basics of fever, thermoregulation, definition, fever vs hyperthermia vs hyperpyrexia, hypothermia, fever of unknown origin, heat related illness.

1. “ALTERATIONS IN BODY
TEMPERATURE”
Dr Ankur Sharma
MD Internal Medicine
Assistant Professor, Department of Medicine
L.N. Medical College and research Centre.

2. THERMOREGULATION
Heat storage = metabolism - work - evaporation ± radiation ±
conduction ± convection.
Where
• Metabolism refers to the chemical reactions occurring within the body that
produce heat. During exercise, the working muscle liberates large amounts
of heat.
• Work is the external work done.
• Evaporation is the heat loss to environment as water vaporized from the
respiratory passages and skin surface.

3. • Radiation is the electromagnetic radiation (heat) transferred to bodies not in
contact, including the ultraviolet light radiation from the sun, which
penetrates through to the surface of the earth, and the infrared radiation
from the body.
• Conduction is the movement of heat to/from the body directly to objects in
contact with the body. Usually, the amount of heat exchanged in this way is
minimal.
• Convection is the transfer of heat to a moving gas or liquid. When a body is
warm, the air molecules that make contact with the body will be warmed,
reducing their density, which causes the molecules to rise and be replaced
with cooler air. Convective heat exchange is increased by movement of the
body in air or water or movement of air or water across the skin.

6. NORMAL CORE BODY TEMPERATURE.
Thermoregulation aims to maintain the core body temperature in
the range of
36.5–37.5°C (97.7–99.5°F).

7. FEVER VS HYPERPYREXIA VS
HYPERTHERMIA.
“a.m. temperature of >37.2°C (>98.9°F) or
a p.m. temperature of >37.7°C (>99.9°F) would define a
fever.”
The normal daily temperature variation, also called the
circadian rhythm, is typically 0.5°C temperature
variation, also called the circadian rhythm, is typically
0.5°C (0.9°F).

8. CIRCADIAN RHYTHM

9. In women who menstruate, the a.m. temperature is generally lower
during the 2 weeks before ovulation; it then rises by ~0.6°C (1°F) with
ovulation and stays at that level until menses occur. During the luteal
phase, the amplitude of the circadian rhythm remains the same.
The daily temperature variation appears to be fixed in early childhood;
in contrast, elderly individuals can exhibit a reduced ability to develop
fever, with only a modest fever even in severe infections.

10. Fever is 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).
A fever of >41.5°C (>106.7°F) is called hyperpyrexia. This extraordinarily high
fever can develop in patients with severe infections but most commonly occurs
in patients with central nervous system (CNS) hemorrhages.
The term hypothalamic fever is sometimes used to describe elevated
temperature caused by abnormal hypothalamic function. However, most
patients with hypothalamic damage have subnormal, not supranormal, body
temperatures.

11. FEVER VS HYPERTHERMIA
FEVER
• Hypothalamic set point is
changed
• Pyrogen mediated hence
antipyretics used in
treatment.
HYPERTHERMIA
• Not changed
• Not mediated by pyrogens.
• Problem with Exogenous heat
exposure and endogenous heat
production are two mechanisms

12. CORE VS PERIPHERAL BODY TEMPERATURE
Core temperature – Lower esophageal , tympanic membrane ,
rectal temperature.
“Rectal temperatures are generally 0.4°C (0.7°F) higher than oral
readings.”
Temperature : Rectal>Oral>Axillary

13. PATHOGENESIS OF FEVER
Receptors of PGE2 are of 4 types. EP-3 is essential for
fever.

14. “Toll-like receptors and are similar in many ways to IL-1
receptors. IL-1 receptors and Toll-like receptors share the
same signal-transducing mechanism”
“Cytokines produced in the brain may account for the
hyperpyrexia of CNS hemorrhage, trauma, or infection. Viral
infections of the CNS induce microglial and possibly
neuronal production of IL-1, TNF, andIL-6. Therefore,
cytokines produced in the CNS can raise the hypothalamic
set point, bypassing the circumventricular organs.”

15. TYPES OF FEVER

17. STAGES OF FEVER

18. CHILLS VS RIGOR
Chills – subjective sensation of
cold.
Rigor – shivering – what is
visible to a physician.

19. FEVER ASSOCIATED WITH INFLAMMATORY
SYNDROMES.

20. DRUG INDUCED FEVER
• Anticholinergic agents - impair sweating
• Calcium channel blockers, beta blockers, and various stimulants also inhibit
sweating by reducing peripheral blood flow.
• Malignant hypertension after general anesthesia
• Neuroleptic malignant syndrome can be triggered by certain antipsychotic
medications, including selective serotonin reuptake inhibitors.
• Drug-induced fever, including DRESS (drug reaction with eosinophilia and systemic
symptoms) - is often accompanied by eosinophilia and also by lymphadenopathy.

