If a sufferer is seriously ill or if vomiting has commenced, the pylorus will be constricted, and oral drugs may not reach their site of absorption. The drugs must be administered parenterally. Some agents are suitable for intramuscular injection if an intravenous line is not available. Sufferers severely affected by seasickness should not dive, and they should lie down and try to sleep. A mild degree of sedation is sometimes very helpful if the patient is being supervised by someone suitably qualified. This can often be achieved by use of an antihistamine that is not only antiemetic but also sedating (e.g. cyclizine). Under these circumstances, a drug such as droperidol in very small doses may also be helpful, but there should be no diving if sedating strategies are used. If there is a prolonged period of interrupted oral intake, intravenous fluid and electrolyte replacement may be required; seagoing medical officers have observed that the fluid may be more important than the drug.
For boat passengers and sailors, acclimatization will develop if progressively increasing periods are spent at sea. Otherwise, it usually takes 2 to 3 days of continuous exposure to adapt to new conditions. The sources of vestibular and proprioceptive stimulation should be reduced to a minimum. This usually means either lying down or being as still as possible. Unnecessary head movements should be avoided. In small craft, staying along the centre line of the craft, toward the stern, incurs the least complex motion. Conflicting visual stimulation is reduced by keeping the eyes closed or by focusing on the horizon. Vulnerable individuals should definitely avoid reading, and noxious stimuli such as smells should be avoided.
Drugs for general use
Most drugs for preventing and treating seasickness are either antihistamines or anticholinergics. This reflects the importance of histaminergic and cholinergic transmission of neural inputs to the vestibular apparatus, the solitary tract nucleus and the vomiting centre itself. Drugs that target the chemoreceptor trigger zone, such as the 5-hydroxytryptamine antagonist ondansetron and the dopamine antagonist droperidol, are not considered particularly effective in motion sickness.
Commonly used antihistamines include cyclizine, dimenhydrinate, promethazine and cinnarizine; and the most commonly used anticholinergic is hyoscine or scopolamine (whose most widely available preparation is a transdermal patch). Various attempts have been made to compare the efficacy of these agents, both within and between the two classes. Graybeil and colleagues4 compared drugs alone and in combinations. They found that the best combination was promethazine hydrochloride 25 mg in combination with 25 mg ephedrine sulphate. Scopolamine was the most effective single drug, but it was more effective also when combined with ephedrine sulphate or d-amphetamine sulphate than as a single drug. In a trial reported by Pyykko and associates5, dimenhydrinate was more effective than one scopolamine patch and about equal to two and had the advantage of needing a shorter period to become effective. Other studies place cyclizine and dimenhydrinate as equal in performance but suggest that cyclizine reduced gastric symptoms and drowsiness6. Use of combined preparations (e.g. hyoscine and dimenhydrinate7) may be more effective than a single compound.
Drugs for divers
The main problem for divers is that all these drugs have some side effects, and none are truly proven safe for diving. Antihistamines may cause dry mouth and drowsiness, whereas anticholinergics also cause dry mouth, variable levels of sedation and occasionally blurred vision. The effects on arousal leave open the possibility of an interaction between motion sickness drugs and nitrogen narcosis. Another frequently cited concern is the question of whether there is any interaction between the drugs and risk of oxygen toxicity. There has been limited investigation of these issues. In hyperbaric chamber dives to 36 metres, transdermal scopolamine was not found to cause decrements in cognitive performance or manual dexterity8. Both scopolamine9 and cinnarizine10 were found not to increase risk of central nervous system oxygen toxicity in rats. Although not a trial in divers or diving, it is perhaps notable that dimenhydrinate was found to induce significant neurocognitive impairment in volunteer subjects, whereas cinnarizine and transdermal scopolamine were not.
