Hypercapnia During CCR Dive and Persisting DCS Symptoms 


  • CCR dive with mandatory decompression and overhead environment (wreck dive), collecting scallops 
  • 165fsw, bottom time of 30-45 mins 

Reported Incident

A well-experienced CCR instructor went for a dive as a crew member of a charter. The dive was to 165 fsw (50 msw) for about 30 minutes at a wreck, however the primary objective for the dive was to collect scallops. The diver described getting into their gear 5 minutes before entering the water instead of the usual 10 minutes before, as well as doing a shorter pre-breathe period than usual; only 1-2 minutes versus typical 3-5 minutes. The diver also reported some seasickness that may have been in part due to fatigue and potential dehydration. 

18 minutes into the dive, the diver reported feeling “out of sorts” but attributed these symptoms to prior seasickness and fatigue. By 30 minutes, the diver described wanting to end the dive and began ascent. During ascent the diver reportedly felt lethargic, slight confusion and some paranoia. As they continued the ascent, the symptoms became more severe and the diver instinctively bailed out to open circuit scuba. They reported difficulty breathing and feeling like they were not receiving enough air even after purging the regulator to try to force air into his lungs. The diver then swam faster to the surface disregarding decompression obligations beginning at 70 fsw (21 msw). 

At the surface the diver called for help. Within 3-5 minutes of surfacing, with the help of the boat crew, they decided to re-immerse and complete some kind of decompression. They dropped down to 30 fsw (9 msw) breathing 100% O2 for about 20 minutes reporting “shaky hands” and lower back tightness. These feelings subsided at around 20 minutes and the diver slowly ascended to 25 fsw (8 msw). The diver ran out of his oxygen at around 35 minutes after re-immersion and stayed at 25 fsw (8 msw) for an additional 8 minutes breathing air. This totaled about 43 minutes of decompression.  

Once back at the surface the diver took two asprin tablets. 45 minutes post decompression the diver resumed his duties as crewmate but avoided any strenuous work activities. They reported feeling good, even remarking that they felt better than when they first entered the water that morning. The boat remained at the site for 2.5 hours and then made the 2.5-hour trip back to shore. Later that evening the diver noted soreness and stiffness in his back muscles as well as a delay in urine stream and general difficulty urinating.  

The following morning the diver described similar back and leg stiffness as well as persisting difficulty urinating. The diver continued his regular daily activities that day helping with some household chores and cleaning gear.  

The second day post dive, with persisting numbness all down their backside and difficulty urinating the diver decided to bike to the ER that evening. He was transported to the Hyperbaric department around two hours after arriving at the hospital and began recompression treatment. The diver reported little change in symptoms except for a slight improvement in the Romberg test. Another shorter treatment under 3 hours was done later in the afternoon (now three days post dive) with little to no reported symptom improvement. As the diver had shown improvement they were discharged that evening only to return to the hyperbaric chamber the next day for another treatment, this time lasting less than 90 minutes. The diver showed little to no change in symptoms after. 

In the two days following this last treatment the diver reports subtle subjective improvement in symptoms.  For instance, being able to comfortably jog for around 10 minutes, something he could not do the few days prior. The diver still reports numbness in his posterior chain, but less pronounced and closer to a “tingling sensation”.  The diver also still reports some difficulty urinating and initiating urination. 

Equipment Configuration 

The diver was using a back mounted CCR packed with Intersorb, 135 minutes total dive time on the scrubber material from dives the previous weekend. The diver reported no noticeable packing or storage issues. 15/60 diluent and deep bailout gas (80cu ft), air inflation and secondary bailout gas (50cu ft), and 100% oxygen decompression bailout gas (40cu ft). 


When reading through the case there is evidence that a more thorough pre-dive check may have been warranted. 5 minutes pre-dive is a limited window to ensure all equipment is available and working as well as going through the rebreather “pre-flight” checklist. Unfortunately, as a crewmate being paid for your time, it is understandable to have more haste getting into the water. This should however not be a consideration when compared to safety.  

The diver also mentions having a better recognition and acceptance of his symptoms may have alleviated the situation earlier. Very early on in the dive he was feeling unwell and should have called the dive earlier at symptom onset instead of waiting for them to worsen. 

The diver mentioned some stigma surrounding seeking out recompression therapy in a chamber. Early treatment may have made a difference in symptoms and recompression or at least medical examination following a serious incident should simply be looked at as medical treatment without stigma.  

Symptoms of DCS should be treated with emergency oxygen until the individual can seek out appropriate medical care or the oxygen runs out. This should have been administered following his surfacing. Again, the diver’s role as a crewmate on the boat may have impacted the actions taken following the event. Had this been a passenger the protocol may have been different. 


Divers should be diligent about doing a through “pre-flight” checklist prior to any dive but especially before a complex technical rebreather dive. This includes a 5 minute pre-breathe. This should be conducted regardless of your role on a dive vessel, safety should be a priority for both crew members and passengers. 

Stigmatization of recompression and medical examinations should not be a factor in your decision to seek medical attention following a diving incident. Symptoms of DCI should be monitored closely, and emergency oxygen should be administered for any suspected cases. 

Any diver should be able to call any dive for any reason without repercussions. If there is any reason you feel unwell or not wanting to start or continue a dive, you should end the dive. No dive is worth compromising your safety. Had the diver called the dive at the start of symptom onset, the indecent may have gone differently.