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A 37-year-old man with type 1 diabetes presented with a few days history of persistent vomiting and lethargy associated with thirst and polyuria. He was not on any regular medication apart from insulin. He had omitted his insulin over the last 24 hours.
Clinical examination revealed him to be dehydrated with a tachycardia of 120 beats/min and blood pressure 130/80 mmHg. He was dyspnoeic with a respiratory rate of 32 breaths/min; the pattern was characteristic of Kussmauls respiration. Laboratory investigations showed a metabolic acidosis with arterial blood gases pH 7.08, bicarbonate 10.7 mmol/l, base excess -22.6 mmol/l and plasma glucose 32.4 mmol/l. Ward testing for urinary ketones was strongly positive (+++ by ketostix). A chest X-ray was performed (figure).
- What does the chest X-ray show?
- What clinical signs would you look for?
The chest X-ray shows mediastinal emphysema with characteristic lines of radiolucency around the mediastinal pleura. There is also radiological evidence of subcutaneous emphysema in the soft tissues in the neck.
Surgical emphysema is frequently palpable in the neck and may be more widespread involving the face, chest or arm. Hamman's sign is variously described as a crepitous, crackling or crunching sound, synchronous with systole that may be heard with the stethoscope. Pleural effusion may accompany mediastinal emphysema caused by oesophageal rupture.
Pneumomediastinum is a well recognised but infrequent complication of diabetic ketoacidosis.1-4 The incidence of this complication is unknown. In most but not all reports there is a history of persistent or severe vomiting.1 3 The prognosis is excellent and there is prompt regression of the pneumomediastinum following correction of the ketoacidosis.1-3 It is thought that in diabetic ketoacidosis hyperventilation induced by acidosis or by severe vomiting causes changes in the intra-alveolar pressure gradient within the lungs.5 The rise in intra-alveolar pressure causes rupture and subsequent dissection of air escaping alongside perivascular sheaths into the mediastinum; air enters into fascial planes particularly in the neck causing subcutaneous emphysema.5 Our patient had no specific symptoms to suggest the diagnosis of pneumomediastinum. Thus, unless a chest X-ray is performed, the diagnosis can be missed. Other recognised pulmonary complications of diabetes mellitus are listed in the box.
Pulmonary abnormalities in patients with diabetes mellitus
bacterial and viral infections
reduced elastic recoil of the lungs
reduced diffusion capacity of the lungs for carbon monoxide
diminished bronchial reactivity
elevated arterial oxygen saturation
elevated arterial oxygen tension
disordered breathing patterns: central hypoventilation, sleep apnoea
pneumomediastinum and pneumothorax
Pneumomediastinum as a complication of diabetic ketoacidosis.