Comparison of induced hypertension, fluid bolus, and blood transfusion to augment cerebral oxygen delivery after subarachnoid hemorrhage
Clinical article
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Object
Critical reductions in oxygen delivery (DO2) underlie the development of delayed cerebral ischemia (DCI) after subarachnoid hemorrhage (SAH). If DO2 is not promptly restored, then irreversible injury (that is, cerebral infarction) may result. Hemodynamic therapies for DCI (that is, induced hypertension [IH] and hypervolemia) aim to improve DO2 by raising cerebral blood flow (CBF). Red blood cell (RBC) transfusion may be an alternate strategy that augments DO2 by improving arterial O2 content. The authors compared the relative ability of these 3 interventions to improve cerebral DO2, specifically their ability to restore DO2 to regions where it is impaired.
Methods
The authors compared 3 prospective physiological studies in which PET imaging was used to measure global and regional CBF and DO2 before and after the following treatments: 1) fluid bolus of 15 ml/kg normal saline (9 patients); 2) raising mean arterial pressure 25% (12 patients); and 3) transfusing 1 U of RBCs (17 patients) in 38 individuals with aneurysmal SAH at risk for DCI. Response between groups in regions with low DO2 (< 4.5 ml/100 g/min) was compared using repeated-measures ANOVA.
Results
Groups were similar except that the fluid bolus cohort had more patients with symptoms of DCI and lower baseline CBF. Global CBF or DO2 did not rise significantly after any of the interventions, except after transfusion in patients with hemoglobin levels < 9 g/dl. All 3 treatments improved CBF and DO2 to regions with impaired baseline DO2, with a greater improvement after transfusion (23%) than hypertension (14%) or volume loading (10%); p < 0.001. Transfusion also resulted in a nonsignificantly greater (47%) reduction in the number of brain regions with low DO2 when compared with fluid bolus (7%) and hypertension (12%) (p = 0.33).
Conclusions
The IH, fluid bolus, and blood transfusion interventions all improve DO2 to vulnerable brain regions at risk for ischemia after SAH. Transfusion appeared to provide a physiological benefit at least comparable to IH, especially among patients with anemia, but transfusion is associated with risks. The clinical significance of these findings remains to be established in controlled clinical trials.
Abbreviations used in this paper:
CaO2 = arterial oxygen content; CBF = cerebral blood flow; CMRO2 = cerebral metabolic rate for O2; CVP = central venous pressure; DCI = delayed cerebral ischemia; DO2 = O2 delivery; IH = induced hypertension; MAP = mean arterial pressure; NNICU = Neurology/Neurosurgery ICU; OEF = O2 extraction fraction; RBC = red blood cell; SAH = subarachnoid hemorrhage; triple-H therapy = hypervolemia, hypertension and hemodilution.
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