Introduction
Materials and methods
General information and definitions of lean manufacturing and the Toyota production system
Jidoka (自働化) | Using intelligent automation—sometimes also referred to as “autonomation” or automation with a human touch—to promote flow. This term describes a quality control supervisory process that prevents the production of continuous defective products by detecting production abnormality, stopping it, immediately fixing or correcting it and investigating the root cause in order to prevent it from reoccurring. |
Heijunka (平準化) | The Heijunka box is a visual production smoothing or production levelling mechanism to produce intermediate goods at a constant rate, thus allowing further processing to be carried out at a constant and predictable rate that distributes the finishing schedule into small time increments. The heijunka box is generally a wall schedule that is divided into a grid of boxes, each one representing a specific unit of time; lines are drawn down the schedule to break it into columns of days or weeks. |
Kaizen (改善) | The term connotes “change for the better” or “improvement”. The Japanese character “kai” stands for “take apart,” and “zen” connotes “make good.” An adequate English translation is “continuous process improvement”. Kaizen is a quality strategy that is aimed at eliminating waste by eliminating any activities that add cost without adding value. |
Kaizen event | A kaizen event or “kaizen blitz” is a team event dedicated to quickly implementing a lean manufacturing method in a particular area in a very short time period. |
Kanban (看板) | “Kan” means visual, and “ban” means card or board; the term implies an inventory control method that historically used cards to signal the need for an item. However, other devices such as plastic markers (Kanban squares) or balls (e.g. golf balls) or an empty transport trolley can also be used to trigger the movement, production or supply of a unit in a factory. Kanban is a textbook example of a demand-driven (economic production) pull system. |
Lean | Short form for lean manufacturing—minimising waste and maximising flow. |
Muda (無駄) | In the literature the term is translated as “waste” but more precisely implies any human activity that absorbs resources without creating value. The Japanese antonym of “muda” can be translated as “usefulness”, which may assist in more adequately identifying the meaning of the Japanese term: anything in a work process that adds cost or time without adding value can be regarded as “muda.” |
Poka-yoke (ポカヨケ) | Poka-yoke means “mistake-proofing”—avoiding (yokeru) inadvertent errors (poka) is a behaviour-shaping constraint, or a method of preventing errors by putting limits on how an operation can be performed in order to force the correct completion of the operation. The original term was Baka-yoke, but as this more precisely connotes "fool-proofing" (or “idiot proofing”) the name was modified to the more companionable Poka-yoke. |
Inventory calculation and push and pull characteristics
Process mapping
Value stream mapping
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Non-value adding (NVA)
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Necessary but non-value adding (NNVA)
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Value adding (VA)
Results
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From the procurement perspective:
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Not applicable since stents are not produced but ordered. Concerning adequate stent orders, this becomes a possible waste of inventory (see below).
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From the medical perspective:
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Given a justified indication for stent implementation from a medical point of view, this type of waste was not considered applicable.
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From the procurement perspective:
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Waiting for orders of stents and other medical equipment coming in at the controlling department from the interventional radiology department. If information flow is interrupted, this may delay the process of ordering and, in the case of missing inventory, this may lead to a delay in medical treatment. Switching from paper/fax orders to electronic/digital ordering to achieve a valid and trackable information flow was indicated. This should also prevent “double orders” and lost faxes/papers. With the new digital ordering process, the former paper/fax option was identified as NVA waste.
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From the medical perspective:
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Waiting for patients/necessary data: patients are transported from the wards to the angio suite by an external transportation service. The transportation system is requested electronically for a given time, but it is known that, especially between 1200 and 1400, the service is congested, with possible delays of up to 1 h. As idle time is very cost-intensive, a supervisory room was created within the angio suite to increase independence. Thus, patients can be transported earlier via the transportation service and wait if applicable in the supervisory room until the intervention can take place. This reduces interruptions and increases smoothness. The former delay possibility was considered NVA waste.
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Waiting for staff, equipment and free angio suites: This includes waiting for staff who are otherwise busy (e.g. on ward, still in another angio suite) or sick (especially in combination with possible bottlenecks during vacation periods); waiting for special equipment (e.g. equipment currently being used in another angio suite); or waiting for a free angio suite because of delays in previous interventions or mismanagement. To prevent these situations, one interventional planner/manager was selected to organise an efficient infrastructure for all interventional subspecialties in the hospital’s angio suites. Before, each subspecialty (angiography/internal medicine, interventional radiology, neuroradiology) independently organised their own staffing and equipment. The new organisational structure also facilitates helping out at other subspecialties if necessary and includes an immediate feedback mechanism with all subspecialties for critical events in the past and possible bottlenecks in the future. Any type of waiting was considered NVA waste.
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From the procurement perspective:
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After ordering stents and medical equipment, external suppliers of medical material organise transportation to the hospital. This transport is necessary and—given the specialisation of producing stents and medical equipment—cannot be substantially abbreviated in terms of logistics and geography.
