Fever

Front 1

Body temperature is controlled by

Back 1

The hypothalamus

Front 2

Which neurons regulate/ control b. temp. in the hypothalamus ?

Back 2

Neurons in both the preoptic anterior hypothalamus and the posterior hypothalamus receive two kinds of signals.

Front 3

Where does these two signals come from ?

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Skin - peripheral nerves that transmit information from warmth/cold receptors in the skin
Blood - Temperature of the blood bathing the region.

Front 4

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These two types of signals are integrated by the thermoregulatory center of the hypothalamus to maintain normal temperature.

Front 5

Dynamics of heat production in a neutral temperature environment

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The metabolic rate of humans produces more heat than is necessary to maintain the core body temperature in the range of 36.5–37.5°C (97.7–99.5°F)

Front 6

A normal body temperature is maintained ordinarily, despite

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environmental variations,

.During a febrile illness, the diurnal variation usually is maintained, but at higher, febrile levels.

Front 7

how does hypothalamic thermoregulatory center balance / maintain heat ?

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excess heat production derived from metabolic activity in muscle and the liver with heat dissipation from the skin and lungs.

Front 8

According to studies of healthy individuals 18–40 years of age,

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the mean oral temperature is 36.8° ± 0.4°C (98.2° ± 0.7°F), with low levels at 6 a.m. and higher levels at 4–6 p.m.

Front 9

Body temperature values defining the 99th percentile for healthy individuals

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The maximum normal oral temperature is 37.2°C (98.9°F) at 6 a.m. and 37.7°C (99.9°F) at 4 p.m.

Front 10

In light of these studies an a.m temperature or a p.m temperature defining fever

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>37.2°C (>98.9°F) >37.7°C (>99.9°F)

Front 11

daily variation

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fluctuations that occur between one day and the next

Front 12

The normal daily temperature variation is typically

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0.5°C (0.9°F)

Front 13

However, in some individuals recovering from a febrile illness, this daily variation can be as great as

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1.0°C.

Front 14

The daily temperature variation appears to be fixed in

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early childhood;

Front 15

reduced ability to develop fever, with only a modest fever even in severe infections.

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elderly individuals

Front 16

Neutral thermal/temperature environment

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an environment created by any method or apparatus to maintain the normal body temperature to minimize oxygen consumption and caloric expenditure, such as in an incubator or Isolette for a premature, sick, or low-birth weight infant

Front 17

Rectal temperatures are generally how much higher than oral readings ?

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0.4°C (0.7°F)

Front 18

The lower oral readings are probably attributable to

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mouth breathing, which is a factor in patients with respiratory infections and rapid breathing.

Front 19

What closely reflects core temperature ?

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Lower-esophageal temperatures

Front 20

Tympanic membrane (TM) thermometers measure

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radiant heat from the tympanic membrane and nearby ear canal and display that absolute value (unadjusted mode) or a value automatically calculated from the absolute reading on the basis of nomograms relating the radiant temperature measured to actual core temperatures obtained in clinical studies (adjusted mode).

Front 21

(Studies in adults with TM thermometers show that) Readings are lower with adjusted-mode TM thermometers and that unadjusted-mode TM values are

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0.8°C (1.6°F) lower than rectal temperatures.

Front 22

In women who menstruate, the a.m. temperature is

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generally lower in the 2 weeks before ovulation; it then rises by 0.6°C (1°F) with ovulation and remains at that level until menses occur.

Front 23

other conditions affecting body temperature

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Postprandial state elevate temp.

Pregnancy and endocrinologic dysfunction also affect body temperature.

Front 24

Normal daily/diurnal body/core temperature range

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Is the normal range of body/core temperature

Front 25

Fever is

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an elevation of body temperature that exceeds the normal daily variation and occurs in conjunction with an increase in the hypothalamic set point [e.g., from 37°C to 39°C (98.6°F to 102.2°F)].

Front 26

Hypothalamus - the thermoregulatory center

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Human thermostat

Front 27

This shift of the set point from "normothermic" to febrile levels very much resembles

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the resetting of the home thermostat to a higher level to raise the ambient temperature in a room.

Front 28

Once the hypothalamic set point is raised,

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neurons in the vasomotor center are activated and vasoconstriction commences.

Front 29

The individual first notices vasoconstriction in the hands and feet.

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Shunting of blood away from the periphery to the internal organs essentially decreases heat loss from the skin, and the person feels cold.

Front 30

For most fevers body temperature increases by

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body temperature increases by 1°–2°C (33.8°–35.6°F).

Front 31

Shivering

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increases heat production from the muscles

Front 32

Nonshivering

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heat production from the liver also contributes to increasing core temperature.

Front 33

Opposite of heat conservation mechanisms

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Heat production mechanisms

Front 34

Shivering is not required

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if heat conservation mechanisms raise blood temperature sufficiently

Front 35

Behavioral adjustments in humans

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Putting on more clothing or bedding to help raise body temperature by decreasing heat loss.

Front 36

Heat conservation mechanism and heat production mechanism

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Vasoconstriction, shivering and increased nonshivering thermogenesis.

Front 37

Maintain the temperature of the blood bathing the hypothalamic neurons that match the new thermostat setting.

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Heat conservation and production mechanisms.

