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.