Abstract WP350: Pumping Against Gravity - Cardiac Function Affects Fluctuations in Cerebral Blood Flow Caused by Head Position Change in Acute Ischemic Stroke

Abstract

Introduction: Acute ischemic stroke (AIS) patients often have the head-of-bed (HOB) elevated to 30 0 while in the Emergency Department (ED). Flat HOB positioning has been shown to impact cerebral flow. Whether this holds true in undifferentiated, ED stroke patients is unknown. Hypothesis: We tested the hypothesis that 0 0 HOB positioning improves middle cerebral artery (MCA) mean flow velocity (MFV) in AIS compared to 30 0 . We secondarily tested the hypothesis that lower cardiac output (CO) is associated with greater fluctuation of MFV. Methods: This was a quasi-experimental study with repeat measurements of MCA MFV at 30 0 and 0 0 HOB position. Patients > 18 years presenting to the ED within 12 hours of symptom onset and a NIHSS ≥ 4 were eligible. After applying non-invasive monitoring of mean arterial pressure (MAP) and CO, an investigator used transcranial Doppler to obtain bilateral MCA MFV at 30 0 and 0 0 HOB position. If a signal was unobtainable on the ischemic side, the contralateral MFV was used for analysis. The primary analysis comprised all subjects with confirmed stroke on subsequent imaging and included student t-test for continuous measures. Secondary analysis used multiple linear regression to test if baseline NIHSS, age, MAP and CO were associated with changes in MFV. Results: There were 38 subjects enrolled, of whom 32 had confirmed AIS and were included in analysis. The mean age was 66 (±15) years and NIHSS 7 (±6). Stroke location was mixed (50% lacunar, 25% posterior and 25% anterior circulation). Averaged across all subjects, the MFV did not significantly increase when changing the HOB position from a 30 0 to 0 0 (+0.7 cm/s, 95% CI -1.6 to 3.1). Nevertheless, 16% (95% CI 5-33%) of subjects had a ≥ 20% increase and 47% (95% CI 29-65%) had any increase in MFV at 0 0 compared to 30 0 HOB. Adjusting for age, NIHSS and MAP, lower CO was associated with greater change in MFV (+2 cm/s [95% CI 0.2-3.7 cm/s] for every 1 L/min lower cardiac output, p=0.03). Conclusions: In conclusion, in a mixed sample of ED AIS patients, lower HOB position does not significantly impact cerebral flow on average, yet a considerable proportion of individuals may benefit from lower HOB position. Low cardiac output may identify those that benefit most.