Heat-related illness and dementia: a study integrating epidemiological and experimental evidence.

BACKGROUND: Heat-related illness (HRI) is commonly considered an acute condition, and its potential long-term consequences are not well understood. We conducted a population-based cohort study and an animal experiment to evaluate whether HRI is associated with dementia later in life. METHODS: The Taiwan National Health Insurance Research Database was used in the epidemiological study. We identified newly diagnosed HRI patients between 2001 and 2015, but excluded those with any pre-existing dementia, as the study cohort. Through matching by age, sex, and the index date with the study cohort, we selected individuals without HRI and without any pre-existing dementia as a comparison cohort at a 1:4 ratio. We followed each cohort member until the end of 2018 and compared the risk between the two cohorts using Cox proportional hazards regression models. In the animal experiment, we used a rat model to assess cognitive functions and the histopathological changes in the hippocampus after a heat stroke event. RESULTS: In the epidemiological study, the study cohort consisted of 70,721 HRI patients and the comparison cohort consisted of 282,884 individuals without HRI. After adjusting for potential confounders, the HRI patients had a higher risk of dementia (adjusted hazard ratio [AHR] = 1.24; 95% confidence interval [CI]: 1.19-1.29). Patients with heat stroke had a higher risk of dementia compared with individuals without HRI (AHR = 1.26; 95% CI: 1.18-1.34). In the animal experiment, we found cognitive dysfunction evidenced by animal behavioral tests and observed remarkable neuronal damage, degeneration, apoptosis, and amyloid plaque deposition in the hippocampus after a heat stroke event. CONCLUSIONS: Our epidemiological study indicated that HRI elevated the risk of dementia. This finding was substantiated by the histopathological features observed in the hippocampus, along with the cognitive impairments detected, in the experimental heat stroke rat model.

Using wet-bulb globe temperature meters to examine the effect of heat on various tennis court surfaces.

In this study, we evaluated the thermal environments of different tennis courts using wet-bulb globe temperature (WBGT) meters. WBGT meters were installed in an outdoor hard court, sand-filled artificial grass court, and clay court (a softball field), and measurements were taken hourly from 9:00 to 17:00 on weekdays from June 1 to September 21, 2022. The results were compared with data from different courts and the nearest Japan Meteorological Agency station (JMA WBGT) based on the Japan Sports Association's guidelines for exercise to prevent heat stroke. The median WBGT on each court was significantly higher for hard courts at the "Warning" (25 ≤ JMA WBGT < 28) level or above, sand-filled artificial grass courts at the "Severe Warning" (28 ≤ JMA WBGT < 31) level or above, and clay courts at the "Danger" (31 ≤ JMA WBGT) level than the JMA WBGT. Compared with the JMA WBGT, hard and sand-filled artificial grass courts are played on under particularly hot conditions. The results of this study could indicate to tournament organizers and coaches the importance of measuring the WBGT on each court surface from an early stage to prevent heat-related incidents.

Thrombomodulin Improves Cognitive Deficits in Heat-Stressed Mice.

BACKGROUND: Thrombomodulin (TM) exerts anticoagulant and anti-inflammatory effects to improve the survival of patients with septic shock. Heat stroke resembles septic shock in many aspects. We tested whether TM would improve cognitive deficits and related causative factors in heat-stressed (HS) mice. METHODS: Adult male mice were exposed to HS (33°C for 2 hours daily for 7 consecutive days) to induce cognitive deficits. Recombinant human soluble TM (1 mg/kg, i.p.) was administered immediately after the first HS trial and then once daily for 7 consecutive days. We performed the Y-maze, novel objective recognition, and passive avoidance tests to evaluate cognitive function. Plasma levels of lipopolysaccharide (LPS), high-mobility group box 1 (HMGB1), coagulation parameters, and both plasma and tissue levels of inflammatory and oxidative stress markers were biochemically measured. The duodenum and hippocampus sections were immunohistochemically stained. The intestinal and blood-brain barrier permeability were determined. RESULTS: Compared with controls, HS mice treated with TM had lesser extents of cognitive deficits, exacerbated stress reactions, gut barrier disruption, endotoxemia, blood-brain barrier disruption, and inflammatory, oxidative, and coagulatory injury to heart, duodenum, and hippocampal tissues, and increased plasma HMGB1. In addition to reducing cognitive deficits, TM therapy alleviated all the abovementioned complications in heat-stressed mice. CONCLUSIONS: The findings suggest that HS can lead to exacerbated stress reactions, endotoxemia, gut barrier disruption, blood-brain barrier disruption, hippocampal inflammation, coagulopathy, and oxidative stress, which may act as causative factors for cognitive deficits. TM, an anti-inflammatory, antioxidant, and anti-coagulatory agent, inhibited heat stress-induced cognitive deficits in mice.

