Introduction: Transcranial Doppler (TCD) is frequently used after subarachnoid hemorrhage (SAH) to monitor vasospasm. SAH affects cerebral autoregulation (CVR), and may be important in clinical decisions. We aimed was to access the utility of TCD and precise CO2 manipulation to evaluate of CVR after SAH.
Methods: 25 controls and 10 SAH patients were studied using continuous bilateral TCD recording of middle cerebral artery (MCA) blood flow velocity (BFV) before and after CO2 manipulation (Respiract® re-breathing system). CO2 levels were normalized from baseline to 40 mmHg (2 minutes), increased to 45 mmHg (2 minutes) and decreased to 40 mmHg (2 minutes). Autoregulation was defined as unit change in MCABFV/change PCO2. Comparisons were made for each hemisphere and between groups. Aneurysms were secured before the test.
Results: Tests were performed between days 2 and 6 after SAH. The male:female ratio was higher in the SAH group than in the control (2, 1.67), as well as age (54.5/38.6). Overall increase in MCA BFV occurred in both groups with higher CO2 levels. Control group showed a pattern of increased velocity with increased CO2 and similar changes in both hemispheres. Autoregulation was intact, with quick and predictable response to CO2. In SAH patients, changes had no establish pattern. Autoregulation was found to be disturbed in most patients and differences between hemispheres in the same subject were frequent. Difference was not related to clinical condition at the time of the test.
Conclusions: TCD coupled with precise control of CO2 is useful to access autoregulation after SAH. The MCA BFV response to CO2 challenge was significantly reduced in SAH patients in both hemispheres (right p=0.03, left p=0.05). Our study confirms that autoregulation is affected by SAH with changes that may not be symmetrical. The relationship with delayed ischemic neurological deficits needs investigation. Feasibility of a bedside test for autoregulation was demonstrated.
Patient Care: Vasospasm is a major cause of morbidity and mortality after SAH. The availability of a bedside test to access autoregulation that is reliable and reproducible is likely to allow for the identification of subgroups of patients with aneurysmal SAH that are at higher risk of ischemic symptoms from vasospasm. This will result in more focused care, with earlier interventions, decrease in ischemic brain damage, decreased costs with ICU monitoring.
Learning Objectives: 1. Understand how precise CO2 manipulation is possible with the Respiract
2. Know of the availability of a new bedside test to access cerebral autoregulation