In electing to use anti–motion sickness agents, divers must accept that the safety case for use in diving has not been comprehensively made for any drug. However, on balance (which includes consideration of the debilitating effects of seasickness on divers who nevertheless enter the water), the risk versus benefit equation probably favours use of a preventive agent in susceptible divers. At the present time, the evidence suggests that use of a non-sedating antihistamine such as cinnarizine or an anticholinergic in the transdermal form (scopolamine) is acceptable. Unfortunately, both these agents can be difficult to source in Australia and New Zealand. Use of the sedating antihistamines (e.g. cyclizine) or those shown to affect performance significantly (e.g. dimenhydrinate) should be avoided. Any drug used for this purpose must be tried previously to ensure that no untoward reactions occur.
Usually, the first sign of seasickness is pallor, although this occasionally may be preceded by a flushed appearance1. This may be followed by yawning, restlessness and a cold sweat, often noticeable on the forehead and upper lip. Malaise, nausea and vomiting may progress to prostration, dehydration and electrolyte and acid-base imbalance, although these latter and more serious manifestations usually appear only in intractable seasickness during long periods at sea. During this progression, there is often a waxing and waning of symptoms, especially before the actual development of vomiting, and vomiting itself often brings temporary relief.
Tolerance develops to a particular motion, and a person may become acclimatized to specific conditions. If there is a change in the intensity or nature of the motion, the individual may again be susceptible. Continuous exposure to constant conditions usually produces tolerance within 2 to 3 days. Tolerance can also develop to repeated shorter exposures. There is a central nervous system habituation to such a degree that after the person disembarks and the motion is stopped, the person feels that he or she is rocking at the frequency of the original ship exposure.
There is considerable variation in susceptibility to seasickness. With increasing age individuals tend to become more resistant, and at least one study suggests that girls and women are more susceptible2. This susceptibility is said to result from a lack of experience with the situations that produce seasickness. Overindulgence in food and alcohol before exposure, and especially the night before, predisposes to motion sickness. Both the number of meals and their energy content correlate with susceptibility to airsickness2.The position on board the vessel can also be important, with least stimuli if the victim is amidships and using the horizon as a visual reference. Any attempt to read aggravates motion sickness. Psychological factors play a part, especially with seasickness that develops before boarding the vessel. Once one person becomes seasick, there is often a rapid spreading among others present.
AETIOLOGY：Motion sickness is caused by a mismatch or conflict of sensorineural information3. Normally, the vestibular stimuli are consistent with the visual and proprioceptive stimuli, all informing the brain of the position of the body – even when it is in motion. When the environment starts moving as well, the information becomes conflicting. The motion sickness occurs at the onset and cessation of sensory rearrangements; when input of vision, vestibular and proprioception is at variance with the stored patterns of recent stimuli information.
Almost everybody is susceptible to motion sickness1. In general, the population can be divided roughly into one third who are highly susceptible, one third who react only under rough conditions and one third who become sick only under extreme conditions. Although anyone with a normally functioning vestibular system is susceptible, people who are totally deaf and have unresponsive vestibular systems are very resistant.
In diving, two situations predispose to seasickness. The first is on the boat going to the dive site, and the second is while the diver is in the water, particularly if attached to the boat, for example, on a shot line during decompression. Most divers are less susceptible to seasickness while swimming underwater than when they are on the boat. For this reason, many divers hurry to enter the water after exposure to adverse sea conditions en route to the dive site. Problems develop because divers are inadequately prepared and equipped as a result of haste or from the debilitating and demoralizing effects of seasickness.
There are many lessons for recreational divers to learn from the data now available, as well as from the diving medical experience and the regulatory requirements of commercial diving, to reduce the incidence of drowning with scuba. They can be summarized as follows.
- Diver fitness. Ensure both medical and physical fitness, so that there is no increased likelihood of physical impairment or loss of consciousness or difficulty in handling unexpected environmental stresses.
- Experience. Ensure adequate experience of the likely dive conditions (dive under the supervision of a more experience diver when extending your dive profile).
