An Analytical Look at Survivable Submersion Times

After the tragic entrapment of a canoeist on the Little River last weekend, I found myself wondering about the odds of surviving a long submersion.  The canoeist’s peers, a team experienced in swiftwater rescue, persisted in their rescue efforts for 37 minutes by repeatedly swimming into a rapid that had just ensnared their friend in an unseen feature and despite initial orders from responding authorities.(1) Thus is the camaraderie and commitment within the boating community; few rescue personnel would have given the same concerted effort at such great risk to themselves. That a pulse and spontaneous respirations were restored following resuscitation is further testament to their efforts. Unfortunately, the victim succumbed to his injuries later that evening in the hospital.

The decision to continue rescue efforts is personal and based on careful consideration of the risk to oneself and the likelihood of good outcome for the victim.  Many boaters would place themselves in harms way given the slightest chance of successful rescue, and I’m sure some would even risk harm to recover the body of a friend. Nobody can argue with those decisions, as long as they are based on an understanding of the chances for successful recovery. While most boaters have an appreciation of the risk involved in a rescue, few understand the relationship between survival and time submerged. I have heard everything from scaling back efforts following the “1-minute window” to pursuing rescue up to an hour in cold water. Medical professionals were present for last week’s rescue, and their decision to continue the rescue was based on a variety of factors.  While contemplating what I would have done, I realized my knowledge was limited to a recollection that children can survive extended periods submerged in cold water, and that Rod Baird survived 6 minutes submerged under Hydroelectric Rock on the Chattooga(2). The following is an exploration of the subject to aid myself, and others, in similar situations.

The Natural Course of Prolonged Submersion

Death or severe disability by drowning is caused primarily by lack of oxygen to the brain. Fatal neurological injury normally occurs within 5 to 7 minutes of submersion, and almost always occurs following 12 to 14 minutes.(3) Survivors may suffer a spectrum of disability ranging from memory loss to persistent vegetative state, as damage to the brain progresses inward from the cortex (higher brain functions) to the brainstem (heartbeat, respirations, reflexes). Challenges following resuscitation include fatal brain swelling, damage to the kidneys and lungs, and electrolyte imbalances which can cause cardiac arrest. Several studies have demonstrated the relationship between submersion time and survival (5,6), including a case series of children that found the risk of death or severe neurological disability to be 10% for 0 to 5 minutes, 56% for 6 to 9 minutes, 88% for 10 to 25 minutes, and 100% for greater than 25 minutes.(7)

Submersion time over 5 minutes makes intact survival unlikely; however, there have been rare cases of survival following prolonged submersion, including the longest case ever documented, a 2.5 year old girl submerged for 66 minutes in 5°C (41°F) water.(8)  One physician writes, “Reports of such ‘miracle’ cases in the medical literature, although fascinating, can readily introduce a false optimism because of the limited reporting of the dismal outcome in the majority of prolonged submersion victims.”(9)  There are 500,000 fatal cases of drowning per year worldwide(10), and exposure-adjusted, person-time estimates for drowning are 200 times as high as such estimates for deaths from traffic accidents(11). Despite this frequency, a 2011 review of medical and news reports with documented submersion time and age found only 43 cases of survival with near-normal functionality following prolonged submersion (> 4 minutes).(4)  Two-thirds were children less than 12 years old, and the remaining adolescents and adults were noted to be small in size. Only 4 survived prolonged submersion in water greater than 6° C (42.8° F), and all were submerged less than 30 minutes. The authors state that “this is likely to be a reflection of the fact that such survival is extremely rare in water warmer than 6 °C, rather than indicating that we have missed a large number of incidents in our search of the literature”, although the possibility of undocumented cases has been raised (12,13).

Cold water lengthens the survival time by two mechanisms. It triggers the mammalian diving reflex, which halts breathing and conserves oxygen by slowing the heart rate and moving blood to vital parts of the body. This response is stronger in children than adults.(14) An opposing “cold shock response” may predominate, which leads to a faster heart rate with potential fatal rhythm disturbances(15). This response also causes immediate aspiration and swallowing of water, which quickly cools the heart and carotid arteries leading to “selective brain cooling”.(4) A reduction of brain temperature by 10° C decreases energy consumption by 50% and doubles the duration of time the brain can survive without oxygen.(16)  This “therapeutic” hypothermia is accelerated by surface cooling in children and small adults with higher surface-area to body mass ratios and less subcutaneous fat.  Panic by the victim (breath holding and vigorous attempts at escape) and protective gear worn in cold water work against these principles and may prevent therapeutic hypothermia.

Relationship between water temp and submerged survival time for the rare instances of survival with full recovery outlined above. From Tipton 2011

Technical Guidelines for Rescue Attempts

There is no universal consensus on rescue efforts in prolonged submersion. A group of experts published the following based on the cases outlined above: “if water temperature is warmer than 6 °C (42.8 °F), survival/resuscitation is extremely unlikely if submerged longer than 30 minutes. If water temperature is 6°C or below, survival/resuscitation is extremely unlikely if submerged longer than 90 minutes.”(4)  They made no differentiation between children and adults given that there have been rare cases of adults surviving prolonged submersion. The possibility that cases of survival longer than 30 minutes in water warmer than 6°C  exist, but have not been identified, has some promoting between 60 minutes (US Lifesaving Association) and 90 minutes (The Joint Royal College Ambulance Liaison Committee) of rescue efforts regardless of water temperature.(12,13) The original authors point to a lack of evidence supporting such guidelines, adding that “when conditions are extreme, rescuers may be put at risk without foundation.”(17) Regardless of differing views, all agree that it is the responsibility of the commander to tailor efforts to the situation at hand, and specified timeframes are simply guides “likely to be of most use when rescuers are placed at high risk by continuing a search and subsequent rescue attempt.”(17) As another medical professional writes: “It is important to emphasize that the victim first needs rescuing and it is the decision to continue these attempts beyond the ‘likely’ survival time that is important for the commander. If the casualty is still awaiting rescue and is beneath unstable ice, in large seas or in the depths of a cave then we would hope rescuers would think carefully about the likelihood of survival versus the risk to those whom we know to be alive right now – the rescuers.”(18)

