Air quality and the risk of out-of-hospital cardiac arrest in Singapore (PAROS): a time series analysis

Background Previous studies have reported positive associations between out-of-hospital cardiac arrest (OHCA) and air pollutant concentrations, but there are inconsistencies across studies. We aimed to investigate the association between pollutant concentrations and the risk of OHCA in Singapore. Methods We did a time series analysis of all cases of OHCA in Singapore reported between July 1, 2010, and Dec 31, 2018, to the Pan-Asian Resuscitation Outcomes Study (PAROS), a prospective, population-based registry. Using multivariable fractional polynomial modelling, we investigated the immediate (day 0) and lagged (up to 5 days after exposure) association between 10 mu g/m(3) increases in concentrations of particulate matter with a diameter of 2 center dot 5 mu m or smaller (PM2.5), particulate matter with a diameter of 10 mu m or smaller (PM10), ozone (O-3), nitrogen dioxide (NO2), and sulphur dioxide (SO2) and 1 mg/m(3) increase in carbon monoxide (CO) and relative risk (RR) of OHCA. Findings We extracted data for 18 131 cases of OHCA. The median age of this cohort of cases was 65 years (IQR 56-80), 6484 (35 center dot 8%) were female, 11 647 (64 center dot 2%) were male, 12 270 (67 center dot 7%) were Chinese, 2873 (15 center dot 8%) were Malay, and 2010 (11 center dot 1%) were Indian. Every 10 mu g/m(3) increase in PM2.5 was associated with increased risk of OHCA (RR 1 center dot 022 [95% 1 center dot 002-1 center dot 043]) over the next 2 days, which decreased over the subsequent 3 days (3-5 days after exposure; 0 center dot 976 [0 center dot 955-0 center dot 998]). For PM10, O-3, NO2, and SO2, we did not observe any associations between increased concentration and risk of OHCA on day 0 or cumulative risk over time (ie, at 0-1 days, 0-2 days, 0-3 days, 0-4 days, 0-5 days, and 3-5 days after exposure). For CO, we observed a cumulative decreased risk of OHCA across 0-5 days after exposure (0 center dot 876 [0 center dot 770-0 center dot 997]) and at days 3-5 after exposure (0 center dot 810 [0 center dot 690-0 center dot 949]). We observed effect modification of the association between increasing PM2.5 concentration and OHCA 0-2 days after exposure by cardiac arrest rhythm (non-shockable 1 center dot 027 [1 center dot 004-1 center dot 050] vs shockable 1 center dot 002 [0 center dot 956-1 center dot 051]) and location of OHCA (at home: 1 center dot 033 [1 center dot 008-1 center dot 057] vs not at home 0 center dot 955 [0 center dot 957-1 center dot 035]). In hypothetical modelling, the number of OHCA events associated with PM2.5 could be reduced by 8% with a 1 mu g/m(3) decrease in PM2.5 concentrations and by 30% with a 3 mu g/m(3) decrease in PM2.5 concentrations. Interpretation Increases in PM2.5 concentration were associated with an initial increased risk of OHCA and a subsequent reduced risk from 3-5 days after exposure, suggesting a short-term harvesting effect. A decrease in PM2.5 concentrations could reduce population demand for emergency health services. Copyright (c) 2022 The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY-NC-ND 4.0 license.

Automated summary

This study found that increased PM2.5 concentrations were associated with an initial increased risk of OHCA, followed by a reduced risk from 3-5 days after exposure. No significant associations were observed between increased concentrations of other pollutants (PM10, O-3, NO2, SO2) and OHCA risk. Decreasing PM2.5 concentrations could reduce the number of OHCA events.