Global Warming and Endocrinology: The Hyderabad Declaration of the South Asian Federation of Endocrine Societies.

Global warming and endocrine disorders are intertwined issues posing significant challenges. Greenhouse gases emanating from human activities drive global warming, leading to temperature rise and altered weather patterns. South Asia has experienced a noticeable temperature surge over the past century. The sizable population residing in the region heightens the susceptibility to the impact of global warming. In addition to affecting agriculture, water resources, and livelihood, environmental changes interfere with endocrine functioning. Resulting lifestyle changes increase the risk of metabolic and endocrine disorders. Individuals with diabetes face heightened vulnerability to extreme weather due to impaired thermoregulation. A high ambient temperature predisposes to heat-related illnesses, infertility, and nephropathy. Additionally, essential endocrine drugs and medical devices are susceptible to temperature fluctuations. The South Asian Federation of Endocrine Societies (SAFES) calls for collaboration among stakeholders to combat climate change and promote healthy living. Comprehensive approaches, including the establishment of sustainable food systems, promotion of physical activity, and raising awareness about environmental impacts, are imperative. SAFES recommends strategies such as prioritizing plant-based diets, reducing meat consumption, optimizing medical device usage, and enhancing accessibility to endocrine care. Raising awareness and educating caregivers and people living with diabetes on necessary precautions during extreme weather conditions are paramount. The heat sensitivity of insulin, blood glucose monitoring devices, and insulin pumps necessitates proper storage and consideration of environmental conditions for optimal efficacy. The inter-connectedness of global warming and endocrine disorders underscores the necessity of international collaboration guided by national endocrine societies. SAFES urges all stakeholders to actively implement sustainable practices to improve endocrine health in the face of climate change.

Epidemiology of heat-related illness in dogs under UK emergency veterinary care in 2022.

BACKGROUND: Dogs are exposed to increasing environmental risk for developing heat-related illness (HRI), with 2022 recorded as the hottest year to date in the UK and most of Europe. METHODS: This study used VetCompass data to report the incidence risk, event fatality rate and canine risk factors for HRI in dogs presenting to Vets Now emergency care practices in the UK during 2022. RESULTS: From the clinical records of 167,751 dogs under care at Vets Now emergency clinics in 2022, 384 HRI events were identified. The 2022 incidence risk of HRI within the Vets Now caseload was 0.23% (95% confidence interval [CI]: 0.21%‒0.25%), with an event fatality rate of 26.56% (95% CI: 21.66%-32.25%). Multivariable analysis identified breed, age and sex/neuter status as risk factors for HRI. Brachycephalic dogs had 4.21 times the odds of HRI compared to mesocephalic dogs (95% CI: 3.22‒5.49, p < 0.001). LIMITATIONS: The clinical data used in this study were not primarily recorded for research and had some substantial levels of missing data (especially patient bodyweight). CONCLUSION: In order to protect canine welfare, improved long-term mitigation strategies are urgently needed to minimise HRI risk and associated fatality in UK dogs.

Climatic changes: knowledge and adaptation behavior to heat-related illness among solid waste disposal workers.

BACKGROUND: Earth's climate changes are progressing at an alarming rate. One of the most severe effects of climate change is extreme heat. This study aimed to assess knowledge and adaptation behavior to heat-related illness (HRI) among solid waste disposal workers in the 10th of Ramadan City, Egypt, and to study the predictors for their knowledge and adaptation behavior. METHODS: An exploratory cross-sectional study was conducted on 220 solid waste disposal workers. A structured interview questionnaire was used to assess the studied workers' sociodemographic and occupational characteristics, heat exposure risk, and their knowledge, and adaptation behavior. RESULTS: The results showed that 40% and 30% of participants had adequate levels of total knowledge and adaptation behavior, respectively. There was a statistically significant relationship between workers' knowledge and both age and education. There was a statistically significant relationship between workers' adaptation behavior and age, duration of employment, working hours, and education. A binary logistic regression for significant predictors of knowledge and adaptation behavior showed that age and education were the most significant predictors. CONCLUSION: Solid waste disposal workers were at high risk of HRI due to their low levels of knowledge and adaptation behavior regarding HRI. Educational health programs that guide workers to follow healthy behaviors and prevent HRI are recommended.

