出典(authority):フリー百科事典『ウィキペディア(Wikipedia)』「2015/01/28 06:34:15」(JST)
An analog medical thermometer showing a temperature of 38.8 °C or 101.8 °F
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ICD-10 | R50 |
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ICD-9 | 780.6 |
DiseasesDB | 18924 |
MedlinePlus | 003090 |
eMedicine | med/785 |
MeSH | D005334 |
Fever (also known as pyrexia[1] or a febrile response) is defined as a body temperature above the normal range due to an increase in the temperature regulatory set-point. There is not a single agreed upon upper limit for normal temperature with sources using values between 37.5 and 38.3 °C (99.5 and 100.9 °F).[1][2] The increase in set-point triggers increased muscle tone and causes a feeling of cold resulting in greater heat production and efforts to conserve heat. This results in an increase in body temperature. When the set-point temperature returns to normal a person feels hot and may begin to sweat.
A fever can be caused by many medical conditions ranging from the not serious to potentially serious. This includes viral, bacterial and parasitic infections such as the common cold, urinary tract infections, meningitis, malaria and appendicitis among others.[3] Non infectious causes include vasculitis, deep vein thrombosis, side effects of medication, and cancer among others.[3]
A fever may be useful as a defense mechanism as the body's immune response can be strengthened at higher temperatures; however, there are arguments for and against the usefulness of fever, and the issue is controversial. With the exception of very high temperatures, treatment to reduce fever is often not necessary. Antipyretic medications such as ibuprofen or paracetamol can be effective at lowering the temperature, which may improve comfort.[4]
Fever is one of the most common medical signs. It differs from hyperthermia, in that hyperthermia is an increase in body temperature over the body's thermoregulatory set-point, due to excessive heat production or insufficient heat loss.[1]
Temperature classification | |
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Hypothermia | <35.0 °C (95.0 °F)[5] |
Normal | 36.5–37.5 °C (97.7–99.5 °F)[6] |
Fever | >37.5 or 38.3 °C (99.5 or 100.9 °F)[1][2] |
Hyperthermia | >37.5 or 38.3 °C (99.5 or 100.9 °F)[1][2] |
Hyperpyrexia | >40.0 or 41.5 °C (104.0 or 106.7 °F)[7][8] |
Note: The difference between fever and hyperthermia is the underlying mechanism. Different sources have different cuts offs for fever, hyperthermia and hyperpyrexia. |
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A wide range for normal temperatures has been found.[2] Fever is generally agreed to be present if the elevated temperature is caused by a raised set point and:
In healthy adult men and women, the range of normal, healthy temperatures for oral temperature is 33.2–38.2 °C (91.8–100.8 °F), for rectal it is 34.4–37.8 °C (93.9–100.0 °F), for tympanic membrane (the ear drum) it is 35.4–37.8 °C (95.7–100.0 °F), and for axillary (the armpit) it is 35.5–37.0 °C (95.9–98.6 °F).[10] Harrison's textbook of internal medicine defines a fever as a morning oral temperature of >37.2 °C (>98.9 °F) or an afternoon oral temperature of >37.7 °C (>99.9 °F) while the normal daily temperature variation is typically 0.5 °C (0.9 °F).[11]
Normal body temperatures vary depending on many factors, including age, sex, time of day, ambient temperature, activity level, and more. A raised temperature is not always a fever. For example, the temperature of a healthy person rises when he or she exercises, but this is not considered a fever, as the set-point is normal. On the other hand, a "normal" temperature may be a fever, if it is unusually high for that person. For example, medically frail elderly people have a decreased ability to generate body heat, so a "normal" temperature of 37.3 °C (99.1 °F) may represent a clinically significant fever.
The pattern of temperature changes may occasionally hint at the diagnosis:
A neutropenic fever, also called febrile neutropenia, is a fever in the absence of normal immune system function. Because of the lack of infection-fighting neutrophils, a bacterial infection can spread rapidly; this fever is, therefore, usually considered to require urgent medical attention. This kind of fever is more commonly seen in people receiving immune-suppressing chemotherapy than in apparently healthy people.
