by Neal W. Pollock, PhD
Spoiler Alert: the most undeserved element in the title is the word “undeserved.”
Describing cases of decompression sickness as “undeserved” generally speaks more from an emotional perspective than a rational one. The driving factors are typically faith in imperfect tools and a desire (conscious or unconscious) to shift responsibility.
Decompression algorithms rely almost exclusively on pressure and time data to predict effects. Enticing pictures can be painted on the authority of any algorithm, but the reality is that all rely on limited input to interpret complex situations for people who are not uniform. Modern decompression models are important constructs that can help us to dive safely, but the products are rudimentary from a physiological perspective, without sufficient sophistication to deserve unquestioned trust.
The dive profile is almost certainly the most important determinant of gas uptake and elimination, but the truth is that we do not yet have sufficient data to quantify the impact of many of the variables that can influence outcomes (Pollock 2016). Instead, algorithms rely on simple measures and mathematical bracketing with the hope of covering the contributing factors. The problem is not in doing this; the problem is in being surprised when the outcome is not what was expected.
Accepting that the dive profile is the most important determinant of decompression risk, there are additional factors that can also have dramatic effects. Exercise is one of these. Pre-dive exercise may have complicated effects on the subsequent diving exposure. Exercise during the descent and bottom phase will increase inert gas uptake and the resulting decompression stress. Mild exercise during the ascent and stop phase can promote inert gas elimination and decrease the resulting decompression stress, but excessive exercise can promote bubble formation and increase decompression stress. Post-dive exercise is likely to increase decompression stress in all cases. Practically, while the concepts are clear, the definition of meaningful thresholds for “mild” and “excessive” exercise is difficult at best, and quantifying real-time effects far exceeds current capabilities.
Thermal state is another potentially dramatic factor (Gerth et al. 2007). Being warm during the descent and bottom phase can substantially increase blood flow and delivery of inert gas to the periphery and increase the subsequent decompression stress. Being cool during the descent and bottom phase can decrease inert gas uptake and decrease the subsequent decompression stress. Being cool during the ascent and stop phase will inhibit inert gas elimination and increase the subsequent decompression stress. Being moderately warm during the ascent and stop phase can promote blood circulation to the periphery and increase inert gas elimination, but excessive heating of peripheral tissues in this same phase can promote bubble formation as heating decreases the solubility of inert gas, effectively increasing the decompression stress.
Again, as with exercise, it is extremely difficult to identify meaningful thresholds for thermal state at different points in a dive, and quantifying real-time effects is not within current capabilities. It is certainly clear that the ambient temperature measured by a dive computer can have little correlation to the thermal status of the diver, and any thought that this information informs decompression models in a meaningful way is misplaced.
The wild card of individual (“predisposition”) factors further highlights the challenges unmet in current decompression models. Not only are these parameters not measured, it is unclear how the information could practically guide the risk assessment at this time if available. While the importance of these factors is hard to assess, it is also noteworthy that some, most often dehydration, may be used as scapegoats to explain away decompression sickness (DCS).
A state of dehydration can adversely affect circulation, potentially impeding inert gas elimination, but this almost certainly has much less impact than the dive profile, exercise, or thermal state in many cases. The impact is also not as straightforward as making it a blame agent might imply. For example, if a state of dehydration impairs inert gas elimination during the ascent and stop phase to increase decompression stress, might it not also decrease inert gas uptake during the descent and bottom phase to reduce the decompression stress?
Sound levels of hydration are good for general health and probably for decompression safety, but a state of dehydration in no way guarantees an outcome of DCS, just like a good level of hydration in no way guarantees an outcome of no DCS. The blame directed to dehydration is probably related to the observation that DCS can be accompanied by clinically important fluid shifts. This, though, is more a consequence of the disease than a cause.