Increasing tree cover and high-albedo surfaces reduces heat-related ER visits in Los Angeles, CA.

There is an urgent need for strategies to reduce the negative impacts of a warming climate on human health. Cooling urban neighborhoods by planting trees and vegetation and increasing albedo of roofs, pavements, and walls can mitigate urban heat. We used synoptic climatology to examine how different tree cover and albedo scenarios would affect heat-related morbidity in Los Angeles, CA, USA, as measured by emergency room (ER) visits. We classified daily meteorological data for historical summer heat events into discrete air mass types. We analyzed those classifications against historical ER visit data to determine both heat-related and excess morbidity. We used the Weather Research and Forecasting model to examine the impacts of varied tree cover and albedo scenarios on meteorological outcomes and used these results with standardized morbidity data algorithms to estimate potential reductions in ER visits. We tested three urban modification scenarios of low, medium, and high increases of tree cover and albedo and compared these against baseline conditions. We found that avoiding 25% to 50% of ER visits during heat events would be a common outcome if the urban environment had more tree cover and higher albedo, with the greatest benefits occurring under heat events that are moderate and those that are particularly hot and dry. We conducted these analyses at the county level and compared results to a heat-vulnerable, working-class Los Angeles community with a high concentration of people of color, and found that reductions in the rate of ER visits would be even greater at the community level compared to the county.

Heat exposure as a cause of injury and illness in mine industry workers.

The objective of this study was to explore the association between ambient temperature and injuries and illnesses experienced by mine industry workers. Eleven years of de-identified data from a mine industry company in Australia was explored in regards to injuries and illnesses occurring due to outdoor exposure. Each case was filtered for reported symptoms, and meteorological data to match the location of the mine site and date reported were sourced. Of the 18 931 injuries and illnesses observed over the 11-year period, 151 cases of heat-related illness due to outdoor exposure were reported. Twenty-five conditions/symptoms of heat-illness were found, with the most prevalent being dehydration (n = 81), followed by heat rash (n = 40), dizziness (n = 24), and headache (n = 23). The mean number of symptoms reported by each worker was 2 ± 1. There was a positive correlation between ambient temperature and injuries/illnesses (r2 = 0.89, P < 0.001), where, as temperature increased so did the number of reported heat-related illnesses. Underreporting of heat-related illness and injury in the mining industry is likely, which is a risk to the health and wellbeing of employees. Workers require industry specific training about the severity of heat stress and the associated prevention strategies.

Injuries and illness of athletes at the Tokyo 2020 Olympic and Paralympic summer games visiting outside facilities.

This study aimed to identify the reasons for transferring athletes to local medical facilities during the Olympic and Paralympic Games. Data on 567 injuries and other illnesses of athletes treated at the on-site clinics were collected from the Tokyo 2020 Organizing Committee. Of these, 84 athletes who required outpatient care during the Games were registered for this survey. During the Olympic and Paralympic Games, 66 (8.3/1 000) and 18 (7.2/1 000) athletes, respectively, consulted external medical facilities. In the Olympic Games, the reasons for these visits included 48 cases (72.7%) of injuries, 13 (19.7%) cases of illnesses, and 5 (7.6%) cases of heat stroke illness (HSI). Of these patients, 56 (84.9%) were treated as outpatients and 10 (15.1%) were hospitalized, while three of these patients required hospitalization for > 7 days. On the other hand, in the Paralympics Games, there were 7 (38.8%) cases of injuries, 9 (50.0%) other illnesses, 1 (5.6%) case of HSI, and 1 (5.6%) other cases, of which 11 (61.1%) were treated as outpatients and 7 (38.9%) were hospitalized, but none was hospitalized for > 7 days. Injuries accounted for 70% of the total cases at the 2021 Olympic Games, but only three (0.05%) were severe cases that required hospitalization for more than 1 week. In contrast, in the Paralympic Games, other illnesses accounted for approximately half of the total cases. This study provides details on the extent of injuries and other illnesses that were transferred to outside facilities, which has not been documented in previous games.

Post-exercise management of exertional hyperthermia in dogs participating in dog sport (canicross) events in the UK.

