Physiological rationale for suppression of fever

Temperature Control in Acute Brain Injury: An Update

Temperature control in severe acute brain injury (SABI) is a key component of acute management. This manuscript delves into the complex role of temperature management in SABI, encompassing conditions like traumatic brain injury (TBI), acute ischemic stroke (AIS), intracerebral hemorrhage (ICH), aneurysmal subarachnoid hemorrhage (aSAH), and hypoxemic/ischemic brain injury following cardiac arrest. Fever is a common complication in SABI and is linked to worse neurological outcomes due to increased inflammatory responses and intracranial pressure (ICP). Temperature management, particularly hypothermic temperature control (HTC), appears to mitigate these adverse effects primarily by reducing cerebral metabolic demand and dampening inflammatory pathways. However, the effectiveness of HTC varies across different SABI conditions. In the context of post-cardiac arrest, the impact of HTC on neurological outcomes has shown inconsistent results. In cases of TBI, HTC seems promising for reducing ICP, but its influence on long-term outcomes remains uncertain. For AIS, clinical trials have yet to conclusively demonstrate the benefits of HTC, despite encouraging preclinical evidence. This variability in efficacy is also observed in ICH, aSAH, bacterial meningitis, and status epilepticus. In pediatric and neonatal populations, while HTC shows significant benefits in hypoxic-ischemic encephalopathy, its effectiveness in other brain injuries is mixed. Although the theoretical basis for employing temperature control, especially HTC, is strong, the clinical outcomes differ among various SABI subtypes. The current consensus indicates that fever prevention is beneficial across the board, but the application and effectiveness of HTC are more nuanced, underscoring the need for further research to establish optimal temperature management strategies. Here we provide an overview of the clinical evidence surrounding the use of temperature control in various types of SABI.

Recognizing the roles of fever in host survival and in medical intervention in infectious diseases

Fever has roles both in host defense against infectious challenges and in guidance of medical intervention. These roles remain insufficiently acknowledged and considered by both health care providers and patients and their families. This review cites reports in support of both roles and provides recommendations regarding the clinician's approach to fever, as well as points relevant for education of patients and their families.

Temperature Management in the ICU

OBJECTIVE

Temperature abnormalities are recognized as a marker of human disease, and the therapeutic value of temperature is an attractive treatment target. The objective of this synthetic review is to summarize and critically appraise evidence for active temperature management in critically ill patients.

DATA SOURCES

We searched MEDLINE for publications relevant to body temperature management (including targeted temperature management and antipyretic therapy) in cardiac arrest, acute ischemic and hemorrhagic stroke, traumatic brain injury, and sepsis. Bibliographies of included articles were also searched to identify additional relevant studies.

STUDY SELECTION

English-language systematic reviews, meta-analyses, randomized trials, observational studies, and nonhuman data were reviewed, with a focus on the most recent randomized control trial evidence.

DATA EXTRACTION

Data regarding study methodology, patient population, temperature management strategy, and clinical outcomes were qualitatively assessed.

DATA SYNTHESIS

Temperature management is common in critically ill patients, and multiple large trials have been conducted to elucidate temperature targets, management strategies, and timing. The strongest data concerning the use of therapeutic hypothermia exist in comatose survivors of cardiac arrest, and recent trials suggest that appropriate postarrest temperature targets between 33°C and 37.5°C are reasonable. Targeted temperature management in other critical illnesses, including acute stroke, traumatic brain injury, and sepsis, has not shown benefit in large clinical trials. Likewise, trials of pharmacologic antipyretic therapy have not demonstrated improved outcomes, although national guidelines do recommend treatment of fever in patients with stroke and traumatic brain injury based on observational evidence associating fever with worse outcomes.

CONCLUSIONS

Body temperature management in critically ill patients remains an appealing therapy for several illnesses, and additional studies are needed to clarify management strategies and therapeutic pathways.

