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 μg/m increases in concentrations of particulate matter with a diameter of 2·5 μm or smaller (PM), particulate matter with a diameter of 10 μm or smaller (PM), ozone (O), nitrogen dioxide (NO), and sulphur dioxide (SO) and 1 mg/m 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 (35·8%) were female, 11 647 (64·2%) were male, 12 270 (67·7%) were Chinese, 2873 (15·8%) were Malay, and 2010 (11·1%) were Indian. Every 10 μg/m increase in PM was associated with increased risk of OHCA (RR 1·022 [95% 1·002-1·043]) over the next 2 days, which decreased over the subsequent 3 days (3-5 days after exposure; 0·976 [0·955-0·998]). For PM, O, NO, and SO, 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 (0·876 [0·770-0·997]) and at days 3-5 after exposure (0·810 [0·690-0·949]). We observed effect modification of the association between increasing PM concentration and OHCA 0-2 days after exposure by cardiac arrest rhythm (non-shockable 1·027 [1·004-1·050] vs shockable 1·002 [0·956-1·051]) and location of OHCA (at home: 1·033 [1·008-1·057] vs not at home 0·955 [0·957-1·035]). In hypothetical modelling, the number of OHCA events associated with PM could be reduced by 8% with a 1 μg/m decrease in PM concentrations and by 30% with a 3 μg/m decrease in PM concentrations.

INTERPRETATION

Increases in PM 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 PM concentrations could reduce population demand for emergency health services.

FUNDING

National Medical Research Council, Singapore, under the Clinician Scientist Award, Singapore and the Singapore Translational Research Investigator Award (MOH-000982-01).