Reversal of transtentorial herniation with hypertonic saline

Over the years, The Hopkins Neurocritical Care group has carefully studied the effect of hypertonic solutions clinically and experimentally. The recent report by Koenig et al.1 invites the following comments. Hypertonic saline or mannitol could improve neurologic examination in a patient with a new mass. We and others have observed rapid dramatic changes with osmotic agents. For example, we have observed dilated pupils and extensor responses at baseline, but soon after injection, pupils normalize and improvement to localization to noxious stimuli is seen. Koenig et al. and the editorialists suggest the immediacy of such a response is reversal of transtentorial herniation (TTH), but evidence of that is not provided; there are few clinical details except a GCS sumscore and no CT or MR studies. We are not certain that the clinical improvement is due to decompression or dislodging of tissue squeezed through the tentorium. In fact, when the effects are studied in mannitol, change in midline shift is not observed as changes are too minimal or almost too subtle to catch the eye on serial MRI.2 Many consider that osmotic diuresis cannot physiologically explain the rapid improvement (within 30 minutes or less in many patients). Alternatively, sudden hypertonicity may cause vasodilatation of the cerebral resistance vessels and with an …