WHEN DOCTORS were powerless to do much to interfere with the course of nature, and a nasty attack of pneumonia, they disguised their impotence by giving plenty of advice on diet. Invariably, patients who had lower respiratory tract infections of bronchitis, bronchiolitis and pneumonia with a fever were advised to push the fluids. Jugs of water were placed by their bedsides in the hope that they might make good the loss from the fever-induced sweating, the hyperventilation, and that this would protect against a reluctance to eat or drink.

We, the old-fashioned doctors, were certain that fluids were what our patients needed, but we didn’t understand about the increased production of an anti-diuretic hormone in patients with lower respiratory tract infections, including pneumonia. This anti-diuretic hormone reduces the excretion of fluids, so that the patient’s fluid balance is maintained despite any sweating.

The BMJ has recently reported work from Dr Michelle Guppy, a GP research registrar and the academic staff of the department of General Practice of the University of Queensland, Australia, on the effect of giving extra fluids to patients with pneumonia and bronchitis. They were investigating the theoretical possibility that additional fluids might lead to fluid overload and dilution of the sodium levels in their blood. Equally theoretically, this could lead to irritability, confusion, lethargy and convulsions in patients given additional fluids if they have pneumonia.

Dr Guppy’s research revealed that two studies had shown reductions in levels of sodium. Usually, low levels are associated with dehydration — however, none of the children showed symptoms of this, despite their pneumonia. There were also other individual cases in which patients with lower respiratory tract infections and fever developed low levels of sodium. These were paradoxically successfully treated once fluid intake was restricted.

The BMJ suggests that the age-old habit of giving additional fluids — more than would normally be taken — to those who have pneumonia and fever should be continued cautiously only until more research has been completed.