Category Archives: mountain

Does that airbag really help?

Sorry for the long hiatus over the holidays. I wish I could say I was doing something fun and exotic, but instead I simply became the curriculum director at my current residency, which changed my workload quite a bit. That being said, back to the wilderness topics.

Since it’s winter, we are going to keep talking about avalanches. Since indications for resuscitation have been discussed before, now we will turn towards prevention. Two main ideas, first, avoid triggering an avalanche, and second, if you find yourself caught in one, try not to get buried. It makes sense, as the data from older studies is pretty clear that people who are buried die at a markedly higher rate than those who are not (52% vs 4%). What’s more, for those that are buried, the quicker they are found decreases their mortality, thus people buried less deep would likely have a higher survival rate.

Source: Hansi Heckmair/ABS

Enter airbags, which were invented to prevent this “critical burial” that causes increased mortality (critical meaning impairment of airways). They do this by basically making you much larger and more buoyant by inflating a large balloon that is strapped to your back. At least, that’s the theory. There wasn’t a lot of strong research devoted to them before implementation, and as they weren’t created by Roche, postmarketing research was lacking as well. Tie observer bias into this (people weren’t reporting near misses that didn’t involve airbags) and you are left with almost nothing of value to base recommendations on.

These authors wanted to fix that, so they did this study to determine the effectiveness of airbags based on preventing critical burial and mortality, as well as documenting frequency and causes of deployment failures. To do this, they looked at prior avalanche accident records from multiple countries, culling only worthwhile data that would show a difference between airbag users and nonusers. Thus, single victim events, small avalanches, or victims who weren’t seriously involved were removed in an attempt to reduce bias.

And once they crunched the numbers, they found out that airbags really do help. If you combine airbag failures with airbag inflations, the absolute risk reduction for critical burial is 29% (56%-27%), and the absolute mortality reduction is 17% (34%-17%). If you combine airbag failures with those not wearing airbags to begin with (why?), then risk reductions for critical burial and mortality are 35% and 23%, respectively. When you combine these values to adjusted mortality, you get a risk reduction of 11%, or a NNT of 9 for mortality with airbag use. Not too shabby.

Deployment failures occurred an alarming 20% of the time. Of these failures, 72% were attributed to operator error (not deploying them appropriately or incorrect maintenance). Slightly concerning, 12% of the failures involved destruction of the airbag during the avalanche. Of course, the absolute failure rate due to destruction or device failure is right at 5%.

So yes, if you’re going anywhere that there’s a risk of avalanches, you should wear an airbag. Also you should carry a beacon. And, like most other life saving measures, be they medical or technical, you’re only as good as what you do. Thus, read the instructions and know how to use it before you go out-of-bounds. However, this study did have a higher mortality of airbag users from prior studies (11% vs 3%), so don’t expect an airbag to make you immortal. Certainly, don’t do stupid things simply because you think you have a safety net (although it’s been shown that this doesn’t really occur). Of note, the usual problems with poor data due to non-standardized reporting as well as a low total number of victims apply to interpretation of this data.

The effectiveness of avalanche airbags
http://www.ncbi.nlm.nih.gov/pubmed/24909367

What leads to rock climbing rescues?

Rock climbing is a popular sport, but most rock climbing areas are either remote or sparsely populated with climbers, leading to poor data collection with regards to rescue events.The US National Park Service has data that shows only 3% of SAR are for technical roped climbing, versus 48% for hiking.  Thus, preventive education for climbers, as well as preparation for SAR, used to need a lot of educated guessing about what types of incidents occur.

Thankfully, there is one place where the density of climbers and the number of SAR events are high enough to get decent data. That place is Boulder County, CO, home of the Rocky Mountain Rescue Group. The incident reports by the RMRG allow consistent data for rock climbing rescues that break them down into specific injuries and climbing practices that led to them. It’s worth noting that climbing SAR accounts for 19.5% of the total SAR for RMRG, which is quite different from what the NPS reports. This is likely due to ease of access to popular climbing sites next to a highly populated area.

