The roentgenographic findings associated with air embolism in sport scuba divers

The Journal of Emergency Medicine, Vol 11, pp 443-449, 1993 Printed in the USA . Copyright 0 1993 Pergamon Press Ltd.

Emergency Radfmlogy

THE ROENTGENOGRAPHIC FINDINGS ASSOCIATED WITH AIR EMBOLISM IN SPORT SCUBA DIVERS

Collen P. Harker, MD,* Tom S. Neuman, Mo,t Linda K. Olson, MD,+

Irving Jacoby, Mo,t and Arthur Santos, MD§

*Department of Radiology, University of Washington Medical Center, Seattle, Washington; TDepartment of Medicine, Division of Emergency Medicine, University of California San Diego Medical Center, San Diego, California;

*Department of Radiology, University of California San Diego Medical Center, San Diego, California; §Southern Colorado Heart and Lung Group, Pueblo, Colorado

Reprint Address: Linda K. Olson, MD, UCSD Medical Center, Department of Radiology, 225 Dickinson Street, San Diego, CA 9210343756

•1 Abstract-Records on all patients with arterial gas embolism (AGE) presenting to UCSD from 1982-1989 and for whom chest radiographs were available were reviewed. Of the 31 patients, 13 roentgenograms (42%) showed evidence of pulmonary barotrauma demonstrated by pneumomediastinum (N = 8), subcutaneous emphysema (N = 3), pneumocardium (N = 2), pneumoperitoneum (N = l), or pneumothorax (N = 1). Pneumopericardfum was not seen. Sixteen (52%) of the 31 patients had pulmonary infiltrates. Radiographic evidence of barotrauma was on occasion subtle, and in four cases was overlooked. Evi- deuce of barotrauma (i.e., extra-alveolar air) was often identified along the left cardiac border, aortic arch, descending aorta, and hffar vessels. Subtle findings of ectopic air can confirm the clinical diagnosis of AGE, however, radiographic evidence of concomitant near drowning occurs more frequently.

0 Keywords - arterial gas embolism (AGE); pulmonary barotrauma; SCUBA diving; pneumomediastinum

ing for about 30% of recreational SCUBA diving fatalities (1). Divers are at a significant risk for devel- oping AGE because of the opportunity for pulmonary overinflation during ascent, and especially during panic ascents. Changes in lung volumes are inversely proportional to pressure variations experi- enced while under water (Boyle’s Law; P,V, = P,V,). Pulmonary overinflation occurs during ascent as decreasing ambient pressure allows overexpan- sion of the lung. Air embolism can then result and is usually diagnosed by history and clinical signs or symptoms. Pulmonary roentgenograms can provide valuable additional information. This article retro- spectively examines the clinical history, physical examination, and chest radiographs of 31 SCUBA divers treated at our facility for AGE from 1982 to 1989.

MATERIALS AND METHODS INTRODUCTION

Self-contained underwater breathing apparatus (SCUBA) diving is an occupational and recreational pursuit of millions of people, with over 3 million persons participating in recreational SCUBA diving in the United States and more than 300,000 new sport divers trained each year. Drowning is reported to be the most common cause of death among divers, but arterial gas embolism (AGE) ranks second, account-

The cases of 26 men and 5 women who were treated for AGE from 1982-1989 and for whom chest roentgenograms (CXR) were still available were reviewed. The clinical record was reviewed for signs and symptoms of AGE and a history of aspiration. A dive profile was obtained (summary of the depth and du- ration of dive at that depth), and the approximate time until recompression was noted. Significant findings on physical examination were also recorded. The

RECEIVED: 28 September 1992; FINAL SUBMISSION RECEIVED: 3 February 1993; ACCEPTED: 22 February 1993

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444 C. P. Harker, T. S. Neuman, L. K. Olson, I. Jacoby, A. Santos

P,02/F,02 ratio was calculated on all patients when arterial blood gas data were available. Logistic regression analyses were performed using standard methodology (2).

The CXRs for each patient were reviewed by two of the authors (CH, LO) (admission or first CXR available within 24 hours). The roentgenographic technique was recorded as posteroanterior (PA), PA/lateral, anteroposterior (AP) portable upright, or AP recumbent. The inspiratory effort was rated as either good or poor. The CXRs were then reviewed for conditions possibly predisposing to barotrauma, for evidence of pulmonary barotrauma, and for evidence of pleural effusion or infiltrate (interstitial or alveolar). Our interpretations were then com- pared to the initial radiologic assessment.

