Subarachnoid hemorrhage following permissive hypercapnia in a patient with severe acute asthma

In this article, we describe a case of a subarachnoid hemorrhage (SAH) in an acute severe asthma patient following mechanical hypoventilation. A 49-year-old man was admitted to an Intensive Care Unit with an acute exacerbation of asthma. After 3 days of mechanical ventilation (hypercapnia and normoxaemia), it was noted that his right pupil was fixed, dilated, and unreactive to light. Computed tomography (CT) scan showed localized SAH within the basilar 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 detectable neurological deficits. A review of similar published reports showed that all patients performed respiratory acidosis, normoxaemia, and hypercapnia. The most frequent neurological sign was mydriasis, and all subjects showed cerebral edema. Since normoxaemic hypercapnia has been associated with absence, or less cerebral edema, we considered additional factors to explain cerebral edema and intracranial hypertension causes. Thus, intrathoracic pressures due to patient's efforts by forcibly exhaling, or during mechanical ventilation, would further increase intracranial pressure by limiting cerebral venous drainage. This case emphasizes the fact that patients with acute severe asthma who have developed profoundly hypercarbic without hypoxia before or during mechanical ventilation, may have raised critical intracranial pressure.