It’s not surprising that more incidents happen in summer and autumn. Weekends accounted for slightly more than half of the incidents as well. The most common victim is a male aged 20-29. In order of frequency, the activities that led to injuries were technical roped climbing (including belay incidents), unroped climbing, bouldering, mountaineering, and lastly simply being a bystander when a rock fall occurs.

For roped climbing, most injuries and incidents were lead falls, accounting for more than a third of incidents, followed by belay accidents at slightly over 20%. Being lost or stranded comes next, and have nearly twice as many victims per incident as any of the other activations. Second fall, anchor failure, rock fall, and medical causes are small players in this data set, accounting for single digit percentages each.

Incidents involving belay or rappelling most commonly resulted from the ropes being used not being long enough to reach the ground. A smaller amount resulted from the belayer losing control of the rope. Many of the rest of the incidents are from ropes getting stuck, with only 1 coming from a knot coming untied.

Unroped climbing includes free climbing as well as scrambling. The distinction is that free climbers are often experienced, and scramblers are not. The authors point out that their data does not distinguish between the two, so level of experience is not factored in to their incidents. They don’t show the data, but report that unroped climbing most often leads to victims being stranded but uninjured. However, they then report that unroped climbers are the most common climbers involved in fatalities, with 39% of fatal incidents.

Rock falls account for few injuries compared to the other activities, but their data demonstrates an important point. While rock falls are seemingly random, they most frequently occur during times of freeze-thaw cycling. Thus, in the spring they occur at lower altitudes, and this elevation goes up during the summer until the weather turns colder again.

Now that the activities have been identified, let’s turn to the injuries themselves. More than half (56.5) of the victims met by the RMRG had 1 or more injuries. Of those injuries, most were lower extremity injuries at 29.5%. This was followed by head injuries at 17%, and spinal injuries at 12.5%. Upper extremity, chest, abdomen, and “dislocated shoulder” (listed separately from upper extremity by the authors) were all less than 3% of the injuries each. Sadly, just under 10% (23/247) were fatalities. Of note, these are the suspected injuries listed by the RMRG, not actual identified injuries at definitive care, so be cautious with interpretation of severity of injury.

So what does this mean? Well, for the SAR guys, it means being prepared for more than just rescuing the lost, as many of them will be injured. However, preventing these incidents would have more health benefits. I’m not sure how to convince people not to climb without safety ropes, but the data shows that it is inherently riskier than all other forms of climbing. Also, making sure that your rope can get the climber all the way to the ground is quite important. When belaying or spectating, don’t stand in the fall line. Lead climbers should be extra careful based on this data set, as they are most at risk of injury.

Limitations are many. This is narrative data that is often presumptive as to injury, as well as missing many features such as length of fall, experience level, and other events leading to injury. There is also reporting bias, as it is likely that many minor injuries do not get reported to SAR. However, it is a robust set of data that hopefully can lead to changes in climbing education at popular areas.

Rock Climbing Rescues: Causes, Injuries, and Trends in Boulder County, Colorado

http://www.ncbi.nlm.nih.gov/pubmed/22727678

Props to the authors for giving a rather comprehensive list of definitions of the climbing terms used in their article. While many readers probably knew them, assuming that all readers do leads to decreased understanding of the article. I wish more authors would be as thorough with their explanations of possibly unfamiliar terms.

Predicting survival after avalanches

More than 150 people die each year after being buried in an avalanche, and mortality is greater than 50% for this condition. Unfortunately, a large amount of resources are used on patients who ultimately expire, so determining which ones are likely to survive can safe costs and allow better utilization of resources such as extracorporeal life support (ECLS) warming and air evacuation.

