1. Fever is defined as an elevation of body temperature above normal circadian variation due to a change in the thermoregulatory center located in the hypothalamus. 2. Physiological variations in temperature include chills or rigors that occur when the thermostat in the hypothalamus is suddenly reset to a higher temperature due to pyrogens. 3. There are different patterns of fever including continuous, remittent, intermittent, and relapsing fever which are characterized by differences in temperature fluctuations and touching of the baseline temperature.

1. PRESENTED BY : ANSHUMAN BAG
B.D.S 3RD YEAR.

2. It is an elevation of body temperature above the normal circadian
variation as a result of the change in the thermoregulatory centre,
located in the hypothalamus.
 Maximal Normal Oral Temperature
At 6.00 AM : 37⁰C (98.6⁰F)
At 6.00 PM : 37.6⁰C (99.6⁰F)
 The normal body temperature is more towards the evening
because of increased BMR and increased skeletal muscle activity.
 Rectal temperature is 0.6⁰C(1⁰F) higher than oral temperature.
 Oral temperature is 0.6⁰C(1⁰F) higher than temperature recorded
in axilla.

3. Physiological Variation of Temperature
 Chill is a sensation of cold that occurs in most fevers .
 Rigor is a profound chill with piloerection associated with
teeth chattering and severe shivering. Chills or rigors occur
when the thermostat , situated in the hypothalamus, is
suddenly reset to a higher temperature due to presence of
pyrogens.
 The body temperature then tends to rise to the newly reset
level in the thermostat by conserving heat in the body by
cutaneous vasoconstriction and involuntary contraction of
skeletal muscles, experienced as chills or rigors.
 Chills or rigors may be commonly seen with bacterial,
rickettsial, protozoal, influenzal infections.
 With every 1⁰F rise of temperature, above 100 ⁰F, the pulse
rate increases by 10, the respiratory rate by 4, and BMR by
7.

4. PATHOGENESIS OF FEVER

5.  Fever with Relative Bradycardia
 Typhoid Fever
 Meningitis
 Viral fever(Influenza)
 Brucellosis
 Leptospirosis
 Drug induced fever.
 Fever with Exanthems
Rash appear on the following day of fever:
 First Day - Chicken Pox
 Second Day - Scarlet Fever
 Third Day – Pox(Small Pox)
 Fourth Day - Measles

6.  Fifth Day – Typhus
 Sixth Day – Dengue
 Seventh Day – Enteric Fever
MNEMONICS:
Very – Varicella(Chicken Pox)
Sick – Scarlet Fever
Person – Small Pox
Must - Measles
Take - Typhus
Double - Dengue
Eggs – Enteric Fever

7.  Febrile Convulsions
It occurs in infants and children less than 5 years old.
Convulsions are common at temperatures more than 40 ⁰C.
It may not be a sign of cerebral disease.
Normal 37⁰C to 37.6⁰C(98.6⁰F to 99.6⁰F)
Febrile Above 37.8⁰C
Hyperpyrexia >41⁰C(> 106⁰F)
Hypothermia < 35⁰C(<95⁰F)

8.  Continuous Fever
The temperature remains elevated above the normal
without touching the baseline and the fluctuation does not
exceed 0.6⁰C, e.g. lobar pneumonia, infective endocarditis ,
enteric fever.
 Remittent Fever
The temperature fluctuation exceeds 0.6⁰C, but without
touching the baseline.
 Intermittent Fever
The elevated temperature touches the baseline in between.
In hectic or septic type of intermittent fever, the diurnal
variation is extremely large, as occurs in septicaemia.
Quotidian fever is a hectic fever occurring daily.

9.  Relapsing Fever
Febrile episodes are separated by normal temperature for
more than one day, e.g. Borrelia infection, rat bite fever.

10.  Drug Fever
 It is prolonged fever and may belong to any febrile pattern.
 There is relative bradycardia and hypotension.
 Pruritis, skin rash and arthralgia may occur.
 It begins 1 to 3 weeks after the start of the drugs and
persists 2 to 3 days after the drug is withdrawn.
 Eosinophilia may be present.
Important commonly used drugs producing fever are
Sulphonamide, Penicillins, Iodides, Anti-TB Drugs,
Anticonvulsants ,etc.
Digoxin does not cause drug fever.

11.  Hyperpyrexia
It is an elevation of body core temperature, above
41⁰C(106⁰F),due to inadequate dissipation of heat. It is a
medical emergency, since they are prone for sudden cardio
respiratory arrest.
Causes of Hyperpyrexia:
 Pontine hemorrhage
 Rheumatic Fever
 Meningococcal meningitis
 Septicaemia
 Cerebral malaria
It is treated with parenteral anti-pyretics to set the elevated
thermostat set point to a lower level. Chlorpromazine is
sometimes helpful in reducing the body temperature.

12. Causes of Hyperthermia without Elevated Resetting of Thermostat
Hyperthermia is characterised by an unchanged setting of the
thermoregulatory centre with an uncontrolled increase in body
temperature that exceeds body’s ability to lose heat. The causes are:
 Heat Stroke
 Malignant Hyperthermia
 Neuroleptic Malignant Syndrome
 Drug induced: Amphetamines, MAO inhibitors, Tricyclic
antidepressants, Atropine
 Thyrotoxicosis
 Pheochromocytoma
 Hypothalamic Fever
 Serotonin Syndrome
 Central nervous system damage