In cardiac surgery, head-down and head-up positions are used to control cardiac filling pressure and for cardiac exposure. Even though benefits of head positioning are not clear, they can also bring some risks. Understanding physiological consequences of positioning can help avoiding serious adverse events and complications. In this prospective study we investigated the effect of head-down and head-up position upon systemic and cerebral haemodynamics and cerebral oxygenation and their correlation with Bispectral Index (BIS) in CABG patients under general anesthesia before surgical incision. Thirty patients were enrolled in to the study. After induction and before surgical incision blood pressure, heart rate, central venous pressure, cardiac output, stroke volume variation, BIS, cerebral oxygen saturation and middle cerebral artery blood flow rate values of the study patients were measured at neutral, head-down and head-up positions. The significance of the difference in terms of the means between the positions was studied with the repeated measures analysis of variance, while the significance of the difference in terms of the mean values was analyzed with Friedman test. Statistically significant increase were recorded in blood pressure, cardiac output, central venous pressure, cerebral blood flow rate and BIS values in the head-down position. The head-up position was associated with decrease in cardiac output. We demonstrated that both positions are safe for cerebral haemodynamics and oxygenation in ischemic heart patients. We showed that the short term head-down position can improve cardiac function, probably due to increased preload in ischemic heart patients with normal ejection fraction; however, the head-up position can be detrimental for systemic haemodynamic even for a short period.

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