RESULTS

Twenty-six of the 3 1 patients were male and the mean age of the divers was 31.7 years, with a range of 16 to 54 years.

Diving profiles revealed a mean maximum depth dive of 62.6 feet, with a range of 8 to 200 feet. Nine-

teen (61 @Jo) of the 3 1 patients had a dive depth greater than 60 feet. The time at depth was not available for 3 patients; however, 13 of the remaining 28 divers (46%) accumulated bottom times greater than 15 minutes. The mean bottom time for all these divers was 15.1 minutes, with a range of 1.5 to 44 minutes. For 11 (38%) of 29 (2 divers were declared dead and not recompressed), 6 or more hours had elapsed from accident to recompression (average time was 5.7 hours, with a range of 1 to 26 hours). Sixteen divers (55%) were admitted with a history of aspiration, and of these, 14 (88%) had chest radiographs compatible with aspiration (Figure 1).

Signs and symptoms prior to assessment in the emergency department are described in Table 1. Physical examination upon arrival in the Emergency Department revealed significant neurologic deficits in 23 (74%) patients (Table 2). These deficits ranged from obvious neurologic findings of coma, paralysis, sensory loss, decreased reflexes, and vision changes to the more subtle findings of decreased coordination, dysmetria, calculation errors, loss of proprioception, and difficulty with constructions. Three (10%) patients were decerebrate, 2 (6%) in cardiac arrest, and 2 (6010) were obtunded on examination.

Flgure 1. Bilateral alveolar lntlltrates consistent with aspiratlon.

Air Embolism in SCUBA Divers 445

Table 1. Signs and Symptoms of Patlents Prior to Presentation at the Emergency Department (N = 31)

Symptoms Number Percentage

Loss of consciousness 25 Chest pain 9 [z; irregular breathing or apnea 9 Vomiting 9 I;::; Extremity weakness or paralysis 7 (23%) Hemoptysis 7 (23%) Sensory loss 6 Cardiac arrest 5 ;:q Confusion 5 (16;) Headache 5 (16%) Vision change Crepitus : I:Z; Dizziness 3 (l&l) Dysarthria 3 Ear Pain 3 I:::; Nausea 3 Shortness of breath 3 s:!; Ataxia 2 Abdominal pain 1 ;;I;; Diffuse joint pain 1 Retro-orbital pain 1

Symptoms Number Percentage

12 (41%) Extremity weakness or paralysis Pulmonary rales or wheezes Hemotympanum Decreased reflexes Vision changes

gaze preference homonymous hemianopsia nystagmus papilledema

Extremity sensory loss Change in gait or ataxia Conjunctivitis Sluggishly reactive pupils Hypotonia Babinski present Decerebrate or decorticate Abdominal tenderness Decreased coordination (rapid

alternating movements) Difficulty following commands Facial palsy Obtunded Calculation errors Constructions difficulty Crepitus Decreased rectal tone Dysmetria Loss of proprioception or

graphesthesia Neck clonus

11 10 10 8 (26%)

7 (24%) 5 (17%) 4 (14%) 4 (14%) 3 (100/b) 3 (10%)

3 2 (‘,Z 0

Table 2. Physical Examination Findings Assessed in the Emergency Department (N = 29, patients in cardiac arrest excluded)

Table 3. Chancterlstlcs of Chest Roentgenogmms in AGE Patlents (N = 31)

Significant Findings: Number Percentage

Infiltrate 16 Alveolar 6 ;ZZ; Interstitial 10

Pneumomediastinum a I:::; Subcutaneous air 3 (10%) Intravascular air 2 Pneumocardium 2 I::; Pleural effusion 1 Pneumothorax 1 I::; Retroperitoneal Air 1 2 x 2 cm pulmonary nodule 1 IZ;

Technique: PAllAT (26%) Portable Upright (16%) Por- table Recumbent (58%)

In addition, 12 (39%) patients were found to have pulmonary rales or rhonchi; 10 of these correlated with chest radiographs revealing either interstitial or alveolar infiltrates.

