Free Water Deficit
The Free Water Deficit in Hypernatremia is calculated using %Total body water fraction.
Hypernatremia occurs due to net water loss or excess sodium intake and it is more common in infants or
elderly population with neurological or physical impairment. The Free Water Deficit is calculated in
hypernatremia and determines the volume (L) of water required to correct dehydration or, to reach the
desired level of sodium in the blood serum, during the initial stages of fluid-replacement therapy. The
goal of therapy is to correct both the serum sodium and the intravascular volume. In patients with
severe dehydration or shock, the initial step is fluid resuscitation with isotonic fluids before free
water correction. It is important to remember that hypernatremia should be corrected over 48 hours with
a decrease in serum sodium not exceeding 0.5 mEq per hour. Patients should be carefully monitored for
the rate of correction, urine output, and ongoing losses. Rapid correction can lead to cerebral edema
and seizures. It is crucial to identify acute versus chronic onset hypernatremia before correcting the
free water deficit.
The Free Water Deficit in Hypernatremia is calculated by estimated total body water fraction, patient
current sodium values and patient age sex range by using below equation.
— Free Water Deficit = %Total Body Water, fraction x [(plasma sodium/140) -1]
— %Total Body Water = Age / Sex coordinate x body weight(kg)
Where Age / Sex coordinate is for
— Child: 0.6
— Adult Male: 0.6
— Adult Female: 0.5
— Elderly Male: 0.5
— Elderly Female: 0.45
Sonani B, Naganathan S, Al-Dhahir MA, et al.
Barma MA, Soiza RL, Donnan PT, et al.
Rubin AN, Espiridion ED, Kattan M, Desmarais EC et al.