- Equipment. Failure to possess appropriate equipment is a risk, but not as much as equipment failure and misuse. Misuse includes the practice of overweighting the diver, as well as an overreliance on the buoyancy compensator.
- Environment. Hazardous diving conditions should be avoided, and one should use extreme caution with tidal currents, rough water, poor visibility, enclosed areas and excessive depths.
- Neutral buoyancy (dive). Ensure neutral buoyancy while diving. This implies not being overweighted and not being dependent on the buoyancy compensator.
- Air supply. An inadequate supply of air for unexpected demands and emergencies may convert a problematical situation into a dangerous one. It also forces the diver to experience surface situations that are worrying and conducive to anxiety, fatigue, unpleasant decision making and salt water aspiration. Equipment failure is not as common a cause of LOA/OOA as is failure to use the contents gauge and/or a decision to breathe the tank down to near reserve pressure.
- Buddy diving. Use traditional buddy diving practice – two divers swimming together. Solo diving, for the whole or part of the dive, is much more likely to result in an unsatisfactory outcome in the event of diving problems. It is the divers who are committed to the traditional buddy diving practices who are likely to survive the more serious of the drowning syndromes.
- Positive buoyancy (after the incident). Positive buoyancy is frequently required if problems develop. Failure to remove the weight belt during a diving incident continues to be a major omission, and it must reflect on training standards. In most situations, unbuckling and then ditching (if necessary) the weight belt is the most reliable course of action once a problem becomes evident. Buoyancy compensators cause problems in some emergency situations, and not infrequently they fail to provide the buoyancy required expeditiously, especially at depth. They are of great value in many cases – but they are not to be relied on.
- Buddy communication. If feasible, inform the buddy before ascent. If correct buddy diving practice is being carried out, the buddy will automatically accompany the injured or vulnerable diver back to safety.
- Rescue. Employ the rescue, water retrievals, first aid facilities (including oxygen) and medical evacuation systems that were planned before the dive.
These factors differentiate a drowning fatality from a successful rescue.
Drowning among divers is very different in both aetiology and responses from drowning in the general population. Divers do not fear immersion, as do many of the customary drowning victims. The usual drowning victims, falling from a boat or deck, are often unprepared for the withdrawal of a respirable atmosphere, surprised by the sudden cold exposure, choking from a gasp and aspiration of water, illogical and unreasoning in survival attempts. Even swimmers presume that air will be constantly available. The scuba diver is fully prepared, enjoying this leisure activity and protected from the environment, carrying his or her own air supply. The diver has also planned for accidents that could cause drowning by employing buoyancy apparatus and an emergency air supply and with companions trained for rescue. The situation of drowning in divers is thus different from most of those described in Chapter 21.
In a prelude to the 1997 Undersea and Hyperbaric Medical Society (UHMS) Workshop on Near Drowning, the Chairman made the following statement in the pre-workshop correspondence: ‘As you know, the drowning literature ignores diving, whilst the diving literature ignores drowning’.
It is paradoxical that drowning, which causes more than 80 times the number of deaths in recreational divers than either decompression sickness or contaminated air, does not rate more than a paragraph or two in some diving medical texts.
In reviewing the literature on drowning, before the 1997 Workshop4, the only papers that could be found that specifically related any of the drowning syndromes to scuba diving were one on the salt water aspiration syndrome5 and one with an anecdotal review followed by a case report6. Nevertheless, of the major seminal reviews presented on this subject, many have been by diving physicians7–10.
A normally functioning diver, with adequate equipment in a congenial ocean environment, is protected from drowning by carrying his or her own personal life support – the scuba equipment. Drowning would occur only in the presence of the following:
- Diver fault (pathology, psychology or technique).
- Failure of the equipment to supply air.
- Hazardous environmental influences.
Nevertheless, the most common ultimate cause of death in recreational scuba divers is drowning. Factual information that clarifies the causes and management is of value in preventing further fatal outcomes.
