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

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Introduction: Acute ischemic stroke (AIS) patients often have the head-of-bed (HOB) elevated to 300 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 00 HOB positioning improves middle cerebral artery (MCA) mean flow velocity (MFV) in AIS compared to 300. 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 300 and 00 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 300 and 00 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 300 to 00 (+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 00 compared to 300 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.

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