Main types of temperature curves
Depending on the daily variation range, four classic types of charts are distinguished:
- Continuous (febris continua): the daily variation stays within 1 °C. Characteristic of diseases such as lobar (croupous) pneumonia and typhoid fever.
- Remittent or lax (febris remittens): fluctuations exceed 1 °C, while values never drop to normal. Often accompanies various viral infections.
- Intermittent (febris intermittens): the range is 1–2 °C. The main feature is a short-term return of temperature to normal for a few hours followed by a new spike.
- Hectic or exhausting: a severe variant with sharp repeated daily fluctuations of more than 2–3 °C and rapid drops. Found in sepsis, severe tuberculosis, and purulent processes (e.g., liver or lung abscesses).
Classification by heating level
According to the degree of temperature elevation, fever is divided into four groups:
- Subfebrile (mild) — from normal to 38 °C.
- Febrile (moderate) — from 38 to 39 °C.
- Pyretic (high) — from 39 to 41 °C.
- Hyperpyretic (excessive) — above 41 °C.
Further increase (above 41–42 °C) is blocked by the endogenous antipyretics system, which prevents death of the organism.
Temperature drop stage (st. decrementi)
When the primary pyrogen (e.g., microbes or non-infectious agents) is eliminated, the production of leukocyte cytokines drops. In the cold-sensitive neurons of the anterior hypothalamus, the biochemical cascade is inhibited: the activity of phospholipase A2 and cyclooxygenase decreases, and the levels of prostaglandin E2 and cAMP drop. Neuronal excitability decreases, and the «set point» (set point) of the thermoregulation center returns to the normal range.
The temperature drop is of two types:
- Lytic drop (lysis): slow, takes several days. This is the most favorable and frequent scenario for the body.
- Critical drop (crisis): rapid fall within a few hours. Accompanied by a sharp activation of heat dissipation — profuse sweating and pronounced dilation of skin arterioles. Dangerous due to a drop in blood pressure and the development of collapse caused by a sharp decrease in venous return to the heart.
Metabolic shifts
Fever requires colossal energy expenditures to supply actively working organs with oxygen and substrates. Under the influence of the sympathoadrenal, hypothalamo-pituitary-adrenal, and thyroid systems, the basal metabolic rate naturally increases. The Q10 effect also comes into play — the direct acceleration of chemical reactions upon thermal stimulation.
- Carbohydrate metabolism: glycogenolysis and glycolysis sharply increase. Glucose oxidation proceeds actively, but its energy efficiency remains low.
- Lipid metabolism: due to the deficit of energy from carbohydrates, a compensatory powerful lipolysis is triggered. This is especially pronounced during the prolonged second stage of fever. Enhanced fat breakdown leads to the accumulation of ketone bodies and an increase in acidosis.
- Protein metabolism: proteolysis (protein breakdown) intensifies, which clinically manifests as a negative nitrogen balance.
Briefly: answers to topical questions
What other types of temperature curves exist besides continuous, remittent, intermittent, and hectic?
The cited sources additionally describe inverse, irregular, and undulating fever.
- Inverse fever (febris inversa) — disruption/inversion of the daily circadian rhythm of thermoregulation: morning body temperature is higher than evening temperature.
- Irregular fever — absence of any pattern in temperature fluctuations; chaotic rises and falls are visible on the chart.
- Undulating fever — in septicopyemia, periods of subfebrile temperature are replaced by rises up to 39–40 °C.
What stages of fever exist prior to the temperature drop stage (st. decrementi)?
Before the temperature drop stage, the first and second stages of the febrile reaction develop sequentially.
- Temperature rise (stadium incrementi) — the first stage, which is caused by a shift in the ratio between heat production and heat loss (most commonly, an increase in heat production with a simultaneous decrease in heat loss).
- Elevated temperature (fastigium, stadium fastigii) — the second stage of fever, characterized by the maintenance of elevated body temperature.
How does water-electrolyte metabolism change at different stages of fever?
Changes in water and ion balance depend on the stage of the febrile reaction.
- Stage I and the beginning of Stage II of fever — increased diuresis. Mechanism: activation of sympathoadrenal influences → increase in filtration pressure.
- Subsequent development of fever — decreased diuresis and water retention in tissues. Mechanism: increased aldosterone secretion.
How to remember curve types: Continuous — Pneumonia (fluctuations up to 1 °C); Remittent — Difference greater than 1 °C (viruses); Intermittent — Disappears for a time (normalizes); Hectic — Pus and sepsis (spikes of 2–3 °C).
Class and exam questions
How does a lytic temperature drop differ from a critical one?
Lysis is a gradual drop in temperature over several days, which is favorable for the patient. Crisis is a sharp decrease within a couple of hours, capable of provoking vascular collapse due to arteriolar dilation and profuse sweating.
Why do people lose weight during a fever?
The body reorganizes its metabolism: carbohydrates burn quickly and inefficiently, so intensive fat breakdown (lipolysis) and protein breakdown (proteolysis) are triggered. This leads to a negative nitrogen balance and weight loss.
What protects the body from overheating above 42 °C?
This function is performed by endogenous antipyretics (glucocorticoids, anti-inflammatory cytokines, nitric oxide). They suppress the synthesis of pyrogens and limit the production of prostaglandin E2 in the thermoregulation center.
What else to study on this topic
- Mechanisms of action of endogenous antipyretics (glucocorticoids, neuropeptides, cytokines).
- The role of nitric oxide (NO) and PGD2 derivatives in the negative feedback mechanism.
- Pathogenesis of the «set point» shift in cold-sensitive neurons of the anterior hypothalamus.
- Causes of acidosis and negative nitrogen balance development against the background of fever.
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