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From the medical perspective:
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Inside the hospital, stents first enter the incoming goods department (first visual inspection), then enter central storage (second intensive inspection), then enter within-hospital package/delivery and finally reach the angio suite’s inventory where they are again finally checked before implementation. Given that stents can be considered specialised—almost custom fit—medical items, a direct delivery to the point of usage was considered smoother. All previous inspections were considered NVA waste and could be eliminated. The architectural position of the angio suites inside the hospital was considered given. The design of the inventory rooms inside the angio suites and the arrangement of the drawers were considered useful and ergonomic.
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From the procurement perspective:
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This type of waste was considered not applicable.
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From the medical perspective:
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The goal was to avoid unnecessary, partial and partially redundant interventions caused by a lack of knowledge, competence or (stent) material. A certified interdisciplinary conference was created with specialists of interventional radiology, vascular surgeons, angiographers from internal medicine and referring physicians in order to discuss patients and their respective needs all together in advance. Any subsequent intervention due to a previously, only partially, conducted medical intervention (either due to partial knowledge, limited material or limited expertise) was considered NVA waste.
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From the procurement perspective:
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Previously, specialised—almost custom fit—medical materials such as stents were centrally ordered, centrally received, centrally stored and finally delivered to the angio suite. The central storage and the unnecessary inspections were eliminated (see waste of transport) by directly requiring the stent producer to transport the item to the angio suite. The central inventory was considered NVA. The order responsibility remained with the central purchasing of the hospital for overall bargaining power.
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From the medical perspective:
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Previously, the whole procurement system was rather push-driven. Average estimates of quantities were used for stent orders and medical equipment, although a feedback mechanism already existed. Still, the risk of medical items reaching expiry dates remained, which for stents especially is very cost-intensive. At the angio suite inventory, a kanban system was implemented. The angio suite’s inventory drawers were labelled with visual icons and became “local supermarkets” that now trigger the ordering of new items when almost empty, thus changing the system to a more demand-driven pull system. At the given quantities, the push-driven inventory approach was considered NVA waste, especially because large inventories of specialised medical materials are very cost-intensive.
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From the procurement perspective:
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Waste of motion has been identified as subsets of previously described waste forms (see waste of inventory, waste of process, waste of transport and waste of waiting).
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From the medical perspective:x
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All interventions require advance preparation of the patient from the nurse, as well as advance preparation of multiple medical items and tools from a rather voluminous inventory (i.e. a large number of different items held within the inventory rather than a large inventory of a few different items only). In order to reduce the probability of possibly forgotten items—which then would reduce process smoothness as they would have to be prepared or organised during an intervention—standard operating procedures (SOP) for all major standard interventions were formulated, including desired image documentation of crucial steps, patient preparation, necessary laboratory values and necessary experience of the physician (or respective sufficient medical supervision expertise). Also all inventory drawers were affixed with pictures of every item they carry, so that each item can also be found quickly by a visual scan. Any motion of patients, physicians, nurses and technicians that was not necessary for the completion of an operation or negatively affected process smoothness was considered NVA waste.
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From the procurement perspective:
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Stents are produced by a relatively small number of medical companies. While it is generally possible to change to a different producer in the case of frequent or increasing defects (or bottlenecks in the timely procurement), it may not always be possible due to specialised characteristics of certain stents in their repertoire. In general, spoiled products from the procurement site were considered negligible.
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From the medical perspective:
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In order to reduce waste of defects and spoilage from the medical perspective, adequate experience of the physician (including mastering possible complications or supervision by a more experienced physician), the nurse and the technician were considered indicative factors for providing adequate preparation of patients, medical items and tools and for allowing for an overall smooth process until final stent implantation without damage to patients, employees and materials. Selecting a responsible interventional planner/manager (see also waste of waiting) was considered helpful to account for sufficient experience, expertise and staff for each subspecialty at all times. Any preventable defect or spoilage of stents and other medical items affecting patients and employees was considered NVA waste.
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Level 1 | Level 2 | Level 3 | |||
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Gross waste | Possible solution | Process and method waste | Possible solution | Micro waste | Possible solution |
In general | Institutional level | In general | Process level | In general | Personal level |
Work-in-progress | Scheduling improvement | Long changeover | Preparation in advance | Excess walking, looking for stock, speed and feed, bending and reaching, double handling | Improving ergonomic behaviour and thinking in advance |
Poor plant layout | Architectural optimisation | Late maintenance | Request in advance | Paperwork | Reduce and delegate as much as possible |
Rejected, returned and damaged products | Prevention and advance identification | Temporary storage | As little as possible | ||
Dirty equipment | Meet hygiene standards | Equipment problems | Check in advance | ||
Rework | Attain best medical practice | Unsafe method | Reject in advance | ||
Container and batch size | Architectural/conceptual efficiency | Poor workplace design for specific processes | Improve set-up in advance as much as possible | ||
Material not delivered to point of use | Clear and binding orders, e.g. visualisation | No SOP | SOP creation |