Treating The Bends Part 2

T H E C H A M B E R O P E R A T O R

By Dennis Guichard

When it comes to anyone's ultimate well-being inside a hyperbaric chamber, it is undoubtedly the skill and experience of the Chamber Operator that is most critical to the success of any treatment.

It’s the Subsea and Hyperbaric Medicine qualified Physician who, of course, assesses any patient's condition upon arrival at the hyperbaric facility and prescribes the suitable course of treatment, it's the Chamber Attendant who ensures your comfort and well-being inside the chamber, but it’s the Chamber Operator who critically manages all the life support systems, ensures adequate oxygen delivery, carefully controls prescribed descent and ascent rates, operates oxygen delivery and air break time schedules, controls the fire risk systems, and is the valuable link between the Physician and the Chamber Attendant.

There is no question that the Chamber Operator is a technical wizard of humbling capability. They are often paramedical or commercial diver medic qualified, but they also have a deep understanding of

diving physics, physiology, dive planning, and decompression theory. They are also commonly formally trained through the Undersea and Hyperbaric Medicine Society in the fundamentals of hyperbaric medicine.

The Netcare St Augustine’s Hospital Hyperbaric Medicine and Wound Care Unit is managed by the incredibly talented and professionally-minded Chad Katz, who runs the day-to-day functional operation of the chamber facilities, assists the facility Physician (Dr Craig Springate) with patient wound care treatments, works as the Chamber Operator doing everyday hyperbaric medicine treatments, is on constant standby 24/7 to help treat any decompression sickness cases referred by the DAN Hotline, and freelances as an experienced Paramedic for various emergency services in his spare time.

Not only is the Chamber Operator managing the safety of any patients in the chamber but also managing the decompression schedules and well-being of any number of Chamber Attendants who might be doing multiple or split-time treatments in the chamber, each of whose tissue loading and decompression status need to be monitored and controlled to ensure they don't bend and become patients themselves.

The internal environment of the chamber must be maintained within prescribed set points to ensure thermal comfort of the occupants, ensure that breathing gasses are provided at an adequate life support level, and ensure that the internal environment of the chamber is at a low fire risk status. The Chamber Operator can't blink for a moment as they keep a keen eye on chamber oxygen levels, carbon dioxide levels, chamber humidity, and chamber air temperature. These conditions need to be kept within a tight range of balance.

In SCUBA diving, we are commonly taught not to exceed a maximum partial pressure of oxygen of 1.6 bar, and ideally not to let that value exceed 1.4 bar to control the risk of central nervous system oxygen toxicity in the water, whilst during a controlled recompression treatment we will have diver patients breathing 100% medical oxygen at 2.8 bar partial pressure for repetitive cycles of 20-minute intervals whilst undergoing decompression sickness treatment.

The risk of oxygen toxicity is high, but the medical oxygen is being administered in a controlled medical environment by an experienced and knowledgeable staff of hyperbaric professionals where the risks are controlled and because the benefits thereof are critical to how hyperbaric medicine works in the treatment of many disorders including decompression sickness.

Functionally speaking, recompression following diagnosis of decompression sickness has many physics-related benefits, including a reduction of any trapped inert gas bubble volume, reducing the surface area to volume ratio of bubbles inducing them to collapse, and enhancing the gas diffusion gradient encouraging inert gas to leave the bubble and dissolve back into the blood plasma.

Additionally, hyperbaric oxygen treatment also helps heal clinical physiological symptoms through various biological mechanisms oxygenating any ischaemic tissue, reducing leukocyte (white blood cell) adhesion in blood vessels, and releasing neurotrophin proteins which are protective of nervous system neurons.

Worldwide we have a range of various recognised treatment tables which we can use for decompression sickness treatments and hyperbaric oxygen therapy. However, in South Africa, it has long been accepted protocol to rely on the US Navy tables for our use.

The primary treatment schedule for mild pain-only decompression sickness is thus the US Navy Table 5, which commences with pressurisation to a chamber depth of 18m seawater, equivalent at a slow controlled descent rate of 6m per minute. The patient will then be given 100% medical oxygen to breathe at that depth via a hood system that provides the oxygen and vents expelled air safety back out of the chamber.

