Hyponatraemic encephalopathy despite a modest rate of fluid intake during a 109 km cycle race
- 1UTC/MRC Research Unit for Exercise Science and Sports Medicine, University of Cape Town, Sports Science Institute of South Africa, Cape Town, South Africa
- Correspondence to: J P Dugas UTC/MRC Research Unit for Exercise Science and Sports Medicine, University of Cape Town, Sports Science Institute of South Africa, PO Box 115, Newlands 7725, Cape Town, South Africa;
- Accepted 30 March 2005
Objective: To report a case of exertional hyponatraemic encephalopathy that occurred despite a modest rate of fluid intake during a 109 km cycling race.
Methods: Men and women cyclists were weighed before and after the race. All subjects were interviewed and their water bottles measured to quantify fluid ingestion. A blood sample was drawn after the race for the measurement of serum Na+ concentration.
Results: From the full set of data (n = 196), one athlete was found to have hyponatraemic encephalopathy (serum [Na+] 129 mmol/l). She was studied subsequently in the laboratory for measurement of sweat [Na+] and sweat rate.
Conclusions: Despite a modest rate of fluid intake (735 ml/h) and minimal predicted sweat Na+ losses, this female athlete developed hyponatraemic encephalopathy. The rate of fluid intake is well below the rate currently prescribed as optimum. Drinking to thirst and not to a set hourly rate would appear to be the more appropriate behaviour.
Competing interests: none declared