Subarachnoid hemorrhage following permissive hypercapnia in a patient withsevere acute asthma

In this article, we describe a case of a subarachnoid hemorrhage (SAH) in a n acute severe asthma patient following mechanical hypoventilation. A 49-ye ar-old man was admitted to an Intensive Care Unit with an acute exacerbatio n of asthma. After 3 days of mechanical ventilation (hypercapnia and normox aemia), it was noted that his right pupil was fixed, dilated, and unreactiv e to light. Computed tomography (CT) scan showed localized SAH within the b asilar cisterns and diffuse cerebral swelling. On the fourth day, a new CT scan showed hemorrhage resorption and a cerebral swelling decrease. In the following days, the patient's condition continued improving with no detecta ble neurological deficits. A review of similar published reports showed tha t all patients performed respiratory acidosis, normoxaemia, and hypercapnia . The most frequent neurological sign was mydriasis, and all subjects showe d cerebral edema. Since normoxaemic hypercapnia has been associated with ab sence, or less cerebral edema, we considered additional factors to explain cerebral edema and intracranial hypertension causes. Thus, intrathoracic pr essures due to patient's efforts by forcibly exhaling, or during mechanical ventilation, would further increase intracranial pressure by limiting cere bral venous drainage. This case emphasizes the fact that patients with acut e severe asthma who have developed profoundly hypercarbic without hypoxia b efore or during mechanical ventilation, may have raised critical intracrani al pressure. (Am J Emerg Med 1999;17:697-699. Copyright (C) 1999 by W.B. Sa unders Company).