The rest of the predisposition factors offer similar challenges. Physical fitness appears to confer some protection against decompression stress, but the quantification of such effects is not yet possible. A history of DCS can go either way, with persons prioritizing blame shifting over understanding or behavioral changes having a higher risk of repeat events, and persons improving understanding and moderating risk factors having a lower risk of repeat events. Increasing age is a risk factor, but the partitioning of chronological vs physiological age still needs to be worked out, as does the interaction between age, physical fitness, and biological health.
Women might have a slightly higher physiological risk, particularly during the first half of their menstrual cycle, but this is likely largely (or more than) mitigated by sex-based differences in risk tolerance and practices. The norms and practices of a buddy can affect individual risk either positively or negatively. Circulation issues include state of hydration, the presence of a patent foramen ovale (PFO), and possibly old injury sites that disrupt circulatory pathways. The presence of a PFO is likely only able to become important in decompression stress if bubbles are present, which will depend on a host of other factors. Biological health elements are likely to offer interesting insights in the future, but the ability to assess and understand them exceeds current capabilities.
The major point here is that there are a lot of unknowns and half-knowns that make it important to not expect any decompression algorithm to describe truth. They offer a first order approximation of risk. They provide what might be reasonable guidance within a wide swath of possible error. Staying within guidelines does not guarantee safety. The goal should be to plan for the possibility of suboptimal elements, perhaps several of them, that could influence outcomes.
Divers often address the recognized shortcomings of dive-computer-based decompression models by altering conservative settings and/or practice. Those who feel they are bends-resistant may push the limits; those who prefer greater peace of mind may add buffers. One of the additional challenges is that not all practices put forward to enhance conservatism will actually act in that way. The best example of this is probably deep stops. The concept of stopping deep to minimize bubble formation was enticing, but flawed. Stopping too deep will certainly minimize the possibility of bubble formation at that point, but at a point when it would never reasonably be expected for bubble formation to occur. The problem is that the time at the deep stop depth allows any tissue that is not fully saturated to take up more inert gas. The additional uptake creates increased decompression stress as the diver ascends. The concept was well intended, but the impact was counterproductive.
One of the conservative settings that is intuitively simple is gradient factors. The M-value describes a theoretical limit of supersaturation that a tissue can tolerate before problematic levels of decompression stress develop. This limit is another first order approximation of risk, with no guarantees of safety if staying within the limit. Gradient factors (GF) simply tailor limits to a different percentage of the M-value. GFs are typically presented as two values, GFlow and GFhigh, presented as GFlow/GFhigh. Those who believe in deep stops may choose a GFlow less than or equal to 20%. Those who do not believe in deep stops will likely choose a GFlow equal to or greater than 30%. Those who feel confident in their overall ability to tolerate decompression stress might choose a GFhigh in the 85% range. Those who want to add more buffers to protect against unknowns and surprises might choose a GFhigh less than or equal to 70%.
Determining whether a case of DCS should be considered “deserved” or “undeserved” is problematic when prescribed limits are based on incomplete data and when they can be altered by a variety of settings. The argument, “My computer said it was okay!” holds little if any weight. A better approach is to focus on the fundamentals. The first fundamental is to consider when DCS is a possibility. As a rough rule of thumb, any dive within the traditional recreational range (40 m/132 ft) that is approaching half the US Navy no-decompression limit carries a non-zero risk of DCS. Similarly, pretty much any dive deeper than the traditional range carries a non-zero risk. “Non-zero risk” repudiates the claim of “undeserved.”
Once the possibility of DCS has been accepted, the most productive deliberation includes an honest assessment of all of the risk factors that may have contributed to the outcome. While trying to pin the blame on one modifiable risk factor can be comforting, it probably does much less to ensure future safety. There are many effects that cannot yet be quantified, but the risk potential can be recognized. Focusing on any one variable can discourage a more honest appraisal of the possibilities.
