negative nitrogen balance |
the cytotoxic effects of lymphocytes are increased | fever may produce stupor or delirium |
the increase in the liver detoxication activity | stress to the fetuses |
| stress to the heart and the respiratory system |
| children are prone to fevers |
| fever in the first trimester of pregnancy increases the risk of neural tube defects in the fetus |