Febricula is an old term for a low-grade fever, especially if the cause is unknown, no other symptoms are present, and the patient recovers fully in less than a week.[14]
Hyperpyrexia is a fever with an extreme elevation of body temperature greater than or equal to 41.5 °C (106.7 °F).[15] Such a high temperature is considered a medical emergency as it may indicate a serious underlying condition or lead to significant side effects.[16] The most common cause is an intracranial hemorrhage.[15] Other possible causes include sepsis, Kawasaki syndrome,[17] neuroleptic malignant syndrome, drug effects, serotonin syndrome, and thyroid storm.[16] Infections are the most common cause of fevers, however as the temperature rises other causes become more common.[16] Infections commonly associated with hyperpyrexia include roseola, rubeola and enteroviral infections.[17] Immediate aggressive cooling to less than 38.9 °C (102.0 °F) has been found to improve survival.[16] Hyperpyrexia differs from hyperthermia in that in hyperpyrexia the body's temperature regulation mechanism sets the body temperature above the normal temperature, then generates heat to achieve this temperature, while in hyperthermia the body temperature rises above its set point due to an outside source.[15]
Hyperthermia is an example of a high temperature that is not a fever. It occurs from a number of causes including heatstroke, neuroleptic malignant syndrome, malignant hyperthermia, stimulants such as amphetamines and cocaine, idiosyncratic drug reactions, and serotonin syndrome.
A fever is usually accompanied by sickness behavior, which consists of lethargy, depression, anorexia, sleepiness, hyperalgesia, and the inability to concentrate.[18][19][20]
Fever is a common symptom of many medical conditions:
Persistent fever that cannot be explained after repeated routine clinical inquiries is called fever of unknown origin.
Temperature is ultimately regulated in the hypothalamus. A trigger of the fever, called a pyrogen, causes a release of prostaglandin E2 (PGE2). PGE2 then in turn acts on the hypothalamus, which generates a systemic response back to the rest of the body, causing heat-creating effects to match a new temperature level.
In many respects, the hypothalamus works like a thermostat.[21] When the set point is raised, the body increases its temperature through both active generation of heat and retention of heat. Peripheral vasoconstriction both reduces heat loss through the skin and causes the person to feel cold. If these measures are insufficient to make the blood temperature in the brain match the new set point in the hypothalamus, then shivering begins in order to use muscle movements to produce more heat. When the hypothalamic set point moves back to baseline either spontaneously or with medication, the reverse of these processes (vasodilation, end of shivering and nonshivering heat production) and sweating are used to cool the body to the new, lower setting.
This contrasts with hyperthermia, in which the normal setting remains, and the body overheats through undesirable retention of excess heat or over-production of heat.[21] Hyperthermia is usually the result of an excessively hot environment (heat stroke) or an adverse reaction to drugs. Fever can be differentiated from hyperthermia by the circumstances surrounding it and its response to anti-pyretic medications.
A pyrogen is a substance that induces fever. These can be either internal (endogenous) or external (exogenous) to the body. The bacterial substance lipopolysaccharide (LPS), present in the cell wall of some bacteria, is an example of an exogenous pyrogen. Pyrogenicity can vary: In extreme examples, some bacterial pyrogens known as superantigens can cause rapid and dangerous fevers. Depyrogenation may be achieved through filtration, distillation, chromatography, or inactivation.
In essence, all endogenous pyrogens are cytokines, molecules that are a part of the immune system. They are produced by activated immune cells and cause the increase in the thermoregulatory set point in the hypothalamus. Major endogenous pyrogens are interleukin 1 (α and β)[22] and interleukin 6 (IL-6). Minor endogenous pyrogens include interleukin-8, tumor necrosis factor-β, macrophage inflammatory protein-α and macrophage inflammatory protein-β as well as interferon-α, interferon-β, and interferon-γ.[22] Tumor necrosis factor-α also acts as a pyrogen. It is mediated by interleukin 1 (IL-1) release.[23]
These cytokine factors are released into general circulation, where they migrate to the circumventricular organs of the brain due to easier absorption caused by the blood–brain barrier's reduced filtration action there. The cytokine factors then bind with endothelial receptors on vessel walls, or interact with local microglial cells. When these cytokine factors bind, the arachidonic acid pathway is then activated.
One model for the mechanism of fever caused by exogenous pyrogens includes LPS, which is a cell wall component of gram-negative bacteria. An immunological protein called lipopolysaccharide-binding protein (LBP) binds to LPS. The LBP–LPS complex then binds to the CD14 receptor of a nearby macrophage. This binding results in the synthesis and release of various endogenous cytokine factors, such as interleukin 1 (IL-1), interleukin 6 (IL-6), and the tumor necrosis factor-alpha. In other words, exogenous factors cause release of endogenous factors, which, in turn, activate the arachidonic acid pathway.
