Background In the context of global climate change, heatwaves pose an increasing threat to human health. Emergency ambulance calls are an important outcome indicator of acute health response in populations during heatwave weather. However, studies on the association between emergency ambulance calls and heatwaves in China have primarily focused on the southern regions, and less attention is paid to the northern regions, which hinders a comprehensive assessment of acute health impact posed by extreme heat.

Objective To quantify the association between heatwaves and emergency ambulance calls in Dezhou City, Shandong Province.

Methods The data on daily records of emergency ambulance calls, meteorological factors, and air pollution from May to September of 2020 to 2022 in Dezhou City, Shandong Province were collected. Heatwaves were defined by combining thresholds at the 90th, 92.5th, 95th, and 97.5th percentiles (P₉₀, P_92.5, P₉₅, and P_97.5) of the year-round daily mean temperature and durations of ≥2, 3, or 4 consecutive days, respectively. A generalized additive model with a distributed lag nonlinear model was used to estimate the relative risk of emergency ambulance calls during heatwave days compared with non-heatwave days.

Results During the study period, a total of 143393 emergency ambulance calls were analyzed, with 59.75% of individuals aged <65 years, 53.38% male, and 44.94% due to respiratory causes. Compared to non-heatwave periods, all 12 types of defined heatwaves were significantly associated with an increased risk of emergency ambulance calls. The heatwave effect intensified progressively with higher temperature thresholds and longer durations. The cumulative relative risk rose from 1.12 (95%CI: 1.07, 1.17) for the P₉₀_2d type to 1.26 (95%CI: 1.14, 1.40) for the P_97.5_4d type. No significant gender difference was observed in the association between heatwaves and emergency ambulance calls. Regarding age, older adults were more vulnerable, with a relative risk of 1.60 (95%CI: 1.42, 1.81) for the most severe heatwave type P_97.5_4d compared with non-heatwave periods. Among the different causes of calls, the association between respiratory diseases and heatwaves was the most pronounced, with the relative risk increasing from 1.22 (95%CI: 1.15, 1.29) for the mildest heatwave type P₉₀_2d to 1.72 (95%CI: 1.54, 1.93) for the most severe heatwave type P_97.5_4d.

Conclusion In Dezhou City, Shandong Province, heatwaves are significantly associated with an increased risk of emergency ambulance calls. The effects of heatwaves on emergency ambulance calls vary by age and disease type, with the elderly and patients with respiratory diseases being more susceptible. These groups should take protective measures.