From the *Department of Anesthesiology and Intensive Care Medicine, University of Bonn, Bonn, Germany; the †Department of Anesthesiology and Intensive Care Medicine, Kreiskrankenhaus Mechernich, Germany; and the ‡Department of Anesthesiology and Intensive Care Medicine, Westküstenklinikum Heide, Germany.
Received for publication June 2004; accepted April 2005.
Reprints: Heiko Lier, MD, Department of Anesthesiology and Intensive Care Medicine, University of Bonn, Sigmund-Freud-Straße 25, 53105 Bonn, Germany (e-mail: Heiko.Lier@ukb.uni-bonn.de).
Since the development of the self-contained underwater breathing apparatus (SCUBA) by Cousteau and Cagnard in 1943, diving has become a very popular sport, and the number of newly certified divers per year is steadily increasing. Doppler-sonographic examinations demonstrated the appearance of circulating gaseous bubbles in the venous system after every dive in almost all divers, with or without symptoms, and regardless of the dive profile or used dive table.1 The risk of an accident related to SCUBA diving has been estimated to be 1:10,000 dives.2,3 Some 2/3 of these accidents are cases of severe decompression sickness (DCS) with neurologic, vestibular, and/or cardiopulmonary symptoms.2 Recently, Germonpre et al4 have shown by means of echocardiography that 30% of the adult population still have a patent foramen ovale (PFO) demonstrable by a distinctive provocative test. The diagnosis of a PFO in asymptomatic, healthy individuals does not have any pathologic relevance. Yet it has been suggested that there might be a correlation between a PFO and the incidence of a DCS.2,5 Under high ambient pressure, there is only a minor hemodynamic difference between an atrial septum defect and a large PFO. Under water, a PFO may, therefore, allow paradoxical shunting of blood and gas bubbles between the right and left heart circulation. In case of a DCS, an decompression-induced increase of small gas emboli may cause increased neurologic symptoms. While the atrial septum defect has been accepted as a contraindication for diving,6 there are no generally accepted guidelines regarding diving ability and PFO up to date. It is therefore the decision of the individual diver to get a preventive medical examination to exclude a PFO.
Divers with PFO have a significantly increased number of brain lesions compared with divers without PFO: among 87 recreational divers with more than 160 logged dives each, 25 (29%) had a PFO, and 13 of them (15%) even had a large PFO. In 11 divers, a total of 41 brain lesions were detected. Three divers had multiple brain lesions. All of these divers had a large PFO.7 Several years before this radiologic study, Wilmshurst et al8 had postulated that cardiac right-to-left shunts were relevant for paradoxical gas embolisms in divers. In 1989, Moon et al9 showed that the percentage of PFOs in divers with DCS was higher than in divers without DCS. According to a study by Schwerzmann et al,10 divers with PFO have a 4.5-fold higher risk for neurologic symptoms and a 2-fold higher risk for ischemic brain lesions compared with divers without PFO. However, the percentage of severe DCS with neurologic, vestibular, and cardiopulmonary symptoms among all cases of DCS is higher in recreational divers (74% compared with 10% among professional divers11). In 1998, Germonpre et al4 found a PFO in 59.5% of the examined divers with DCS symptoms. The difference between this value and the one found by Moon et al9 is probably due to the fact that Germonpre et al4 used a standardized Valsalva maneuver as provocation for the reopening of the foramen ovale.4 Other groups also found a significantly increased incidence of cerebral DCS among divers with PFO,12 especially when no obvious mistake was made during decompression.4 The risk of paradoxical air embolism is especially increased if the diameter of the PFO is larger than 2 mm.13 However, the relative risk of a severe DCS for divers with a PFO is not known yet. Statistical probabilities for a DCS in divers with a PFO have been calculated to be about 1 case in 2000 dives (4.314 or 5.711 cases in 10,000 dives).
