Friday, November 28, 2008

Max's head circumference, by the numbers

Last update: 22:34 03-Mar-2009 (data through this night's measurement: blanks indicate no measurements on indicated days)

The figure shows a time series of Max's head circumference, measured in cm. The neurosurgeons and NICU team use a lot of factors when deciding whether to tap a patient, or even whether to install a shunt. However, their decisions seem to depend ultimately on the level and change in head circumference.

For background, I'm told that "normal" growth is between 0.5 cm and 1.0 cm per week, with the maximum normal growth rate happening in the weeks immediately following birth. The curves then flatten out. Max is currently below the median for weight but in the 90th percentile for head circumference. The docs look for "curve jumping", when a patient moves from the 90th to 95th percentile, for example, especially if his weight remains at, e.g., the 40th percentile.

Note that changes on the order 0.5 cm are hard to distinguish from background noise or measurement error. These measurements are taken with measuring tape, by different nurses, at different times of the day, perhaps pre- or post-LP.