Previous surveys illustrated the importance of drowning as the ultimate cause in 74 to 82 per cent of recreational scuba diving fatalities11–15. Of note in the more detailed surveys13–18 was the high frequency of multiple contributing factors to each death. Drowning tended to obscure those preceding factors. The drowning sequelae and drowning pathology were results of the environment in which the accident occurred, not the initiating or primary causes of the accident.
For example, any loss of consciousness or capability when engaging in terrestrial activities is unlikely to cause death. It would do so more frequently if the victim was diving underwater.
The aspiration of sea water that causes clinical features in scuba divers who retain consciousness is discussed in Chapter 24. Sometimes, this progresses to the other manifestations of near drowning and drowning, and these conditions were compared in one survey of fatalities (drownings) and survivors (near drownings)16 in recreational diving. The observations were as follows.
Of the 100 fatalities, 89 per cent occurred in male divers and 11 per cent occurred in female divers. Of the 48 survivors, 52 per cent were male and 48 per cent female. Compared with the diving population at the time (30 per cent female, 70 per cent male), male divers were overrepresented in the scuba drowning cases, as they are in almost all other forms of drowning9. The surprise was that female divers appeared to be overrepresented in the ‘survivor’ series.
Whether female divers had more accidents or whether they only reported them more frequently could not be deduced. However, it does appear as if accidents in female divers result in fewer deaths.
In the fatalities, 38 per cent of these divers had no known formal qualification. This group was approximately equally divided among:
- Those in whom documentation was inadequate.
- Those without training, but who were experimenting with scuba under their own or their friends’ cognizance.
- Those who were engaged in introductory dives, brief resort courses or ‘dive experiences’ with a recognized commercial organization.
Of the survivors, 81 per cent had completed basic training, and only 4 per cent had no training.
Surprising numbers in both groups were under formal training at the time – 8 per cent of the fatalities and 15 per cent of the survivors.
Experience did not directly correlate with training. In both the fatality and survivor series, the divers were equally represented among inexperienced divers (<5 dives), novice divers (5 to 20 dives) and experienced divers – one third each.
Of the fatalities, more than half these divers were experiencing diving situations to which they had not been previously exposed, whereas one third had previous experience of the conditions in which they died. The others were unable to be assessed.
The buddy or dive leader appeared to be considerably more experienced than the diver in most of these cases, thereby possibly explaining why the diver died and the buddy lived.
In 100 diving fatalities, more than a third were observed to have either a panic response or rapid or abnormal movements (Table 25.1). The survivors reported these sensations in more than one half of cases. The increased incidence in the surviving group could be attributed to this being a reported sensation, whereas the fatality figure represented only the observed behaviour.
Table 25.1 Behaviour among fatalities and survivors of drowning in divers
More than half the divers who died showed no change in their behavior before drowning, with loss of consciousness being the first objective warning in one third. It was the first manifestation noted in one fourth of the survivors.
Of interest was the absence of panic in many of the cases, even though it is a frequent cause of other diving deaths11–13,17. Drowning scuba divers frequently drown quietly – possibly because of the effects of previous aspiration (hypoxia), depth (narcosis) or training (‘don’t panic’).
A request for a supplementary air supply was made by twice as many divers who died (21 per cent) as survivors. This may bring into question the value of relying on a buddy to respond to such a request. Alternatively, with the survivors, more frequently buddies offered the emergency air supply – a preferred sequence. Occasionally, there was the apocryphal underwater tussle for a single regulator. When the low-on-air diver went for an air supply, he or she more frequently sought the companion’s primary regulator than the octopus.
Medical conditions (history)
This is a contentious area, not only regarding the incidence of medical disorders but also their significance. Authors differ in their assessments of this, and none are free of selection bias.
Medical history data from fatality records are inevitably underestimates. In one analysis13, when a purposeful attempt was made to acquire the medical history, in less than half of the cases could this be obtained.