Modelling the Efficacy of Febrile Heating in Infected Endotherms

Fever is a response to infection characterised by an increase in body temperature. The adaptive value of this body temperature increase for endotherms is unclear, given the relatively small absolute temperature increases associated with endotherm fever, its substantial metabolic costs, and the plausibility for pathogens to adapt to higher temperatures. We consider three thermal mechanisms for fever's antimicrobial effect: (1) direct growth inhibition by elevating temperature above the pathogens optimal growth temperature; (2) further differentiating the host body from the wider environment; and (3) through increasing thermal instability of the pathogen environment. We assess these by modelling their effects pathogen on temperature dependent growth, finding thermal effects can vary from highly to minimally effective depending on pathogen species. We also find, depending on the specification of a simple physical model, intermittent heating can inhibit pathogen growth more effectively than continuous heating with an energy constraint.

Randomised comparative trial of the efficacy of paracetamol syrup and dispersible tablets for the treatment of fever in children

Objective

Fever is the most common reason for the presentation of children in the outpatient department. Paracetamol is marketed in different formulations for ease of administration to the paediatric population. These include syrups, dispersible tablets and rectal inserts. Dispersible tablets disintegrate rapidly in liquid and are subsequently taken orally, providing another oral formulation. We determined if there is a difference in the antipyretic efficacy of the syrup and the dispersible formulation of paracetamol, thereby prompting the development of the latter (another oral formulation) for use in children.

Methods

A randomised, controlled, double-blind intervention of a single dose of both formulations was given to febrile children, and their temperatures were documented twice in 30-minute intervals. Temperature changes were compared statistically.

Results

The mean temperatures at recruitment were 38.2 ± 0.5°C and 38.3 ± 0.6°C for the dispersible and syrup group, respectively. There was no significant difference between the temperature changes at T2 (30 minutes) and T3 (60 minutes) between the two study arms. However, the temperature was significantly different at T1 (baseline), T2 and T3 within the dispersible and syrup groups.

Conclusion

The decreasing trend in temperature was similar in both groups. Both preparations produced statistically similar antipyretic effects with no reported adverse drug reaction.

Suppressed anti-inflammatory heat shock response in high-risk COVID-19 patients: lessons from basic research (inclusive bats), light on conceivable therapies

The major risk factors to fatal outcome in COVID-19 patients, i.e., elderliness and pre-existing metabolic and cardiovascular diseases (CVD), share in common the characteristic of being chronic degenerative diseases of inflammatory nature associated with defective heat shock response (HSR). The molecular components of the HSR, the principal metabolic pathway leading to the physiological resolution of inflammation, is an anti-inflammatory biochemical pathway that involves molecular chaperones of the heat shock protein (HSP) family during homeostasis-threatening stressful situations (e.g., thermal, oxidative and metabolic stresses). The entry of SARS coronaviruses in target cells, on the other hand, aggravates the already-jeopardized HSR of this specific group of patients. In addition, cellular counterattack against virus involves interferon (IFN)-mediated inflammatory responses. Therefore, individuals with impaired HSR cannot resolve virus-induced inflammatory burst physiologically, being susceptible to exacerbated forms of inflammation, which leads to a fatal "cytokine storm". Interestingly, some species of bats that are natural reservoirs of zoonotic viruses, including SARS-CoV-2, possess an IFN-based antiviral inflammatory response perpetually activated but do not show any sign of disease or cytokine storm. This is possible because bats present a constitutive HSR that is by far (hundreds of times) more intense and rapid than that of human, being associated with a high core temperature. Similarly in humans, fever is a physiological inducer of HSR while antipyretics, which block the initial phase of inflammation, impair the resolution phase of inflammation through the HSR. These findings offer a rationale for the reevaluation of patient care and fever reduction in SARS, including COVID-19.

The use of ibuprofen to treat fever in COVID-19: A possible indirect association with worse outcome?

Fever has been reported as a common symptom occurring in COVID-19 illness. Over the counter antipyretics such as ibuprofen and acetaminophen are often taken by individuals to reduce the discomfort of fever. Recently, the safety of ibuprofen in COVID-19 patients has been questioned due to anecdotal reports of worsening symptoms in previously healthy young adults. Studies show that ibuprofen demonstrates superior efficacy in fever reduction compared to acetaminophen. As fever may have benefit in shortening the duration of viral illness, it is plausible to hypothesize that the antipyretic efficacy of ibuprofen may be hindering the benefits of a fever response when taken during the early stages of COVID-19 illness.

