Cerebral Blood Flow and Oxygen Delivery in Aneurysmal Subarachnoid Hemorrhage: Relation to Neurointensive Care Targets

Abstract

Background: The primary aim was to determine to what extent continuously monitored neurointensive care unit (neuro-ICU) targets predict cerebral blood flow (CBF) and delivery of oxygen (CDO₂) after aneurysmal subarachnoid hemorrhage. The secondary aim was to determine whether CBF and CDO₂ were associated with clinical outcome.

Methods: In this observational study, patients with aneurysmal subarachnoid hemorrhage treated at the neuro-ICU in Uppsala, Sweden, from 2012 to 2020 with at least one xenon-enhanced computed tomography (Xe-CT) obtained within the first 14 days post ictus were included. CBF was measured with the Xe-CT and CDO₂ was calculated based on CBF and arterial oxygen content. Regional cerebral hypoperfusion was defined as CBF < 20 mL/100 g/min, and poor CDO₂ was defined as CDO₂ < 3.8 mL O₂/100 g/min. Neuro-ICU variables including intracranial pressure (ICP), pressure reactivity index, cerebral perfusion pressure (CPP), optimal CPP, and body temperature were assessed in association with the Xe-CT. The acute phase was divided into early phase (day 1-3) and vasospasm phase (day 4-14).

Results: Of 148 patients, 27 had underwent a Xe-CT only in the early phase, 74 only in the vasospasm phase, and 47 patients in both phases. The patients exhibited cerebral hypoperfusion and poor CDO₂ for medians of 15% and 30%, respectively, of the cortical brain areas in each patient. In multiple regressions, higher body temperature was associated with higher CBF and CDO₂ in the early phase. In a similar regression for the vasospasm phase, younger age and longer pulse transit time (lower peripheral resistance) correlated with higher CBF and CDO₂, whereas lower hematocrit only correlated with higher CBF but not with CDO₂. ICP, CPP, and pressure reactivity index exhibited no independent association with CBF and CDO₂. R² of these regressions were below 0.3. Lower CBF and CDO₂ in the early phase correlated with poor outcome, but this only held true for CDO₂ in multiple regressions.

Conclusions: Systemic and cerebral physiological variables exhibited a modest association with CBF and CDO₂. Still, cerebral hypoperfusion and low CDO₂ were common and low CDO₂ was associated with poor outcome. Xe-CT imaging could be useful to help detect secondary brain injury not evident by high ICP and low CPP.

Keywords: Aneurysmal subarachnoid hemorrhage; Cerebral blood flow; Cerebral oxygen delivery (cerebral pressure autoregulation); Clinical outcome; Xenon-enhanced computed tomography.

Fig. 1

CBF measurements in two patients. The figure demonstrates two Xe-CT scans of two different patients. Patient 1 (a, b) exhibits extensive hypoperfusion particularly in the left hemisphere, whereas patient 2 (c, d) exhibits more normal CBF. CBF, cerebral blood flow, Xe-CT, xenon-enhanced computed tomography

Fig. 2

CBF and oxygen delivery in relation to clinical outcome after aneurysmal subarachnoid hemorrhage (a, b). A significant association between the CBF indices/CDO₂ indices and clinical outcome was only present in the early phase. For those with unfavorable clinical outcome, global cortical CBF was lower (median 32 [IQR 22–40] vs. 36 [IQR 29–48] mL/100 g/min, p = 0.03) with a higher burden of hypoperfusion (median 21% [IQR 10–48] vs. 10% [IQR 2–20], p = 0.01) and critical hypoperfusion (median 3% [IQR 0–9] vs. 0% [IQR 0–3], p = 0.01). Similarly, those with unfavorable outcome had a lower CDO₂ (median 5 [IQR 3–6] vs. 6 [IQR 4–7], p = 0.01) and higher burden of poor CDO₂ (median 35 [IQR 25–63] vs. 11 [IQR 3–41], p = 0.02) and severe CDO₂ (median 5 [IQR 0–20] vs. 0 [IQR 0–2], p = 0.001). However, no difference was found in the vasospasm phase between unfavorable and favorable outcome regarding CBF indices and CDO₂ indices. Circles and stars indicate outliers (1.5–3 IQRs from the end of the box) and extreme outliers (more than 3 IQRs from the box), respectively. CBF, cerebral blood flow, CDO₂, cerebral delivery of oxygen, ∆CPPopt, CPP − CPPopt, IQR, interquartile range, CBF, cerebral blood flow, CDO₂, cerebral delivery of oxygen, CPP, cerebral perfusion pressure, CPPopt, optimal CPP, HHH, hypervolemia, hypertension, and hemodilution, ICP, intracranial pressure, PRx, pressure reactivity index, PTT, pulse transit time