Chest radiographs (Table 3) were all judged as adequate even though 74% of them were obtained as portable films. Sixteen (52%) of 31 roentgenograms revealed infiltrates, 6 (19%) alveolar and 10 (32%) interstitial. One patient had a small left pleural effusion. Eight (26%) patients had pneumomediastinum (Figure 2). Three patients (10%) had subcutaneous air (one of which was missed), and 1 (3%) patient had retroperitoneal air. Two patients had pneumocardium (60/o) and associated intravascular air (Fig- ure 3). One of these patients had a pneumothorax. No radiograph revealed evidence of chronic obstruc- tive pulmonary disease or blebs, although one patient had a 2 x 2 cm nodule in the right upper lobe. There were no old chest films available for comparison.

Five radiologic findings were missed on initial evaluation: three examples of pneumomediastinum, one of perihilar infiltrate, and one of subcutaneous air. All of these patients were treated with immediate recompression for AGE, given their classic clinical histories and physical examinations. There was a sta- tistically significant relationship (p c .OS) between the presence of infiltrates and the P,OJF,O, ratio. The presence or absence of radiographic abnormalities in this group of divers did not correlate either with survival or with long-term neurologic outcome. There also was no relationship between the dive profile of patients and the presence or absence of radiologic abnormalities, nor did the time to recompression correlate with the presence of radiologic abnormalities. There was a rapid resolution of radiographic abnormalities, such that by the second or third day of hospitalization the radiograph was usually near normal.


Figure 2. Pneumomediastinum was most often seen along the left cardiac border (arrow), over the main pulmonary artery (arrowhead) or adjacent to the aortic arch.

DISCUSSION

Air embolism in the vascular system can be catego- rized as venous gas embolism (VGE) or AGE, de- pending on the entry site of air. VGE is the most common form of air embolus. It occurs when air enters the systemic venous circulation and passes to the right side of the heart and then to the lungs. In divers, VGE is generally due to the liberation of a gas phase in systemic tissue beds due to supersaturation secondary to a reduction in ambient pressure. VGE is generally considered to be part of the pathogenesis of decompression sickness.

In contrast to VGE, AGE is the basis of morbidity and mortality in diving accidents associated with pulmonary barotrauma (PBT). Most commonly, air enters the systemic circulation via the pulmonary veins when a diver breath-holds and ascends in the water. The external reduction in atmospheric pressure then allows intra-alveolar overdistention and overpressur- ization to occur, resulting in air being introduced into

the pulmonary venous circulation, and AGE then en- sues.

To briefly review diving physiology, air volumes in the lungs follow Boyle’s Law (PIVI = P,V,). At a depth of 33 feet of sea water (fsw), the lung volume of a snorkeler who has inhaled to total lung capacity (TLC) at the surface will be one-half of the original volume at the surface. Conversely, the lung volume of the SCUBA diver who inhales to TLC at 33 fsw

Figure 3. Patient undergoing CPR with pneumocardium and intrava8cular air. (A) Notice lucency representing air In left ventricle and ascending aorta; (6) Air withln subclavian; (C) Air wlthin carotid vessels.

(4


(W

v-2 Figure 3. Continued


and ascends will double by the time the surface is colleagues (12) examined 88 SET with air embolism. reached. Therefore, SCUBA divers must continue to In their paper, 16 patients were noted to have abnor- ventilate during ascent so the volume of air in the mal postrecompression radiographs; however, once lungs can be exhaled safely as it expands (3,4). again no details of the abnormalities were described.

Pulmonary overinflation with AGE can occur at almost any depth while breathing compressed air. Smith (5) reported that lethal air embolism can result from breath-holding during ascent from depths as little as 10 feet. A case has been described of a 21- year-old man who died during an attempt to swim across a 25-yard pool at a depth of 6 feet (6). Factors that may precipitate pulmonary overpressure include unintentional breath-holding, panic, or sharing a sin- gle air supply (i.e., “buddy breathing”) (7). An AGE can also occur after an apparently normal ascent in divers with unsuspected air-trapping due to pulmonary disease, such as a mucus plug, a pulmonary bleb, or a broncholith (8).

Clearly, one problem in analyzing data on SCUBA divers lies in comparing SCUBA divers and SET casualties, since the absence of gas loading (i.e., presence of significant amounts of gas in solution within body tissues), the immediate recompression in SET casualties, and the immediate rescue of the vic- tim when loss of consciousness occurs are quite dif- ferent from SCUBA diving cases. As a result, concomitant near drowning secondary to a loss of consciousness is a major clinical issue in sport SCUBA divers and is rarely, if ever, encountered in SET. The presence of radiographic infiltrates compatible with coexistent near drowning in a series of patients with AGE has not been previously reported.

