Estimate or calculate? How surgeons rate volumes and surfaces

Surgeons frequently describe the shape of intraoperative findings using visual judgement and their own sense of proportion or describing these findings in comparison to commonly used or metaphoric subjects. The aim of the study was to analyse the reliability of surgeon's estimations of dimensions.

The study was performed in two phases. First, physicians had to estimate the metric proportions of four well-known objects. Second, surgeons were asked intraoperatively to estimate the liver resection surface after partial hepatectomy. The exact surface of the resection plane was measured using computed tomography-guided planimetry of the resection specimen. Physician's estimations and the exact measurements of the well-known objects and the liver resection surface were compared. Systematic error was defined by the natural logarithm of estimated/real size.

We found a large individual discrepancy in estimating the metric proportions of commonly used objects and a tendency to underestimate both commonly used objects and liver resection surface. Experienced liver surgeons were more accurate in estimating liver resection surface compared with younger staff members.

We found a large bias in estimating the dimension of both commonly used objects and the surface area of liver parenchyma transection. Obviously, estimating errors are more influenced by the individual subject who estimates than by the object itself. In clinical routine, surgeons should rely more on simple measuring devices than on their own sense of proportion. Education in how to estimate more correctly human liver resection surfaces can be achieved by ex vivo studies using porcine livers.