In this survey no attempt was made to draw statistical differences regarding the correlation between past illnesses and drowning; however, there was no doubt as to the contribution in the survivor group (Table 25.2). Some of both groups should not have been classed as medically fit for diving (see Chapters 53 to 59).
Table 25.2 Medical disorders among fatalities and survivors of drowning in divers
The adverse influences of water conditions were expected (see Chapter 5). Probably the only surprise was the frequency with which drowning occurred in calm waters – in more than half the cases. Strong tidal currents were slightly more frequent in the fatality group.
Fresh water or sea water
Most of the accidents occurred in the ocean, without obvious differences between the fatality (93 per cent) and survivor groups (98 per cent). The extra difficulty of performing rescues in cave diving (2 per cent) was expected.
Depth of incident
The depth of the aspiration or drowning incident was not necessarily the depth of the original problem. Thus, a diver who used most of the air supply and then panicked and ascended may not have exhibited any evidence of aspiration until reaching the surface.
As in previous surveys, many problems developed on the surface. Approximately half the fatalities occurred on the surface or on the way to the surface. Frequently, the diver no longer had adequate air to remain underwater. Another 20 per cent occurred in the top 9 metres, and the rest were distributed over the remaining depths. This finding implies that just reaching the surface is not enough. Successful rescue then requires the victim to remain there.
The survivors more accurately reported the depth at which the incident developed, as opposed to the depth at which the incident was noted by others. Nevertheless, almost two thirds of these incidents occurred in the top 10 metres.
In the fatality and the survivor groups, the dive was the deepest of their diving career in 26 per cent and in 33 per cent, respectively. In almost half the ‘inexperienced’ and ‘novice’ divers, the depth was beyond that which had previously been undertaken. This finding suggests that these groups are especially susceptible to the various problems associated with depth (panic, air consumption, visibility, narcosis and logistical difficulty with rescue).
This suggests that it is not so much the environment that is the problem, but the diver’s limited experience of that environment. The risk of ‘diving deeper’ without extra prudence and supervision is apparent. Any dive deeper than that previously experienced should be classified and treated as a ‘deep dive’, irrespective of the actual depth.
Visibility was usually acceptable, but it seemed to be more frequently adverse in the fatalities (38 per cent) compared with the survivors (18 per cent).
The cases, in general, demonstrated the adverse effects of various environments, especially with tidal currents, white (rough) water, poor visibility and deeper diving than previously experienced. There was not a great deal of difference between the two groups, except in the higher incidence of strong tidal currents, night diving and cave diving in the fatalities. The figures, however, were small. Such adverse environments may affect the victim directly or may negatively influence rescue and resuscitation.
In most fatalities, the equipment showed no structural abnormality, and only in 20 per cent were there significant or serious faults contributing to the fatality. This finding corresponded with the reported incidence by the survivors (18 per cent).
Equipment faults were most frequently found with buoyancy compensators and regulators (both first and second stages).
The incidence of equipment misuse was more frequent but more difficult to ascertain in the fatality series – and it depends on one’s definition (fatalities 43 per cent, survivors 38 per cent). Misuse of equipment included the use of excessive weights (fatalities 25 per cent, survivors 27 per cent). It also included the failure to carry equipment that could have been instrumental in survival (e.g. buoyancy compensator, contents gauge, snorkel) – in 12 per cent and in 8 per cent, respectively. Difficulties in using buoyancy compensators were also frequent.
Various diving techniques contributed to the drowning incidents or influenced rescue and survival. They included a compromised air supply, buoyancy factors, buddy rescue and resuscitation attempts.
In 60 per cent of the fatalities, either an out-of-air (OOA) or a low-on-air (LOA) situation had developed. There was insufficient air in the tank for either continuing the planned dive or returning to safety underwater. In the survivors, there was a lower incidence (35 per cent) of compromised air supply, but it was still very high. The survivors were more likely to have air in their tanks to cope with the emergency.