Assessing the Risk
DCS symptoms may develop due to frank violations of accepted practice, but many cases are shrouded in ambiguity. An honest and objective assessment will almost certainly improve understanding and future outcomes more than claiming an “undeserved hit” will. It is unlikely that any two exposures will truly be identical, either for two divers sharing one dive or one diver repeating a given dive. Subtle differences can accumulate to have a meaningful impact. These differences coexist with the probabilistic nature of decompression stress, effectively that a safe outcome experienced once or several times may not guarantee the same for all future exposures.
Once all reasonable contributing factors have been considered, some room should be left for doubt. Appreciating the knowns, the unknowns, and the complexity of interactions can promote thoughtful practice without frustration. Practices can be optimized without guarantees. The first step is getting rid of the escapism that accompanies the “undeserved” label.
Gerth WA, Ruterbusch VL, Long ET. The influence of thermal exposure on diver susceptibility to decompression sickness. NEDU Report TR 06-07. November, 2007; 70 pp.
Pollock NW. Factors in decompression stress. In: Pollock NW, Sellers SH, Godfrey JM, eds. Rebreathers and Scientific Diving. Proceedings of NPS/NOAA/DAN/AAUS Workshop. Wrigley Marine Science Center, Catalina Island, CA; 2016; 145-56.
InDEPTH: In Hot Water: Do Active Heating Systems Increase The Risk of DCI? by Reilly Fogarty
Neal Pollock holds a Research Chair in Hyperbaric and Diving Medicine and is an Associate Professor in Kinesiology at Université Laval in Québec, Canada. He was previously Research Director at Divers Alert Network (DAN) in Durham, North Carolina. His academic training is in zoology, exercise physiology, and environmental physiology. His research interests focus on human health and safety in extreme environments.
Hyperbaric Chambers Are Turning Away Divers. Will There Be One Nearby When You Need It?
Unfortunately, it’s hard to make a business case for treating divers versus wound and burn care victims. As a result, many hyperbaric chambers no longer treat divers, leaving fewer facilities available for divers in need and increasing their post-dive time to treatment. InDEPTH editor Ashley Stewart reports on this growing crisis in the US and what can be done!
By Ashley Stewart
Steven Wells was diving on the scuttled wreck of the USS Oriskany off the coast of Florida in 2016 when a problem with his buoyancy compensator caused a rapid ascent to the surface.
Wells’ dive buddies followed the emergency action plan for the Oriskany listed on the Florida Fish and Wildlife Conservation Commission’s website at the time and brought Wells straight to Naval Air Station Pensacola, the nearest facility with a hyperbaric chamber. The facility turned him away because there was no one there to run it.
Wells was taken 30 minutes away to Baptist Hospital, which also has a chamber capable of treating his injuries, but the hospital had years earlier decided only to use it for wound care. Doctors there decided Wells would be taken by ambulance more than an hour away to Mobile, Alabama, the nearest facility that accepts divers.
By the time Wells arrived at the only chamber that would help him, it was too late.
“I got a call from the hospital saying, ‘Your husband is on life support. You need to get here now,’” Rachel Wells said of her late-husband of more than 23 years.
Julio Garcia — the program director of Springhill Medical Center’s wound care and hyperbaric facility where Steven Wells was to be treated — told InDEPTH that while no one can be certain how sooner treatment would have affected the outcome of Wells’ case, it would have given him the best chance for a full recovery.
Each year in the US, there are about 400 serious cases of decompression illness (DCI) — a category including both arterial gas embolism and decompression sickness — in divers, according to one 2020 paper. The Divers Alert Network (DAN) hotline dealt with 587 cases annually over the past five years.
The availability of hyperbaric chambers to treat decompression illness is something many divers take for granted. We try to avoid dive-related injuries through training, but expect treatment to be available when we need it.
The reality — as Steven and Rachel Wells tragically learned — is that only a minority of divers are close to care for diving-related injuries, according to medical professionals in the field. The estimates vary, but it’s generally believed there are about 1,500 hyperbaric medicine facilities in the US and only 67 are currently treating diving accidents, according to DAN.
