Bob Luttman, Robert Luttman & Associates
Critical Path Method (a.k.a. PERT Charts)
Failure Mode Effect Analysis (a.k.a. Variance Effect Analysis)
The Critical Path Method (a.k.a. PERT)
The critical path method (CPM) was invented by project managers in the early 1950's. The US Navy adapted and improved it to manage the Polaris missile project in the late 1950's. Naming the technique PERT (Program Evaluation and Review Technique) the Defense, Aerospace, and other industries adopted the tool as the major project tool to this day.
So, what does this have to do with healthcare? Two things. Your IS department probably has one for their Year 2000 project (hopefully it finishes before New Years Eve 1999). Second, it is the origin of the term critical path.
I have already presented a PERT chart back when we were discussing the Cascade Effect. We showed the following diagram:
This PERT chart shows the relationship between each activity, no activity can begin before its precedent activities are completed. The precedents are the activities that the arrows come from. The time (in days) for each activity is noted in its box (for example Patient Teaching has an expected time of T=2 days).
These relationships create pathways through the process. Summing the times along each pathway gives the pathways length or duration. The longest pathway is the critical pathway, the critical pathway is the longest pathway in the process. The process cannot end before the critical pathway ends.
Trust me, you can do this manually but it is infinitely easier to use project management software. The price is cheap.
In the diagram the critical pathway consists of the bold faced boxes. This clinical pathway - a highly simplified one - will have a LOS equal to the length of the critical pathway.
Any project to shorten the LOS must start with the critical pathway. The chart illuminates the cascade effect for any variance. A case manager can focus on completing these activities and attaining these outcomes to meet LOS goals.
PERT Charts also make a great "what if…" tool during pathway design. In fact, we advocate pathway design using PERT Charts. Post-it notes, 3 x 5 cards, project management software, or even chalkboards are all methods for capturing the flow and the data.
The process also helps people think parallel. Do I really need to wait for Respiratory to finish before I start my job?
One last, technical, note. The difference between PERT and CPM is in the times for each activity or outcome. CPM simply takes the expected (usually average) time, PERT uses the best case, expected case, and worst case estimates to calculate the duration:
Average Time = (Best Case + (4 x Expected Case) + Worst Case) / 6
This extends the possible analyses to explore Best Case vs. Worst Case patients. Who are they? Why are they Best / Worst Case? Can (should) we create separate pathways for the three groups? How can we improve Worst Case patients? Learn from the Best Case patients?
What if......?
That is the question PERT can answer.
