Electric fans for reducing adverse health impacts in heatwaves
Editorial Group: Cochrane Gynaecological Cancer Group
Published Online: 11 JUL 2012
Assessed as up-to-date: 11 JUN 2012
Copyright © 2012 The Cochrane Collaboration. Published by John Wiley & Sons, Ltd.
How to Cite
Gupta S, Carmichael C, Simpson C, Clarke MJ, Allen C, Gao Y, Chan EYY, Murray V. Electric fans for reducing adverse health impacts in heatwaves. Cochrane Database of Systematic Reviews 2012, Issue 7. Art. No.: CD009888. DOI: 10.1002/14651858.CD009888.pub2.
- Publication Status: New
- Published Online: 11 JUL 2012
Heatwaves are hot weather events, which breach regional or national thresholds, that last for several days. They are likely to occur with increasing frequency in some parts of the world. The potential consequences were illustrated in Europe in August 2003 when there were an estimated 30,000 excess deaths due to a heatwave. Electric fans might be used with the intention of reducing the adverse health effects of a heatwave. Fans do not cool the ambient air but can be used to draw in cooler air from outside when placed at an open window. The aim of the fans would be to increase heat loss by increasing the efficiency of all normal methods of heat loss, but particularly by evaporation and convection methods. However, it should be noted that increased sweating can lead to dehydration and electrolyte imbalances if these fluids and electrolytes are not replaced quickly enough. Research has also identified important gaps in knowledge about the use of fans, which might lead to their inappropriate use.
To determine whether the use of electric fans contributes to, or impedes, heat loss at high ambient temperatures during a heatwave, and to contribute to the evidence base for the public health impacts of heatwaves.
We sought unpublished and published studies that had been published in any language. The review team were able to assess studies reported in English, Chinese, Dutch, French and German; and reports in other languages would have been translated into English as necessary. We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE, CINAHL, the Indian biomedical literature (IndMED and MedIND) and databases of Chinese literature (Chinese Journal Net and Digital Periodical of WanFang Data). The most recent electronic searches were done in April 2012. We also checked the reference lists of relevant articles and the websites of relevant national and international organisations, and consulted with researchers and policy makers with experience in strategies to manage heatwaves to identify additional studies. The titles and abstracts from each search were checked independently by two review authors. The full text articles that we retrieved were checked independently by at least two authors for their relevance and for references to potentially eligible studies.
Randomised trials and other experimental designs, such as interrupted time series and controlled before-and-after studies, comparing the use of electric fans with no fans during a heatwave were eligible for this review. The electric fans could be hand-held (battery operated), portable or mounted on the wall or ceiling, or in a window. We sought interventions delivered to anyone for whom a heatwave was likely to have serious adverse health impacts. This would include people of all ages but with a particular focus on some groups (for example older people). Populations from high-, middle- and low-income countries were eligible for the review.
Data collection and analysis
If we had identified eligible studies, they would have been assessed independently by at least two review authors and data would have been extracted on the characteristics of the study, its participants and interventions, as well as the effects on health outcomes. The primary outcomes were mortality, hospital admission and other contacts with healthcare services.
We did not identify any eligible studies despite the extensive searching and correspondence with several experts in this topic area. We identified retrospective, observational studies, usually with a case-control design, that investigated the association between the use of electric fans and health outcomes, including death. The results of these studies were mixed. Some studies found that the use of fans was associated with better health outcomes, others found the reverse.
The evidence we identified does not resolve uncertainties about the health effects of electric fans during heatwaves. Therefore, this review does not support or refute the use of electric fans during a heatwave. People making decisions about electric fans should consider the current state of the evidence base, and they might also wish to make themselves aware of local policy or guidelines when making a choice about whether or not to use or supply electric fans. The main implication of this review is that high quality research is needed to resolve the long standing and ongoing uncertainty about the benefits and harms of using electric fans during a heatwave, for example randomised trials comparing the health effects in people with electric fans to those in people without them.