It is difficult to find information on the radiologic picture of pulmonary barotrauma associated with AGE. Because immediate recompression and resusci- tation techniques are necessary, radiography has not generally been used to suggest or support the diagnosis. Given the secondary role of radiography in diving accidents and the subtleties of the roentgenographic findings, it is not surprising that little has been recorded on this topic.

Moses in 1964 evaluated United States Navy submarine escape training (SET) casualties, including survivors and nonsurvivors, between the years of 1928 and 1957 (9). A total of 62 SET casualties were described in the study, 44 of whom showed clinical or autopsy findings of AGE. Posttreatment chest radiographs were available from these 44 patients with AGE; however, no discussion of the radiologic findings on those 44 cases is to be found within the report.

Pulmonary overinflation is an uncommon occurrence, but it can present a significant risk to SCUBA divers. Although there are no statistics on the exact incidence of pulmonary overinflation, it probably occurs more often than we suspect given the studies describing asymptomatic extra-alveolar air. We be- lieve our study of 31 patients to be the first series in which chest radiographs were obtained prior to recompression in patients with clinically apparent AGE (Table 3). The radiologic characteristics of pulmonary barotrauma were classic (pneumomediastinum, subcutaneous air, retroperitoneal air, pneumothorax); however, we also found 2 cases of pneumocardium and intravascular air. All cases of pulmonary barotrauma resolved after recompression treatment. Coexistent evidence of aspiration was fre- quent .

Leitch and Green, in a review of AGE in 117 divers from 1965 to 1985, noted that in 58 patients with AGE and respiratory symptoms, 7 had mediastinal emphysema (10). The diagnosis of mediastinal emphysema in this study included as diagnostic criteria subcutaneous emphysema, pneumoperitoneum, and voice change. Four patients also had pneumothorax. However, the total number of divers for whom chest radiographs were available is not listed, nor was it clear whether the radiographs that were obtained were pre- or post-recompression. James, in an analysis of 170 asymptomatic SET, found that pre- and postascent chest radiographs showed one trainee with mediastinal emphysema and another trainee with mediastinal and subcutaneous emphysema (11). How- ever, neither of these individuals were believed to have suffered an air embolism. Finally, Elliott and

As the diagnosis of AGE is usually made on the basis of clinical findings or history (the sudden ap- pearance of neurologic deficits compatible with the occlusion of a portion of the cerebral circulation), chest roentgenography is not a necessary part of the diagnostic work-up of AGE. It should be considered, however, that concomitant near drowning is a fre- quent occurrence in AGE victims and management of these patients must include careful attention to their gas exchange. As a result, we consider chest roentgenography and arterial blood gas analysis to be important aspects of the evaluation of AGE victims and frequently we obtain these studies prior to recompression therapy. A CXR should certainly be obtained on all patients in respiratory distress to eval- uate for pneumothorax. Finally, there are occasional patients in whom the clinical diagnosis of AGE is not clear. In those situations, the presence of ectopic air seen on a CXR would confirm the presence of pul-


monary barotrauma and thus help substantiate a diagnosis of AGE.

CONCLUSION

In summary, all of the cases of AGE in our study were clearly diagnosed on the basis of clinical history and physical examination and were treated with recompression, regardless of the radiographic findings. Radiographic manifestations of ectopic air were seen in 42% of our patients, a much higher percentage than has been previously thought. Although evidence of PBT may be obvious, subtle presentations may

also occur. Locations that seem to yield the most in terms of positive radiographic findings include the left heart border, the descending aorta, aortopulmo- nary window, and superior mediastinum. Addition- ally, in suspected cases of AGE, radiographic evidence of extra-alveolar air may help confirm the diagnosis of PBT. Finally, radiographic evidence of near drowning appears to occur frequently in patients with PBT and AGE.

Acknowledgments-The authors wish to thank Marsha Earnshaw for her photographic work on this paper, Cathy Fix for editorial assistance, and Shelley Van Buren for typing.

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The roentgenographic findings associated with air embolism in sport scuba divers

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