Demographic characteristics included sex, age and length of hospital stay (in days). Clinical characteristics consisted of blood pressure, body temperature, symptoms, laboratory tests [leukocyte, lymphocyte, hemoglobin, international normalized ratio (INR), activated partial thromboplastin time (APTT), prothrombin time (PT)], presenting symptoms, treatment and days in the intensive care unit (ICU).

We classified hypertension according to the 95th percentile method from the standard blood pressure table for children published by the fourth report of the National Heart, Lung, and Blood Institute (9). Blood pressure tables included the 50th, 90th, 95th, and 99th percentiles (with standard deviations) by sex, age, and height. Blood pressure was classified as normal if it was below the 90th percentile; pre-hypertension, if it was between the 90th and 95th percentiles, except in adolescents, in whom pre-hypertension was defined as ≥120/80 mmHg; stage I hypertension, if it was between the 95th and 99th percentile plus 5 mmHg; or stage II hypertension, if it was in the >99th percentile plus 5 mmHg. Stage II hypertension accompanied by clinical symptoms was diagnosed as acute hypertension (10).

Presenting symptoms were classified as non-specific [headache, vomiting, convulsions, Glasgow Coma Scale score (GCS), or Children Coma Scale on admission], or focal deficit (hemiplegia, facial paralysis, dysarthria, aphasia, ataxia, sensory and eye movement).