Does air pollution impact on OHCA risk? A study by University of Sydney

Now that COVID-19 is going backwards, the world is slowly trying to return to its normal activities, and pollution will increase its presence in the air again. In this article we wish to analyse an aspect that regards EMS and pollution. Would air pollution increase the risk of out-of-hospital cardiac arrest (OHCA)? Let’s check an international study out!

An international study found out that, even form the short-term exposure to low concentrations of fine particulate matter PM2.5, there is an increased risk of out-of-hospital cardiac arrest (OHCA). The study noted that an association with gaseous pollutants (air pollution) such as those from coal burning/mining, bushfires and motor vehicles, in particular.

The relation between air pollution and OHCA – The source

Science Daily, which reported this study, communicated that the nationwide study of data come from Japan, chosen for its superior monitoring, population density and relative air quality, which is believed to be by far the largest of its kind. It provides comprehensive evidence of the relationship between PM2.5 and cardiac arrests, in particular out-of-hospital cardiac arrest (OHCA).


The relation between air pollution and OHCA – Collection of data

The University of Sydney led the study and the results have been published on The Lancet Planetary Health. The study aims to determine the associations between exposure to ambient air pollution and the incidence of OHCA (out-of-hospital cardiac arrest).

Professor Kazuaki Negishi, cardiologist and Head of Medicine of the University of Sydney School of Medicine and senior author, declared that precious researches made on the relation between air pollution and the acute cardiac cases (like the OHCA), were incomplete and inconsistent. Today we can say that more than 90% of OHCAs occurred at PM2.5 levels lower than the WHO guideline, a daily-average of 25 micrograms per cubic metre (?g/m3).


The danger of the out-of-hospital cardiac arrest (OHCA)

Professor Negishi explains that the out-of-hospital cardiac arrest (OHCA) is a major medical emergenc. Less than one in 10 people worldwide survives these events and there has been increasing evidence of an association with the more acute air pollution, or fine particulate matter such as PM2.5.

The study analysed around a quarter of a million of out-of-hospital cardiac arrest (OHCA) cases and a clear link yo yhe acute air pollution has been reported. The declaration is important: the study supports the recent evidence that there is no safe level of air pollution, since their findings pointed out that there is an increased risk of cardiac arrest despite air quality generally meeting the standards.

The important aspect is that air pollution worldwide will worsen from increasing numbers of cars as well as disasters such as bushfires. That means that the impacts on cardiovascular events, in addition to respiratory diseases and lung cancer must be taken into account in health care responses, according to Professor Negishi.



Improving air quality is the solution to the high riks of OHCA

The paper concludes that there is an “urgent” need to improve air quality. The authors state that a global approach to tackle this crucial health issue is necessary for our planet.


Research key findings and what it means

The University of Sydney data:

The study drew upon data from Japan because the country keeps comprehensive records of its air pollution levels as well as a high-quality, nationwide repository of out-of-hospital cardiac arrest (OHCA).

The researchers found a 1- 4 percent increased risk associated with every 10 ?g/m3 increase in PM2.5.

Put another way, Sydney has recently been experiencing increased air pollution because of bushfire smoke and, on its worst day PM2.5 surpassed the standard of 25 ?g/m3 to jump to more than 500 ?g/m3 in the suburb of Richmond, comparable to levels of continuous cigarette smoking. There are about 15,000 OHCA cases annually in Australia so in a hypothetical situation, if there is a 10-unit increase in the daily average of PM2.5, it could lead to another 600 OHCA cases resulting in 540 deaths (10% survival rate globally).

The Lancet Planetary Health paper compared out-of-hospital cardiac arrest (OHCA) that occurred up to three days after the air pollution recorded; however, the effects on the heart can occur up to five-seven days after acute air pollution, Professor Negishi says, so the entire cardiovascular impacts could be worse than indicated.

Also analysed were the impacts regarding sex and age.

Although the impacts did not divide along gender lines, for people aged over 65, PM2.5 exposure was significantly associated with incidence of all-cause OHCA.

The data revealed an association between short-term exposure to carbon monoxide, photochemical oxidants and sulphur dioxide and all-cause OHCA (out-of-hospital cardiac arrest) but not with nitrogen dioxide. Professor Negishi explains that it was likely that the levels of nitrogen dioxide, for example from car emissions, were not high enough to result in OHCA.

Adding to known impacts of air pollution on cardiovascular mortality generally, this study plugs important gaps in knowledge about the effects of short-term exposure to acute air pollution on out-of-hospital cardiac arrest (OHCA).

The authors state: “Combined with air quality forecasts, our results can be used to predict this emergency condition and to allocate our resources more efficiently.”

Air pollution fast facts

There are two main sources of PM2.5 worldwide:

1. Traffic/motor vehicles

2. Bushfires (massive annual events in California and the Amazon as well as in Australia)

Both PM2.5 and PM10 cannot be seen by the human eye and increase the chances of cardiac arrest, meaning the heart stops, which if untreated tends to result in death within minutes.
Particulate matter PM10 is relatively course dust, created for example from grinding operations and stirred up on roads; in comparison, PM2.5 is fine particulate matter, which can travel further into the body and stay for longer.
The most dangerous air pollution is PM2.5 — fine particulate matter that measures about 3 percent the diameter of a human hair.

This research is a collaboration between the University of Sydney, the University of Tasmania/Menzies Institute for Medical Research, Monash University, the University Centre for Rural Health in Australia and Gunma University in Japan.


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