SH6: CEREBRAL BLOOD FLOW IN UPRIGHT POSITION FOR SHOULDER SURGERY

Abstract

There has been concern over the safety of the upright position for shoulder surgery from anaesthetists uncomfortable with the risk of reduced cerebral blood flow (CBF). Because there are no studies documenting what happens to CBF during upright surgery we aimed to measure CBF through an indirect and non-invasive method using recently available Ultrasound monitoring equipment.

This study randomised patients into awake (interscalene block alone) and GA with block, and indirectly measured the CBF by using a validated Doppler technique on carotid flow both before and during the shoulder procedure. Non-invasive and invasive measurements of mean arterial pressure were made throughout the procedure, together with doppler measurement of carotid flow following preoperative measurement of carotid contribution to cerebral flow in the radiology department by an experienced sonographer. All measurements recorded in real time and charted independently.

This study has shown that CBF in both groups were consistent with the expected values, and CBF remained proportionate in supine to upright. CBF values in the block alone group were generally lower than the GA group. In the GA group the MAP dropped lower, requiring use of adrenergic drugs to bring the pressure up. Despite the significant drop in MAP, the CBF was still high. This could signify cerebral autoregulation is a significant factor in the upright position.

We have shown the feasibility of use of DOppler to indirectly measure CBF during upright surgery. Despite the predicted drop in MAP in this position with GA, we could NOT show a concurrent drop in CBF, demonstrating that much more complex factors regulate the CBF in these patients. Clearly, monitoring is the key to safe administration of anaesthetic in the upright position.