Renal tubular sodium and water metabolism in brain tumour patients submitted to craniotomy.

PURPOSE: To evaluate the effect of Brain Tomour (BT) and Neurosurgery (NS) on the renal handling of H2O and Na, and the clinical importance of SIADH in this setting.

METHODS

Fourteen patients with BT pre-op for NS and 6 controls (C) pre-op for general surgery, were assessed in a controlled prospective trial. All patients were normovolaemic, with normal renal function. They received 400 mg of lithium carbonate (Li) 8 hours before each of two test periods (I and II) and a standard water load only before period II. Clearances studies were performed pre-op (period I) and 24 hours post-op (period II).

RESULTS

Serum Na was normal at all times. Despite normovolaemia, a 1% decrement in serum osmolality and the water load, ADH dramaticaly increased from time I to II mainly in the BT group (36.2 +/- 9.4 vs 7.1 +/- 0.6 pmol/L, p = 0.02). FENa, FELi and FEUricA were significantly more elevated in the BT group pre and post-op (at time II respectively 4.6 +/- 1.6 vs 1.1 +/- 0.3%; 29.3 +/- 4.9 vs 22.6 +/- 5.5; 26.0 +/- 8.1 vs 11.3 +/- 2.2, p = 0.03). Proximal and distal H2O re-absorption and distal fractional Na re-absorption were identical in both groups pre and post-operatively.

CONCLUSIONS

1-BT and NS always induce a SIADH. 2-There was a primary Na loss at the proximal tubule level not explained by ADH increment, that did not significantly changed H2O handling. 3-To prevent hyponatraemia, hypotonic I.V. fluids should be avoided, but more importantly saline must be provided to this potentially salt-wasting condition.