[Hyponatremia in Duchenne muscular dystrophy on mechanical ventilation]

To evaluate the pathomechanism of hyponatremia occasionally seen in Duchenne muscular dystrophy (DMD) on intermittent positive pressure ventilation (IPPV), we performed a comparative study on 26 DMD patients, 7 IPPV in trachetomized intermittent positive pressure ventilation (TIPPV), 6 nasal intermittent positive pressure ventilation (NIPPV), 6 cuirass respirator (CR), and 7 spontaneous breathings (SB). We followed fluctuation of serum sodium levels for several years. Since the serum sodium level was gradually reduced with years on mechanical ventilation, we speculated positive relationship between hyponatremia and antidiuretic hormone (ADH) secretion. Serum sodium levels of 135.6 +/- 2.8 mEq/L in average on IPPV (TIPPV + NIPPV) patients was significantly lower than the levels of 137.8 mEq/L +/- 0.98 on CR patients and 138.8 +/- 0.69 mEq/L on SB patients. Plasma ADH levels in IPPV patients were not reduced when plasma osmolarity was less than 280 mOSm/L. Previous reports showed that ADH was inappropriately secreted only during IPPV with positive end expiratory pressure (PEEP). Ours is the first report of inappropriate secretion of ADH during IPPV without PEEP. It becomes clear that inappropriate ADH secretion is one of the causes of hyponatremia in DMD, though the exact mechanism is not clear. We should bear in mind the change of serum electrolyte level in ventilated DMD patients, especially patients on antidepressant known to release of ADH.