Why do we study so carefully what the thermometer shows us with every cold? What determines the tactics of our further treatment to a greater extent: the state of health or the numbers on the thermometer? And if, due to the peculiarities of the body, the temperature increases slightly with an infectious disease, as it happens in the elderly, how can we determine how serious the situation is?
For us, an increase in body temperature is always an alarm signal, because it is quite often one of the symptoms of a disease. We understand that a decrease in temperature after taking antipyretics will not be an indicator of recovery. The right approach to your health requires first identifying the possible cause of hyperthermia.
Causes of temperature rise
An increase in body temperature in response to any pathological effect is a non–specific reaction of the body, which is needed to launch and strengthen the defense mechanisms. Under normal conditions, our body maintains a relative constancy of temperature (temperature homeostasis). The body protects itself from overheating by increasing the processes of heat transfer: intense sweating, expansion of subcutaneous capillaries. The restructuring of thermoregulation processes with a reset to a higher temperature level is fundamentally different from the normal reaction of the body to overheating and is called “fever”.
The center of thermoregulation is located in the hypothalamus, and sometimes hyperthermia can develop with its direct damage (traumatic brain injuries, brain tumors), but these are quite rare situations. In the vast majority of cases, the invasion of bacteria, viruses or other harmful substances into the body leads to the reinstallation of the thermoregulation center to a higher point. External and internal “stimuli” of the thermoregulation center are called “pyrogens”. External (exogenous) pyrogens are certain substances that enter the body from the environment. Most often they are of an infectious nature: toxins and products of the metabolism of microorganisms. Internal (endogenous) pyrogens are formed in the body during inflammatory processes, allergic reactions, and the breakdown of tumor tissues. Thus, the spectrum of diseases accompanied by an increase in body temperature is quite wide.
Among the variety of pathologies, it is essential to distinguish two main groups: infectious and non-infectious. The combination of the clinical picture of the disease with laboratory indicators allows differentiating “infectious” and “non-infectious” fever.
An increase in temperature caused by an infectious process occurs in acute and chronic diseases caused by bacteria, viruses and fungi.
- after blood transfusions (blood transfusions);
- after the introduction of vaccines, serums;
- in the presence of foci of aseptic (non-infectious) inflammation in the body (for example, with pancreatitis, gout, thrombophlebitis and other diseases);
- with allergic and autoimmune diseases;
- with the development of malignant tumors (including the hematopoietic system – leukemia) hyperthermia the body is included in the concept of the so-called paraneoplastic reactions of the body;
- in the presence of large hematomas (bleeding) – the increase in temperature in this case is caused by increased destruction of red blood cells (hemolysis of red blood cells);
- in the presence of necrotic (dead) tissue (e.g., myocardial infarction);
- if damaged, have the thermoregulation center in the brain (for example, after a traumatic brain injury or in the presence of a brain tumor);
- with some endocrine diseases (for example, with hyperthyroidism – pathology of the thyroid gland, accompanied by its hyperfunction) .
Degrees of temperature rise
The degree of increase depends on many factors, including the state and reactivity of the body, concomitant intoxication.
A slight increase in body temperature in some cases is a normal reaction of the body: with intense physical exertion, after eating, with strong emotional stress, in women during ovulation (an increase of 0.6-0.8 C). High ambient temperature also causes hyperthermia: in hot weather, the body temperature is 0.1-0.5 C higher than in cold weather.
The normal body temperature of an adult during the day fluctuates, remaining in the range of 36 – 37C (when measured in the armpit). The permissible range of daily fluctuations is usually 0.1-0.6 C and should not exceed 1C. The maximum body temperature is recorded in the evening from 17 to 21 hours, and the minimum in the morning from 3 to 6 hours. Elevated body temperature from 37 to 38C is called subfebrile (from Lat. sub under, below + febris fever). Moderately elevated from 38 to 39C is called febrile. High from 39 to 41C is called pyretic (from the Greek pyretos heat). Excessively high body temperature above 41C was called hyperpyretic.
