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Purpose: Craniosynostosis corrections are routinely performed under hypotensive anesthesia to reduce blood loss, with target mean arterial pressures (MAP) around 50mmHg. Following our experience utilizing Near-Infrared Spectroscopy (NIR) for monitoring cerebral oxygenation during cranial remodeling procedures, we noted that while often intraoperatively measured oxygenation values were falling lower than recommended, they were readily reversed by raising mean arterial pressure. While the majority of published studies on cerebral autoregulation have been in adults, one study has suggested that children may have a higher minimum limits for cerebral autoregulation (60mmHg).1. Based on these observations, we sought to measure the effects of two different mean arterial pressure levels (standard hypotension vs. minimal hypotension) on blood loss during craniosynostosis corrections.
Methods: Following IRB approval, 75 children requiring craniosynostosis corrections were prospectively randomized into two groups: one treated with the standard hypotension (MAP = 50 mmHg) and the second with a minimal hypotension (MAP = 60 mmHg). Aside from the anesthesiologists, all caregivers were blinded and strict transfusion criteria were followed. Multiple variables were analyzed including estimated blood loss as measured directly off a cell saver, and the need for blood transfusions. Comparisons between groups were analyzed using t-tests. Analysis of variance procedures were utilized to control for differences in age, patient weight, and surgical procedures. Categorical variables were analyzed using chi-squared statistics, or Fisher’s exact for small cell counts. All analyses used SAS9.3 (SAS Institute, Cary, NC).
Results: Our analyses revealed that both groups (standard vs. minimal hypotension) were similar among all measured parameters, with no statistically significant differences noted between either group: mean age (43 vs. 50 months), weight (20.1 vs. 18.5 kgs.), type of procedure (anterior remodeling (25 vs. 25) vs. posterior (12 vs. 15)), preoperative Hemoglobin levels (12.9 vs. 13gm/dl.). There were also no differences noted in calculated blood loss as ascertained by captured cell saver products (245 vs. 274cc.), nor in postoperative Hemoglobin levels (8.8 vs. 9gm/dl.). Eleven of 75 patients (14.7%) received allogenic transfusions, but there were no statistically significant differences found between transfusion rates in the standard (7/39, 18.0%) vs. minimal hypotension (4/36, 11.1%) groups.
Conclusions: Craniosynostosis corrections are undertaken to not only improve appearance, but to also to reduce elevated intracranial pressures (with the corollary of increasing cerebral blood flow). Following our observations utilizing NIR monitoring, in which cerebral hypoxia was frequently found with a MAP target of 50 mmHg, we sought to evaluate the effects of performing corrections at higher MAP levels. This prospectively randomized study found no statistically significant differences in intraoperative blood loss, and absolute transfusion requirements, between the two target levels for hypotensive anesthesia (standard hypotension: MAP = 50 mmHg and minimal hypotension: MAP = 60mmHg). We speculate that for centers having higher transfusion rates, raising MAPs would have an even lower impact on overall transfusion rates. Based on these findings, we recommend that surgeons consider performing craniosynostosis corrections with minimum hypotension, in order to improve cerebral blood flow, and overall total body perfusion.
1. Neurosurg Anesthesiol. 2003;15:307-12.