Exercise is a common trigger of heat-related illness (HRI) events in dogs, accounting for 74% of canine HRI cases treated under primary veterinary care in the United Kingdom. However, few empirical studies have evaluated the effectiveness of differing cooling methods for dogs with exertional hyperthermia or HRI. This study aimed to prospectively evaluate effects of ambient conditions and post-exercise management practices (cooling methods and vehicular confinement) on the post-exercise temperature change of dogs participating in UK canicross events. Canine temperature was recorded at three intervals post-exercise: as close as possible to 0- (immediately post-exercise), 5-, and 15-min post-exercise. Ambient conditions and post-exercise management were recorded for 115 cooling profiles from 52 dogs. In 28/115 (24.4%) profiles, the dog's temperature increased during the first 5-min post-exercise. Overall, 68/115 (59.1%) profiles included passive cooling (stood or walked outside), 35 (30.4%) active cooling (cold-water immersion or application of a cooling coat), and 12 (10.4%) involved no cooling and were immediately housed in vehicles. No dogs developed hypothermia during the study and no adverse effects were observed from any cooling method. In hyperthermic dogs, overall post-exercise body temperature change was significantly negatively associated (i.e. the dogs cooled more) with 0-min post-exercise body temperature (ß = -0.93, p < 0.001), and not being housed in a vehicle (ß = -0.43, p = 0.013). This study provides evidence cold-water immersion (in water at 0.1-15.0 °C) can be used to effectively and safely cool dogs with exertional hyperthermia. Progressive temperature increases in many dogs - even after exercise has terminated - supports the message to "cool first, transport second" when managing dogs with HRI. When transporting dogs post-exercise or with HRI even after active cooling, care should be taken to cool the vehicle before entry and promote air movement around the dog during transport to facilitate ongoing cooling and prevent worsening of hyperthermia during travel.

Symptoms of heat illness and water consumption habits in mine industry workers over the summer months in Australia.

Mine industry workers (n=515) from various locations in Australia completed a questionnaire to assess the prevalence of symptoms associated with heat-related illness and water consumption habits during a summer season. Participants read from a pre-defined list and noted any heat-related symptoms that they had experienced. The most prevalent symptoms experienced were fatigue, headache, sweating, and dark coloured urine, with 77% of respondents reporting at least one symptom. Workers with shorter employment durations had higher rates of reporting multiple symptoms (rates ratios: 1.40-1.72). The most prevalent water consumption amounts over an 11-12 h shift were 2-4 L by 37.3% of total respondents, followed by 1-2 L by 36.5% of respondents. Employers should inform workers about the severe implications of heat-related illnesses, implement regular water breaks, and educate personnel about the importance of water intake. Providing employees with self-check methods of hydration status is recommended to increase awareness of their hydration status.

Extreme Heat and Occupational Health Risks.

Climate change poses a significant occupational health hazard. Rising temperatures and more frequent heat waves are expected to cause increasing heat-related morbidity and mortality for workers across the globe. Agricultural, construction, military, firefighting, mining, and manufacturing workers are at particularly high risk for heat-related illness (HRI). Various factors, including ambient temperatures, personal protective equipment, work arrangements, physical exertion, and work with heavy equipment may put workers at higher risk for HRI. While extreme heat will impact workers across the world, workers in low- and middle-income countries will be disproportionately affected. Tracking occupational HRI will be critical to informing prevention and mitigation strategies. Renewed investment in these strategies, including workplace heat prevention programs and regulatory standards for indoor and outdoor workers, will be needed. Additional research is needed to evaluate the effectiveness of interventions in order to successfully reduce the risk of HRI in the workplace.

l-Carnitine pretreatment ameliorates heat stress-induced acute kidney injury by restoring mitochondrial function of tubular cells.