What is the danger of temperature rise
In addition to the harmful effects on pathogenic microorganisms and stimulation of the immune response, high temperature has a number of negative effects.
Hyperthermia changes the metabolism, causes the loss of water and salts. When the body overheats, the sweating process significantly increases. Fluid loss is accompanied by blood thickening, and the risk of blood clots increases.
High temperature is a great danger for people with cardiovascular diseases. When it increases by 1C, the pulse increases by 8-10 beats per minute. The heart works with a high frequency, in unfavorable conditions of blood thickening and metabolic disorders. Sometimes with hyperthermia in patients with cardiac pathology, rhythm disturbances are recorded, which is due to activation of the sympatho-adrenal system and electrolyte imbalance.
In patients with fever, frequent shallow breathing is observed: the frequency of respiratory movements increases, but the depth of inspiration decreases. Insufficient oxygen is supplied to organs and tissues, hypoxia develops.
High temperature accelerates redox processes, which means that the oxygen demand of cells sharply increases: when the temperature rises by 0.6 C, the level of basal metabolism increases by about 10%. Due to the lack of oxygen in the cells, a large number of “acidic” metabolites are formed, which disrupt the function of tissues and organs. Such a failure of metabolic processes, leading to “acidification” of the body, is called “acidosis”. That’s why fever can be accompanied by intoxication. This is most often observed in children, but if the inflammatory process proceeds for a long time, intoxication also occurs in adults.
With an increase in the activity of metabolic processes, carbohydrate reserves are primarily used, after their reserves are exhausted, fats and proteins are used. As a result of the increased breakdown of proteins, their loss of up to 300-400 grams per day is possible. Therefore, in case of fever, it is necessary to give children easily digestible carbohydrates (for example, juices).
With hyperthermia, the function of the gastrointestinal tract is suppressed: appetite decreases, enzyme secretion decreases, motility and absorption processes are impaired. As a result, it is possible to develop a syndrome of impaired absorption and constipation. This has a particularly unfavorable effect on elderly patients.
Patients with high body temperature are threatened by dangerous conditions of the central nervous system, due to increased permeability of the blood-brain barrier and insufficient oxygen supply to the brain. Hyperthermia may be accompanied by arousal. The most dangerous complication that occurs in children with an immature thermoregulation system is febrile convulsions.
Which temperature should be lowered and which should not
Temperature rise is an evolutionary mechanism of protection against pathogenic microorganisms. Upon contact with viruses, bacteria and their toxins, the cells of the immune system (leukocytes) produce special substances that trigger an inflammatory response. The temperature reaction is accompanied by a number of characteristic changes in metabolism and physiological functions aimed at strengthening cellular and humoral immunity. In conditions of high temperature, antibodies and defense cells are more actively produced, the reproduction of viruses and bacteria is inhibited. Many pathogens become sensitive to antibacterial drugs only at elevated temperatures. Its unjustified decrease suppresses the severity of the immune response. However, a very high temperature is dangerous for the body. Hyperthermia above 40C can lead to the development of brain edema and disruption of the functions of vital organs.
The threshold temperature at which it is necessary to make a decision on taking antipyretics is considered from 38C and above. But each person tolerates hyperthermia differently. Therefore, you should focus on well-being and the presence of concomitant diseases. This is especially important in relation to children.
A rise in body temperature above 38C is dangerous for children of the first 6 months of life, as well as for children from 6 months to 3 years old who are at risk for the development of febrile seizures. In accordance with the recommendations, antipyretic therapy is prescribed for children of the first 3 months of life at a temperature above 38.0 C, for children older than 3 months (previously healthy) – above 39.0 C.
Adult patients with severe diseases of the respiratory, cardiovascular and central nervous systems, the course of which may worsen with fever, show a decrease in temperature above 38.0 C.
For young people without concomitant pathology, taking antipyretic drugs is indicated at 39.0 C and above.