PGE2 release comes from the arachidonic acid pathway. This pathway (as it relates to fever), is mediated by the enzymes phospholipase A2 (PLA2), cyclooxygenase-2 (COX-2), and prostaglandin E2 synthase. These enzymes ultimately mediate the synthesis and release of PGE2.
PGE2 is the ultimate mediator of the febrile response. The set point temperature of the body will remain elevated until PGE2 is no longer present. PGE2 acts on neurons in the preoptic area (POA) through the prostaglandin E receptor 3 (EP3). EP3-expressing neurons in the POA innervate the dorsomedial hypothalamus (DMH), the rostral raphe pallidus nucleus in the medulla oblongata (rRPa), and the paraventricular nucleus (PVN) of the hypothalamus . Fever signals sent to the DMH and rRPa lead to stimulation of the sympathetic output system, which evokes non-shivering thermogenesis to produce body heat and skin vasoconstriction to decrease heat loss from the body surface. It is presumed that the innervation from the POA to the PVN mediates the neuroendocrine effects of fever through the pathway involving pituitary gland and various endocrine organs.
The brain ultimately orchestrates heat effector mechanisms via the autonomic nervous system. These may be:
In infants, the autonomic nervous system may also activate brown adipose tissue to produce heat (non-exercise-associated thermogenesis, also known as non-shivering thermogenesis). Increased heart rate and vasoconstriction contribute to increased blood pressure in fever.
There are arguments for and against the usefulness of fever, and the issue is controversial.[24][25] There are studies using warm-blooded vertebrates[26] and humans[27] in vivo, with some suggesting that they recover more rapidly from infections or critical illness due to fever. A Finnish study suggested reduced mortality in bacterial infections when fever was present.[28]
In theory, fever can aid in host defense.[24] There are certainly some important immunological reactions that are sped up by temperature, and some pathogens with strict temperature preferences could be hindered.[29]
Research[30] has demonstrated that fever assists the healing process in several important ways:
Fever should not necessarily be treated.[32] Most people recover without specific medical attention.[33] Although it is unpleasant, fever rarely rises to a dangerous level even if untreated. Damage to the brain generally does not occur until temperatures reach 42 °C (107.6 °F), and it is rare for an untreated fever to exceed 40.6 °C (105 °F).[32]
Some limited evidence supports sponging or bathing feverish children with tepid water.[34] The use of a fan or air conditioning may somewhat reduce the temperature and increase comfort. If the temperature reaches the extremely high level of hyperpyrexia, aggressive cooling is required.[16] In general, people are advised to keep adequately hydrated.[35] Whether increased fluid intake improves symptoms or shortens respiratory illnesses such as the common cold is not known.[36]
Medications that lower fevers are called antipyretics. The antipyretic ibuprofen is effective in reducing fevers in children.[37] It is more effective than acetaminophen (paracetamol) in children. Ibuprofen and acetaminophen may be safely used together in children with fevers.[38][39] The efficacy of acetaminophen by itself in children with fevers has been questioned.[40] Ibuprofen is also superior to aspirin in children with fevers.[41] Additionally, aspirin is not recommended in children and young adults (those under the age of 16 or 19 depending on the country) due to the risk of Reye's syndrome.[42]
Using both paracetamol and ibuprofen at the same time or alternating between the two is more effective at decreasing fever than using only paracetamol or ibuprofen.[43] It is not clear if it increases child comfort.[43]
About 5% of people who go to an emergency room have a fever.[44]
A number of types of fever were known as early as 460 BC to 370 BC when Hippocrates was practicing medicine including that due to malaria (tertian or every 2 days and quartan or every 3 days).[45] It also became clear around this time that fevers were a symptom of a disease rather than a disease in and of itself.[45]
Pyrexia is from the Greek pyr meaning fire. Febrile is from the Latin word febris, meaning fever, and archaically known as ague.
