NORMOBARIC OXYGENATION AS A FIRST-AID MEASURE IN DECOMPRESSION SICKNESS

Article 8

Normobaric Oxygenation as a First-Aid Measure
In Decompression Sickness


by:

Lim Ju Boo

Regional Staff Officer (Training Division)

St. John Ambulance Malaysia

My youngest sister, a Singaporean, often likes to come up here to Malaysia to Tioman Island, and other nearby islands to scuba dive to some depths. Another friend of mine, an astronomy enthusiast also does the same, and he also does some star gazing in the outreaches of some dark islands where the skies are clearer after the dive. Both of them complain (although my sister has never told me directly, except through her husband) of some joint and muscular pains at night each time they scuba dive. Their complain is unbiased, since my sister and my friend do not know each other, and they do separate diving, so they may be accepted as unbiased observation in a case study. I suspect their *symptoms (see foot-notes) is an indication of a condition called ‘bends’.

Perhaps at this point I should explain what bends are, since I suspect it was not taught in the St. John Ambulance (SJAM) first-aid classes (not that I know of). It was definitely not taught in the Red Crescent first-aid course nor in the First Responder course did I attend. I know it was not taught because I was at ‘concert pitch’ (keyed-up, tuned in to hear and record every note or word, right or wrong), on what the instructors said. I suspect not many first-aiders know what ‘bends’ is, let alone the first-aid for this condition. So I shall begin by explaining what bends is all about, before I proceed with a discussion on the subject.

Bends, used to be called caisson disease, medically called ‘decompression sickness’, is the result of gas mixtures (chiefly the inert, less soluble nitrogen) forming gas bubbles in the tissues of diver ascending too rapidly to the surface. The solubility of gas mixtures (compressed air carried in the cylinders by the diver) varies at various pressures as the divers ascend to the surface after a dive. At depths, divers accumulate large quantities of inert gas (chiefly nitrogen, - 78% in the compressed air) in their tissues. Normally the amount of gas can be held dissolved in the tissues such blood and body fat as the diver descends, the higher the pressure, the greater the solubility. Because of differences in solubility with partial pressures as the diver ascends to the surface, the less soluble ones will bubble out in the body tissues first. This is specially true as the pressure decreases rapidly when the diver makes a rapid ascend, leaving little time for the blood to clear the less soluble gasses. This is like opening a bottle of beer, and you see all the bubbles of carbon dioxide spewing out from the bottle. Partial pressure of a gas is the product of the percentage of a gas in a gas mixture, multiplied by the total pressure in that mixture.

In decompression sickness, bubbles may block blood vessels, causing various symptoms, from impairment of the nervous systems – muscular weakness, paraesthesia, dermatomal numbness and pain, paraplegia, bowel and bladder disturbances, CNS (Central Nervous System) changes, visual disturbances, or dys-coordination and balance due to gas bubbles within the labyrinth (semicircular canals, vestibules, cochlea) of the ears causing vestibular damage (‘the staggers’). More seriously, is a crushing chest-pain (angina pectoris) from gas bubbles forming in the coronaries of the heart, and circulation to the lungs (pulmonary gas embolism). There maybe dyspnoea (‘the chokes’). If the gas is released into muscles, skin and lymphatics, it may cause pain in limbs, pruritus (itchiness), marbled skin, painful lymph nodes, lymphoedema (fluid accumulation in tissues due to obstruction of lymph vessels). Some of them, especially if they involve the heart or brain, can cause sudden death. All these can be avoided if the diver ascends slowly by allowing the un-dissolved gases to escape slowly via the blood to the lungs.

In scuba-diving and hyperbaric medicine, the victim is placed in a recompression chamber. Pressure within the chamber is raised by pumping in air. This procedure forces the bubbles to re-dissolved into the tissues, and the victim becomes asymptomatic (no symptom) again. The pressure within the chamber is then slowly decreased to release the gas slowly to escape to the lungs via the blood. So far, so good! But such procedure can only be carried out at certain centers equipped with recompression chambers, and I understand there are only a few in this country. The main centre is at the Naval Hospital in Lumut where the recompression chamber may be filled with compressed air or pure oxygen up to 2 atmosphere pressures. The other two centers for hyperbaric therapy are at Kuantan and Labuan. The one at Lumut treats not only bends, but also other medical conditions where hyperbaric oxygenation is indicated, such as in gangrene, in AMI (acute myocardial infraction), and in carbon monoxide poisoning. The therapy normally last for 1 –2 hours. The treatment is very expensive because pure compressed oxygen is used, and imagine you have to fill up the whole chamber with it under twice the atmospheric pressure. The chamber is sufficiently large to accommodate not only the victim, but also medical personnel inside. The other two centers in Kuantan and Labuan are less sophisticated, and they are used only for the treatment of decompression sickness.

