Little's Law Applied to the ER

Little's Law is a fundamental equation in operations. It's like F = m*a to physics and CO=HR*SV to critical care.

Applying it in the ED, Little's law states:

Number of patients in ED = Arrival rate of patients/hr * Avg length of stay in ED/Pt

Two of these numbers are readily available. Number of pts in ED and the arrival rate.

For example, lets assume that the ED bed capacity is 50 beds and normally has 40 beds occupied at a given time. The arrival rate on an average day is 10 pts/hr. What is the average length of stay in the ED?

Avg length of stay = # of pts in ED / arrival rate

= 40 pts / (10pts/hr)

= 4 hrs

Based upon this, we can figure out average LOS in ED and work on factors to decrease total ED length of stay for patients.

* More on Little's Law (pdf)