Plain language summary
Electric fans for reducing the health effects of heatwaves
Heatwaves are set to become more common and their effects can be devastating. For example, up to 30,000 people may have died because of the heatwave that occurred in Europe during August 2003. One way to try to get relief from the heat is to use an electric fan, but whether this will do more good or harm is uncertain. A fan might help to increase heat loss if the temperature is below 35 °C and the fan is not directly aimed at the person, but, when temperatures are above 35 °C, the fan might actually contribute to heat gain. Excess sweating can also lead to dehydration and other health problems. It is important, therefore, to know about the potential benefits and harms of electric fans when choosing whether to use one. This applies if the decision is about your own use of a fan, but it is also relevant to broader public health decisions, such as whether to give electric fans to groups of people during a heatwave. This is particularly important for people who are considered more vulnerable to the effects of heat, such as older adults who are less able to cool down through sweating or increasing the flow of blood to their skin.
This Cochrane Review tried to provide some of the answers that would help decision makers. We looked for high quality research that had compared groups of people using fans with groups who didn't use them during a heatwave However, we didn't find any research that met our requirements. We did find some studies which used designs that are less reliable for answering this sort of question, and these had mixed results. Some suggested that fans might reduce health problems, while others suggested that the fans might make things worse.
Therefore, the research that has been done to date does not resolve uncertainties about the health effects of electric fans during heatwaves. People who have to make decisions should consider the current evidence, alongside local policies and guidelines when making their choices. They may wish to help resolve the continuing uncertainty by conducting the type of high quality research that would provide the reliable evidence needed to determine the benefits and harms of using electric fans during a heatwave.
Plain language summary
Električni ventilatori za smanjenje negativnih utjecaja toplinskih valova
Električni ventilatori za smanjenje negativnih utjecaja toplinskih valova
Toplinski valovi će postati sve češći, a njihovi učinci mogu biti razorni. Primjerice, čak 30.000 ljudi je vjerojatno umrlo od posljedica toplinskih valova koji su u Europi zabilježeni tijekom kolovoza 2008. Jedan od načina na koji se ublažava vrućina jest korištenje električnih ventilatora, ali nije sigurno da li to donosi više koristi ili štete. Ventilator može pospješiti gubitak topline ako je temperatura ispod 35 Celzijevih stupnjeva i ako ventilator nije direktno usmjeren prema čovjek, ali kad su temperature iznad 35 Celzijevih stupnjeva, ventilator može doprinijeti zagrijavanju. Dodatno znojenje može dovesti do dehidracije i drugih zdravstvenih problema. Stoga je važno znati potencijalne koristi i štete od električnih ventilatora kad se razmišlja o tome hoće li ga se koristiti ili ne. To se odnosi i na osobne odluke o korištenju ventilatora, a isto tako i na javnozdravstvene odluke, kao što je odluka o korištenju električnih ventilatora u prostorijama u kojima borave skupine ljudi tijekom toplinskih valova. Ovo je pitanje osobito važno za osobe koji su osjetljiviji na vrućinu, kao što su starije osobe koje imaju manju sposobnost hlađenja znojenjem i povećanjem protoka krvi u koži.
Cochrane sustavni pregled sažeo je dokaze iz literature, koji mogu pomoći osobama koje donose odluke. Autori su u literaturi tražili visoko kvalitetne dokaze u kojima su se uspoređivale osobe koje su koristile ventilatore s osobama koje ih nisu koristile tijekom toplinskoga vala Međutim, nisu pronađena istraživanja koja su udovoljila tim kriterijima. Pronađena su istraživanja koja nisu bila randomizirana, i stoga su bila ustrojena na manje pouzdan način. Ta su istraživanja imala vrlo različite rezultate. U nekima je zaključeno da ventilatori mogu smanjiti zdravstvene probleme uzrokovane toplinskim valovima, dok je u drugima zaključeno da ventilatori mogu zdravlje pogoršati.
Stoga se može zaključiti da sva istraživanja koja su na ovu temu obavljena do danas nisu uspjela riješiti dvojbu o učincima električnih ventilatora na zdravlje tijekom toplinskih valova. Osobe koje odlučuju trebale bi razmotriti trenutne dokaze, zajedno s lokalnim politikama i smjernicama kad donose odluke. Trenutne dvojbe mogu se razriješiti provođenjem visoko kvalitetnih randomiziranih kontroliranih ispitivanja koji će dati pouzdane dokaze o koristima i štetama električnih ventilatora za vrijeme toplinskih valova.
Translated by: Croatian Branch of the Italian Cochrane Centre