Fever

The fever, pyrexia or febrile syndrome is a syndrome (set of signs and symptoms) that manifests generally, although not always, when a warm-blooded animal has a body temperature higher than that considered normal for its species and whose main clinical sign is hyperthermia. For example, in humans, it is equivalent to a temperature of 37.5 °C or higher.

In general, it is the organism's response to agents of an infectious nature (which is the most frequent) or to non-infectious causes (resorption toxins, lesions in certain nervous territories, etc.). Hyperthermia is the most common medical sign in infectious diseases. It should be noted that, semiologically speaking, fever or febrile syndrome are not synonymous with hyperthermia, since the latter term refers to a clinical sign, while fever is a syndrome that generally presents with the sign of hyperthermia.

Signs of fever

Signs of fever are:

• Circular disorders: Pulse increases in parallel with temperature; at each degree of temperature elevation there is an increase of 10-15 pulses per minute. Talk about it. dynamic fever when the pulse is strong; adynamic fever when the pulse is weak from the beginning and consecutive to heart depletion, and dissociated fever when there is no increase in pulses along with the increase in temperature.

• Blood pressure: An acute fever access is increased, but when the temperature is stabilized, it is usually normal or subnormal. When the central temperature rapidly increases there is peripheral vasoconstriction (the patient feels cold and has feverish tremors: this is the state of chill). At this time the body temperature rises because the heat produced exceeds widely the heat eliminated. The temperature at its maximum becomes a peripheral vasodilation (the individual feels heat and looks for fresh places, there is profuse sweat, muscle flacy and rapid temperature drop). At this time the loss of heat over production predominates.

• Respiratory disorders: The respiratory rate increases relative to the temperature increase (thermal polypnea).

• Digestive disorders: The secretions of the digestive system in general are diminished, as is gastrointestinal peristalism, since there is a tendency to constipation. There is also diminished or abolished appetite, but, instead, thirst increases.

• Humor disordersDuring the fever, the blood concentrates and decreases chloremia, as well as the excretion of chlorides and the amount of urine. This occurs even if chlorides are in sufficient quantities. And if it increases further, it is observed that they are easily held in the interstitial fluid. At the time of temperature drop, the blood is diluted, a polyuria occurs and there is a discharge of the retained chlorides.

There is also an increase in protein catabolism during fever with a greater excretion of urea, which is accentuated when the temperature drops. Also fat catabolism increases during fever. And when the diet does not provide enough carbohydrates, a tendency to acidosis occurs. In the urinalysis we verified an albumin called febrile.

• Sensor disorders: The individual is paranoid, delusional and in certain cases depressed.

• Facies: We observe what is called febril facies. Thus the febril subject presents an unliving expression, there is atonement and even sometimes delusion.

• Hypertermia: As mentioned above, it is the main sign of the fever, although not essential, and is an increase in body temperature above what is considered normal, and is caused by a physiopathological event (infection, inflammation). Do not confuse fever with hyperthermia. Fever is a mechanism present in several animals that acts as an adaptive response, helping the body to fight organisms that cause disease and arises in response to substances called pirogens that are derived from bacteria or viruses that invade the body, or that are produced by the cells themselves.

The normal temperature of the human body is between 35 and 37 °C. Fevers above 40.5 °C can threaten vital proteins, causing cellular stress, heart attack, tissue necrosis, paroxysmal seizures, and delirium.^{[citation needed]}

Due to children's underdeveloped immune systems, they are more prone to high fevers.^{[citation needed]}

Exogenous pyrogens

They are substances external to the human body. They can be microorganisms, products of microorganisms such as endotoxins released by gram (–) bacteria, or lipoteichoic acid or peptidoglycan from gram (+) bacteria; chemical agents (amphotericin, phenothiazides).

Endogenous pyrogens

• Endogenous pyrogens are cytokines that induce fever and include Interleukin-1 (IL-1), IL-6, IL-8, IL-12, macrophage-inflammatory protein-1 (MIP-1), interferon-g (IFN-g) and tumor necrosis factor (TNF).

• Polypeptides produced by a wide variety of host cells such as monocytes or macrophages, neoplastic cells that explain the existence of fever in cancers.

Endogenous pyrogens converge to a brain region that regulates fever, the preoptic area of previous hypothalamus (POA: preoptic area). Controvert mechanism, since endogenous pyrogens have to go through the hematoencephalic barrier which is impermeable to them. At least two routes are evidenced: active transport through the hematoencephalic barrier by specific carriers for cytokines; transfer of message where the hematoencephalic barrier has fenestrations, that is to say in the circumventricular organs sensorial particularly in the organum vasculosum laminae terminalis (OVLT).

But there are other alternative pathways: circulating cytokines induce the generation of BBB-permeable prostaglandin E2 (PGE-2) and perhaps prostaglandin F2a (PGF-2a), the most proximal putative mediator of fever, by endothelial cells of the cerebral or perivascular microvasculature such as microglia and meningeal macrophages.