The failure to use the available contents gauge, in both groups, was a source of concern, which could sometimes be attributed to the conditions placing other stress on the diver (e.g. depth, anxiety, tidal current, deepest dive ever). In many more cases, there was a voluntary decision to dive until the tank was near reserve or ‘ran out’.
One surprising feature was the failure in both groups (8 per cent and 13 per cent) to reopen the valve of the scuba tank after initially testing the tank pressure before the dive. Thus, even though there was plenty of air in the tank, it was unavailable other than to sometimes allow a rapid descent to a few metres. Only then was the diver aware that further air was not available. In none of these cases was there a buddy check of equipment – breathing near the water surface and checking the equipment before descent.
In a smaller number of cases there was a failure to ensure that the cylinder tap was adequately turned on. Reducing tank pressure resulted in a restriction of air supply – sometimes obvious only at depth.
Buoyancy was frequently a vital factor in reaching the surface and in remaining there as an unconscious diver and being found, rescued and resuscitated in time. The three major influences on this are buoyancy compensators, weights and the companion (buddy) diver practice.
In the survivor group. the buoyancy compensator was inflated by the victim or rescuer (35 per cent and 25 per cent) in twice as many cases as in the fatality group (15 per cent and 16 per cent). This figure is even more relevant when the delay in producing buoyancy in the fatality group is considered (see later).
These weights were as shown in Table 25.3.
Although in 30 per cent of the fatality cases the weights were ditched, in practice this was not as valuable as it sounds. In most of the instances in which the rescuer ditched the weights, the victim was probably no longer salvageable because of the delay (see later).
The survivor group not only ditched the weights more frequently, but often this was done by the victim. When it was done by the rescuer, it was usually performed early in the incident.
Buoyancy action by survivors
The fatality and survivor groups differed in that the survivors more often performed an action (ditching weights, inflating buoyancy compensator) that resulted in their achieving positive buoyancy during and following the incident.
An interesting observation was made when the victim and buddy were both in difficulty, usually based on an LOA/OOA situation. In the ensuing situation, irrespective of whose problem developed first, the overweight diver tended to be the one who died, and the buoyant diver was the one that survived. In the 14 instances, the ratio was 6:1.
All this gives support to the current instructor agencies’ emphasis on buoyancy training, although one could argue for its inclusion in introductory courses more than in advanced courses.
COMPANION DIVER PRACTICE, RESCUE AND RESUSCITATION
In most cases of significant aspiration of water, rescue depends on rapid action undertaken by either the victim or the companion (buddy) diver. Once a diver gets into difficulty and is unable to carry out safety actions by himself or herself, the diver is heavily reliant on the buddy or dive leader. The fatality and survivor populations were very different in this respect.
In the fatality group, less than half the victims had an experienced buddy available to assist them. In 21 per cent of the fatalities, the dive was a solo one. In 38 per cent, the diver had separated from his or her buddy, and in 12 per cent the diver had separated from the group, before the serious incident. Thus, a voluntary separation happened in 50 per cent of the cases before the fatality. The separation was initiated in most cases because the victim could not continue (usually because of an LOA situation). The victim then attempted to return alone, essentially making it a solo dive.
The diver was separated from the buddy or the group during the actual incident, and often by the incident, in 21 per cent of cases. However, in almost half of these cases, the separation was produced because the diver was following the buddy or the group. The others occurred during the ‘rescue’.
Thus, separation made early rescue and resuscitation improbable. In 9 per cent, the victim was swimming behind his or her companion or companions, and thus the victim was not visible to the ‘buddy’ at the time of the incident.
In summary, 80 per cent of the victims did not have a genuine buddy, by virtue of their elected diving practice. In fewer than 1 in 10 deaths was there continued contact with the buddy or group during and following the incident.
