We continue with the six part series covering the five principles of lean improvement. Thus far, I have discussed creating flow and what that means to a lean organization. Next, I will discuss the second principle known as pull.
A lean system desires that work flow nonstop through the entire value stream (VS). In every VS, constant flow from one value-added step to the next typically doesn't exist. This means a hand-off from station to station occurs. Pull first directs us to examine this handoff. Establishing a clear method for handing off from one process to the next is called "creating a tight connection." Defining the alert to tell the supplying process to start or to deliver is called "trigger." A trigger is like a starter's pistol signaling runners to start. Even with a tight connection and a trigger, we still don't necessarily have pull. A key component of pull is that the sending process stops producing and waits if a trigger isn't received.
An example of push in healthcare presents when a department processes a patient and sends them down (pushes them) to the next department where they wait. When someone gets or "pulls" the patient from the waiting room, this is often, and incorrectly called pull. True pull is present only if the sending department actually stops processing patients when the receiving department "stops pulling".
One hospital spent months trying to connect their Post Acute Care Unit (PACU), post surgery, to the nursing division. They had implemented phone calls, standard work and many other things with little progress. When the patient was ready to move, the PACU began their push to the nursing division. In the spirit of pull, team members agreed to implement a pull system. This means that even if a patient is ready to move, PACU holds the patient until nursing pulls them. This could mean PACU holding patients longer and the number of patients in PACU growing and if all spaces were filled, surgery would have to stop.
Since stopping surgery is a major issue, the hospital is putting in safe guards, but is closely guarding against the PACU being able to call or push patients to the nursing division. One safe guard will be an andon signal for PACU to pull if the number of patients starts getting dangerously close to capacity.
Standard work defines the response to this andon signal which involves management's intervention. Lean tools are used to make this pull system work. Tools include visual boards in nursing to know if a bed is available. A checklist to complete when a problem occurs. An andon light to alert key people of a potential problem and standard work for staff to use. People foresee the problems that will surface if a pull system is implemented and use these reasons to argue against it.
A pull system reduces WIP inventory and in reducing inventory it lowers the water level allowing existing problems to come to the surface. This surfacing of issues and the need to urgently resolve them is another purpose of a pull system. It may be counterintuitive to try a pull system, but the results are amazing. Flow increases and process noise reduced.
President, Breakthrough Horizons