Direct transmission to the POA of pyrogen messages via peripheral afferents (mostly vagal) activated by cytokines.

Clinical signs of fever

Home (cold or chilly state)

• Increased heart rate.
• Increased frequency and breathing depth.
• Tremors that are due to increased contritions and muscle-skeletal tension.
• Pale and cold skin due to vasoconstriction.
• Complaints of cold feeling.
• Cyanotic ungueal milks due to vasoconstriction.
• The appearance of “Hen’s skin” due to the contraction of the erecting muscles of the hair.
• Stop sweating.
• Increased body temperature.
• Loss of concentration.

Course

• A lack of chills.
• Skin that looks hot.
• Sensation of not being cold or heat.
• Pulse and respiratory rate increase.
• Increase of thirst.
• Dehydration from mild to severe.
• Light sleepiness, inability to rest, or delirium and seizures due to irritation of nerve cells.
• Herpetic lesions on the lips.
• Loss of appetite (if the fever is prolonged).
• Apathy, weakness and muscle aches due to protein catabolism.
• Deference (fever decline).
• The skin appears red and is hot.
• Sweating.

Fever levels

• Feb.: When axillary temperature is between 37.0 °C and 38 °C. (or when rectal temperature is between 38.0 °C and 39 °C). It is known colloquially in countries like Venezuela with the name heat or fog and in some regions of Spain as well distemplation ^{[chuckles]required]}.
• Fiber: When axillary temperature is between 38 °C and 40 °C. (or when rectal temperature is between 39 °C or 41 °C)
• Hyperpirexia: When axillary temperature is equal to or greater than 40 °C. (or when rectal temperature is equal to or above 41 °C)

In humans, temperatures above 41 °C are usually fatal.^{[citation needed]} Whenever we doubt a patient's axillary temperature, we can take a rectal temperature. The actual temperature of the patient will be the one indicated by the thermometer by subtracting 1 °C from the displayed temperature. For example, if a patient shows an axillary temperature and we doubt whether it is the correct temperature (we are going to put the case of a patient who presents signs and symptoms of fever but the thermometer shows us a temperature of 37 °C), then we will take the rectal temperature. If the thermometer indicates 39.5 °C, we will subtract 1 °C and that will be the indicative temperature (38.5 °C).

Causes

Fever is usually related to stimulation of the body's immune system. In this sense, it can be useful for the immune system to take advantage of infectious agents, making the human body less receptive to the replication of viruses and bacteria that are sensitive to temperature.

In addition to infections, the abuse of amphetamines and the withdrawal of a psychotropic substance in a person addicted to it, as well as the reception of heat emitted by industrial machinery or heat stroke, are causes of fever.

Reactions in humans to different body temperatures

Normal

• 36 °C: normal body temperature; this can range from 35.5 to 37 °C

Hot

• 37 °C (bladder): temperature above 37 °C but below 38 °C, for 24 hours
• 38 °C (fiever): there is sweat accompanied by blond, with tachycardias and dyspnea. Exhaustion may arise.
• 39 °C (moderate fever): the feeling of heat and weakness increases. Epileptics and children may suffer seizures at this point.
• 40 °C (urgency): dizziness, dizziness, weakness, dehydration, nausea, vomiting, headache and deep sweat.
• 41 °C: all the above most accentuated; there can also be confusion, hallucinations, delusions and drowsiness.
• 42 °C: besides the above, the subject may have paleness or blush. It can reach the coma, with hypertension or hypotension and a large tachycardia.
• 43 °C: Normally death occurs here or leaves various brain damage as sequelae, accompanied by continuous seizures and shock. There may be a cardiorespiratory strike.
• 44 °C: in most cases death occurs at 43 °C of temperature, however, there are some cases of people who have reached 44 °C of temperature.
• 45 °C: very few people have survived at 45 °C of temperature, as usually death occurs between 42 and 44 °C. There are usually severe brain damage, although there are cases of people who after reaching that temperature have led to a normal life.

Cold

• 35 °C: mildly low temperature although considered within the normal limit. The normal temperature of the human body ranges from 35.5 to 37 °C
• 34 °C (hypothermia): it is called hypothermia when the temperature is less than 35 °C. There is severe tremor, loss of movement capacity on fingers, cyanosis and confusion. There may be changes in behavior.
• 33 °C: moderate confusion, numbness, repflexia, progressive loss of tremor, bradycardia, dyspnea. The subject does not react to certain stimuli.
• 32 °C (moderate hypothermia): hallucinations, delirium, great confusion, very adored, even reaching the coma. The tremor disappears, the subject can even believe his temperature is normal. There is snatch, or the reflexes are very weak.
• 31 °C: There is a coma, it is very strange that you are aware. Absence of reflexes, severe bradycardia. There is a possibility that serious heart problems arise.
• 28 °C (urgency): severe heart alterations, can be accompanied by apnea and even appear or be dead.
• 26 to 24 °C or lower: here death usually occurs due to cardiorespiratory alterations, however, some patients have survived being apparently dead at temperatures below 24 °C.

Some types of fever