Fever phobia is the name given by medical experts to parents' misconceptions about fever in their children. Among them, many parents incorrectly believe that fever is a disease rather than a medical sign, that even low fevers are harmful, and that any temperature even briefly or slightly above the oversimplified "normal" number marked on a thermometer is a clinically significant fever.[46] They are also afraid of harmless side effects like febrile seizures and dramatically overestimate the likelihood of permanent damage from typical fevers.[46] The underlying problem, according to professor of pediatrics Barton D. Schmitt, is "as parents we tend to suspect that our children’s brains may melt."[47]
As a result of these misconceptions parents are anxious, give the child fever-reducing medicine when the temperature is technically normal or only slightly elevated, and interfere with the child's sleep to give the child more medicine.[46]
Fever is an important feature for the diagnosis of disease in domestic animals. The body temperature of animals, which is taken rectally, is different from one species to another. For example, a horse is said to have a fever above 101 °F (38.3 °C).[48] In species that allow the body to have a wide range of "normal" temperatures, such as camels,[49] it is sometimes difficult to determine a febrile stage.
Fever can also be behaviorally induced by invertebrates that do not have immune-system based fever. For instance, some species of grasshopper will thermoregulate to achieve body temperatures that are 2 - 5 °C higher than normal in order to inhibit the growth of fungal pathogens such as Beauveria bassiana and Metarhizium acridum.[50] Honeybee colonies are also able to induce a fever in response to a fungal parasite Ascosphaera apis. [50]
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リンク元 | 「100Cases 27」「発熱」「100Cases 16」「血栓性血小板減少性紫斑病」「熱」 |
拡張検索 | 「Bolivian hemorrhagic fever」 |
年齢 | 原因 |
乳児(生後3ヶ月未満) | 敗血症、細菌性髄膜炎、尿路感染症、肺炎、B群溶連菌感染、グラム陰性桿菌 |
乳児(生後3ヶ月以降) | ウィルス感染(突発性発疹などの発疹性疾患)、中耳炎、尿路感染症、消化器・呼吸器疾患、川崎病 |
幼児、学童期 | 溶連菌感染症、伝染性単核球症、膠原病、factitious fever(詐病)、学校での感染症の流行 |
see also step beyond resident 2 救急で必ず出会う疾患編 p.20
実熱 | 虚熱 | |
発病 | 急速に発病 | 緩徐に発病 |
症状 | 悪寒、高熱 顔面紅潮 苦痛あり、四肢運動多 声大きく明瞭 口渇強い 便秘 色調濃い尿 |
軽度悪寒、熱覚 顔面蒼白 苦痛少なく、静かに臥床 声小さい 口渇少ない 軟便、下痢 薄い色調の尿 |
脈 | 早く大きく、緊張 | 小さく早く、緊張なし |
舌苔 | 厚くて乾燥、白~黄~褐色 | 薄くて白い、無苔、鏡面舌 |
その他 | 頭痛、関節痛、無汗~発汗 | 倦怠感、眩暈感、盗汗 |
実熱 | 麻黄湯 | 悪寒、発熱、頭痛、関節痛 |
葛根湯 | 悪寒、発熱、頭痛、肩背部のこり | |
小柴胡湯 | 午後からの発熱、食欲不振、口の苦み | |
柴胡桂枝湯 | 詳細孤島の症状、関節痛、腹痛 | |
大柴胡湯 | 胆嚢炎、便秘 | |
柴陥湯 | 詳細孤島の症状、咳嗽、胸痛 | |
黄芩湯 | 発熱、腹痛、下痢 | |
虚熱 | 桂枝湯 | 発熱、軽度の頭痛、発汗 |
桂麻各半湯 | 発熱、発疹 | |
参蘇飲 | 発熱、食欲不振、咳嗽、あつがる | |
柴胡桂枝乾姜湯 | 微熱、上半身の自汗、盗汗、食欲不振、背部の冷汗 | |
竹じょ温胆湯 | 発熱、咳嗽、不眠 | |
補中益気湯 | 微熱、倦怠感、食欲不振、盗汗 | |
滋陰降火湯 | 微熱、下半身の脱力感、盗汗、咳嗽 | |
滋陰至宝湯 | 微熱、倦怠感、食欲不振、精神不安定状態 | |
真武湯 | 陰病、微熱、食欲不振、倦怠感、いつも寝ている | |
麻黄細辛附子湯 | 陰病、微熱、寒がる |
(⇔溶血性尿毒症症候群 HUS は血小板減少、細血管障害性溶血性貧血、腎障害。精神症状と発熱は特徴的ではない)
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