A major complication of heat-related illness is the development of acute kidney injury (AKI) and damage to kidney tubular cells. Because kidney tubular cells use fatty acids as a major energy source, impaired fatty acid oxidation (FAO) may be associated with kidney injury due to heat stress. Carnitine is essential in the transportation of fatty acid into mitochondria for FAO. To date, there has been little attention given to the role of carnitine in heat-related illness and AKI. To evaluate the relationship between carnitine inadequacy and heat-related illness severity or AKI, we examined serum carnitine levels in patients with heat-related illness. We also used heat-stressed mice to investigate the effect of l-carnitine pretreatment on various kidney functions such as mitochondrial activity, proinflammatory changes in kidney macrophages, and histological damage. We observed an elevation in serum acylcarnitine levels, indicating carnitine insufficiency in patients with severe heat-related illness and/or AKI. l-Carnitine pretreatment ameliorated ATP production in murine tubular cell mitochondria and prevented a change in the kidney macrophage population dynamics observed in AKI: a decrease in tissue-resident macrophages, influx of bone marrow-derived macrophages, and change toward proinflammatory M1 polarization. In conclusion, carnitine insufficiency may be closely associated with severe heat-related illness and related AKI. Enhancement of the FAO pathway by l-carnitine pretreatment may prevent heat stress-induced AKI by restoring mitochondrial function.NEW & NOTEWORTHY Enhancing fatty acid oxidation (FAO) after acute kidney injury (AKI) improves renal outcomes. This report shows that carnitine insufficiency, which could inhibit FAO, correlates to severe heat-related illness and AKI in a clinical study. We also demonstrate that administering l-carnitine to mice improves mitochondrial respiratory function and prevents deleterious changes in renal macrophage, resulting in improved renal outcomes of heat-induced AKI. l-Carnitine may be an effective preventive treatment for severe heat-related illness and related AKI.

Incidence and risk factors of heat-related illness in dogs from New South Wales, Australia (1997-2017).

Heat Related Illness (HRI) in dogs is expected to increase as heatwaves surge due to global warming. The most severe form of HRI, heat stroke, is potentially fatal in dogs. The current study investigated the incidence and risk factors for HRI in dogs in NSW, Australia, from 1997 to 2017. We identified 119 HRI cases during this period, with a fatality rate of 23%. Dog breeds at elevated risk of HRI were Australian Stumpy Tail Cattle Dog, British Bulldog, French Bulldog, Maremma Sheepdog, Italian Greyhound, Chow Chow, Airedale Terrier, Pug, Samoyed, English Springer Spaniel, Labrador Retriever, Golden Retriever, Cavalier King Charles Spaniel, Border Collie, Staffordshire Bull Terrier, and pooled non-Australian National Kennel Council breeds (which included the American and Australian Bulldog) when compared with cross breeds (i.e., the reference variable). As expected, HRI cases were more likely in December and January, during the Australian summer and during hotter years (e.g., 2016). There were no differences in the risk of HRI between males and females nor between desexed or un-desexed dogs; but older dogs were at increased risk of HRI. These findings underscore the need for data collection that will enable the incidence of HRI in dogs to be monitored and to better understand canine risk factors particularly as temperatures will continue to rise due to global warming. The risk of mortality from HRI underpins the need for education programs focussed on prevention and early identification of HRI so that owners present affected dogs to their veterinarian as promptly as possible.

Population vulnerability to heat: A case-crossover analysis of heat health alerts and hospital morbidity data in Victoria, Australia.

OBJECTIVE: From 2010 to 2022, the Victorian Department of Health operated a heat health alert system. We explored whether changes to morbidity occurred during or directly after these alerts, and how this differed for certain population groups. METHODS: We used a space-time-stratified case-crossover design and conditional logistic regression to examine the associations between heat health alerts and heat-related and all-cause emergency department (ED) presentations and hospital admissions at the state-wide level, with models created for the whole population and subgroups. Data were included for the warm season (November-March) from 2014 to 2021. RESULTS: Increases occurred in heat-related ED presentations (OR 1.73, 95% CI: 1.53-1.96) and heat-related hospital admissions (OR 1.23, 95% CI: 1.16-1.30) on days on or after heat health alerts. Effect sizes were largest for those 65 years and older, Aboriginal and Torres Strait Islander people, and those living in the most disadvantaged areas. CONCLUSIONS: We confirm that increases in morbidity occurred in Victoria during heat health alerts and describe which population groups are more likely to require healthcare in a hospital. IMPLICATIONS FOR PUBLIC HEALTH: These findings can inform responses before and during periods of extreme heat, data-driven adaptation strategies, and the development of heat health surveillance systems.

An Easy-to-Use Prehospital Indicator to Determine the Severity of Suspected Heat-Related Illness: An Observational Study in the Tokyo Metropolitan Area.

