The syndrome of inappropriate secretion of antidiuretic hormone and fluid restriction in meningitis - How strong is the evidence?

In patients with meningitis, fluid restriction is recommended to counter th e syndrome of inappropriate secretion of antidiuretic hormone (SIADH) and t o reduce cerebral oedema. However, any effects of an increased plasma level of ADH upon cerebral oedema would be due not to fluid retention but to hyp oosmolality. In a literature review of fluid and electrolyte disturbances a nd the effect of fluid therapy in bacterial/tuberculous meningitis, the pre valence of hyponatraemia, hypoosmolality and SIADH varied considerably; app arently, non-osmotic stimuli for the secretion of ADH, e.g. intracranial hy pertension and hypovolaemia, were present in most patients. Neither clinica l nor experimental studies have confirmed that fluid restriction reduces th e cerebral oedema in meningitis. Furthermore, compared with maintenance the rapy, fluid restriction did not improve outcome in a randomized controlled study. Thus, me find no evidence to support the use of fluid restriction in patients with meningitis. Fluid therapy in acute bacterial meningitis shou ld aim at avoiding hypovolaemia and hypoosmolality based on the assumptions that (i) ADH is increased by non-osmotic stimuli; (ii) elevated ADH is les s important for cerebral oedema than severe hypoosmotality, which mag in it self induce or aggravate oedema; (iii) maintenance fluid therapy aiming at isoosmolality,will not worsen neurological outcome; and (iv) hypovolaemia i s difficult to detect, and detrimental for cerebral perfusion, in these pat ients.