A passage from a book I am working on... The OP may find it useful. Who knows
GAS TOXICITY: The strange transformation of gases at depth
A diver does not have to venture very deep in the water column before breathing compressed gas opens him up to the potential of gas toxicity. This toxicity can take several forms: hyperoxia, hypoxia (and anoxia), hypercapnia, narcosis, and in special cases, carbon monoxide poisoning. Even the air we breathe comfortably every day of our lives on dry land, goes through a Jekyll and Hyde transformation underwater.
INERT GAS NARCOSIS
For example, even in relatively shallow water – certainly no deeper than newly certified sport-divers are advised to dive – one of the side-effects from breathing compressed air is nitrogen narcosis. The effects of narcosis can begin to impair a diver’s ability to “think fast and straight” within a few metres of the surface. Breathing normal compressed air at more extreme depths – and how deep that is depends on many factors besides the lineal distance to the surface – reaction times can slow dramatically, rational decision-making may be impaired, situational awareness can disappear. This behavior, while fine and even amusing in a clown at a kid’s birthday party, can have devastating consequences underwater. Extreme reactions to nitrogen narcosis – sometimes tagged as inert gas narcosis – have been shown to turn a usually cautious and meticulous diver into someone who was a danger to himself and everyone diving with him.
However, that said, this type of severe reaction to the effects of narcosis are not guaranteed. They simply do not visit every diver who dives deep. Or, more accurately, they do not visit all divers to the same extent. Every diver suffers some impairment, but individual divers react differently to that impairment. Also, for some, its effects increase gently and for others they arrive in a fire truck with the sirens blaring. Some report its effects as deep as 60 metres (200 feet) on air as “mild” while others would be comatose at that depth on that gas.
So, rather than generalise about its effect, we’d do better to understand that narcosis is not a monster that hangs around at a specific depth waiting to attack us. There is no red line at X-metres or Y-feet beyond which lay dragons and demons. The four horsemen of the apocalypse will not ride us down if we breathe air below some magical depth. Narcosis is not so easily pigeonholed.
Now that’s not to say that one day, Pestilence, War, Famine, and Death will not suddenly appear out of the gloom approaching at a full gallop. That may indeed be in your stars if you dive deep on air or any other gas. It’s just that nobody can tell you the depth at which these visions will occur or indeed, if your reaction to extreme narcosis will instead cause you to chill out, see paisley fish, and start humming Grateful Dead tunes to yourself.
To complicate the issue even more, while I am unaware of any hard-edged physiological studies that are able to explain why the face narcosis presents to a diver can be benign one day, and cruel the next, this certainly is the case. I have witnessed a diver who was perfectly comfortable working with a specific narcotic loading one day, act like a character from Monty Python’s Flying Circus at the same depth and narcotic load a few days later.
This incident and others like it, lend credence to the suggestion that there is far more at work than a simple lineal relationship between nitrogen partial pressure and the effects of narcosis.
OTHER FACTORS
Among the factors that are thought to contribute to the rapidity of onset, and the severity of narcosis include:
- Increased partial pressures of CO2 (the result of hard work, swimming against a current, working with camera equipment, skip-breathing, etc.)
- Thermal Stress (being cold at depth)
- Being drunk or diving with a hangover or diving under the influence of “recreational” drugs
- Diving tired or after a poor night’s sleep (which is a type of fatigue many poor sailors suffer on live-aboard vacations)
- High WOB (work of breathing) related to the breathing resistance within the system being used (both open-circuit, semi-closed circuit and closed-circuit)
- Anxiety or apprehension: including fear of nitrogen narcosis
- Side-effects from various prescription and over-the-counter medications (motion sickness meds for example)
- Rapid descent (especially when coupled with the following…
- Vertigo or temporary disorientation caused by the diver having no ‘up’ reference such as in clear ‘blue water’ or in water with very poor visibility
- Task-loading stress (unfamiliarity with equipment, buddy, environment et al.)
- Temporal stress (feeling rushed and under pressure to accomplish a task for example)
- Diving with a cold or flu
- Increased oxygen partial pressure (see below)
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ADAPTION
Adaptation to narcosis is a rather controversial sub-topic. Some experienced divers suggest that with practice and experience, and with the help of some simple breathing and preparatory techniques, the effects of narcosis can be controlled. The degree of control is specific to individuals, and tolerances to narcosis can vary from day to day: but many experienced deep divers will tell you that “adaptation” to narcosis does take place.
In his book on diving medicine, Peter Bennett, founder of DAN (Diver’s Alert Network) and currently the Senior Director of the Center for Hyperbaric Medicine and Environmental Physiology at Duke University Medical Centre, wrote: “the novice diver may expect to be relatively seriously affected by nitrogen narcosis, but subjectively at least there will be improvement with experience. Frequency of exposure [to narcosis] does seem to result in some level of adaptation.”
The actual mechanics of adaptation are neither completely understood nor proven but there is a consensus among a segment of experienced deep divers who agree that the effects of narcosis seem to lessen with repeated, progressively deeper exposures.
