The difference, which was seen in both drivers and passengers of crashed vehicles, in victims of all kinds of crashes, and in people whose blood-alcohol levels were under the legal limit to drive, suggests that alcohol does something to the body that increases its vulnerability to injury.
The new results will be published in the April issue of the journal Alcoholism: Clinical & Experimental Research by a team from the U-M Health System and the U-M Transportation Research Institute.
They represent the most in-depth clinical study to date demonstrating the connection between alcohol use and injury severity: Earlier population and animal studies have suggested the effect, but it has never been thoroughly examined in a clinical setting.
Among other things, the researchers hope their finding could improve emergency medical treatment for all types of injuries, if first-responders, doctors and nurses ask whether patients have been drinking when they triage and evaluate them.
They also hope it will spur research on exactly what alcohol does to the human body on the microscopic level – perhaps leading to therapies that could reduce the impact of injury in people with alcohol in their systems.
"Drivers and passengers who had any level of alcohol in their bodies were, on average, more than one and a half times as likely to experience a serious injury as someone who hadn't been drinking, and their injury severity was 30 percent higher, controlling for the severity of the crash they were in, whether they were wearing their seat belt, or whether they had a high alcohol tolerance," says Ronald Maio, D.O., M.S., a U-M emergency medicine physician who helped lead the study. Maio directs the U-M Injury Research Center.
"We as a society may be grossly underestimating the burden of injury attributable to alcohol, and the need for more research and preventive efforts," Maio adds. "Until we can learn more about this effect and how it can be prevented, anyone who drinks before getting in a motor vehicle, even as a passenger, should give themselves more time to sober up, and stop drinking long before they leave."
The data were drawn from 1,362 motor vehicle crash victims ages 18 years or older who came to the emergency rooms of two different Michigan hospitals and were treated and released, admitted to the hospital, or died from their injuries.
The patients had been driving or riding in cars, vans or pickup trucks; motorcycle accidents were excluded. Just over three-quarters of the patients had been driving the vehicle at the time of the crash. Twenty-one percent of the patients had been drinking prior to the crash.
The study took into account the patients' medical conditions, their scores on a standard scale of injury severity, results from tests of their blood alcohol levels, answers to questions about their alcohol use, and information from police reports on the nature and severity of the crashes they were in, including seatbelt use, which allowed them to estimate the strength of the crash forces.
Maio and his colleagues believe it is the most detailed study of its kind ever performed. Previous studies that suggested no connection between injury severity and alcohol did not include considerations of crash severity or the full range of injury.
According to the National Highway Traffic Safety Administration, alcohol-related motor vehicle crashes killed more than 17,440 people in 2001, and injured 300,000 more, costing $45 billion. Alcohol is well known to reduce the judgment and performance of drivers and others engaging in activities that require concentration, quick reaction, and precise movement.
This knowledge has led to laws that set limits on the level of alcohol that drivers can have in their blood, most commonly set by states at 0.08 or 0.1 percent of blood volume. It has also led to major public-health campaigns aimed at preventing drunk driving – such as efforts to encourage those who have been drinking to let someone else drive them home. A federal law passed in 2000 requires all states to have a legal limit of 0.08 by October, 2003, or risk losing federal highway construction funds. Fourteen states have yet to comply.
But the U-M study shows that that even drivers and passengers with blood-alcohol percentages less than 0.1 percent suffered worse injuries and had higher likelihood of severe injury than those who were completely sober. "Basically, this shows that alcohol can make one's risk of injury from a crash worse, and in fact the effect may be strongest in relatively minor crashes," says Maio. He notes that the effect of alcohol on injury varies with blood alcohol levels.
Though the exact mechanism for the increased injury is still a mystery, the researchers point to animal studies showing that alcohol affects the membranes of cells. The kinetic energy of a vehicle crash could be enough to burst cell membranes that have been altered by alcohol, thereby increasing the severity of injury, Maio says. But only further research will tell for sure.
In the meantime, the researchers suggest that emergency medicine staff – at the crash scene and at the hospital – should begin taking alcohol intake into account when triaging and treating crash victims. Other injuries that result from some sort of impact – such as falls or assaults – may also be affected by alcohol intake, Maio suggests, though further research is needed.
And, as society grapples with measuring and reducing the impact of alcohol-related crashes, the researchers say their data should be taken into account. "Because excess injury results even at alcohol levels below 0.10 percent, previous analyses of alcohol-related injury costs may have underestimated the true cost of alcohol in motor vehicle crashes," they write.
In addition to Maio, the team included former UMTRI director and professor emerita Patricia Waller, Ph.D., Elizabeth Hill, Ph.D., formerly of the U-M Department of Psychiatry; and Frederic Blow, Ph.D., associate professor of psychiatry and a member of UMTRI and the U-M Addiction Research Center. The study was funded by the National Instiute on Alcohol Abuse and Alcoholism, UMTRI, UMARC, and the U-M Department of Emergency Medicine.