UK SPORT DIVING MEDICAL COMMITTEE |
Adobe Acrobat version available here
Submersion or near-drowning
Medical referees are often involved in assessing divers after underwater incidents and also in providing training and instruction on resuscitation. New guidelines have been published by the American Heart Association on resuscitation standards, and this includes special circumstances such as submersion incidents. Overall little has changed since the last revision, but there are some new terms and definitions worth identifying. Some measures of prognostic information are also described.
The
following terms are recommended in
place of "drowning" or "near-drowning":
The classification of salt water and fresh water victims is clinically irrelevant and the most important prognostic factors are the duration of submersion and the duration and severity of hypoxia. The following factors predict poor prognosis: submersion for more than 25 minutes, resucitation for more than 25 minutes, no cardiac output on arrival at hospital, ventricular tachycardia or fibrillation on the initial ECG, fixed pupils, severe acidosis and respiratory arrest.
In terms of resucitation guidelines there has been no significant change for basic resucitation (ie that provided by divers or onlookers) but the following points are worth reinforcing when training divers: there is no need to clear the airway of aspirated water, and in particular the Heimlich manoeuvre should not be routinely performed for resuscitation since it delays ventilation and produces complications. It should only be performed if a foreign body is suspected in the upper airway. Chest compressions are often effective in removing such objects anyway. If there are no signs of circulation then airway management, ventilation, and chest compressions should be continued whilst waiting for equipment and help. If the victim is hypothermic and in a shockable rhythm then up to 3 shocks should be given, but if this is unsuccessful then further attempts should be delayed until the body core temperature rises above 30ºC.
Vomiting is very likely (occurring in 86% of victims requiring CPR) and should be managed by turning the victim on their side and clearing the mouth. All victims requiring resucitation should be transferred to hospital, even if the resuscitation was brief. In ITU, additional treatment with induced hypothermia, steroids, barbiturates or intracranial pressure monitoring makes no difference to neurological outcome.
Circulation 2000;102(supplI):I-233-I-236 Submersion or near-drowning
New medical system
The new system was launched in the Scottish Sub-Aqua Club in April and has been running without mishap. There have been no unforseen problems and the number of divers requiring medical examinations has not changed so far. There have been more general enquiries but these have been resolved without further assessment or investigation. The overall failure rate has increased which is encouraging from a safety point of view. The SSAC is a smaller organisation than BSAC or the SAA and it has been easier to introduce this change. In addition all medical records are stored centrally so it will be possible to monitor the safety of the new system accurately.
The BSAC and SAA NDO's met with the UKSDMC on 15th October 2000 to discuss administrative issues and the new medical system should start soon in these organisations. The main topics discussed included the need for storage of the medical forms, the repetition frequency and clarifying how divers should contact medical referees. Overall the medical principles remain the same for each organisation and the same form will be used across the board as previously. Divers may still require medicals if travelling abroad but these can now be performed by approved medical referees.
For
those interested in more details
of the safety audit performed in
the SSAC population:
Medical supervision of sport
diving in Scotland. Glen S, White
S, Douglas J. Br J Sports Med
2000;34:375-378
Detection of patent foramen ovale
Right-to-left shunting through a patent foramen ovale is a risk factor for decompression illness, cerebral ischaemia in young patients and migraine with aura. In clinical practice young patients with stroke are often referred for transoesophageal echocardiography to exclude patent foramen ovale, but this is an invasive test which can be unpleasant for patients. It is also unsuitable as a screening test for healthy volunteers in research. Transcranial Doppler ultrasound detection of bubbles in the cerebral circulation gives indirect evidence of shunting of any type including pulmonary arteriovenous fistuale as well cardiac lesions such as PFO and gives no information about cardiac anatomy.
 |
A
recent study using transthoracic
echocardiography with harmonic
imaging (a technique to improve
the image quality) confirms that
this is as good as the
transoesophageal approach.
Intravenous contrast is given,
along with manoeuvres to
increase the chance of
right-to-left shunting including
Valsalva, coughing or abdominal
compression. The study involved
111 patients with cerebral
embolism, and shunts at atrial
level were found in 57 with no
difference between TOE and TTE
in terms of sensitivity or
specificity. This is an important result which confirms the approach taken to screen divers by TTE only, and will also be useful in research studies of shunting and decompression sickness. In clinical practice young patients with strokes are now being screened by TTE with harmonic imaging. Echocardiography technology is advancing almost daily with huge increases in computer processing power and image quality. Three dimensional reconstruction is also possible, and can give a surgeons view of the defect. |
PFO closure is usually performed under general anaesthetic because of the need to perform TOE during device deployment, but transthoracic views are now good enough to allow the procedure to be performed quickly under local anaesthetic.
Transthoracic echocardiography using second harmonic imaging. Kühl H, Hoffman R, Merx M et al. J Am Coll Cardiol 1999;34:1823-30
Anticoagulation and diving
The
anticoagulation medical standard
is due to be revised to include
specific recommendations on diving
practice to reduce the risk of
decompression illness with the
possibility of haemorrhage into
areas of injury including the
spinal cord lesions. The specific
diving limits recommended include:
The new medical standard will be reviewed at the next committee meeting.