The question of choosing a drug is decided in each case individually.
Fever in newborns
Separately, it should be said about the increase in temperature in newborns and children of the first year of life. Immediately after birth, the child’s body is quite ready for independent thermoregulation. Newborns have sufficiently developed sweating and the ability to vasomotor reactions. However, the imbalance between heat generation and heat transfer develops in infants more often than at a later age. In the first year of life, due to insufficiently expressed subcutaneous fat and a relative increase in the specific surface area of the body, the heat transfer process always prevails. An additional increase in heat generation is carried out in newborns due to increased oxidative processes in brown adipose tissue (non-contractile thermogenesis). Contractile thermogenesis (the ability to enhance heat generation due to involuntary muscle contraction) they are missing. Within a day after birth, children show the ability to develop fever, but at first it is less pronounced than at an older age. Therefore, infectious diseases in infants may not be accompanied by a significant increase in body temperature, but if this occurs, it indicates the severity of the disease .
Temperature at COVID-19
The initial manifestations of coronavirus infection are similar to the course of many acute respiratory viral infections. The first may be weakness, headache and muscle pain, they are joined by catarrhal manifestations: nasal congestion, slight sore throat. Then, as with many acute respiratory infections, the temperature rises from 37C to 39C. This reaction of the body is registered in most patients with COVID-19. The duration and level of temperature rise during infection with SARS-CoV-2 depends on many factors: the immune response, the amount of the pathogen that has entered the body, developing complications. Some carry the infection without a significant increase.
The temperature reaction in COVID-19 is a natural response of the body that mobilizes the immune system upon contact with the virus. Therefore, taking antipyretic drugs at a temperature below 38.5 C is not recommended, except in situations where the patient does not tolerate an increase in temperature.
As a rule, the elevated temperature lasts 1-3 days, sometimes up to 5-6 days. If it is higher than 37.5 C for five consecutive days, this is a reason to seek medical help, since a more severe course of the disease with the development of complications is possible.
If a young person has a high fever without concomitant chronic pathology, he can call a doctor at home to assess the condition and prescribe appropriate therapy.
If the temperature above 37.5 C persists for several days in people over 65 years of age or with serious concomitant diseases, you definitely need to call an ambulance for transportation to a hospital.
One of the serious consequences of the new coronavirus infection is hyperinflammatory reactions. This is an excessive immune reaction provoked by the SARS-CoV-2 virus.
An indirect sign of the development of a hyperinflammation reaction may be a return rise in temperature. Febrile fever above 38 degrees after temperature normalization is also a reason to call a doctor at home.
A sharp increase in temperature of more than 38C with a significant deterioration in well-being and the addition of shortness of breath – indications for calling an ambulance team and urgent hospitalization.
A feature of the COVID-19 course is the long-term preservation of subfebrile temperature (no higher than 37 degrees). Subfibrility can persist for up to a month during the recovery process. In this case, in the absence of other symptoms and satisfactory well-being, complications are unlikely.
When to see a doctor
Young people without concomitant pathology should seek medical help with hyperthermia over 39C. Patients belonging to risk groups (elderly, with chronic diseases, young children, pregnant women) should call a doctor at home already with subfebrile 37.9C and moderate 38.0-39.0C fever, for timely therapy. An ambulance team should be called in case of severe intoxication, signs of respiratory, cardiac, renal or multiple organ failure. Urgent medical care is required for patients with fever with any signs of damage to the central nervous system (confusion, agitation or lethargy, convulsions). If the fever above 38.5C is not stopped by antipyretic drugs in the recommended age dosages within 48 hours, it is also worth calling an ambulance team so that doctors provide emergency care and resolve the issue of hospitalization.
An increase in temperature is an organism’s signal of danger, which should not be ignored. A serious cause for concern is hyperthermia in vulnerable groups of the population (children, the elderly, pregnant women). But even at a young age and in the absence of chronic diseases, when the temperature rises, you should seek medical help.