High mobility group box 1 protein released in the course of aseptic necrosis of tissues sensitizes rats to pyrogenic effects of lipopolysaccharide

It is still an open question as to whether or not aseptic injuries affect the generation of fever due to exogenous pyrogens including bacterial products. Therefore, in the present paper we have investigated the course of endotoxin fever in rats induced with lipopolysaccharide (LPS; given intraperitoneally in a dose of 50 μg/kg) 48 h after subcutaneous administration of turpentine oil (TRP; 0.1 mL per rat) that causes aseptic necrosis of tissues. We found that febrile response was significantly augmented in the animals pre-treated with turpentine compared to control rats (pre-treated with saline), and that observed excessive elevation of body temperature (Tb) was accompanied by enhanced release of fever mediators: interleukin-6 (IL-6) and prostaglandin E₂ (PGE₂) into plasma. Moreover, we found that sensitization to pyrogenic effects of lipopolysaccharide was associated with the increase in plasma level of high mobility group box 1 protein (HMGB1), one of the best-known damage-associated molecular patterns (DAMP), which was recently discovered as inflammatory mediator. Since the injection of anti-HMGB1 antibodies weakened observed hyperpyrexia in the animals pre-treated with turpentine, we conclude that HMGB1 is a plasma-derived factor released in the course of aseptic injury that enhances pyrogenic effects of LPS.

Therapy of retained fetal membranes in cattle: Comparison of two treatment protocols

This prospective study was conducted to compare two treatment protocols for retained foetal membranes (RFM) in cattle. The routine therapy consisting of intrauterine tetracycline boluses was compared with the administration of ozone foam, both intrauterine therapies without attempts to manually remove the placenta. Cows undergoing caesarean section, suffering from uterine torsion or prolapse of the uterus, and other illnesses than RFM on the first day post-partum were excluded. Values for baseline variables as age, breed, yearly milk yield, parity, pregnancy duration, calving season and number of routine intrauterine treatments were not different between the groups. Number of days with rectal temperature >39.7 °C within the first 10 days in milk (DIM) were greater in the ozone group. Number of escape therapies were recorded when there was imposing of this therapy as a result of cows having a fever (based on rectal temperature >39.7 °C) and a significant reduced food intake. Escape therapies consisted of parenteral administration of tetracyclines and NSAIDS during the first 10 DIM. Number of escape therapies, however, was not different between the groups. Results from use of a logistic regression model with fever as a dichotomous variable indicated there was no effect of breed, studbook, type of stall, pasture, business and no effect of age or milk yield. In a second assessment, cows were evaluated until 200 DIM. Results from a survival analysis indicated group (Te/Oz) did not affect rate of culling from the herd.

Reverse Engineering the Febrile System

Fever, the elevation of core body temperature by behavioral or physiological means, is one of the most salient aspects of human sickness, yet there is debate regarding its functional role. In this paper, we demonstrate that the febrile system is an evolved adaptation shaped by natural selection to coordinate the immune system to fight pathogens. First, we show that previous arguments in favor of fever being an adaptation are epistemologically inadequate, and we describe how an adaptationist strategy addresses this issue more effectively. Second, we argue that the mechanisms producing fever provide clear indications of adaptation. Third, we demonstrate that there are many beneficial immune system responses activated during fever and that these responses are not mere byproducts of heat on chemical reactions. Rather, we show that natural selection appears to have modified several immune system effects to be coordinated by fever. Fourth, we argue that there are some adaptations that coordinate the febrile system with other important fitness components, particularly growth and reproduction. Finally, we discuss evidence that the febrile system may also have evolved an antitumor function, providing suggestions for future research into this area. This research informs the debate on the functional value of fever and antipyretic use.

INSURMOUNTABLE HEAT: THE EVOLUTION AND PERSISTENCE OF DEFENSIVE HYPERTHERMIA

Fever, the rise in body temperature set point in response to infection or injury, is a highly conserved trait among vertebrates, and documented in many arthropods. Fever is known to reduce illness duration and mortality. These observations present an evolutionary puzzle: why has fever continued to be an effective response to fast-evolving pathogenic microbes across diverse phyla, and probably over countless millions of years? Framing fever as part of a more general thermal manipulation strategy that we term defensive hyperthermia, we hypothesize that the solution lies in the independent contributions to pathogen fitness played by virulence and infectivity. A host organism deploying defensive hyperthermia alters the ecological environment of an invading pathogen. To the extent that the pathogen evolves to be able to function effectively at elevated temperatures, it disadvantages itself at infecting the next (thermonormative) host, becoming more likely to be thwarted by that host's immune system and outcompeted by wild ecotype conspecifics (a genetically distinct strain adapted to specific environmental conditions) that, although more vulnerable to elevated temperatures, operate more effectively at the host's normal temperature. We evaluate this hypothesis in light of existing evidence concerning pathogen thermal specialization, and discuss theoretical and translational implications of this model.