Unreliable diving medicals
A postal survey of 81 diving doctors in Queensland has shown significant variability in assessing fitness to dive. 52 doctors replied to the survey which included 15 clinical scenarios. The published guidelines suggested that 10 out of the 15 cases should have been referred to specialists (67%) but only 17% of responses suggested referral. One doctor failed 13 of the 15 cases outright, whereas another failed only 4. One case was passed fit despite guidelines strongly recommending failure. It is disappointing that there is such diversity of opinion despite published guidelines. The authors conclude that the guidelines should be modified to avoid ambiguity but medical education is also important.
Scuba diving medical examinations in practice: a postal survey. Simpson G, Roomes D. Med J Aust 1999;171:1595-8 with comment 584
Risk factors for bubble production
Some divers are more at risk of decompression sickness than others. Recreational divers using tables designed for the military place themselves at higher risk because such tables were designed using highly trained and physically conditioned divers who have different physiological characteristics from the average UK diver, who tend to be heavier than the average population, and cannot be described as elite sports participants. This risk is well described in observational studies, and also in the original caisson studies of tunnel workers.
A recent study of 40 recreational divers examined the link between various physical characteristics and the number of venous bubbles produced after a 35 metre dive using the COMEX 1987 decompression table with a bottom time of 25 minutes and stops at 6 msw for 3 minutes, and at 3 msw for 15 minutes. As expected, half of the divers had detectable cardiac bubble signals but a very clear relation was found between the bubble count and the age of the diver, weight, percentage body fat, and an inverse relation was demonstrated with physical fitness measured by VO2 max.
Statistically significant differences were confirmed between the group with no bubbles, and those with the highest bubble grades for age, weight, and VO2 max (but not body fat). Previous research has been performed on pigs where a measure of bubbling tendency was performed before starting a training programme to increase their aerobic fitness. Similar work has been performed in rats, and this confirms that the bubbling tendency is reduced as aerobic fitness increases.
The conclusion from these studies must be that divers should be encouraged to maintain or improve their level of fitness. This is concerning because there are signs that the fitness of divers and the general population is declining with increases in body mass index and the number of smokers. In the future dive computers may be programmed to include risk assessment with divers entering their individual characteristics including weight, age, sex. Until then divers need to take responsibility for their own risk reduction and should be educated accordingly.
Circulating venous bubbles in recreational diving: relationships with age, weight, maximal oxygen uptake and body fat percentage. Carturan D, Boussuges A, Burnet H, Fondarai J, Vanuxem P, Gardette B. Int J Sports Med 1999;20:410-414
Predicting middle ear barotrauma
 |
Ear clearing difficulty remains one of the most common problems for divers, and middle ear barotrauma is the most frequent dysbaric injury. Predicting which divers are at risk of injury is difficult, and the usual method is to look for ear drum mobility during a Valsalva manoeuvre. A study of 22 sports divers compared three methods of assessing Eustachian tube function and found that it was possible to predict those who were likely to be at risk of middle ear barotrauma on the basis of a combination of Valsalva, Toynbee and nine-step tests. The positive predictive value for the three tests was 0%, 25% and 83% respectively. Combining the Toynbee and nine-step tests increased the positive predictive value to 100%. The Toynbee test involves pinching the nostrils while swallowing and the muscles at the back of the throat pull open the Eustachian tube allowing pressures to equalise. The best functional test of ear clearing difficulty is practical training in the pool and this paper confirms the poor predictive value of routine examination of the ear during Valsalva maneouvres. Divers who have difficulty clearing their ears can be examined in more detail using the tests described in this paper. |
Use of the nine-step inflation/deflation test as a predictor of middle ear barotrauma in sports scuba divers. Uzun C, Adali MK, Tas A, Koten M, Karasalihoglu AR, Devren M. Br J Audiol 2000;34(3):153-63
Neurological decompression illness
A case controlled study of decompression illness has been published looking at 100 consecutive divers referred for investigation compared with controls. The aim of the study was to identify underlying physical causes, and in particular to establish the role of paradoxical embolism or lung disease in causing neurological decompression illness. Consistent with previous research, right-to-left shunting through a patent foramen ovale was much more common in divers with neurological DCI than controls (52% versus 12%, p<0.001, highly significant). In most cases with right-to-left shunting symptoms developed after a short delay after surfacing, with a peak between 11-20 minutes, and the majority occurring within 30 minutes.
This is in contrast to divers where pulmonary baroatrauma was thought to be the underlying cause, and symptoms started immediately on surfacing in most of these cases. The majority of shunts were detected after a single injection of intravenous bubble contrast without provocation manoeuvres such as Valsalva, abdominal compression or coughing. Evidence suggests that only large shunts are significant, and in the previously published autopsy study of patent foramen ovale, large defects (10mm or more in diameter) were only found in 1.3% of the study population. This is more consistent with the low incidence of decompression illness, rather than the overall prevalence of 20-25% which also includes very small defects described as "probe patent"- such defects may be only 1-2 mm in diameter, and are unlikely to be clinically significant.
Relationship between the clinical features of decompression illness and its causes. Wilmshurst P, Bryson P. Clinical Science 2000;99:65-75
| Back to research | Back to newsletter index | UKSDMC home |