Practical Guidelines for Rescue Attempts

In dangerous swiftwater environments, the likelihood of survival should continuously be reassessed by the trip leader or individual leading the rescue. For the average person trapped underwater, intact survival is most likely if rescued within 5 minutes, and unlikely following 10 minutes. Cases of survival longer than this are rare, but efforts may be extended in controlled environments with acceptable risk. Guidelines vary between 30 minutes for water exceeding 6°C (4), to 90 minutes regardless of water temperature (12). The one consensus is that likelihood of survival decreases greatly with time submerged, and this should be considered in light of the risk to the rescuer.

Situational awareness is key, and each rescue will be unique. Accessible location, experienced team, and low risk to the rescuers make prolonged efforts more reasonable. Water colder than 6°C and small size of the person entrapped may increase the length of survival. Rivers in both rainfed and snowmelt regions may be colder than 6°C in the winter, but typically exceed this temperature in the spring, summer, and fall (see figures below the Conclusion section for average temperatures based on USGS data from a variety of popular whitewater runs(19)).  For example, from March 10th to 16th this year, the Little River fluctuated from 4.4 to 10 °C (NOAA).  Of course, rivers vary widely in temperature due to a variety of factors (distance from source, air temperature, reservoir release), and each river should be considered independently for the implications on rescue efforts. Lastly, whitewater is dynamic, and the possibility of air pockets should be factored in to any consideration of submerged time.

Conclusion

The rescue attempt that spurred this discussion was certainly conducted within accepted timeframes for possible survival, and it is admirable that the team persisted through difficult conditions to give their peer a chance, however small. Nobody can fault such selflessness, and I hope a similarly skilled crew is present should I ever become entrapped on the river. I also hope that each rescuer would be able to make an informed decision given the circumstances and consider their risk against my chance of survival. I would never wish for heroics that are not founded in purpose and reason.

Frequency of kayaking and seasonal differences between snowmelt and rain-dependent regions, based on averaged USGS data, from Moore 2010.

References:

  1. American Whitewater Accident Database. Accident #3693. http://www.americanwhitewater.org/content/Accident/detail/accidentid/3693/. Accessed March 19, 2013.
  2. Chattooga River Fatalities and Near Fatalaties Since 1970. http://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5302792.pdf. U.S. Forest Service.
  3. Orlowski JP. Drowning, near-drowning, and ice-water drowning. JAMA. 1988; 260: 390-1.
  4. Tipton MJ and Golden FS. A proposed decision-making guide for the search, rescue and resuscitation of submersion (head under) victims based on expert opinion. Resuscitation. 2011; 82: 819-24.
  5. Szpilman D. Near-drowning and drowning classification: a proposal to stratify mortality based on the analysis of 1,831 cases. Chest. 1997; 112: 660-5.
  6. Manolios N and Mackie I. Drowning and near-drowning on Australian beaches patrolled by life-savers: a 10-year study, 1973-1983. The Medical journal of Australia. 1988; 148: 165-7, 70-1.
  7. Quan L, Wentz KR, Gore EJ and Copass MK. Outcome and predictors of outcome in pediatric submersion victims receiving prehospital care in King County, Washington. Pediatrics. 1990; 86: 586-93.
  8. Bolte R and Black P. The use of extracorporeal rewarming in a child submerged for 66 minutes. JAMA. 1988; 260: 377-9.
  9. Suominen P, Baillie C, Korpela R, Rautanen S, Ranta S and Olkkola KT. Impact of age, submersion time and water temperature on outcome in near-drowning. Resuscitation. 2002; 52: 247-54.
  10. Peden M MK, Sharma K. The injury chart book: a graphical overview of the global burden of injuries. Geneva: World Health Organization, 2002.
  11. Mitchell RJ, Williamson AM and Olivier J. Estimates of drowning morbidity and mortality adjusted for exposure to risk. Injury prevention : journal of the International Society for Child and Adolescent Injury Prevention. 2010; 16: 261-6.
  12. Perkins GD. Rescue and resuscitation or body retrieval—The dilemmas of search and rescue efforts in drowning incidents. Resuscitation. 2011; 82: 799-800.
  13. Perkins GD. Reply letter: Rescue and resuscitation or body retrieval. Resuscitation. 2011; 82: e5.
  14. Gooden BA. Why some people do not drown. Hypothermia versus the diving response. The Medical journal of Australia. 1992; 157: 629-32.
  15. Shattock MJ and Tipton MJ. ‘Autonomic conflict’: a different way to die during cold water immersion? The Journal of physiology. 2012; 590: 3219-30
  16. Szpilman D, Bierens JJLM, Handley AJ and Orlowski JP. Drowning. New England Journal of Medicine. 2012; 366: 2102-10.
  17. Tipton M, Golden F and Morgan P. Drowning: guidelines extant, evidence-based risk for rescuers? Resuscitation. 2013; 84: e31-2.
  18. Ramm H and Robson B. Reference editorial – Rescue and resuscitation or body retrieval. Resuscitation. 2011; 82: e3.
  19. Moore RD, Schuman TA, Scott TA, Mann SE, Davidson MA and Labadie RF. Exostoses of the external auditory canal in white-water kayakers. The Laryngoscope. 2010; 120: 582-90.

“Screaming Meanies” on the Little River. Photo by author in 2007.