Besides information assessing the size of the shunt during rest and after provocation (Valsalva maneuver), additional anatomic variations like an atrial septum aneurysm can have clinical relevance. It is possible to diagnose a right to left heart hemodynamic shunting with transcranial Doppler sonography (TCD) and transthoracic (TTE) or transesophageal (TEE) echocardiography. Examinations should be performed using a contrast agent and both under spontaneous breathing and after a provocative test (Valsalva maneuver).15 The method with the highest diagnostic sensitivity and specificity is the TEE16; however, this method is rather invasive and expensive. With regard to sensitivity, TCD is superior to TTE and seems to be the best screening method. Admittedly, TCD cannot distinguish between a cardiac or pulmonary shunt.16 Using transmitral Doppler in the apical 4-chamber view, the sensitivity of the TTE can be increased to 100% and the specificity to 94%.13 TTE with second harmonic imaging17 is another highly sensitive alternative to the semi-invasive TEE.
The American Academy of Underwater Sciences and the Undersea and Hyperbaric Medicine Society Diving Committee meetings repeatedly discussed the issue of mandatory PFO diagnostics in divers. According to M. A. Lang (Smithsonian Institution, Marine Sciences Program and Scientific Diving Officer), a mandatory PFO screening was not warranted due to a poor cost-benefit analysis (Personal communication, February 2004). Although professional and military diving both have standards of medical routine examinations, the US Navy and the Association of Diving Contractors, representing the commercial diving industry, also do not propagate medical standards that include a PFO screening test for all divers. The Recreational Scuba Training Council Medical Statement is the most widely used medical screening recommendation for recreational divers in the world today and is endorsed by the Undersea and Hyperbaric Medicine Society. The Professional Association of Diving Instructors' worldwide president, Dr. Drew Richardson, stresses that the Recreational Scuba Training Council Medical Statement does not require a mandatory screening for PFO (Personal communication, February 2004). The European Committee for Standardization's “Recreational Diving Services: Safety Related Minimum Requirements for the Training of Recreational Scuba Divers” final draft prEN 14153-2, dated May 2003, underlines that a medical examination is not in fact required if the candidate has completed an appropriate questionnaire. Similar wording exists in all 3 standards for divers and instructors. Richard Moon, MD (Medical Director, Center for Hyperbaric Medicine and Environmental Physiology, Duke University Medical Center, and Medical Director, Divers Alert Network), also emphasizes an association between PFO and certain types of decompression illness. Nevertheless, he does not recommend screening for a factor that is common in the general population (eg, PFO), which predicts rare events (eg, DCS, Personal communication, February 2004).
For a diver who has already had a DCS, such an examination is certainly indicated-especially if the DCS occurred without violation of the decompression rules.6,18 We would recommend that a diver with a history of DCS diagnosed with a PFO stop diving. If he insists in continuing to dive, he should at least strictly follow the rules to avoid the formation of gas bubbles and hence reduce the risk of a paradoxical gas embolism. It remains uncertain if the risk of a DCS can be minimized by using certain gas mixtures with reduced nitrogen content (Nitrox) for a diver with PFO. Thus, no general recommendation can be made here with regard to Nitrox diving.
A possible option for divers with PFO is the minimal invasive closure of this septal defect using cardiac catheter technology.19 Although this method has already been successfully used for divers at risk, a benefit analysis cannot be conducted yet because of lack of follow-up data.
Both the high cost-benefit ratio and the low probability of a diver with PFO suffering from DCS do not support a change in fitness to dive certification practices at present for recreational divers. Nevertheless, divers with a persistent foramen ovale may have a higher risk of developing a severe DCS. Divers should be made aware of this possibility. It remains the individual recreational divers' own decision whether they will undergo a screening examination and assume the responsibility for the cost of such an investigation.
In contrast, we believe that it is highly advisable for professional divers, dive instructors, and any other divers who frequently dive beyond the scope of occasional recreational diving to exclude the presence of PFO by the means described here.
After a DCS incident of unknown origin-especially if the decompression rules were followed-we would recommend further investigations to rule out the presence of a PFO. Divers diagnosed with a PFO should be informed about the treatment option of a percutaneous, minimally invasive closure of the PFO19 and the accompanying risks. In the absence of treatment, we would recommend that divers with previous DCS and known PFO cease diving entirely.
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