The victims seemed flagrantly to disregard the ‘buddy’ system – as did their companions, the organization that conducted the dive or the ‘dive leader’. Group diving conferred little value because the ‘leader’ often had insufficient contact with individual divers to be classified as a buddy, and the responsibility of others was not clear – especially toward the last of the ‘followers’.
In only 20 per cent was the diver reached within 5 minutes of the probable incident time, and thereby have a real chance of successful resuscitation. In another 12 per cent, the diver was recovered within 6 to 15 minutes, and theoretically there was a slight chance of recovery with these divers, had the rescue facilities been ideal and had fortune smiled brightly.
Resuscitation was not a feasible option for most of the eventual fatalities, who were obviously dead or showed no response to the rescuers’ attempts, in 9 out of 10 cases. This is explained by the excessive delay in the rescue in most cases.
In the surviving group, most were rescued by their companion. Some form of artificial respiration or cardiopulmonary resuscitation was required in 29 per cent of the cases. Oxygen was available and used, usually in a free-flow system, in 52 per cent of cases.
No specific data were available on the buddy divers assisting the survivors, other than the subjective assessment of whether the survivor believed the buddy to be of much value, as follows:
- The buddy was immediately available to the survivor in 71 per cent of cases.
- The buddy was considered to be of assistance in 58 per cent of cases.
- The buddy supplied an independent air source in 15 per cent of cases.
- The buddy inflated the buoyancy compensator in 25 per cent of cases.
- The buddy ditched the weight belt in 25 per cent of cases.
- The buddy attempted buddy breathing in 4 per cent of cases.
In 52 per cent of cases, the diver surfaced under control of the buddy.
The attitude toward buddy diving practice in the survival group appeared to be very different from that in the fatality group.
The frequency of oxygen use probably represented a more sophisticated and organized diving activity, which may also be related to more conscientious buddy behaviour.
The axiom is that to rescue an incapacitated diver successfully, one must know where he or she is and reach the diver quickly. This implies some form of buddy responsibility. Once reached, the buddy divers seemed to be of considerable value – implying good training or initiative in this aspect of diver safety.
In recent years there has been a promotion of solo diving and reliance on oneself, as compared with buddy diving practices. The foregoing data indicate that the traditional buddy concept, correctly practised, is of more value.
Diving includes snorkelling. Snorkellers who rarely leave the surface still expose themselves to many hazards, including drowning (see Chapter 61). There are few well-documented series of these incidents. Walker described 90 snorkelling deaths between 1972 and 1987, although many had no forensic assessment1. Edmonds and Walker described 60 such deaths between 1987 and 1996, all of which had coroners’ inquiries and/or autopsy investigations2. Lippmann and Pearn described a further 130 cases, up until 20063.
Surface drownings caused about 25 to 45 per cent of the snorkellers’ deaths. Drowning followed hypoxia from breath-hold diving, usually after hyperventilation, in 15 to 20 per cent (see Chapters 16 and 61 for these conditions).
Surface drownings tended to occur in an older but wider range age group than the hypoxic drownings, but at a younger age than those who die of the other major cause, cardiac disease. These snorkellers were often aquatically inexperienced, less fit tourists who engaged in commercial reef-snorkelling trips or solo swimming. Frequently, they had medical disorders that made them more vulnerable, such as epilepsy, respiratory diseases such as asthma, salt water aspiration and vomiting. Adverse environmental factors, such as currents and choppy surface conditions, were contributors in 15 per cent. The absence of fins in 40 per cent made coping with aquatic conditions more difficult. Overall, the physical unfitness and aquatic inexperience that led to panic and aspiration dominated the situation.
Historically, drowning has been incriminated as the cause of death in 74 to 82 per cent of recreational diving deaths, compared with the more high-profile diseases of decompression sickness (<1 per cent) and contaminated air supply (<1 per cent).
Comparisons of divers who drown with those who survive from near drowning reveal the importance of the following:
- Personal factors, including both medical and physical fitness.