The estimates vary, but it’s generally believed there are about 1,500 hyperbaric medicine facilities in the US and only 67 are currently treating diving accidents, according to DAN.
“The problem is only getting worse, not better,” Garcia, the Springhill Medical Center program director, said. Garcia has been sounding the alarm about this problem for more than a decade. His hospital takes patients from as far away as Florida cave country and treated 20 DCI cases in 2022. Those patients had an average transportation time of 11.5 hours, according to an InDEPTH analysis of Garcia’s records.
Florida stands out because it’s a popular diving destination, DAN Research Director Frauke Tillmans said, but the situation is not much better across the US. Many of the 1,500 hyperbaric medicine facilities, like Pensacola’s Baptist Hospital, have transitioned to treating wound care only for economic reasons. Emergency hyperbaric services are expensive to train and staff, and come with increased liability.
Time to treatment can be important in DCI cases
Time is of the essence when treating DCI. Divers Alert Network Director of Medical Services Camilo Saraiva told InDEPTH time to treatment is a “pivotal determinant” when it comes to outcomes for DCI patients. “Swift intervention significantly influences the effectiveness of therapeutic recompression,” Saraiva said.
Decompression sickness, for example, results from rapid changes in pressure and can form gas bubbles in body tissues. Initiating recompression therapy minimizes bubble size and number, Saraiva said, enhancing their elimination and reducing the risk of further vascular obstruction and tissue damage.
“The timely provision of hyperbaric oxygen therapy not only aids in bubble resolution but also mitigates the potential for neurological deficits and other severe complications, highlighting the critical role of early treatment in optimizing outcomes for DCI patients,” Saraiva said.
The 2018 paper “In water-recompression” stated delays to recompression in military and experimental diving are typically less than two hours and more than 90% of cases are completely resolved during the first treatment.
Frank K. Butler and Richard E. Moon, hyperbaric medicine experts, wrote in a 2020 letter to the Undersea and Hyperbaric Medicine journal editors suggesting a minority of patients who need life-saving hyperbaric oxygen treatment (HBO2) are close to a major hospital with a 24-hour emergency hyperbaric facility.
“Despite the urgent need for treatment, most hyperbaric chambers will decline to accept emergent patients at present,” Butler and Moon wrote. “Patients may eventually receive HBO2 but after a significant delay and a transfer of several hundred miles. Many never receive indicated HBO2, often resulting in poorer patient outcomes.”
Patients who are delayed treatment, they wrote, face the possibility in some cases of “death, permanent neurological damage, permanent loss of vision, or loss of an extremity, most of which would have been readily preventable had emergent HBO2 been administered.”
Why fewer chambers treat dive injuries
As recently as two decades ago, according to Butler and Moon, the majority of hyperbaric treatment facilities were available 24/7 to treat emergency patients. The percentage of those facilities now treating emergency patients is unclear, but it’s universally agreed the number has fallen significantly.
The reasons for the loss of emergency HBO2 facilities, Butler and Moon suggest, include “a better economic return when chambers focus on wound care patients as opposed to emergencies; the greater legal liability involved with treating high-acuity emergency patients; and the increased training and staffing requirements that would be required to manage critically ill patients — especially diving injuries and iatrogenic gas embolism patients.”
A letter from an administrator at Baptist Hospital — which sent Steve Wells to Springhill Medical Center — viewed by InDEPTH shows the hospital discontinued hyperbaric emergency services in December 2010, citing lack of staffing for specialty trained hyperbaric physicians who can provide 24-hour patient care. Baptist has yet to respond to InDEPTH’s request for comment.
