Quicker detection risk-adjusted cumulative sum charting procedures

When a patient is operated on, the surgical outcome depends on two major factors: (i) the patient's health condition and (ii) the surgical process comprising the surgeon, the supporting staff, operating environment, and equipment. An outcome is usually represented by one if a patient dies within 30 days of an operation and zero otherwise. Another method of measuring the outcome is to use survival time with truncation on the 30th day for monitoring purposes. In order to monitor a surgical process effectively, the health condition of a patient must be taken into consideration. This is usually done using a log-likelihood ratio statistic based on an outcome, that is, risk adjusted according to the health condition of the patient. The 30-day wait results in delay in signaling when a deterioration occurs. The consequence of having to wait even though a death has occurred is the potential loss of lives because of delay in signaling. Regular updating of patients' information can improve the sensitivity of a charting procedure. The main objective of this article is to develop and study the class of risk-adjusted cumulative sum procedures that are updated on a regular basis based on patients' current conditions, without having to wait 30 days. Our study shows that these charts do in fact signal earlier and there are differences among the various updating techniques and monitoring statistics.