Greetings all,
Over the past two days, we've treated two separate divers with decompression illness. They had both decompressed using hyperoxic mixes (one with 40% N2O2, the other with 100% O2) and surfaced with symptoms of DCI. They both initially attributed their symptoms to CNS O2 toxicity and refused surface oxygen for fear of making their "O2 toxicity" worse.
This may be an indicator of a larger knowledge deficit among divers. Below, I've excerpted a post from our Facebook page. The site won't let me post a link because I have less than five posts. [mod edit - FB link: Facebook - Duke Diving]
Diver number 1: a middle-aged male with 30 years' diving experience who made two spearfishing dives on nitrox. The dives: 134'/34 minutes on 30.8% nitrox with a 5 minute stop at 15 feet using 40% nitrox. He had a 2 1/2 hour surface interval followed by a second dive, 124'/37 minutes, also on 30.8% nitrox. On his second dive, he reported that his ascent alarms were flashing while he was surfacing with a fish. He put the fish in the boat and returned to 15', where he completed a 5 minute stop, again on 40% nitrox. He reported swimming against the current and exerting himself more than normal but did not report any unusual symptoms during the dive. Following the dive, he experienced symptoms of spinal cord decompression sickness (tingling and weakness in both legs). He refused surface oxygen because he thought his symptoms were due to O2 toxicity. Of note, his calculated pO2 for his bottom mix at the deeper depth, 134 feet, was 1.56 ATA. This exceeds the normal recommended maximum pO2 of 1.2 ATA.
Diver number 2: a slightly younger man diving for shark's teeth. The dives: 106'/85 minutes using compressed air, with decompression on 100% O2 using his computer. He had a 90 minute surface interval, followed by a second dive to 106', this time with a bottom time of 100 minutes, again with decompression on 100% O2 per his computer. He reported no problems on his dive but surfaced with symptoms of inner ear decompression sickness (nausea, vertigo, tinnitus and hearing loss). He also refused surface O2 for fear of oxygen toxicity.
Discussion: both divers were treated here at Duke within one day of one another. Both had been breathing hyperoxic decompression gases, both had decompression sickness, and both feared oxygen toxicity from surface O2.
Symptoms of central nervous system O2 toxicity can be remembered using the acronym "VENTTID/C".
V: Vision. Blurred or tunnel vision, or other visual disturbances.
E: Ears. Ringing or roaring in the ears.
N: Nausea.
T: Twitching of the muscles, usually the facial muscles.
T: Tingling in the extremities, typically the fingers and toes.
I: Irritability. Any personality change.
D: Dizziness.
C: Convulsions.
CNS O2 toxicity is dependent on two things: the partial pressure of O2, and the length of exposure. The higher the partial pressure of O2, the shorter the exposure necessary to bring about O2 toxicity. It's generally agreed that the threshold pO2 for a risk of CNS O2 toxicity is 1.6 atmospheres absolute (ATA). In other words, when the pO2 in a diver's breathing gas reaches 1.6 ATA, there is a risk of O2 toxicity. The risk rapidly diminishes when the partial pressure of O2 decreases.
There is NO risk of CNS oxygen toxicity when breathing 100% oxygen on the surface. Even if a diver did experience O2 toxicity at depth, breathing surface oxygen would not cause it to return. If a symptom like those described above persists after a dive, it is NOT due to oxygen toxicity. In both of the above cases, the divers were deprived of the benefit of surface O2 due to a deficit in their knowledge.
Divers, please pass this information along. Administration of surface oxygen in a diver with DCS has been shown to improve outcome. A diver is NOT at risk of CNS oxygen toxicity when breathing surface O2.
Over the past two days, we've treated two separate divers with decompression illness. They had both decompressed using hyperoxic mixes (one with 40% N2O2, the other with 100% O2) and surfaced with symptoms of DCI. They both initially attributed their symptoms to CNS O2 toxicity and refused surface oxygen for fear of making their "O2 toxicity" worse.
This may be an indicator of a larger knowledge deficit among divers. Below, I've excerpted a post from our Facebook page. The site won't let me post a link because I have less than five posts. [mod edit - FB link: Facebook - Duke Diving]
Diver number 1: a middle-aged male with 30 years' diving experience who made two spearfishing dives on nitrox. The dives: 134'/34 minutes on 30.8% nitrox with a 5 minute stop at 15 feet using 40% nitrox. He had a 2 1/2 hour surface interval followed by a second dive, 124'/37 minutes, also on 30.8% nitrox. On his second dive, he reported that his ascent alarms were flashing while he was surfacing with a fish. He put the fish in the boat and returned to 15', where he completed a 5 minute stop, again on 40% nitrox. He reported swimming against the current and exerting himself more than normal but did not report any unusual symptoms during the dive. Following the dive, he experienced symptoms of spinal cord decompression sickness (tingling and weakness in both legs). He refused surface oxygen because he thought his symptoms were due to O2 toxicity. Of note, his calculated pO2 for his bottom mix at the deeper depth, 134 feet, was 1.56 ATA. This exceeds the normal recommended maximum pO2 of 1.2 ATA.
Diver number 2: a slightly younger man diving for shark's teeth. The dives: 106'/85 minutes using compressed air, with decompression on 100% O2 using his computer. He had a 90 minute surface interval, followed by a second dive to 106', this time with a bottom time of 100 minutes, again with decompression on 100% O2 per his computer. He reported no problems on his dive but surfaced with symptoms of inner ear decompression sickness (nausea, vertigo, tinnitus and hearing loss). He also refused surface O2 for fear of oxygen toxicity.
Discussion: both divers were treated here at Duke within one day of one another. Both had been breathing hyperoxic decompression gases, both had decompression sickness, and both feared oxygen toxicity from surface O2.
Symptoms of central nervous system O2 toxicity can be remembered using the acronym "VENTTID/C".
V: Vision. Blurred or tunnel vision, or other visual disturbances.
E: Ears. Ringing or roaring in the ears.
N: Nausea.
T: Twitching of the muscles, usually the facial muscles.
T: Tingling in the extremities, typically the fingers and toes.
I: Irritability. Any personality change.
D: Dizziness.
C: Convulsions.
CNS O2 toxicity is dependent on two things: the partial pressure of O2, and the length of exposure. The higher the partial pressure of O2, the shorter the exposure necessary to bring about O2 toxicity. It's generally agreed that the threshold pO2 for a risk of CNS O2 toxicity is 1.6 atmospheres absolute (ATA). In other words, when the pO2 in a diver's breathing gas reaches 1.6 ATA, there is a risk of O2 toxicity. The risk rapidly diminishes when the partial pressure of O2 decreases.
There is NO risk of CNS oxygen toxicity when breathing 100% oxygen on the surface. Even if a diver did experience O2 toxicity at depth, breathing surface oxygen would not cause it to return. If a symptom like those described above persists after a dive, it is NOT due to oxygen toxicity. In both of the above cases, the divers were deprived of the benefit of surface O2 due to a deficit in their knowledge.
Divers, please pass this information along. Administration of surface oxygen in a diver with DCS has been shown to improve outcome. A diver is NOT at risk of CNS oxygen toxicity when breathing surface O2.
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