SINGAPORE - A nation-wide study found that lower air quality, as measured by the Pollutant Standards Index (PSI), is associated with higher risk of out-of-hospital cardiac arrest (OHCA).
After studying data from more than 8,000 cases from 2010 to 2015, researchers found that the incidence of OHCA increased when Singapore's PSI was above 50, which is in the moderate (51 to 100) and unhealthy (above 100) ranges.
Local PSI levels often spike due to trans-boundary haze.
Compared to the healthy range, the risk of cardiac arrest increased by 10 per cent in the moderate range and 30 per cent in the unhealthy range, said Associate Professor Marcus Ong, the senior author of the study, which was led by the Singapore General Hospital (SGH) and included the Singapore Health Services, Monash University (Australia), the Singapore Civil Defence Force and Duke-NUS Medical School.
Older males above 65 were found to be most vulnerable. The mean age of cardiac arrest patients was 66, while 65 per cent of the patients were male.
Prof Ong, who is a senior consultant at SGH's department of emergency medicine, said the study revealed strong evidence linking high PSI levels with higher short-term risk of OHCA.
The spike in numbers of OHCA usually started on the day of high PSI levels and lasted at least five days after, he said.
The excess risk was also highest in the first three days after PSI levels increased.
Prof Ong said this may be due to the body needing to work harder to breathe normally on such days, though there are multiple factors at play.
He said: "It (the study) gives some urgency to solving this issue of trans-boundary haze because it has a direct public health impact and a direct relationship with excess mortality."