Файл: 100_Cases_in_Clinical_Medicine.pdf

ANSWER 99

The flow–volume curve shows the same low flow throughout the whole volume of the vital capacity. It is similar in both inspiration and expiration as shown in the flow volume loop (Fig. 99.2). This situation is typical of a rigid large-airway obstruction. It is not reversible with bronchodilator therapy. The spirometry trace of volume against time in such cases shows a straight line of the same reduced flow right up to the vital capacity. These findings are typical of a narrowing in a larger airway. On examination, this airway narrowing is likely to produce a single monophonic wheeze which may be heard over a wide area of the chest.

!Differential diagnosis of rigid large-airway obstruction

The situation may easily be confused with asthma if the peak flow and the wheezing are accepted uncritically. In asthma, the spirometry will show a reduced FEV1 but the flow rate (and therefore the slope of the line relating volume and time) will vary. The wheezing in asthma comes from many narrowed airways of different calibre and mass, and the wheezes are often described as polyphonic.

The fixed flow in inspiration and expiration in this case suggest a rigid large-airway narrowing. If the narrowing can vary a little with pressure changes, then the pattern will depend on the site of the narrowing (Figs 99.3 and 99.4). If it is outside the thoracic cage, as in a laryngeal lesion, it will be more evident on inspiration. If the site is intrathoracic, the flow limitation will be greater in expiration. Large-airway narrowing can be caused by inflammatory conditions such as tuberculosis or Wegener’s granulomatosis, damage from prolonged endotracheal intubation or by extrinsic pressure such as a retrosternal goitre. However, the commonest cause is a carcinoma of a large airway.

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Some further investigation of the large airways is required. The great majority of symptomatic lung tumours are visible on plain chest X-ray but central lesions in large airways may not be seen. Further investigation could be a bronchoscopy or a computed tomography (CT) scan. A bronchoscopy to see and biopsy any lesion would be best. In this case, fibre-optic bronchoscopy showed a carcinoma in the lower trachea reducing the lumen to a small orifice. Treatment was by radiotherapy with oral steroids to cover any initial swelling of the tumour which might increase the degree of obstruction in the trachea.

KEY POINTS

•Large-airway narrowing produces characteristic findings on visual displays of respiratory function but is more difficult to identify from the numbers alone.

•A small proportion of central lung tumours may present with local symptoms but a normal chest X-ray.

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CASE 100: PAIN IN THE LEG

History

A 22-year-old woman is admitted to hospital with a painful left leg. She uses intravenous drugs and injects into veins in the arms and the groins. The left leg has become swollen and painful over the last week. She has had two previous admissions to hospital within the last 6 months, once for an overdose of heroin and once for an infection in the left arm. She smokes 20 cigarettes daily and drinks up to 40 units of alcohol per week.

Examination

Her pulse is 84/min and regular. Her blood pressure is 124/74 mmHg. Her temperature is 37.2°C. The heart sounds are normal and there are no abnormal findings on examination of the respiratory system. She has a swollen left calf with some local tenderness. There are puncture sites in both groins but no obvious sepsis.

INVESTIGATIONS

Ultrasound of left leg: venous thrombus extending into the left femoral vein

Venous access is difficult but a line is inserted in the right arm and she is treated with subcutaneous low-molecular-weight heparin, intravenous vitamins and benzodiazepines, and a methadone-replacement regime. On the fourth day of her admission she became much more unwell.

Further examination

Her pulse is 112 per minute and regular. Her blood pressure is 88/50 mmHg although she seems warm and well perused. The respiratory rate is18/min, jugular venous pressure is not raised, there are no new heart murmurs and oxygen saturation is 97 per cent on room air. Her temperature is 37.6°C.

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ANSWER 100

The initial diagnosis was a deep vein thrombosis. This complication is not unusual in intravenous drug users and can be associated with sepsis although there was no sign of this on the initial investigations. She has been treated for the thrombosis and for alcohol withdrawal and her opiate use.

There are a number of possibilities for her acute deterioration. The deep vein thrombosis would have predisposed her to a pulmonary embolus, but the normal respiratory rate, lack of elevation of jugular venous pressure and normal oxygen saturation make this unlikely. As an intravenous drug user she might have taken more drugs even under supervision in hospital.

The tachycardia and lowered blood pressure raise the possibility of haemorrhage which might be precipitated by the anticoagulants. However, the raised CRP, white cell count and abnormal electrolytes in a warm, well-perfused patient suggest sepsis as the likely cause. In an intravenous drug user one would think of infective endocarditis which may occur on the valves of the right side of the heart and be more difficult to diagnose. Lung abscesses from septic emboli are another possibility in an intravenous drug user with a deep vein thrombosis, and a chest X-ray should be taken although the lack of respiratory symptoms makes this less likely. In this case the intravenous line has been left in place longer than usual because of the difficulties of intravenous access and it has become infected. Lines should be inspected every day, changed regularly and removed as soon as possible. The previous hospital admissions raise then possibility of infections such as methicillin-reistant Staphylococcus aureus (MRSA). In this case MRSA was found in blood cultures and treated with intravenous vancomycin with good effect.

On recovery and discharge there were problems with the question of anticoagulation. Warfarin treatment raised difficulties because of the unreliability of dosing, attendance at anticoagulant clinics and blood sampling. It was decided to continue treatment as an outpatient with subcutaneous heparin for 6 weeks.

KEY POINTS

•Patients using intravenous drugs often pose problems in venous access, and sampling for tests such as international normalized ratio (INR).

•Indwelling venous lines should be changed regularly and removed as soon as possible.

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INDEX

References are by case number with relevant page number(s) following in brackets. References with a page range e.g. 25(68–70) indicate that although the subject may be mentioned only on one page, it concerns the whole case.

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