Of the 3 common causes of cardiac arrest after avalanche, only hypothermia is likely to have good outcomes. Trauma and hypoxia have poor outcomes. Most algorithms have providers stop resuscitation for severe trauma, and airways packed with snow. However, ascertaining hypoxia vs hypothermia is less obvious. Prior attempts used potassium >10 mmol/L or >12 as a surrogate marker for cellular death from hypoxia, but no other markers are used.

So these authors took 20 years of data from the North French Alps, which ended up being only 48 patients with cardiac arrest.  18 of them had ROSC pre-hospital, and only of those 2 were eligible for ECLS. 19 of the 30 without ROSC were also eligible for ECLS. In total, only 8 survived, 5 from the pre-hospital ROSC group, and 3 from the non-ROSC. Of the 8 survivors, only 3 had favorable neurologic outcomes.

All of these were patients with rescue collapse, that is loss of vital signs after extrication or transfer. 3 other patients with rescue collapse died however. Other indicators for survival in their analysis are the presence of a rescue pocket, K <4.3 (nobody survived above 4.2, but some nonsurvivors had levels below this), and coagulation disturbances. Interestingly, their data showed no overlap of prothrombin time between survivors and non-survivors, but they sadly did not give the values, only as ratios. Other values such as PaO2, PaCO2, lactate, and bicarb are not predictive.

Unfortunately, for such a long time period of collections, there were very few survivors. The retrospective nature also limits analysis. It does look like we need to reduce the cutoff for resuscitation from values of K from 10-12 mmol/L to a lower number (7?). Also, identification of coagulation abnormalities may help. Perhaps POC thromboelastograms may be a way to identify those that do not merit resuscitation.

Survival after avalanche-induced cardiac arrest
http://www.ncbi.nlm.nih.gov/pubmed/24971508

Does fear make you a better climber?

Climbing requires a significant amount of mental and physical energy. The climber needs to think about their line, their holds, and any potential consequences of any error. Free soloers don’t utilize harnesses, and are more at risk of disaster with any fall.

So can fear help them climb safely? The article doesn’t answer this directly. What it does is show the effect of adding cognitive tasks to physical activities, and should serve as a warning for anyone who performs tasks that have life or death implications.

What they did was interesting, and had jumped off from earlier work. The authors took 15 experienced climbers, and gave them 5 tasks to complete. 3 were bouldering tasks, and 2 were simply memory tasks. The memory tasks were to listen to words during 3 minutes, and recall as many as possible for the 90 seconds afterwards. Of the bouldering tasks, 1 was just going back and forth for 3 minutes, and the other 2 required listening to a list of words while climbing, and then recalling them immediately afterwards. 

What makes it intriguing is the differences between the  memory tasks. Apparently there is a list of Affective Norms for English Words, and it rates words based on emotions. The categories are happiness, sadness, anger, fear, and disgust. So for the seated and climbing memory tasks, one used a list pulled from 40 words with the highest fear score, and the other pulled from 40 words that scored low on all 5 categories.

It is not surprising that there was a difference in recall between seated memory tasks and those with climbing. However, it is surprising that there was a significant difference in climbing efficiency and distance between the fear and neutral dual-tasks. Sure, they’re not huge differences, but the time of the test was only 3 minutes. Combine that with experienced climbers and a course height, limited to less than 3.3m which shouldn’t have been a struggle for them, and it makes the difference real.

The authors state that fear “words” may cause the climber to subconsciously use more caution, or be slower as if they had actual fear. This may or may not be the reason behind the shorter distances and diminished efficiency compared to non-fear-inspiring words. Multiple other references point towards real fear certainly causing decreased performance, so the concept  isn’t completely out there.

The other point that is important is that there was a large difference in recall with physical activity, with the participants remembering less than 50% of the words. Thus, if you take nothing else from this article, remember that half of what you way to the search and rescue guys while they are working will be forgotten, and you’ll make them slower in the process.

Of note, this article uses the word “whilst” 10 times, which has to be some sort of record.

The impact of fear words in a secondary task on complex motor performance: a dual-task climbing study
http://www.ncbi.nlm.nih.gov/pubmed/23873435