A couple of years ago, I had surgery. For the operation I was having performed, they did it by laparoscopic surgery. This is also known as minimally invasive or keyhole surgery and is typically done on the abdominal region. Basically, they “insufflated” (inflated) my torso with carbon dioxide so that they could see under my abdominal wall with tiny cameras and then work with tiny surgical instruments. They use carbon dioxide because it naturally diffuses after surgery.
Of course, I wasn’t aware of any of this, because I was out like a light. What I did get to see as a result of my laparoscopic surgery, however, was the immediate aftermath.
So, why is this of any interest? Well, when I woke up from my surgery, despite being groggy, I probably had one of the weirdest reactions that the nurses were expecting. I came to in the actual surgery theatre, which is in itself a tad unusual. As I came round, a nurse said, “hi Chris, you’ll still feel a little woozy for a bit and you’ll notice some strange effects on your body, but the surgery went well and you should start feeling better soon”.
What I picked up on instantly, were the words “notice some strange effects on your body”. I asked her what she meant and she told me that I had a slight case of subcutaneous emphysema and that it would go away on its own fairly quickly. I guess the average Joe would either be a little concerned that they had “subcutaneous emphysema” and would not likely have any clue what it was.
My reaction was what made the nurses laugh. My hand immediately flew up to my neck, IV drip and all, setting off a warning beep from my monitor and I started prodding my neck, saying “so cool”.
So what is subcutaneous emphysema? It is a condition whereby air or some other gas gets into the tissue just under the skin. This happens most commonly in the neck area or chest. When the skin is touched, it creates a crackling sensation and noise as the gas is pushed around. What had happened to me is that some of the carbon dioxide from the surgery had migrated up and just under the skin at the base of my neck.
So I merrily lay there in no pain (there were some damn fine painkillers at work) crackling my skin, smiling and as giddy as a kid.
The reason I was excited about having subcutaneous emphysema was that it was a real life opportunity to come face to face (well, fingers to neck) with a condition I teach about but hopefully will never have to deal with as a professional scuba diving instructor.
As a scuba diver, you actually learn about such conditions very early on in your dive career. We discuss it briefly on the Open Water course, but most people have no clue as to what it is that we are actually describing. In fact, it is not until the Rescue Diver course that we start looking more closely at this form of emphysema and its three related cousins.
Subcutaneous emphysema is one of the four types of emphysema commonly associated with DCI … otherwise known as Decompression Illness. DCI is an umbrella term encapsulating both Decompression Sickness and Lung Overexpansion Injuries. Emphysemas occur generally through one part of DCI: lung overexpansion injuries.
If you are relatively new to diving, you are likely asking, “what is a lung overexpansion injury?”
When we go scuba diving, we breath compressed air at depth and thus under pressure. When we breathe underwater, our lungs equalize with the surrounding pressure with each breath. Technically, if we hold our breath during an ascent using compressed air, then the reduction in surrounding pressure and the expanding gas can result in a lung overexpansion injury. More properly, lung overexpansion injuries are called lung barotraumas or pulmonary barotraumas and ordinarily these conditions are life threatening. Let me just make it clear, however … lung barotraumas are in fact, very very rare, especially if people have been properly trained. When they do occur, however, it is usually as a result of breath-holding and an excessive ascent rate so that the gas expands faster in the lungs than it can be released.
When this happens, the lungs don’t “explode”, they simply tear. Air in the lungs then escapes into the surrounding tissue and bloodstream. There are four common effects of a lung overexpansion injury: subcutaneous emphysema, pneumothorax, mediastinal emphysema and an arterial gas embolism (also called an air embolism). This is an illustration of a dive-related subcutaneous emphysema:
Lung overexpansion injuries are obviously a very serious injury, but they are also very easily avoided. The most obvious measure we can adopt to avoid a lung overexpansion is to remember the most important rule of scuba diving, to always breathe and never hold our breath. In particular, it is critical to breathe out as we ascend, as this reduces the differential between the ambient pressure of the water around us and the pressure of the compressed air in our lungs. Additionally, if we make sure that we slowly ascend during our dives (as PADI likes to say “be a SAFE Diver … Slowly Ascend From Every Dive), this further decreases any sudden changes in pressure that may prevent us from being able to equalize our lungs quickly enough.
Slowly means slowly. The way that scientists and divers have determined the safest ascent rates in the past is to use Doppler ultrasonic detectors to determine the amount of nitrogen bubbles that form in our bodies after a dive (called “venous bubbles”). These bubbles have principally been used to determine our susceptibility to getting Decompression Sickness (otherwise known as DCS or “The Bends”), however, they have also been used somewhat to determine the best ascent rate to prevent both DCS and lung overexpansion injuries. Just as an aside, certain studies suggest that venous bubbles occur on virtually every dive, regardless of our ascent rate, but at the safest rates, these bubbles are so small (they’re also known as “silent bubbles”) that their impact on divers is negligible. Effectively, what that says is that all divers experience extremely mild forms of DCS on virtually every dive, but that it is so inconsequential that is has no long-term impact.
