The incidence of spontaneous subarachnoid hemorrhage with change in barometric pressure.

The authors' observation of an apparent increased incidence of patients presenting with spontaneous subarachnoid hemorrhage (SAH) during stormy weather prompted them to retrospectively review admissions data during an 18-month period to look for an association between SAH and changes in barometric pressure (BMP). Of the 39,049 cases examined, 76 had confirmed SAH. Continuous graphs of BMP were used to categorize days as being "flat" days (change in BMP < or = 0.15; dpHg) or "change" days (change in BMP > 0.15; dpHg). Days on which patients presented with SAH were significantly correlated with change days (P < .004). There was significantly more SAH during the winter months (October to March), than during the remaining summer months (P < .02). The correlation of SAH with change in BMP did not hold if these summer months were examined alone. The risk ratio of having an SAH on an inclement day during the winter months was 1.99 (95% confidence interval, 1.11 to 3.60). The reason for this association is not clear at this time.