Diving Medicine

By Dr. David Sawatzky

Frequently, I receive reader questions. The following (edited) enquiries raise several issues of interest.

Does Nitrox Have a Taste?

Should Nitrox taste any different from regular air? I’ve noticed a difference. Air is odourless and tasteless in contrast to Nitrox, which I found to have this weird, very subtle, but noticeable odd taste.

Air is Nitrox and the air that you breathe while diving should not have any detectable taste or odour. Therefore, Nitrox should not have any taste or odour.  If it does, the Nitrox, the regulator, or the tank could be contaminated.

That said, our senses of taste and smell can detect some chemicals in concentrations as low as a few parts per billion.  Therefore, an odd taste or smell in air or Nitrox is not always dangerous or significant.  However it should always be investigated.

Samples of the Nitrox in question, drawn from the scuba tanks, and air taken from the retail outlet’s filling station, were taken by the store and sent for analysis. Nothing unusual was detected.  Therefore, either the diver was imagining the taste, or the concentration of whatever he noticed was too low to be detected, and too low to be of concern.

CO Poisoning and Red Lips

Now to the main issue: when my buddy and I got to the bottom at 70 feet (21m), on a wreck in a freshwater lake, I noticed the Nitrox I was breathing (36 percent 02) had a slightly different odour/taste. Six or seven minutes later I began to cough violently. My buddy and I went into buddy breathing mode and I stopped coughing. When I tried to breathe from my own regulator,  I started to cough violently again. We aborted the dive and buddy breathed to the surface.

My buddy was also breathing Nitrox from the same source but at a slightly lower concentration (34 percent 02). On the surface I began dry heaving and coughing. This continued for about five to 10 minutes and when I got on the boat I was immediately administered 02. The dive master aboard said I had red lips and that the cause of this incident could have been CO poisoning. Later, back on shore, I was a little shaken but okay.

When fossil fuels are ‘burned’ the carbon based compounds are combined with oxygen to form water and carbon dioxide (CO2).  When inadequate oxygen is available, carbon monoxide (CO) is produced.  Small amounts of CO are produced by all internal combustion engines.

Carbon dioxide is a major waste product when we convert food to energy in the body. Our exhaled breath is approximately 4 percent CO2.  As a result we have some tolerance to CO2 and even breathing in two or three percent CO2 does not usually cause serious problems.  Higher concentrations, or breathing CO2 while diving, can result in loss of consciousness and death.

Carbon monoxide is deadly.  It binds to hemoglobin molecules 250 times tighter than oxygen and prevents that hemoglobin molecule from carrying any oxygen.  It also binds to some of the critical enzymes in the mitochondria inside our cells and prevents them from working.  The net result is that the cells ‘starve’ for lack of energy and die.  Two severely affected tissues are the brain and the heart.

Carbon monoxide poisoning is very common and results in a large number of deaths every year.  House furnaces malfunction allowing CO to build up in the air in the house, people use their barbeques inside, people run cars inside a closed garage (a common way to commit suicide), etc.  Being in the same enclosed space as any internal combustion engine or fire can result in CO poisoning.

Carbon monoxide poisoning often presents with headache, nausea and vomiting.  It can rapidly lead to loss of consciousness and result in permanent brain damage or death.  Carbon monoxide is odourless, tasteless and cannot be detected by the person who is breathing it.

If the intake of a compressor is too close to the exhaust of a car or other gas-burning motor, CO2, CO, and other contaminates can be pumped into dive tanks.  Air in dive tanks should not contain CO in more than 10 parts per million.  Cigarette smoke contains CO at approximately 400 parts per million.  We are all exposed to small amounts of CO but less than 1 percent of our hemoglobin should be bound to CO.  A heavy smoker can have up to 15 percent of their hemoglobin inactivated by CO!

In a diver, the symptoms of CO poisoning may not present until the diver surfaces.  While diving, we are breathing higher than normal partial pressures of oxygen and as a result our cells may be getting enough O2 even though CO deactivates some of the hemoglobin molecules and mitochondrial enzymes. When we surface and are breathing a normal partial pressure of O2, these cells may be receiving inadequate O2 and the signs and symptoms of CO poisoning appear.

Treatment of CO poisoning involves removing the person from the source of CO, getting them lots of fresh air and giving them 100 percent oxygen.  A person who suffers from CO poisoning can appear to make a complete recovery only to develop significant, permanent brain dysfunction several weeks later.  If they have experienced loss of consciousness or other serious symptoms, they should be treated with hyperbaric oxygen (in a chamber) as quickly as possible as this seems to prevent the subsequent development of neurological problems.

So what about the red lips?  Carboxyhemoglobin (hemoglobin bound to CO) is cherry red. People badly poisoned with CO can have red lips and bright red colour under their nails.  The problem is that this indication requires a very high percentage of the hemoglobin to be bound to CO, and this degree of poisoning is usually fatal.  Even in severely poisoned CO patients the cherry red lip sign is unreliable.  Consequently, this common sign of CO poisoning is useless in the real world.

Getting back to our diver with the cough (not a symptom of CO poisoning), the red lips were almost certainly not a real finding and he was not poisoned with CO.

Most Likely Explanation

The most important details in the diver’s story are that he started coughing while at depth, he stopped coughing when breathing from his buddy’s regulator, started again when he went back on his own regulator, and that he had dry heaves and coughing for five to 10 minutes after he surfaced.  He then made what seems to be a complete recovery.  Problems with the Nitrox were pretty well ruled out by the normal gas analyses.

Coughing while diving is very common and frequently it is due to the diver inhaling a spray of water into their lungs.  The most common causes of this are a small tear in the mouthpiece of the regulator, a small tear in the exhaust diaphragm of the regulator, a small piece of debris holding the exhaust diaphragm partially open, a fold in the exhaust diaphragm so that the opening is not completely covered, and ice crystals if you are diving in very cold water.

I recall a personal incident early in my diving career when I was coughing badly at the end of a winter dive that I could not talk. I’d inhaled ice crystals into my lungs.  I have also had many small tears in the mouthpiece.  After one particularly ‘wet’ dive I looked closely and found a small tear in the mouthpiece of my regulator.  I also carefully checked my other four regulators and found tears in the mouthpieces of three of them!  Mouthpieces should be checked frequently and replaced if any defects are found.

When you take a breath with this kind of malfunctioning regulator, you get a small spray of water into your lungs.  You can sometimes block the water with your tongue but if it gets into your lungs you will immediately start to cough.  The water causes some irritation of the lungs (salt water is worse than fresh water) so you may cough for several minutes after you surface.  In addition, most divers would be quite anxious in this circumstance (especially if someone suggests you may be suffering CO poisoning) and this can result in additional symptoms.

The diver who sent me this story was very happy with my explanation as to what had most likely happened to him during this dive.  He did not mention if he found a tear in the mouthpiece or any other problems with his regulator.