Sodium excretion in conscious and anesthetized dogs after large saline infusions

Summary

Sodium and fluid balance were compared in conscious and anesthetized dogs, receiving large saline infusions. Prior to the experiments both groups of animals were kept on a high sodium diet.

• 1. While conscious animals excrete the infused saline completely within 10 h, the anesthetized animals retain 20–80%, depending on the duration of anesthesia prior to the onset of infusion.

• 2. Increase of hematocrit during anesthesia indicates a shift of plasma fluid into the extravascular space. This is probably caused by an increased permeability of the capillaries for protein induced by the barbiturate agent (Nembutal). The escape of a large fraction of the infused saline into the extravascular space is followed by a diminution of sodium excretion.

• 3. In conscious dogs the fraction of the infused saline, which escapes into the extravascular space, returns into the vascular space shortly after cessation of the saline infusion. The early return of fluid maintains the augmented level of plasma volume and is accompanied by continuous sodium excretion. In contrary, in anesthetized animals, the amount of fluid extravasated during saline infusion is much greater and does not return to the vascular space. With the diminution of plasma volume sodium excretion ceases.

• 4. Injection of hyperoncotic albumin solution promotes fluid movement from the interstitial to the vascular space and increases sodium excretion in proportion to the increase of plasma volume.

It is concluded that during saline infusion the increase in plasma volume is the primary conditioning factor for sodium excretion. The additional expansion of the interstitial space per se is without effect.