There’s also the issue of pay. Garcia, the Springhill program director, said the current rate of pay for doctors who administer hyperbaric treatments regardless of length is around $150. A typical hyperbaric treatment for other conditions is about two hours. Diving treatments are usually six or seven, he said. “What doctor wants to get paid $150 to be up all night for seven hours, at that point making less than the technician?” Garcia said. “The fix is that healthcare payers need to pay more for the supervision of the treatment for diving injuries. Make it something that’s worth a doctor’s time besides the goodness of their hearts.”
Silence from lawmakers
Medical and diving organizations in 2020 sent a letter to the House and Senate, federal government agencies, governors of Florida and California, and the American Hospital Association expressing concerns about the lack of availability of chambers to treat diving injuries.
“There are approximately three million recreational scuba divers in the US,” the letter stated. “In the unlikely event that they suffer a diving-related injury, they trust that the US medical system will provide state-of-the-art care for their injuries, but the steadily- decreasing number of hyperbaric treatment facilities in the US willing to treat them emergently for decompression sickness or arterial gas embolism often places them at much greater risk than they realize.”
Garcia has on his own contacted lawmakers, reporters, medical systems — even private space companies like SpaceX because his facility is also the only one nearby treating altitude decompression sickness from space and air travel.
Little has changed, Garcia said.
Garcia showed InDEPTH a 2014 letter from a Defense Health Agency director who said, while there are three Undersea and Hyperbaric Medicine Society-accredited clinic hyperbaric medicine facilities and two additional facilities that can treat civilian emergencies, they are not staffed 24/7 and not designed for patients with other medical illnesses. Garcia at the time requested the creation of a federal grant to support the expansion of 24/7 hyperbaric services, but the director said that was outside of the agencies’ purview.
Two years after this exchange, Steven Wells was taken to and turned away from one of these facilities — the NAS Pensacola, listed on the Florida Fish and Wildlife Conservation Commission’s (FWC) emergency action plan at the time.
The Florida Fish and Wildlife Conservation Commission website now shows a map of the nearly 4,000 artificial reefs across Florida’s 1,350 miles of coastline. Two chambers, one in Mobile, Alabama, and one is Orlando, cover 500 of those miles densely packed with dive locations, according to Garcia.
The FWC website now shows a map of the nearly 4,000 artificial reefs across Florida’s 1,350 miles of coastline. Two chambers, one in Mobile, Alabama, and one is Orlando, cover 500 of those miles densely packed with dive locations, according to Garcia. A report from the University of West Florida estimated the sinking of the Oriskany, scuttled in 2006, generated nearly $4 million for Pensacola and Escambia County in the next year alone.
An FWC spokesperson said the agency provides diver safety reminders and recommended actions on its website “as a courtesy” and is not intended for emergency response. FWC and Visit Florida did not respond to inquiries about how much Florida’s government spends on advertising the artificial reefs and other diving activities, or whether any effort to expand the availability of hyperbaric facilities to treat the divers who show up as a result.
“My question is what is my husband’s life worth compared to your chambers,” Rachel Wells, Steven Wells’ widow said. “Why did he have to die?”
DIVER: A Crisis in Emergency Chamber Availability by Dan Orr (April 2022)
Divenewswire: A Crisis Lurking Below the Surface Emergency Hyperbaric Treatment Availability by Dan Orr (August 2021)
Undersea and Hyperbaric Medicine (2020): Emergency hyperbaric oxygen therapy: A service in need of resuscitation – an open letter by Frank K. Butler, MD, and Richard E. Moon, MD
InDEPTH: A New Look at In-Water Recompression (IWR) (2019) by Reilly Fogarty
Diving and Hyperbaric medicine (2018): In-water Recompression, Doolette DJ and Mitchell SJ
InDepth Managing Editor Ashley Stewart is a Seattle-based journalist and tech diver. Ashley started diving with Global Underwater Explorers and writing for InDepth in 2021. She is a GUE Tech 2 and CCR1 diver and on her way to becoming an instructor. In her day job, Ashley is an investigative journalist reporting on technology companies. She can be reached at: firstname.lastname@example.org.