OHSU Researchers Find Time Is Best Predictor Of Survival In Search And Rescue Missions

02/25/11  Portland, Ore.

After 2 days, chances of finding lost people alive are slim.

Oregon is home to forested valleys, high desert, mountain ranges and rolling rivers, and lately, it seems, to a lot of lost people. How many times have you turned on the news to hear a report of someone who went climbing on Mt. Hood, hiking in the Columbia River Gorge or traveling on rural Oregon roads and didn't return home when expected?

Oregon Health & Science University emergency medicine researchers set out to develop a model that could be used by search and rescue teams to determine when a search and rescue (SAR) mission could be terminated without abandoning potential survivors. The model found time to be the most important variable in determining whether a person will be found alive. Ninety-nine percent of people found alive were found within the first 51 hours after being reported missing. Their findings are published in the most recent edition of Wilderness and Environmental Medicine

Oregon is home to forested valleys, high desert, mountain ranges and rolling rivers, and lately, it seems, to a lot of lost people. How many times have you turned on the news to hear a report of someone who went climbing on Mt. Hood, hiking in the Columbia River Gorge or traveling on rural Oregon roads and didn't return home when expected?

Oregon Health & Science University emergency medicine researchers set out to develop a model that could be used by search and rescue teams to determine when a search and rescue (SAR) mission could be terminated without abandoning potential survivors. The model found time to be the most important variable in determining whether a person will be found alive. Ninety-nine percent of people found alive were found within the first 51 hours after being reported missing. Their findings are published in the most recent edition of Wilderness and Environmental Medicine

The uncertainty of when to end a search takes an emotional toll on the loved ones of the missing person and the searchers. Terminating a search when there is little hope for survival decreases the risk to rescuers and conserves valuable resources. Currently little information exists to help searchers determine when to end a SAR mission, and not much is known about the factors that predict survival.

OHSU researchers reviewed all 4,244 search and rescue missions initiated in Oregon from 1997 – 2003. Only those searches with outcome information were included in the final analysis. The searches were divided into two groups: the derivation cohort (1997-2000) included 1,040 searches involving 1,509 people. The validation cohort (2001-2003) included 1,262 searches involving 1,778 people. The first group was used to establish the rule and the second group was used to test the rule.

A computer model was used to analyze several variables from a state database including age and gender of missing persons, type of search (air, water, land) and length of search. Weather data, including amount of precipitation on the day the search began and minimum and maximum daily temperature, was collected retrospectively for weather stations near where the search took place.

"This analysis does have some limitations, said Terri Schmidt, M.D., professor of emergency medicine, OHSU School of Medicine and member of the OHSU Center for Policy and Research in Emergency Medicine. "For instance, we could not look at medical conditions of the lost individuals or outdoor experience. Intuitively we assume these are significant factors to survival."

The model found a high rate of survival for people found within 17 hours of first being reported missing, a moderate rate of survival for those missing between 17 and 51 hours, and a low rate of survival for individuals missing for more then 51 hours. The analysis also found people reported missing in May through October were less likely to survive, as were people older than 60. Individuals reported missing on land were more likely to be found alive than those reported missing from a water-based activity.

"This is not to say that all searches should be called-off after 51 hours," said Annette Adams, MPH, research instructor in the OHSU Center for Policy and Research in Emergency Medicine. "We believe this is a good first step in using statistical data to develop a rule to help search and rescue teams. With more data, we could use this method to develop a rule for when to abandon a search or change it to a recovery operation."

"What this analysis really tells us is that time is critical," said Schmidt. "As soon as you think a person is missing, call for help."

The uncertainty of when to end a search takes an emotional toll on the loved ones of the missing person and the searchers. Terminating a search when there is little hope for survival decreases the risk to rescuers and conserves valuable resources. Currently little information exists to help searchers determine when to end a SAR mission, and not much is known about the factors that predict survival.

OHSU researchers reviewed all 4,244 search and rescue missions initiated in Oregon from 1997 – 2003. Only those searches with outcome information were included in the final analysis. The searches were divided into two groups: the derivation cohort (1997-2000) included 1,040 searches involving 1,509 people. The validation cohort (2001-2003) included 1,262 searches involving 1,778 people. The first group was used to establish the rule and the second group was used to test the rule.

A computer model was used to analyze several variables from a state database including age and gender of missing persons, type of search (air, water, land) and length of search. Weather data, including amount of precipitation on the day the search began and minimum and maximum daily temperature, was collected retrospectively for weather stations near where the search took place.

"This analysis does have some limitations, said Terri Schmidt, M.D., professor of emergency medicine, OHSU School of Medicine and member of the OHSU Center for Policy and Research in Emergency Medicine. "For instance, we could not look at medical conditions of the lost individuals or outdoor experience. Intuitively we assume these are significant factors to survival."

The model found a high rate of survival for people found within 17 hours of first being reported missing, a moderate rate of survival for those missing between 17 and 51 hours, and a low rate of survival for individuals missing for more then 51 hours. The analysis also found people reported missing in May through October were less likely to survive, as were people older than 60. Individuals reported missing on land were more likely to be found alive than those reported missing from a water-based activity.

"This is not to say that all searches should be called-off after 51 hours," said Annette Adams, MPH, research instructor in the OHSU Center for Policy and Research in Emergency Medicine. "We believe this is a good first step in using statistical data to develop a rule to help search and rescue teams. With more data, we could use this method to develop a rule for when to abandon a search or change it to a recovery operation."

"What this analysis really tells us is that time is critical," said Schmidt. "As soon as you think a person is missing, call for help."