Water deficit

A bedbound 70 kg 40 year old male had no access to water for many days. He is found by a neighbour and brought to the ER. His serum Na is 170 mmol/L.
A. What is the total water deficit?
B. How would you correct it? For fluid orders, specify the fluid type and rate of administration.
Answer

A. Water deficit is calculated by the formula:

                                                             plasma [Na+]
Water deficit = Current body water x (——————— - 1)
                                                                   140

Where current body water is about 60% and 50% of lean body weight in younger men and women, respectively, and is 50% and 45% in elderly men and women, respectively.

The water deficit in this case would be 0.6 X 70 X (170÷140 -1), or 9 L.
B. Water should ideally be replaced orally but often this is difficult due to altered sensorium. It is reasonable to provide water intravenously.
One should not allow serum Na to fall by more than 12 meq/L/day.
Since the Na is elevated by 30 mmol/L and that it should not be correct more than 12 meq/L/day, it should be correct over 30 meq ÷ 12 meq/L/day = 2.5 days or 60 hours.
Therefore, D5W could be administered at 9000 cc ÷ 60 hours = 150 cc/hour. Recall, this does not take into account ongoing losses.