Rapid hospital arrival decreases mortality risk in heat-related illnesses. We investigated an easy-to-use indicator of life-threatening severity of heat-related illnesses in a community setting to enable quick hospitalization by using data extracted from prehospital transportation records of a database from 2016 that included information on the clinical severity of suspected heat-related illnesses in patients (n = 2528) upon hospital arrival. Patient-related risk factors (adjusted odds ratio, aOR [95% confidence interval, CI]) included age, vital signs, location of the patient, and illness severity, and respiratory rate (3.34 [1.80-6.22]), heart rate (2.88 [1.57-5.29]), axillary body temperature (7.79 [4.02-15.1]), and consciousness level (38.3 [5.22-281.1]) were independent risk factors for heat-related illness severity. On-site blood pressure was not an independent factor for illness severity. Heart rate > 120 beats/min, respiratory rate > 24 breaths/min, and temperature > 38.6 °C (highest areas under the receiver operating characteristic curves [95% CI]: 0.80 [0.75-0.87]; 0.73 [0.67-0.81]; and 0.83 [0.77-0.91], respectively) predicted life-threatening illness severity. Changes in the vital signs of patients with heat-related illnesses, particularly tachycardia and tachypnea, constitute sensitive, easy-to-use indicators that facilitate rapid identification of severity by laypersons and transport of patients before aggravation to a life-threatening situation.

Heatstroke-induced acute kidney injury and the innate immune system.

Heatstroke can cause multiple organ failure and systemic inflammatory response syndrome as the body temperature rises beyond the body's ability to regulate temperature in a hot environment. Previous studies have indicated that heatstroke-induced acute kidney injury (AKI) can lead to chronic kidney disease. Therefore, there is an urgent need to elucidate the mechanism of heatstroke-induced AKI and to establish methods for its prevention and treatment. Recent reports have revealed that innate immunity, including neutrophils, macrophages, lymphocytes, and mast cells, is deeply involved in heat-induced AKI. In this review, we will discuss the roles of each immune cell in heat-induced renal injury and their potential therapeutic use.

Cooling Methods Used to Manage Heat-Related Illness in Dogs Presented to Primary Care Veterinary Practices during 2016-2018 in the UK.

The management of heat-related illness (HRI) in dogs has received limited attention in the veterinary literature, especially regarding effective cooling methods. Guidelines published in 2016 for prehospital management of dogs with HRI advised "cool first, transport second", and recommended using cold-water immersion and evaporative cooling (water application with air movement) as the optimal approaches to reduce the patient's temperature. The current retrospective cross-sectional observation study analysed electronic patient records from the VetCompass programme to describe the cooling methods used in dogs with HRI presented to primary care veterinary practices during 2016-2018. Of 623 HRI events identified, 341 (54.74%, 95% CI 50.81-58.60%) included information on cooling in their clinical record. Of these, 74/341 (21.70%, 95% CI 17.65-26.38%) were cooled prior to transport for veterinary care. Overall, 23.97% (95% CI 19.24-29.44%) were cooled using one of the two recommended cooling methods, whilst the most common cooling method recorded was the application of wet towels (51.31%, 95% CI 45.34-57.24%). Canine cooling guidance and messaging in both the public and veterinary sectors requires urgent review to ensure that the most effective cooling methods are promoted because delays to canine temperature reduction worsen patient outcomes.

Heat, heatwaves, and ambulance service use: a systematic review and meta-analysis of epidemiological evidence.

Ambulance data has been reported to be a sensitive indicator of health service use during hot days, but there is no comprehensive summary of the quantitative association between heat and ambulance dispatches. We conducted a systematic review and meta-analysis to retrieve and synthesise evidence published up to 31 August 2022 about the association between heat, prolonged heat (i.e. heatwaves), and the risk of ambulance dispatches. We initially identified 3628 peer-reviewed papers and included 48 papers which satisfied the inclusion criteria. The meta-analyses showed that, for each 5 °C increase in mean temperature, the risk of ambulance dispatches for all causes and for cardiovascular diseases increased by 7% (95% confidence interval (CI): 5%, 10%) and 2% (95% CI: 1%, 3%), respectively, but not for respiratory diseases. The risk of ambulance dispatches increased by 6% (95% CI: 4%, 7%), 7% (95% CI: 5%, 9%), and 18% (95% CI: 12%, 23%) under low-intensity, severe, and extreme heatwaves, respectively. We observed two potential sources of bias in the existing literature: (1) bias in temperature exposure measurement; and (2) bias in the ascertainment of ambulance dispatch causes. This review suggests that heat exposure is associated with an increased risk of ambulance dispatches, and there is a dose-response relationship between heatwave intensity and the risk of ambulance dispatches. For future studies assessing the heat-ambulance association, we recommend that (1) using data on spatially refined gridded temperature that is either very well interpolated or derived from satellite imaging may be an alternative to reduce exposure measurement bias; and (2) linking ambulance data with hospital admission data can be useful to improve health outcome classification.