Fever: suppress or let it ride?

While our ability to detect and manage fever has evolved since its conceptualization in the 5(th) century BC, controversy remains over the best evidence-based practices regarding if and when to treat this physiologic derangement in the critically ill. There are two basic fields of thought: (I) fever should be suppressed because its metabolic costs outweigh its potential physiologic benefit in an already stressed host; vs. (II) fever is a protective adaptive response that should be allowed to run its course under most circumstances. The latter approach, sometime referred to as the "let it ride" philosophy, has been supported by several recent randomized controlled trials like that of Young et al. [2015], which are challenging earlier observational studies and may be pushing the pendulum away from the Pavlovian treatment response.

Heat shock protein 70 is associated with CSFV NS5A protein and enhances viral RNA replication

The non-structural 5A (NS5A) protein of classical swine fever virus (CSFV) is proven to be involved in viral replication and can also modulate cellular signaling via to its ability to interact with various cellular proteins. Here, HSP70/NS5A complex formation is confirmed by coimmunoprecipitation and GST-pulldown studies. Additionally, the N-terminal amino acids (29-240) of NS5A were identified as the interaction region through in vivo deletion analyses, and confocal microscopy showed that NS5A and HSP70 colocalized in the cytoplasm. Overexpression of HSP70 via the eukaryotic expression plasmid pDsRED N1 or lentivirus significantly promoted viral RNA synthesis. Whereas the knockdown of HSP70 by lentivirus-mediated shRNA or inhibition by quercetin markedly decreased the viral load. These data suggest that HSP70 plays a critical role in the viral life cycle, particularly during the virus RNA replication period. The investigation of HSP70 protein functions may be beneficial for developing new strategies to treat CSFV infection.

Does paracetamol help or hinder healing in bacterial infections?

Community nursing teams, alongside other primary care services and nurses in working in community hospitals, are caring for people who are older, sicker and require more complex care. The nurse's ability to use evidence to make informed judgements is vitally important to patient care. Nurses often give paracetamol that is prescribed on an 'as required' basis to patients with bacterial infections who are pyrexial. This practice is supported by guidelines from the National Institute of Health and Care Excellence and the British National Formulary. This article reviews the evidence and suggests that the administration of paracetamol in people with pyrexia should be reconsidered and given on an individualised basis rather than as a routine.

Population-level effects of suppressing fever

Fever is commonly attenuated with antipyretic medication as a means to treat unpleasant symptoms of infectious diseases. We highlight a potentially important negative effect of fever suppression that becomes evident at the population level: reducing fever may increase transmission of associated infections. A higher transmission rate implies that a larger proportion of the population will be infected, so widespread antipyretic drug use is likely to lead to more illness and death than would be expected in a population that was not exposed to antipyretic pharmacotherapies. We assembled the published data available for estimating the magnitudes of these individual effects for seasonal influenza. While the data are incomplete and heterogeneous, they suggest that, overall, fever suppression increases the expected number of influenza cases and deaths in the US: for pandemic influenza with reproduction number , the estimated increase is 1% (95% CI: 0.0-2.7%), whereas for seasonal influenza with , the estimated increase is 5% (95% CI: 0.2-12.1%).