Ideally, we would hope to see a resolution of the pain symptoms within 10-minutes of breathing oxygen at depth. Otherwise, the US Navy Table 5 can be extended with two additional 20-minutes cycles, or we can change the treatment protocol to US Navy Table 6, which is also longer and offers more time for a resolution of symptoms.

US Navy Table 5 is a relatively quick treatment lasting just 2-hours and 15- minutes, whereas US Navy Table 6 is 4- hours and 45-minutes long, offering extended periods of breathing 100% medical oxygen at 'depth'. Both Tables 5 and 6 include slow controlled ascent rates of just 0.3-metres per minute, carefully and delicately controlled by the super-skilled Chamber Operator.

US Navy Table 4, which is used for the treatment of more severe cases of decompression sickness, is 38-hours 35- minutes long, and US Navy Table 8, which is used for uncontrolled ascents when more than 60-minutes of compulsory decompression have been omitted (if you even survive an ascent and tissue loading of that nature), can be up to 65-hours 29- minutes long.

Last but not least, it is an essential function of the Chamber Operator to keep a fully detailed logbook recording every aspect of every treatment, as this information forms parts of the legal

framework of operating a hyperbaric facility. Relatively straightforward, perhaps on a singular short hyperbaric or decompression sickness treatment profile, but endlessly more complicated on those long treatment tables where teams of doctors, chamber attendants, and chamber operators have to work in shifts to ensure continuity of adequate patient treatment and also manage the decompression status of the attendants.

According to the latest 2019 DAN Diving Report, 2,423 decompression sickness cases for the four years, 2104 through to 2017. Of those cases, around 23% were Type 1 pain-only joint bends, 26% were skin bends, and 45% were the more serious Type 2 neurological bends, i.e., bubbles in the spinal cord and brain. Although a recent publication on PubMed is now also suggesting that Cutis Marmorata (skin bends) may, in fact, rather be a symptom of microbubbles embolising on the brain stem (the site of autonomic nervous system regulation of skin blood vessel dilation and constriction) and thus much more serious than we’ve always believed.

The consequences of this hypothesis are that Cutis Marmorata skin decompression sickness should no longer be considered a mild innocuous form but rather a severe neurological form and treated accordingly. It's also thus a frightening realisation then that some 71% of bends, according to recorded DAN worldwide statistics, are the more serious forms of neurological decompression sickness which are also often known not to always heal completely without residual complications.

It appears that we're also literally at an endpoint of our long-standing early belief in thinking that it is a hypothetical algorithm that is always going to keep us safe by preventing decompression sickness when in reality, we all embody a wide range of individual susceptibilities that throw the basis of any algorithm's general framework of assumptions into vast disarray. When statistics show us that some 86% of decompression sickness cases are from divers completely within their maximum allowable dive time limits, it becomes clear that there is certainly more going on physiologically in our bodies than just the simplistic formation of microbubbles at the end of any dive.

We seem to be moving into an exciting new realm of more closely considering individual diver bubble generation risk profiles, which may differ wildly from one diver to the next and from one day to the next in any individual. It's critical, of course, first and foremost, to adhere to all the guidance around effective dive profile management to help minimise the generation of bubbles in our tissues and venous systems. Still, it is equally fascinating how each of our physiologies responds to the presence of microbubbles after any dive, which seems equally central to whether we might present with decompression sickness.

Every scuba dive generates microscopic bubbles in our tissues and venous bloodstream; there is no such thing as a bubble-free dive. And it seems that decompression sickness is then a result of how our bodies individually respond on any given day to how those microscopic bubbles interfere with the endothelial lining of our blood vessels and perhaps lead to vascular inflammation.

There are many questions in decompression theory for which there frustratingly don't seem to be any conclusive answers. Still, we seem to be making some exciting strides forward thanks to a handful of phenomenal minds worldwide asking the 'deep' questions.

Whatever physiological mechanism it is that brings you to us, you can undoubtedly be grateful for the incredible skill of the Chamber Operator in helping you heal.