As a result of countless studies over the last 20 or so years, there have been different safe rates of ascent suggested. Interestingly, the rate of ascent that has been prevalent since the 1960’s is actually based on a very unscientific basis. For the longest time the suggested safe diving ascent rate for almost all divers was (and still is for some training programmes) no faster than 18m/60 feet per minute. Where did this rate of ascent come from? From the late 1800’s through to the 1950’s, there was no agreed on rate of ascent and it was all over the place. Some physiologists recommended rates of 3 feet (1 metre) per minute, whereas others were slightly faster at 30 feet (9 metres) per minute. From 1920 to 1957 the generally accepted rate of ascent was 25 feet (7.5 metres) per minute.
But then in 1958, the U.S. Navy Diving Manual was introduced. During the production of the manual, it was the obstinacy of a single person that ultimately dictated the rate that was relied on by both the U.S. Navy and a number of schools of dive training. The Navy finally changed its rate of ascent in 1993; however, many schools of training continue to use the 1958 rate to date. It was a gentleman by the name of Commander Francis Fane of the West Coast Underwater Demolition Team who caused the rate that existed for over 50 years. Fane demanded a rate of ascent for his frogmen of 100 feet (30 metres) per minute or faster. Fane’s divers were “no decompression divers”, however, and other Navy groups, which primarily consisted of decompression divers, had an ascent rate that was typically 10 feet (3 metres) per minute. A compromise, therefore, was reached at 60 feet (18 metres) per minute. This rate was then advocated by and adopted by early recreational diving tables and even computers, all based on a purely empirical finding.
Studies as far back as 1999, however, have also identified that a rate of ascent of 18m/60 ft produces far more venous bubbles than a much slower ascent rate of 9 m/30 feet per minute and is, accordingly, riskier for DCS and, slightly less so, lung overexpansion injuries. As a result, most modern dive computers are set to an ascent rate of 9 m/minute or even slower. Funnily enough, many training programmes have now slightly adapted their approaches and advise and tell students to ascend no faster than 18 m/minute or whatever speed the computer tells you to ascend, whichever is slower. This is now taught instead of the industry “standard” of 18 m/minute. Invariably, the computer is slower and some have suggested that this new approach, of “either or” is to protect those schools that previously adopted the 18m/minute standard.
The Diver’s Alert Network (DAN), one of the foremost authorities on diving medicine and medical theory, even considers the rate of 9 m/minute as being too rapid an ascent to the surface. In fact, recent DAN studies have suggested not only a 9 m/minute ascent rate, but also the inclusion of a deeper stop, in conjunction with a shallower stop. In 2011, DAN studies indicate that there is a significantly lower potential of DCS in dives where a 1-2 minute stop is made at half the maximum depth dived to, along with a shallower stop for 2-3 minutes as well at 6-7 m. Here’s a link to that research: DAN Article
What this all boils down to is that safe diving means ascending very very very slowly and making a couple of safety stops if air permits. Which shouldn’t be a problem since scuba diving is all about being relaxed. Watch your air consumption, relax, enjoy the dive, monitor your No Decompression Limits and then make a slow an ascent as you can. A common suggestion is to ascend slower than your smallest air bubbles (some people say the size of champagne bubbles). Even slower cannot hurt.
It is even more important to ascend very very slowly in the final stages (i.e. the shallowest) because this is where the pressure changes and affects our body the most. This is why in the last 15-feet/5 metres we should actually ascend as slow as absolutely possible. Further, making a safety stop and rising at a metre a minute for the last 5 metres reduces our nitrogen saturation (the major cause behind DCS) by huge percentages.
Another step we can take to assist and prevent subcutaneous emphysemas or their nastier cousins raising their heads is to take courses that help us to better understand the phenomena. The most obvious and earliest course, at least under the PADI system of education and through the Toronto Scuba Centre, is the Rescue Diver course. Ultimately, it is only through the Instructor Development Course, through personal interest and through experience (especially experiencing real-life DCS instances) that we start to truly appreciate the harmful effects of ascending too fast. The Rescue Diver course, however, opens our eyes to the many forms that Decompression Illness can take and the most effective and immediate treatment that a rescue diver can provide.
Is there anything else we can think of that can increase our chances of getting the bends or a lung overexpansion injury? Well, unfortunately, there is. Anything that weakens us physically is certainly thought to increase our susceptibility to the bends, although not perhaps as much to lung overexpansion injuries. Some very recent studies have suggested that moderate exercise before diving may actually be beneficial to reducing our chances of getting DCS, however, generally we advise that if any “secondary” variables apply to you to exercise particular caution regarding pushing the limits for DCS. Secondary variables include such things as obesity, heavy drinking, smoking, heart disease, etc. Basically, anything that physically weakens you overall.
During the Rescue Diver course we identify the obvious and not so obvious symptoms of DCI, as well as how to assist a diver in the water and out of the water. We train you how to get a diver in clear distress to the surface, how to help them at the surface and how to treat a person until such time as we can transfer that person to the appropriate emergency medical services. DCI is no joke, despite my fascination with my own subcutaneous emphysema. Knowing how to spot it, knowing what to do and knowing how to do it all calmly and collectedly is critical.
Hopefully, none of you ever experience subcutaneous emphysema, let alone any symptom of DCI. Here’s the rub: if you want to avoid any of the DCI effects, live moderately healthily, exercise and take particular caution if a secondary variable applies to you and SLOWLY ASCEND FROM EVERY DIVE!!!