- Diving experience.
- Faulty equipment and misuse of equipment.
- Hazardous environments.
- Neutral buoyancy being maintained during the dive and not being dependent upon the buoyancy compensator.
Other factors that increase the likelihood that diving problems will have an unsuccessful outcome include the following:
- An inadequate air supply.
- The failure to employ correct buddy diving practices.
- Inadequate buddy communication.
- Failure to achieve positive buoyancy after a diving incident.
- Inappropriate or delayed rescue and resuscitation.
Most of the clinical manifestations of SWAS respond rapidly to rest and the administration of oxygen. Warming the patient is of symptomatic benefit. In general, no other treatment is required.
There is a possibility that some of the clinical manifestations may not entirely be caused by to the aspiration of water, but by the body’s (and specifically the respiratory tract’s) response to aspirated organisms, foreign bodies or irritants carried to the lungs with the sea water aspiration.
In the differential diagnosis of SWAS, the possibility of other occupational diseases of divers must be considered:
Acute infection – The aspiration syndrome may mimic an acute respiratory infection that develops soon after a dive. It is often claimed that a mild upper respiratory infection is likely to be aggravated by diving. This is questionable with the number of divers who continue to dive, uneventfully, despite such infections. Differentiation between SWAS and an acute infection can be made from the history of aspiration, serial chest x-ray studies, spirometry and a knowledge of the natural history of the infectious diseases. In the first few hours of this syndrome, the possibility of both influenza and early pneumonia are often considered – to be dismissed as the symptoms clear within hours.
Decompression sickness with cardiorespiratory or musculoskeletal manifestations – If there is a likelihood of cardiorespiratory symptoms of decompression sickness (‘chokes’), recompression therapy is indicated. Decompression sickness should be considered in patients who conduct deeper, prolonged or repetitive diving. The specific joint pains and abnormal posturing characteristic of the ‘bends’ are quite unlike the vague generalized muscular aches, involving the limbs and lumbar region bilaterally, seen with SWAS. The immediate beneficial response to the inhalation of 100 per cent oxygen in SWAS is of diagnostic value. With decompression sickness, any relief is more delayed. Chest x-ray studies, lung function tests and blood gas analyses may be used to confirm the diagnosis. Decompression sickness responds rapidly to recompression therapy (as does SWAS to hyperbaric oxygenation). Otherwise, except for the occurrence of a latent period, the clinical history of the two disorders is dissimilar.
Pulmonary barotrauma – Serious cases of pulmonary barotrauma result in pneumothorax, air emboli and mediastinal emphysema occurring suddenly after a dive. In minor cases of pulmonary barotrauma, confusion with the SWAS may arise. In these patients, the diagnosis and treatment of the former must take precedence until such time as the natural history, chest x-ray findings, spirometry and blood gas analysis demonstrate otherwise. Oxygen is appropriate first aid treatment for both disorders. Hyperbaric oxygen is also an effective (but unnecessary) treatment for SWAS.
Hypothermia – The effects of cold and immersion are usually maximal at, or very soon after, the time of rescue. The clinical features are likely to be confused with SWAS only when both conditions exist. The body temperature is higher than normal in SWAS and lower than normal in hypothermia.
Key West scuba divers’ disease6 – This and other infective disorders resulting from contaminated equipment may cause some confusion. Fortunately, these illnesses usually take longer to develop (24 to 48 hours) and to respond to therapy. There is thus little clinical similarity in the sequence and duration of the clinical manifestations.
Asthma – Some patients have hyperreactive airways to hypertonic saline (sea water), analogous to an asthma provocation test (see Chapter 55). Such patients have the clinical signs of asthma (expiratory rhonchi, especially with hyperventilation, typical expiratory spirometry findings and positive asthma provocation tests). They respond to salbutamol or other beta agonists.
Immersion pulmonary oedema – This disorder may be either a complication or an initiator of SWAS.