MISREADING OF HEAD CIRCUMFERENCE SCALE ON UK-WHO NEONATAL AND INFANT CLOSE MONITORING (NICM) CHART IN BABIES WITH VERY LARGE HEADS
A clinical error associated with plotting head circumference on the UK-WHO NICM chart has been reported. In a child whose head circumference already exceeded the 99.6th centile at term, the left hand length scale was consistently misread as the head circumference scale, leading to avoidable delay in recognition of intra cranial expansion. It is important for staff to be aware of this possible confusion.
On the 2-weeks to 6-months chart, in order to accommodate both head and length curves, the head circumference scale extends to 39cm on the left axis and 47cm on the right, with both axes increasing in 1cm intervals. The head circumference scale then merges with the length scale, in a different colour, starting at 42cm on the left axis and 58cm on the right, and increasing in 2cm intervals (see figure below). If that distinction is not recognized and the left length scale is used erroneously to plot head circumferences exceeding 39cm, the resulting centiles will be too low and may mask intracranial expansion (see figure below).
It is thus important that staff plotting head circumference in children under 3 months distinguish between the length and head circumference scales on the left axis, and ensure that head circumferences exceeding 39cm are always plotted using the right axis.
The RCPCH are developing a new edition of the chart in which the labeling will be modified to avoid confusion in future. However, staff using existing stock need to be aware of the potential for confusion.
Click on the image below for a larger and more clear view.