Perfluoromethane to Reduce Decompression Sickness a􀅌er Heliox Dives

Abstract

Methods: A model of decompression sickness (DCS) after 200 fsw heliox (80-20) dives was developed in a 20 kg Yorkshire swine model. Animals were trained to walk on a treadmill. On the day of the study they were sedated with midazolam, morphine and dexmedetomidine, briefly sedated further with inhaled isoflurane to allow placement of an intravenous catheter then placed in a Panepinto sling and administered breathing gas using a hyperbaric head tent. Compression time was 8 minutes. Time at maximum depth was 60 minutes, after which animals underwent linear decompression to the surface. After a total of 20 animals were used to develop the model by incrementally increasing bottom time, an additional 46 animals were randomized to a breathing gas switch to perfluoromethane (CF4)-oxygen (80-20) or continue to breathe heliox. In the first 6 animals decompression time was 10 minutes with the CF4-O2 group making the gas switch 5 minutes prior to decompression. For the remaining 40 animals, decompression time was 5 minutes, with the CF4-O2 group making the gas switch 10 minutes prior to decompression. At the surface all animals were switched to air breathing. After assessment for inguinal lymph node gas and venous gas emboli (VGE) using ultrasound imaging, sedation was reversed with flumazenil, naloxone and atipamezole, then animals were followed for up to 3 hours. Gait and cutis marmorata area were assessed every 15 minutes. Pulse oximetry was recorded continuously. At any sign of either cardiorespiratory or spinal cord DCS, or in their absence at 3 hours post surfacing, animals were euthanized. Brain, spinal cord and a piece of lung were then removed. The lung sample was weighed and placed in an oven for dehydration and subsequent assessment of wet:dry ratio. Neurological tissues were fixed in buffered formalin, then sections were obtained for histology using H&E staining. Results: With all randomized animals included, survival was 100% in the CF4-O2 group vs. 25% in the He-O2 group. When the 6 animals with 10-minute decompression time were excluded, only 14% of animals in the He-O2 group survived for 3 hours (P<0.0001). Gait in the CF4-O2 group was significantly better than in the He-O2 group (P<0.0001), and cutis area was less (P<0.0001). Arterial oxygenation was also higher in the CF4-O2 group (P<0.0001); VGE scores were lower (P<0.0001) and lung water was less (P=0.0259). Histological hemorrhagic severity was lower in the CF4-O2 animals in cerebellum (P=0.0017), thoracic cord (P-0.0255) and lumbar cord (P=0.0105). Conclusions: The results of this study strongly support the efficacy of CF4 as a decompression breathing gas to reduce decompression stress in divers or allow for longer bottom time.