21. More common causes of drug-induced fever are
• allopurinol,
• carbamazepine, lamotrigine, phenytoin,
• sulfasalazine,
• furosemide,
• antimicrobial drugs (especially sulfonamides, minocycline, vancomycin, -lactam
antibiotics, and isoniazid),
(I saw, beta on phone in mini van)
• some cardiovascular drugs (e.g., quinidine), and some antiretroviral drugs (e.g.,
nevirapine).

22. FEVER WITH RASH
Very Sick Person Must Take Double Tea
Day 1 – varicella
Day 2 – scarlet fever
Day 3 – pox ( small pox)
Day 4 - measles
Day 5 – typhus ( scrub typhus)
Day6 - dengue
Day 7 – typhoid.

23. FEVER ASSOCIATION WITH PR, RR, OXYGEN
CONSUMPTION.
With every 1°F rise of temp >100 F
i. Pulse rate increases 10,
ii. Respiratory rate by 4
iii. BMR by 7
iv. Oxygen consumption increases by 13%.

24. RELATIVE BRADYCARDIA
1. Typhoid fever
2. Yellow fever
3. Meningitis
4. Viral fever (Influenza)
5. Brucellosis
6. Leptospirosis
7. Drug induced fever

25. HOW DOES ANTIPYRETICS WORK?

26. HEAT RELATED ILLNESS
Wet-bulb globe temperature is a commonly used index to assess
the environmental heat load. This calculation considers the
• ambient air temperature,
• the relative humidity,
• and the degree of radiant heat.

27. When there is an excessive heat load, unacclimated individuals can develop a variety
of heat-related illnesses. Heat waves exacerbate the mortality rate, particularly among
the elderly and among persons lacking adequate nutrition and access to air-
conditioned environments.
Secondary vascular events, including cerebrovascular accidents and myocardial
infarctions, occur at least 10 times more often in conditions of extreme heat.

28. MINOR HEAT-EMERGENCY SYNDROMES
• Heat Edema
• Miliaria rubra (lichen tropicus/ prickly heat)
• Heat syncope (exercise associated syncope )
• Hyperventilation tetany.

29. HEAT CRAMPS
Aka exercise-associated muscle cramps are intermittent, painful, and involuntary
spasmodic contractions of skeletal muscles.
They typically occur in an unacclimated individual who is at rest after vigorous exertion
in a humid, hot environment.
The typical patient with heat cramps is usually profusely diaphoretic and has been
replacing fluid losses with copious water or other hypotonic fluids.
In contrast, cramps that occur in athletes during exercise last longer, are relieved by
stretching and massage, and resolve spontaneously.

30. HEAT EXHAUSTION
The physiologic hallmarks of heat exhaustion—in contrast to
heatstroke—are the maintenance of thermoregulatory control
and CNS function. The core temperature is usually elevated but is
generally <40.5°C (<105°F)
1. Water depletion
2. Salt depletion
Mild neurologic and gastrointestinal influenza-like symptoms are
common. These symptoms may

31. HEAT STROKE
• Total loss of thermoregulatory function.
• Typical vital-sign abnormalities include tachypnea, various
tachycardias, hypotension, and a widened pulse pressure.
• Most important intervention is rapid cooling.

32. TYPES OF HEAT STROKE

33. COOLING STRATEGIES
Evaporative cooling is frequently the most practical and effective
technique. Cool water (15°C [60°F]) is sprayed on the exposed
skin while fans direct continuous airflow over the moistened
skin. Cold packs applied to the neck, axillae, and groin are useful
adjuncts.
Immersion cooling in ice-cold water is an alternative option in
EHS but can induce peripheral vasoconstriction and shivering.

34. PYREXIA OF UNKNOWN ORIGIN
FUO was originally defined by Petersdorf and Beeson in 1961 as
an illness of >3 weeks’ duration with fever of ≥38.3°C (≥101°F)
on two occasions and an uncertain diagnosis despite 1 week of
inpatient evaluation.
Two important changes
i. in-hospital evaluation requirement has been eliminated from
the definition.
ii. exclusion of immunocompromised patients,

35. Accordingly, FUO is now defined as follows:
1. Fever ≥38.3°C (≥101°F) on at least two occasions
2. 2. Illness duration of ≥3 weeks
3. 3. No known immunocompromised state
4. 4. Diagnosis that remains uncertain after a thorough
history-taking, physical examination, and the following
obligatory investigations: determination of erythrocyte
sedimentation rate (ESR) and C-reactive protein (CRP) level;
CBC, LFT, lactate dehydrogenase, creatine kinase, ferritin,
antinuclear antibodies, and rheumatoid factor; protein
electrophoresis; urinalysis; blood cultures (n = 3); urine
culture; chest x-ray; abdominal ultrasonography; and
tuberculin skin test (TST) or interferon γ release assay

36. HYPOTHERMIA
Unintentional drop in the body’s core temperature below 35°C
(95°F).
There are 2 types
1. Primary accidental hypothermia is a result of the direct
exposure of a previously healthy individual to the cold.
2. Secondary hypothermia which develops as a complication of a
serious systemic disorder or injury and has a very high
mortality.