We report a case of reduced cerebral oxygenation which had the possibility of leading to an adverse outcome if it had not been detected by the routine use of cerebral oximetry. This case study illustrates that an inadvertent re-adjustment of a single-stage venous cannula within the superior vena cava resulted only in the cerebral oximetry device alerting to a potential problem. All other monitoring devices remained within standard operating parameters, with no deviation throughout the duration of the incident.