Bret Gilliam, while writing on the topic in an article for Diver Magazine, stated:
“For the diver who regularly faces deep exposures, a tolerance far in excess of the unadapted diver will be exhibited. A gradual work-up to increasing depths is the best recommendation. I refer to making each first dive of the day progressively deeper than the day before to build tolerances, i.e. Day one: first dive to 150 feet, Day two: first dive to 175 feet etc. Subsequent dives on Day one and Day two would be shallower than the first. This process should be over several days’ time if the diver has been away from deep diving for more than two weeks. Adaptation appears to be lost exponentially as acquired so no immediate increased narcosis susceptibility will necessarily be evident but divers are cautioned to exercise great conservatism if any lay-off is necessitated.”
Gilliam, a pioneering technical diver whose 40-year career in the sport includes founding Technical Diving International and registering a world-record deep dive on air to 145 metres (475 feet) in 1993, is surprisingly circumspect about deep-air diving.
“I would like to emphasize that deep air diving below 218 feet [slightly deeper than 66 metres] is generally not recommended given the alternatives available in today’s industry. This depth represents the outer limits of recommended oxygen exposures at 1.6 ATA of oxygen. For high risk or particularly demanding dives this depth should be adjusted shallower. Many veteran air divers now opt for mixed gas that virtually eliminates narcosis and oxygen toxicity problems.”
SYMPTOMS
However well one may tolerate narcosis, and in spite of conditioning and experience, eventually, it influences the performance of all divers. It should be added that even when breathing gases containing copious amounts of helium as a strategy to reduce narcosis, some level of impairment must always be assumed when diving. The classic textbook symptoms of narcosis are light-headedness, slowed reflexes, euphoria, reduction of peripheral vision, localized numbness or tingling, and difficulty making decisions (euphemistically called cotton-wool head).
Individuals who recognise that all dives are conducted under some narcotic loading – and who have prepared themselves to dive deep – constantly monitor themselves for more subtle signs that signal things are beginning to slide. These early symptoms often start with difficulty reading gauges, especially the finer graduations on depth and pressure gauges. Sounds begin to distort and become somewhat louder. Time seems to pass more slowly… or more quickly. Perceptual narrowing adds a degree of added complexity to the operation of basic equipment such as clips, buttons and switches.
An experienced diver can learn to control these deficiencies and work within them, but these shifts in perception can present real danger and cannot be underestimated. No assumptions can be made that what was fine at depth “Y” yesterday will be acceptable at the same depth today. Getting chilled during pre-dive preparations, feeling the effects of a poor night’s sleep etc. can result in dangerous oversight. Self-monitoring and stress-assessment are critical skills before and during a dive. A diver at 60 metres with a poor perception of time and depth, as well as confusion about the location of a safe exit and remaining gas volume, has a diminished chance of survival.
What follows is a list of symptoms. Your mileage may vary but learning these and being on the lookout for them, may help you avoid a brush with the four horsemen.
- Light-headedness
- Euphoria
- Impaired neuromuscular coordination
- Hearing sensitivity or hallucination
- Slowed mental activity
- Decreased problem solving capacity
- Overconfidence
- Short-term memory loss
- Improper time perceptions
- Inability to focus on fine work
- Exaggerated movements
- Numbness and tingling in lips, face and feet
- Stupor and a sense of carelessness
- Sense of impending blackout
- Levity or tendency to laughter
- Depressive state
- Visual hallucination or disturbances
- Perceptual narrowing
- Less tolerance to stress
- Exaggerated (oversized) handwriting
- Amnesia
- Loss of consciousness
- Retardation of higher mental processes
- Retardation of task performances
- Slurred speech
- Poor judgment
- Slowed reaction time and reflex ability
- Loss of mechanical dexterity
YET ANOTHER INFLUENCE ON NARCOSIS… PERHAPS
In addition to the effects and influences of an elevated nitrogen partial pressure, cold, workload, stress et al., on a diver’s perceptions and performance at depth, there is the issue/controversy surrounding oxygen narcosis: or more correctly, the debate over whether oxygen is or is not also narcotic.
This particular question seems no closer to being resolved as I write this than it was a couple of decades ago when some fledgling technical diver first posed the question.
David Sawatzky is a very experienced technical diver, a member of the advisory board for a major training agency, and a medical doctor whose resume includes spells doing research into diving physiology for the Canadian military. In the late 1990s, he published an article on the topic of oxygen narcosis in which he stated: “The scientific data available do NOT support the conclusion that oxygen is narcotic. They also do not and cannot show that oxygen has no narcotic effect. Oxygen might somehow be involved in the entire question of narcosis and [diver] performance but it is clearly not more narcotic than nitrogen. The narcotic gases are all chemically inert in the body. In contrast, oxygen is one of the most chemically active substances in nature.”
After reading Dr. Sawatzky’s article, and after private conversations with him and other medical doctors who’ve research the subject, plus interviews with many professional and non-professional divers, and 20 years’ experience conducting dives using nitrox, pure oxygen, trimix, heliox and a couple of more exotic gases myself, what I hear is this. If you are looking for scientific evidence about oxygen narcosis and how it may or may not add to the effects of nitrogen narcosis, you are going to be hard-pressed. It seems difficult to measure the influence of oxygen with any quantitative accuracy at this date. This may change but as it stands, since a change cannot be measured, in practical terms, oxygen narcosis either is not there or is too small to matter.
Frankly, as interesting as the debate over oxygen narcosis may be, I believe deep divers have other oxygen toxicity concerns on which to focus.
