Surgical site infections
An interdisciplinary team has been meeting to try to reduce
the postoperative surgical site infection (SSI) rate for certain
surgical procedures. A g type of control chart (based on the
geometric distribution) for one type of surgery is shown in
fig 3. Instead of aggregating SSIs in order to calculate an
infection rate over a week or month, the g chart is based on a
plot of the number of surgeries between occurrences of
infection. This chart allows the statistical significance of each
occurrence of an infection to be evaluated11 rather than
having to wait to the end of a week or a month before the
data can be analysed. This ability to evaluate data immediately
greatly enhances the potential timeliness of the
analysis. The g chart is also particularly useful for verifying
improvements (such as reduced SSIs) and for processes with
low rates.
An initial intervention suggested by the team is to test a
change in the postoperative wound cleaning protocol. As
shown in fig 3, however, this change does not appear to have
had any impact on reducing the infection rate. Although this
intervention did not result in an improvement, the control
chart was useful to help prevent the team from investing