We lose fluid through the gut, kidney, lungs and skin. We can easily collect and measure urine (roughly 0.5ml/kg/hr). However, water lost from skin, lungs and faeces is slightly more difficult to measure. These are termed insensible losses which roughly amount to 500mls. Insensible loss increases in sickness, for example when febrile, having diarrhoea, or in the presence of inflammation. When febrile, insensible losses increase by 100/ml/day/degree centigrade.
How much fluid would you prescribe to meet daily maintenance requirements in an adult?
Teacher's Comment
Our daily fluid and salt requirement has to balance our losses. We lose about 60 mmol of potassium and 100mmol of sodium in a day. Therefore to meet maintenance requirements, patients should receive sodium 50-100 mmol/day and potassium 40-80mmol/day.