Case history

A 72 year old woman was brought in from home with a Glasgow coma scale score of 14 out of 15 (eyes 4, verbal 4, and motor 6). Her family reported a six week history of increasing lethargy, general weakness, and confusion. She had had tuberculosis at the age of 20 and recalled some kind of surgery at this time. On examination she had no focal neurology. Her left lung base was dull to percussion, and she had decreased entry of air in the same area. Oxygen saturations were 60% on room air. She received 40% oxygen but deteriorated clinically. She had blood gases analysed (box) and a chest x ray done (figure).

X ray image of the woman's chest

Questions

(1) What does her chest x ray show?
(2) What has caused this?
(3) What would you expect to find in her left supraclavicular region?
(4) What is the cause of this woman's confusion and why did it deteriorate with supplemental oxygen?
(5) What kind of defect would you expect this woman's spirometry to show?

Answers

(1) Raised left hemidiaphragm with loops of bowel beneath. Cardiac monitor leads.
(2) Left phrenic nerve crush. Other causes of a raised hemidiaphragm include perforated viscus, subphrenic abscess, and interpostion of bowel between the diaphragm and liver.
(3) A 1-2 cm long linear scar from the surgical incision made for the phrenic nerve crush.
(4) Hypoxia exacerbated by hypercapnia due to type II respiratory failure with supplemental oxygen.
(5) Restrictive defect with a reduction in forced vital capacity but a preserved ratio of forced expiratory volume in one second to forced vital capacity. (Forced vital capacity is the total volume of gas expired on forced expiration and forced expiratory volume in one second is the volume of gas expired in the first second of forced expiration.)

Analysis of blood gases

• pH 7.2
• Paco₂ 11.5 kPa
• Pao₂ 6.5 kPa
• Base excess +1 mmol/l
• Bicarbonate 25 mmol/l
• Oxygen saturation on 40% oxygen 77%

Discussion

The women has had a left phrenic nerve crush. Before the introduction of effective antituberculous chemotherapy in 1944 this was used as a treatment for tuberculosis. Since Mycobacterium tuberculosis thrives best in environments with high oxygen concentrations, minimising oxygen availability shortens the duration of the disease. Reducing the nerve supply and, therefore, the lung volume achieves this. The optimal result causes partial, rather than complete, phrenic nerve crush to retain maximal lung function in the long term. Other surgical techniques using the same principle include artificial pneumothorax and pneumoperitoneum, thoracoplasty, and plombage--the insertion of acrylic balls or solid inert material into the extrapleural space.

Loss of volume in the left lung has resulted in a restrictive defect leading to type II respiratory failure and the retention of carbon dioxide. Common signs of carbon dioxide retention are bounding pulse, papilloedema, flapping tremor, warm peripheries, and drowsiness. To achieve adequate oxygenation without causing hypercapnia, the patient needs artificial ventilation or nasal intermittent positive pressure ventilation. Although this could potentially extend life, its use in these circumstances raises ethical questions because the chances of subsequent weaning from ventilatory support would be slim.

The rising incidence of resistance to multiple drugs also means that bacteriological confirmation and the patient's sensitivity to drugs are important. Current recommended chemotherapy for patients with fully sensitive organisms is combination treatment with four drugs--rifampicin, isoniazid, pyrazinamide, and ethambutol--for two months, and then rifampicin and isoniazid alone for four months. Omit ethambutol in previously untreated white HIV negative patients who have not had contact with known drug resistant tuberculosis. Include pyridoxine in the regimen for malnourished, alcohol dependent, HIV positive patients, and patients with chronic renal failure, as they are increased risk of peripheral neuropathy from isoniazid and ethambutol.

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