Optimising the management of fever and pain in children

Fever and pain in children, especially associated with infections, such as otitis media, are very common. In paediatric populations, ibuprofen and paracetamol (acetaminophen) are both commonly used over-the-counter medicines for the management of fever or mild-to-moderate pain associated with sore throat, otitis media, toothache, earache and headache. Widespread use of ibuprofen and paracetamol has shown that they are both effective and generally well tolerated in the reduction in paediatric fever and pain. However, ibuprofen has the advantage of less frequent dosing (every 6-8 h vs. every 4 h for paracetamol) and its longer duration of action makes it a suitable alternative to paracetamol. In comparative trials, ibuprofen has been shown to be at least as effective as paracetamol as an analgesic and more effective as an antipyretic. The safety profile of ibuprofen is comparable to that of paracetamol if both drugs are used appropriately with the correct dosing regimens. However, in the overdose situation, the toxicity of paracetamol is not only reached much earlier, but is also more severe and more difficult to manage as compared with an overdose of ibuprofen. There is clearly a need for advanced studies to investigate the safety of these medications in paediatric populations of different ages and especially during prolonged use. Finally, the recently reported association between frequency and severity of asthma and paracetamol use needs urgent additional investigations.

Fever literacy and fever phobia

OBJECTIVE

To identify the percentage of parents who define the threshold for fever between 38.0°C and 38.3°C, which has not been reported previously, and to describe parental attitudes toward fever and antipyretic use.

STUDY DESIGN

Thirteen-question survey study of caregivers.

RESULTS

Overall, 81% of participants defined the threshold for fever as <38.0°C, 0% correctly defined fever between 38.0°C and 38.3°C, and 19% defined fever as >38.3°C. Twenty percent of children brought to clinic for a chief complaint of fever were never truly febrile. Ninety-three percent of participants believed that high fever can cause brain damage. For a comfortable-appearing child with fever, 89% of caregivers reported that they would give antipyretics and 86% would schedule a clinic visit.

CONCLUSION

Our finding that 0% of parents correctly defined fever is both surprising and unsettling, and it should inform future discussions of fever between parents and clinicians.

hsp70 and a novel axis of type I interferon-dependent antiviral immunity in the measles virus-infected brain

The major inducible 70-kDa heat shock protein (hsp70) is host protective in a mouse model of measles virus (MeV) brain infection. Transgenic constitutive expression of hsp70 in neurons, the primary target of MeV infection, abrogates neurovirulence in neonatal H-2(d) congenic C57BL/6 mice. A significant level of protection is retained after depletion of T lymphocytes, implicating innate immune mechanisms. The focus of the present work was to elucidate the basis for hsp70-dependent innate immunity using this model. Transcriptome analysis of brains from transgenic (TG) and nontransgenic (NT) mice 5 days after infection identified type I interferon (IFN) signaling, macrophage activation, and antigen presentation as the main differences linked to survival. The pivotal role of type I IFN in hsp70-mediated protection was demonstrated in mice with a genetically disrupted type I IFN receptor (IFNAR(-/-)), where IFNAR(-/-) eliminated the difference in survival between TG and NT mice. Brain macrophages, not neurons, are the predominant source of type I IFN in the virus-infected brain, and in vitro studies provided a mechanistic basis by which MeV-infected neurons can induce IFN-β in uninfected microglia in an hsp70-dependent manner. MeV infection induced extracellular release of hsp70 from mouse neuronal cells that constitutively express hsp70, and extracellular hsp70 induced IFN-β transcription in mouse microglial cells through Toll-like receptors 2 and 4. Collectively, our results support a novel axis of type I IFN-dependent antiviral immunity in the virus-infected brain that is driven by hsp70.

Clinical and demographic factors associated with antipyretic use in gram-negative severe sepsis and septic shock

BACKGROUND

Antipyretic therapy is commonly prescribed for patients with infection, but studies of its impact on clinical outcomes have yielded mixed results. No data exist to characterize the use of antipyretic medications in patients with severe sepsis or septic shock.

OBJECTIVE

To identify clinical and demographic factors associated with antipyretic medication administration in severe sepsis and septic shock.

METHODS

This single-center, retrospective, cohort study assessed febrile patients (temperature ≥ 38.3 °C) with gram-negative severe sepsis or septic shock at an 1111-bed academic medical center between January 2002 and February 2008. Patients were excluded if they had liver disease, acute brain injury, or allergy to acetaminophen. Generalized estimating equations were used to estimate the effect of clinical factors on treatment of patients with antipyretic medications.

