Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Chapter 10 Alterations in Temperature Regulation
Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Thermoregulation Skin temperature: reflection of the surface temperature of the body, relatively unreliable Core body temperature: reflection of the balance between heat gain and heat loss by the body The hypothalamus: the thermal control center –Receives information from peripheral and central thermoreceptors and compares it with its temperature set point –Directs cooling or warming mechanisms
Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Methods of Obtaining Core Temperature From a rectal temperature From the esophagus using a flexible thermometer From a pulmonary artery catheter that is used for thermodilution measurement of cardiac output From a urinary catheter with a thermosensor that measures the temperature of urine in the bladder
Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Factors Affecting Core Temperature Vasoconstriction and shivering A decrease in temperature by vasodilation Sweating Metabolism Fever
Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Heat Loss Occurs through transfer of body core heat to the surface through the circulation Methods of heat loss –Radiation –Conduction –Convection –Evaporation
Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Physiology of a Fever The pyrogen activates the hypothalamus to induce changes in its set point via the second messenger cyclic adenosine monophosphate (cAMP). –Thermostatic set point is increased. –Initiation Shivering Vasoconstriction Fever is established.
Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Pyrogens Exogenous or endogenous substances that produce fever –Exogenous pyrogens are derived from outside the body. Bacterial products, bacterial toxins, or whole microorganisms –Exogenous pyrogens induce host cells to produce fever-producing mediators. Interleukin-1, interleukin-6, and tumor necrosis factor
Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Araya has contracted a bacterial infection. As a result of the infection, his core body temperature has risen to 39°C. The increase is most likely due to __________. −A. exogenous pyrogen −B. endogenous pyrogen −C. the immune system
Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer A. exogenous pyrogen Rationale: Bacterial cell wall products will cause the hypothalamus to increase the body’s set temperature in an attempt to slow the bacterial replication.
Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins The Four Stages of Fever Prodrome –Mild headache, fatigue, malaise, fleeting pains Chill –Uncomfortable sensation of being chilled, shaking Flush –Cutaneous vasodilation, skin warm and flushed Defervescence –The initiation of sweating
Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Common Manifestations of Fever Anorexia Myalgia Arthralgia Fatigue
Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Patterns of Fever Intermittent –Temperature returns to normal at least once every 24 hours. Remittent –Temperature does not return to normal and varies in either direction.
Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Patterns of Fever (cont.) Sustained or Continuous –The temperature remains above normal with minimal variations. Recurrent or Relapsing –There is one or more episodes of fever as long as several days with one or more days of normal temperature between episodes.
Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Elderly Febrile Response Mechanisms for the blunted fever response –Disturbance in sensing by the hypothalamus –Alterations in release of endogenous pyrogens –Failure to elicit responses Vasoconstriction of skin vessels Increased heat production Shivering
Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Methods of Fever Treatment Modifications of the external environment intended to increase heat transfer from the internal to the external environment Support of the hypermetabolic state that accompanies fever Protection of vulnerable body organs and systems Treatment of the infection or condition causing the fever
Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Fever and Heart Rate 1°C rise in temperature produces a 15 beats/minute increase in heart rate. Most persons respond to an increase in temperature with an appropriate increase in heart rate.
Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Fever and Heart Rate (cont.) The observation that a rise in temperature is not accompanied by the anticipated change in heart rate can provide useful information about the cause of the fever. –No increase in HR Legionnaire disease, drug fever –More increase than expected Hyperthyroidism, pulmonary emboli
Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Question One reason why fever has a systemic effect on the body due to which of the following? −A. Increased heart rate −B. Increased fluidity of the blood −C. Decreased viscosity of blood −D. Increased permeability of the blood–brain barrier
Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer A. Increased heart rate Rationale: A 1°C increase in temperature will result in a 15 beats/minute increase in heart rate.
Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Differentiation Between Fever and Hyperthermia Fever –Upward displacement of the thermostatic set point of the thermoregulatory center in the hypothalamus Hyperthermia –Set point is unchanged. –Mechanisms that control body temperature are ineffective during situations when heat production outpaces the ability of the body to dissipate that heat.
Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Hyperthermia Definition –An increase in body temperature that occurs without a change in the set point of the hypothalamic thermoregulatory center Occurrence –When the thermoregulatory mechanisms are overwhelmed by heat production, excessive environmental heat, or impaired dissipation of heat
Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Hyperthermia (cont.) Manifestations –Heat cramps, heat exhaustion, heatstroke, drug fever, malignant hyperthermia, neuroleptic malignant syndrome
Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Manifestations of Fever Increases in the metabolic rate Increases in oxygen demands Use of body proteins as an energy source
Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Hyperthermia will manifest as which of the following? −A. Dilation of the pupils −B. Decreased respiratory rate −C. Cramps −D. Weak and irregular pulse −E. Stupor
Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer C. Cramps Rationale: Cramps will result due to changes in cell membrane permeability.
Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins PFAPA Syndrome Periodic Fever Aphthous (small ulcerative stomatitis) Pharyngitis Adenopathy (cervical) –Occurring every 21 to 28 days
Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Fever in the Elderly Even slight elevations in temperature may indicate serious infection or disease, most often caused by bacteria. This is because the elderly often have a lower baseline temperature, and although they increase their temperature during an infection, it may fail to reach a level that is equated with significant fever.
Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Drug-Related Fever Versus Infectious Fever Drug fever –Interfere with heat dissipation –Alter temperature regulation –Direct pyrogen –Cause tissue injury –Induce an immune response Infectious fever –Exogenous pyrogens Bacterial by- products Stimulation of inflammatory molecules
Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Malignant Hyperthermia Autosomal dominant metabolic disorder Heat generated by uncontrolled skeletal muscle contraction can produce severe and potentially fatal hyperthermia. –Inappropriate Ca 2+ release Also results in hypermetabolism Triggered by stresses or general anesthetic agents
Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Neuroleptic Malignant Syndrome Caused by psychotropic drugs that block dopamine receptors in the basal ganglia and hypothalamus Hyperthermia –Alterations in the function of the hypothalamic thermoregulatory center caused by decreased dopamine levels or –Uncontrolled muscle contraction like that occurring with anesthetic-induced malignant hyperthermia
Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Hypothermia Definition: a core temperature (i.e., rectal, esophageal, or tympanic) less than 35°C Persons at risk –Infants –Elderly and inactive persons living in inadequately heated quarters –Malnourished persons –Persons using alcohol and sedative drugs –Persons with certain diseases
Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Signs and Symptoms of Hypothermia Poor coordination, stumbling Slurred speech Irrationality and poor judgment Amnesia Hallucinations Blueness and puffiness of the skin
Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Signs and Symptoms of Hypothermia (cont.) Dilation of the pupils Decreased respiratory rate Weak and irregular pulse Stupor
Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Treatment of Hypothermia Rewarming –Passive rewarming –Active total rewarming –Active core rewarming Support of vital functions Prevention and treatment of complications
Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Infantile Hypothermia Infantile hypothermia –High ratio of surface area to body mass Surgical hypothermia –While many other operative cases that undergo general and regional anesthesia experience unintentional hypothermia
Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins Signs of Toxicity in Infants Lethargy Poor feeding Hypoventilation Poor tissue oxygenation Cyanosis