DAN MEDICAL
Tell-tale signs during a training course could have given a diver a vital clue, but they were missed. A year later his symptoms were back with a vengeance. So what is a bleb, anyway? Lana Sorrell explains all.
The diver
On a recent trip to Bonaire with his dive-club, Rick (a pseudonym) was completing his fourth dive of the day, which was his 14th dive in a three-day series, and his 145th lifetime dive.
Certified some two years earlier, Rick was 38 and in good health, with no significant medical history except for what he described as “athlete’s asthma” as a child.
The incident
Before beginning his third dive of the day, Rick had felt tightness in his chest. He put it down to eating leftover pizza for lunch, and had even mentioned that he needed to take an antacid.
The chest discomfort resolved itself during the boat-ride to the dive-site, so he proceeded with the dive, descending to a maximum depth of 14m.
Rick took a lot of photographs during the dive, and would occasionally invert himself to see inside the reef.
After he surfaced from the following dive, Rick boarded the boat and immediately noticed a change in his voice, a sore throat and crackles under the skin around his neck.
When Rick had been completing the second dive of his wreck-diver certification a year before, he had surfaced completely exhausted, with a burning sensation in his throat.
After he removed his gear he had noticed a change in his voice, and what he described as water under the skin around his neck. Other divers in his group discounted his symptoms as bad gas or water in the ears.
That evening, Rick had taken an over-the-counter pain-reliever and Benadryl, and went to bed early.
All the symptoms had gone by the following morning, and he had completed the last two dives of the course without any problems.
The diagnosis
A doctor at the local hospital on Bonaire carried out a complete neurological assessment of Rick and diagnosed pulmonary barotrauma (pressure injury to the lungs) and subcutaneous emphysema (air under the skin).
The chest X-ray was unremarkable. The doctor noted no complications apart from the subcutaneous emphysema in the neck, which did not affect the airway, so he administered high-flow oxygen and allowed Rick to return to his resort.
A CT scan the following day revealed abundant mediastinal air around the heart and lungs and in the neck. It also showed at least two large “blebs” (cystic air-pockets) in the upper parts of Rick’s lungs. He returned to hospital daily so that doctors could monitor his progress.
Because of the risk of a pneumothorax during air travel, Rick was admitted to the hospital two days after the incident to breathe 100% oxygen for six hours. The doctor took these aggressive measures to speed Rick’s recovery and allow him to travel home with his group.
A follow-up CT scan three days after the incident (and one day before his scheduled departure) showed the same blebs as before, but much less extra-alveolar air in the mediastinum.
After consulting with pulmonary specialists both locally and in the USA, the treating doctor cleared Rick to fly home with his group.
Discussion
Pulmonary barotrauma generally occurs at the end of a dive, when trapped gas causes alveoli (air sacs in the lungs) to expand during ascent and ultimately rupture if normal exhalation is impaired by breath-holding or a lung problem.
Gas from a ruptured lung can leak into one or more of four places:
- The area around the heart (pneumomediastinum, also known as mediastinal emphysema)
- The pleural space between the lungs and chest wall (pneumothorax)
- The bloodstream (arterial gas embolism [AGE])
- Under the skin around the upper chest and neck (subcutaneous emphysema)
The risk of pulmonary barotrauma is greater in people who have blebs in their lungs. Blebs are abnormal, balloonlike air-sacs most often caused by inflammation, which destroys the thin walls that separate alveoli.
Although these are common in smokers, they have also been found in non-smokers. Blebs empty air slowly because of their thin, non-elastic wall. On exhalation during ascent, pressure can build, causing rupture.
People with blebs are also at risk of spontaneous pneumothorax (collapsed lung). Those with a history of spontaneous pneumothorax are automatically disqualified from diving, because of the high risk of pulmonary barotrauma.
There is a consensus among diving doctors that, despite the appearance of normal lungs via testing or imaging, someone with a history of spontaneous pneumothorax should not dive under any circumstances.
Rick’s pulmonary barotrauma manifested as pneumomediastinum, the principal symptom of which is a substernal ache, or chest tightness.
This is likely to be what Rick was feeling before his third dive. Occasionally a diver might experience sharp pain in the shoulders, back or neck that may be aggravated by deep breathing, swallowing, movement of the neck or trunk, coughing or lying flat.
Voice changes, such as the Donald Duck voice that results from breathing helium, are also common.
The crackling sensation Rick described under the skin around his neck is known as subcutaneous crepitation (grating or rattling). The air was trapped under the skin when it escaped from the chest cavity and into the soft tissues of the neck.
Breath-holding, rapid ascent and certain lung diseases can cause pulmonary barotrauma, the risk of which is increased by lung diseases such as asthma (if not optimally medicated) because of the risk of bronchospasm and/or obstruction of air passages.
Lung scarring or inflammation caused by sarcoidosis or interstitial fibrosis prevents proper gas exchange and increases risk of pulmonary barotrauma.
In addition, people who have previously experienced a spontaneous pneumothorax or pneumomediastinum are at increased risk. Generally, anyone with lung conditions that might increase the risk of pulmonary barotrauma is advised to avoid scuba-diving.
For those with underlying lung diseases, risk of pulmonary barotrauma increases with rapid ascents, especially conducted close to the surface, where the relative pressure changes are greatest.
Diving doctors recommend that anyone who has experienced pulmonary barotrauma be properly evaluated before returning to diving. Unfortunately, Rick didn’t recognise his symptoms during the training dives a year earlier as subcutaneous emphysema, so went on diving without talking to a doctor.
Fortunately for him, he recognised his symptoms after the second occurrence and was properly treated. He has since returned to diving after two successful operations to correct the blebs.
ASK DAN’S EXPERTS
When trying to provide rescue breaths in the water to an injured diver, why couldn’t I use my spare regulator’s purge button? That seems easier to me than trying to manage a pocket mask.
Using the purge button of a regulator second-stage has been proposed many times, but any advantage it may seem to offer does not outweigh the potential risks and complications.
If the regulator mouthpiece is not already in an unresponsive diver’s mouth, trying to replace it can be difficult and time-consuming. Without a good seal and a means to occlude the diver’s nostrils, any attempts to ventilate will be unsuccessful.
Even if the mouthpiece can be successfully placed in the diver’s mouth, there is a risk of it pushing the relaxed tongue to the back of the throat and blocking the airway.
If the mouthpiece remained or was placed in the diver’s mouth without blocking the airway, the next challenge would be administering air.
Purge-buttons have no true regulatory capability. They effectively override the second stage’s function of stepping down gas from intermediate pressure to ambient pressure, and so deliver intermediate-pressure gas directly from the first stage. Delivering breathing gas to the lungs at too high a pressure might over-inflate them, potentially leading to serious injury.
If the diver’s airway is not maintained in an open position, the breathing gas delivered by the purge-button could be forced into the stomach, causing gastric distention. This places the diver at risk of regurgitation, which can further compromise the airway and lead to aspiration.
Delivering rescue breaths using a pocket-mask or similar method provides tactile feedback via changes in pressure required to ventilate the lungs, while supplying rescue breaths with the purge-valve eliminates this important feedback.
Using a purge-valve also precludes the option of supplementing the gas with 100% oxygen.
Rescue methods currently taught by training agencies are the result of years of practical experience. Purge-valves were never designed to function as rescue equipment. When ventilating an injured diver, rely on established methods.