RESULTS

Although 76% of patients in this febrile cohort (n = 241) were prescribed an antipyretic agent, only 42% received antipyretic therapy; 95% of the doses were acetaminophen. Variables associated with antipyretic treatment were maximum body temperature (OR 2.11, 95% CI 1.53 to 2.89), time after sepsis diagnosis (OR 0.88, 95% CI 0.82 to 0.95), surgery during hospitalization (OR 0.49, 95% CI 0.31 to 0.80), death within 36 hours (OR 0.35, 95% CI 0.15 to 0.85), and mechanical ventilation (OR 0.58, 95% CI 0.34 to 0.98). Severity of illness factors, demographic factors, and patient treatment location did not predict who would receive antipyretic therapy.

CONCLUSIONS

Most febrile episodes in patients with gram-negative severe sepsis or septic shock were not treated with antipyretic medications. Further studies are needed to demonstrate the effect of antipyretics on clinically relevant outcomes in severe sepsis and septic shock.

Approach to the febrile patient in the ICU

Fever is a normal adaptive brain response to infectious and noninfectious causes involving a cytokine-mediated response, the generation of acute phase reactants, and the activation of numerous physiologic, endocrinologic and immunologic systems. Ninety percent of patients with severe sepsis in the intensive care unit (ICU) will experience fever during their hospitalization, while the half of the new detected febrile episodes are of noninfectious origin. In the ICU, fever should be treated in cardiorespiratory and neurosurgical patients and in those in whom temperature exceeds 40 degrees C (104 degrees F). Antipyretic therapy must be justified regardless of the metabolic cost (if fever exceeds its physiologic benefit), the result (if the symptomatic relief adversely affects the course of the febrile illness) and the side effects.

The significance of altered temperature after traumatic brain injury: an analysis of investigations in experimental and human studies: part 2

Raised body temperature is a common occurrence after severe traumatic brain injury (TBI). It is widely accepted that experimental evidence points to a harmful effect of raised temperature both during and after TBI. Consequently, the policy of many neurocritical care units is to implement therapies for body temperature control. This article reviews the evidence that links spontaneous temperature changes with worsened outcome after experimentally-induced and human brain trauma. The current evidence-base and rationale for treatment of raised temperature after TBI is presented with discussion positing areas for further work to explore the notion that raised temperature may not be deleterious in all neurosurgical patients.

Regulation of a lymphocyte-endothelial-IL-6 trans-signaling axis by fever-range thermal stress: hot spot of immune surveillance

The pleiotropic cytokine, interleukin-6 (IL-6), has emerged in recent years as a key regulator of the transition from innate to adaptive immunity through its ability to modulate leukocyte recruitment at inflammatory sites. This review highlights a newly identified role for IL-6 trans-signaling, initiated by an agonistic complex of IL-6 and a soluble form of IL-6 receptor alpha, in heightening immune surveillance of peripheral lymphoid organs during febrile inflammatory responses. Inflammatory cues provided by the thermal component of fever trigger IL-6 trans-signaling to act at discrete levels in the multistep adhesion cascade that governs the entry of blood-borne lymphocytes across 'gatekeeper' high endothelial venules (HEVs) in lymph nodes and Peyer patches. IL-6 trans-signaling-dependent mechanisms have been elucidated during thermal stimulation of primary tethering and rolling of lymphocytes along the lumenal surface of HEVs as well as during secondary firm arrest of lymphocytes in HEVs prior to their migration into the underlying parenchyma. These mechanisms profoundly increase the probability that lymphocytes that continuously patrol the body will engage in productive encounters with target antigens sequestered within lymphoid organs. Findings that the lymphocyte-HEV-IL-6 trans-signaling biological axis functions as a thermally-sensitive alert system that promotes immune surveillance provide insight into one of the unresolved mysteries in immunology regarding the benefits of mounting a febrile reaction during inflammation.

Primary immune surveillance: some like it hot

The thermal element of fever has been found to be beneficial in models of infectious disease. The contributions of fever-range temperatures to the efficacy of the adaptive immune response have only begun to be delineated. There is accumulating evidence that fever-range thermal stress bolsters primary immune surveillance of lymph nodes and Peyer patches by augmenting lymphocyte extravasation across specialized vessels termed high endothelial venules. Molecular mechanisms have recently come to light by which the thermal component of fever alone may promote lymphocyte trafficking, and thereby the probability of mounting a defense against microbial infection. Acquired knowledge of the molecular changes associated with thermal stress may allow for the development of novel therapies for a variety of disease processes.