Front 38

Hypothalamic thermoregulation

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Fever > increased hypothalamic set point to febrile set point > heat conservation and production mechanisms to reach or match set point > antipyretics or infection clears > as a response set point reset decreases > vasodilation and sweating to reach or match set point.

Front 39

Behavioral changes to facilitate heat loss

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Removal of clothing

Front 40

Blood temperature at the hypothalamic level

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Is equivalent to the body core temperature

Front 41

Hyperpyrexia

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A fever of >41.5°C (>106.7°F)

Front 42

Pathological causes of hyperpyrexia

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Severe infections and

most commonly CNS hemorrhages

Front 43

Natural "thermal ceiling"

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41.1°C (106°F)

Front 44

Neuropeptides functioning as central antipyretics

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In the preantibiotic era, fever due to a variety of infectious diseases rarely exceeded , and this has been speculated to be the natural "thermal ceiling" .

Front 45

In rare cases, the hypothalamic set point is elevated as a result of

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local trauma, hemorrhage, tumor, or intrinsic hypothalamic malfunction.

Front 46

Hypothalamic fever

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Used to describe elevated temperature caused by abnormal hypothalamic function. However, most patients with hypothalamic damage have subnormal, not supranormal, body temperatures.

Front 47

Hyperthermia also called

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Heat stroke

Front 48

Hyperthermia is characterized/ unique/ distinct by

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An uncontrolled increase in body temperature more than the body's ability to lose heat.

(compared with fever where setting of the hypothalamic thermoregulatory center is unchanged)

Front 49

Mechanisms causing dangerously high internal temp. or hyperthermia

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Exogenous heat exposure and endogenous heat production

Front 50

Excessive heat production can easily cause hyperthermia

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despite physiologic and behavioral control of body temperature. For example, work or exercise in hot environments can produce heat faster than peripheral mechanisms can lose it.

Front 51

Heat stroke in association with a warm environment may be categorized as

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exertional or nonexertional.

Front 52

Exertional heat stroke typically occurs in

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individuals exercising at elevated ambient temperatures (warm weather) and/or humidity.

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Dissipate

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To cause to lose (energy, such as heat) irreversibly.

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In a dry environment and at maximal efficiency

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Sweating can dissipate ~ 600 kcal/h, requiring the production of >1 L of sweat

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Dissipation of kcal/hour

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Medically saying heat loss.

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Conditions that may precipitate exertional heat stroke.

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Even in healthy individuals, dehydration or the use of common medications (e.g., over-the-counter antihistamines with anticholinergic side effects)

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Nonexertional heat stroke

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Typically occurs in either very young or elderly individuals, particularly during heat waves.

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Causes of nonexertional heat stroke

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The elderly, the bedridden, persons taking anticholinergic or antiparkinsonian drugs or diuretics, and individuals confined to poorly ventilated and non-air-conditioned environments are most susceptible.

Front 59

Drug-induced hyperthermia has become increasingly common as a result of the increased use of

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prescription of psychotropic drugs and illicit drugs.

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Prescription psychotropic drugs

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monoamine oxidase inhibitors (MAOIs), tricyclic antidepressants, and amphetamines

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Illicit drugs

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phencyclidine (PCP), lysergic acid diethylamide (LSD), methylenedioxymethamphetamine (MDMA, "ecstasy"), or cocaine.

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LSD

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Lysergic acid diethylamide

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PCP

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Phencyclidine

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Ecstasy, MDMA

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methylenedioxymethamphetamine

Front 65

Malignant hyperthermia

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occurs in individuals with an inherited abnormality of skeletal-muscle sarcoplasmic reticulum that causes a rapid increase in intracellular calcium levels in response to halothane and other inhalational anesthetics or to succinylcholine.

Often fatal.

Front 66

Features of malignant hyperthermia

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Elevated temperature, increased muscle metabolism, muscle rigidity, rhabdomyolysis, acidosis, and cardiovascular instability develop within minutes.

Front 67

The neuroleptic malignant syndrome

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This disorder appears to be caused by the inhibition of central dopamine receptors in the hypothalamus, which results in increased heat generation and decreased heat dissipation.

Front 68

features of neuroleptic syndrome

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use of neuroleptic agents or the withdrawal of dopaminergic drugs and is characterized by "lead-pipe" muscle rigidity, extrapyramidal side effects, autonomic dysregulation, and hyperthermia.

Front 69

neuroleptic agents

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antipsychotic phenothiazines, haloperidol, prochlorperazine, metoclopramide

Front 70

The serotonin syndrome

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seen with selective serotonin uptake inhibitors (SSRIs), MAOIs, and other serotonergic medications,

Front 71

How is neuroleptic malignant syndrome distinct from the serotonin syndrome ?

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has many features that overlap with those of the neuroleptic malignant syndrome (including hyperthermia) but may be distinguished by the presence of diarrhea, tremor, and myoclonus rather than lead-pipe rigidity.

Front 72

Causes of hyperthermia syndrome

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Heat stroke (exertional and non-exertional), drug-induced hyperthermia, neuroleptic malignant syndrome, serotonin syndrome, malignant hyperthermia endocrinopathy, CNS damage.

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Endocrinopathies causing hyperthermia syndrome

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Thyrotoxicosis and pheochromocytoma

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CNS damage causing hyperthermia syndrome

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Cerebral hemorrhage, status epilepticus, hypothalamic injury.