The following observations were made on clinical cases of SWAS1,2:
On specific interrogation, a history of aspiration was given in 90 per cent. Often, the novice diver did not realize the significance of the aspiration as the causal event of the syndrome.
Most divers noted an immediate post-dive cough, with or without sputum. It was usually suppressed during the dive. Only in the more serious cases was the sputum bloodstained, frothy and copious (as seen routinely in near drowning cases).
The following symptoms were observed:
- Rigors, tremors or shivering – 87 per cent
- Anorexia, nausea or vomiting – 80 per cent
- Hot or cold (feverish) sensations – 77 per cent
- Dyspnoea – 73 per cent
- Cough – 67 per cent
- Sputum – 67 per cent
- Headaches – 67 per cent
- Malaise – 53 per cent
- Generalized aches – 33 per cent
The signs and symptoms usually reverted to normal within a few hours and rarely persisted beyond 24 hours, unless the case was of greater severity.
There was often a delay of up to 2 hours before dyspnoea, cough, sputum and retrosternal discomfort on inspiration were noted. In the mild cases, respiratory symptoms persisted for only an hour or so, whereas in the more severe cases, they commenced immediately following aspiration and continued for days. The respiratory rate roughly paralleled the degree of dyspnoea. Physical activity and respiratory stimulants appeared to aggravate the dyspnoea and tachypnoea, as did movement and exercise.
Auscultation of the chest revealed crepitations or occasional rhonchi, either generalized or local, in about half the cases. Rarely, they were high pitched and similar to those observed in obstructive airways disease.
Administration of 100 per cent oxygen was effective in relieving respiratory symptoms and removing any cyanosis.
X-ray study of the chest revealed areas of patchy consolidation, or a definite increase in respiratory markings, in about half the cases. These usually cleared within 24 hours, but they remained longer in severely affected patients. X-ray studies taken after the incident and repeated within a few hours sometimes showed a variation of the site of the radiological abnormality.
Expiratory spirometry performed repeatedly over the first 6 hours showed an average drop of 0.7 litres from the baseline in both forced expiratory volume in 1 second and vital capacity measurements. Even those patients who had no respiratory symptoms had a reduction in lung volumes. Arterial blood gases revealed oxygen tensions of 40 to 75 mm Hg with low or normal carbon dioxide tensions, indicative of shunting (perfusion) defects.
Patients often complained of being feverish. Malaise was the next most prominent feature. Headaches and generalized aches through the limbs, abdomen, back and chest were important in some cases, but usually not dominant. Anorexia was transitory.
The feverish symptoms were interesting – and are also seen in near drowning cases. Shivering, similar in some cases to a rigor and in other cases to generalized fasciculations, was more common in the colder months. It was precipitated or aggravated by exposure to cold, exercise or breathing 10 per cent oxygen (a research procedure, not recommended clinically). It was relieved by administration of 100 per cent oxygen. It occurred especially in patients exposed to cold because of duration and depth of dive, inadequate thermal clothing and environmental conditions during and after the dive.
The association of shivering with hypoxia and cold had been described previously3. The shivering occurs concurrently with the pyrexia, which also takes an hour or two to develop.
Pyrexia was verified in half the cases, up to 40°C (mean, 38.1°C; standard deviation [SD] = 0.6), and the pulse rate was elevated (mean, 102 per minute; SD = 21), over the first 6 hours.
Some patients obtained relief from these symptoms by either hot water baths or showers or by lying still in a warm bed.
In some patients, there was an impairment of consciousness, including transitory mild confusion or syncope with loss of consciousness on standing. These were clinically approaching the near drowning cases described (see Chapter 22), and they were treated accordingly.
Haemoglobin, haematocrit, erythrocyte sedimentation rate and electrolytes remained normal. The white blood cell count was usually normal, although mild leucocytosis (not in excess of 20 000 per cubic millimetre) was observed in a few cases, with moderate polymorphonuclear leucocytosis and a shift to the left.
Lactic dehydrogenase estimations revealed a mild rise in some cases. X-ray and lung volume changes were as described earlier.
Examination of the diving equipment may reveal the cause of the aspiration. Inspection of the second stage regulator, breathing against the regulator with the air supply restricted and having another diver use the equipment under similar conditions all may identify the problem. See the section on re-enactment of a diving incident in Chapter 51.