Impact of fever-range thermal stress on lymphocyte-endothelial adhesion and lymphocyte trafficking

The evolutionarily conserved febrile response has been associated with improved survival during infection in endothermic and ectothermic species although its protective mechanism of action is not fully understood. Temperatures within the range of physiologic fever influence multiple parameters of the immune response including lymphocyte proliferation and cytotoxic activity, neutrophil and dendritic cell migration, and production or bioactivity of proinflammatory cytokines. This review focuses on the emerging role of fever-range thermal stress in promoting lymphocyte trafficking to secondary lymphoid organs that are major sites for launching effective immune responses during infection or inflammation. Specific emphasis will be on the molecular basis of thermal control of lymphocyte-endothelial adhesion, a critical checkpoint controlling lymphocyte extravasation, as well as the contribution of interleukin-6 (IL-6) trans-signaling to thermal activities. New results are presented indicating that thermal stimulation of lymphocyte homing potential is evident in evolutionarily distant endothermic vertebrate species. These observations support the view that the evolutionarily conserved febrile response contributes to immune protection and host survival by amplifying lymphocyte access to peripheral lymphoid organs.

The Effects of Drugs on Thermoregulation

Body temperature is a balance of the hypothalamic set point, neurotransmitter action, generation of body heat, and dissipation of heat. Drugs affect body temperature by different mechanisms. Antipyretics lower body temperature when the body's thermoregulatory set point has been raised by endogenous or exogenous pyrogens. The use of antipyretics may be unnecessary or may interfere with the body's resistance to infection, mask an important sign of illness, or cause adverse drug effects. Drugs may cause increased body temperature in five ways: altered thermoregulatory mechanisms, drug administration-related fever, fever from the pharmacologic action of the drug, idiosyncratic reactions, and hypersensitivity reactions. Certain drugs cause hypothermia by depression of the thermoregulatory set point or prevention of heat conservation. By affecting the balance of thermoregulatory neurotransmitters, drugs may prevent the signs and symptoms of hot flashes.

Clinical review: fever in intensive care unit patients

Fever is a common response to sepsis in critically ill patients. Fever occurs when either exogenous or endogenous pyrogens affect the synthesis of prostaglandin E2 in the pre-optic nucleus. Prostaglandin E2 slows the rate of firing of warm sensitive neurons and results in increased body temperature. The febrile response is well preserved across the animal kingdom, and experimental evidence suggests it may be a beneficial response to infection. Fever, however, is commonly treated in critically ill patients, usually with antipyretics, without good data to support such a practice. Fever induces the production of heat shock proteins (HSPs), a class of proteins critical for cellular survival during stress. HSPs act as molecular chaperones, and new data suggest they may also have an anti-inflammatory role. HSPs and the heat shock response appear to inhibit the activation of NF-kappabeta, thus decreasing the levels of proinflammatory cytokines. The anti-inflammatory effects of HSPs, coupled with improved survival of animal models with fever and infection, call into question the routine practice of treating fever in critically ill patients.

Treating fever in children: paracetamol or ibuprofen?

Community health practitioners frequently prescribe or advise parents on antipyretic medications for children with fevers. This mini-review sets out to examine the evidence for the relative effectiveness of two of the most widely available and commonly used over-the-counter medicines - paracetamol and ibuprofen. A systematic literature search was undertaken to identify all studies comparing the effects of the two drugs. The Medline, Embase, Cinahl and RCN databases were searched. Eight randomized controlled trials that reported temperature differences at time-points between 1 and 6 hours after administration were identified. Statistical meta-analysis showed no clear benefit for one drug over another 1 hour after administration. However, by 6 hours after administration ibuprofen was clearly superior resulting in a mean temperature 0.58 degrees C lower than paracetamol. Both drugs appeared well tolerated and no evidence of difference in short-term adverse effects was observed. Both drugs are effective antipyretics but the longer action of ibuprofen may make it preferable in some circumstances.

Fever: beneficial and detrimental effects of antipyretics

Although various forms of therapy have been used, since antiquity, to lower the temperature of febrile patients, it is still not known whether the benefits of antipyretic therapy outweigh its risks. Justifications for the use of antipyretic drugs, and the evidence pertaining to these rationales, are examined. Antipyretic therapy in sepsis, and adverse effects of antipyretic medications, are also reviewed.