So what do we do? What is the first-aid for bends I mean? Of course I understand what you are going to say since you were not taught about bends in the first aid classes. The simplest answer to give is to bundle up the victim to such a centre. That’s the simplest thing. But what is the immediate (first-aid) measure? Now that we know what bends is all about, we are now in a better position to critically discuss the first-aid treatment at a more advanced level. Can we just give oxygen to increase the partial pressure? Yes you may, but….

Most divers and diving medicine specialists know that the application of normobaric (at normal atmospheric pressure) oxygen as FIRST-AID (before transport to a hyperbaric centre) after a bubble disease incident is highly effective. However, as yet certain technical difficult acted as a constraint in using normobaric oxygen at the site of the accident. Administering pure oxygen through nasal cannula, or through an ill-fitting face mask, or even through a nonrebreather mask is only partially helpful, but not totally useful. That still won’t solve the problem of getting the other gasses out. Remember what we discuss about solubility of gasses and their partial pressure in our above introduction? Now you can guess why ill-fitting oxygen mask is unsatisfactory. Some work has already been done to overcome this difficulty by a newer first-aid technique. To make it more effective, any first line therapy of bubble disease should follow three main principles:

1. Maximal partial pressure of inhaled oxygen, abbreviated as PO2 (oxygen and other gas mixture in a cylinder, each exert part of the total pressure), i.e. 100 kpa (about 750 mm Hg, or 1 atmospheric pressure) in normobaric, and 280 kpa in hyperbaric (say inside a compression chamber if available, or go back to the sea again and administer the oxygen under the sea where the pressure is higher) conditions; minimal partial pressure of inhaled nitrogen which ideally be near zero

2. Immediate start of first-aid therapy, if possible at the diving site itself, but not later than 2 hours after the onset of the first symptoms.

3. For an efficient normobaric oxygenation (100 %), the standard design without oxygen reservoir is obsolete, for it offers at most 40 % oxygen to the lungs. Currently the following technical approaches for an efficient normobaric oxygenation are available : open one-way systems with tightly fitting mask and oxygen reservoir bag (Ambu or Leardal bag, etc); open system on demand regulation and tightly fitting mouth piece (SCUBA, or Bird-respirator type); closed systems with CO2 absorber (oxygen rebreathing diving gear).

Any first-aid oxygen gear, or an ambulance fitted with the closed system is a genuine technical advance, because it needs 15 times less oxygen than open system (about 90 liters oxygen for a 3-hours oxygenation run). Such an apparatus is thus of light weight, far less cumbersome, and of course highly efficient. Importantly, the first-aid should start immediately at the site of the mishap and maintained throughout the period of transport to the nearest hyperbaric oxygen unit. Some work on this advancement in first-aid for compression sickness was conducted in Germany by Wendling, J., and was published in a journal on Sports Medicine (1).

Perhaps I should warn my youngest sister who never tells me anything, about decompression sickness. But I believed she knows about this, as she is a qualified scuba diver. And perhaps to my argumentative and talkative astronomy-scuba diving friend as well, I should also give this first-aid advice (provided he doesn’t argue with me until I sometimes have to put my head down, closed my eyes, and cover my ears with both my hands to be nullified).

Still on the subject on decompression sickness, here is another critical comment. For several years now, a controversy arises as to how to position a patient after a decompression accident with acute gas embolism (the pathology I have already explained). The usefulness of the so-called Trendelenburg position, based on experimental evidence gathered on dogs , has recently been challenged. The basis assumption was that cerebral embolism may be reduced by the hydrostatic effect of putting the head below the body’s centre of gravity. This position however requires a lot of technical resourcefulness, and may be difficult without an adjustable stretcher , and this often delayed the first therapeutic intervention, say at the site of the incident. Recent advances in experimental research shows that, contrary to the old theory, positioning the head below feet level increases the intra-cranial pressure (I think this is common sense reduction, due to pooling effect of blood flow and CSF), injuring the blood-brain barrier, even when performed under hyperbaric oxygen therapy. (My commonsense tells me there is there is no need to conduct an experiment to demonstrate this!).

Now a wide consensus has emerged from a study which should be communicated to all paramedics, first responders and first-aiders so that no more time is wasted fighting and quarrelling over the question how to position the patient by unduly complicated means and angles. Summarizing a report which I read, the current recommendations asks for laying the injured diver horizontally on his/her back, or sideways, if he/she is concious. The recommendation is that it is far more important to control its vital functions, give first-aid, administer oxygen in closed circuit (already discussed above), and shorten as much as possible, the transport time to the nearest hyperbaric therapy centre (Lumut Navy Hospital, or the General Hospitals in Kuantan or Labuan) Good luck to you all first-aiders who may have to deal with
scuba divers. Hope the paramedics will also read this (2).