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Theory of Constraints

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Theory of Constraints

What is it and how can it help me?

Theory of Constraints is an approach that shows how we can manage bottlenecks and their associated constraints. A bottleneck determines the pace at which the whole process can work, whilst the constraint is the bit of kit or resource that causes the bottleneck. For more information on bottlenecks see 'A comprehensive guide to demand and capacity'.

Take, for example, a simplified version of a typical patient pathway outlined below. The theoretical numbers indicate the volume of patients that can be processed at each step within a given time period, for example one week.

GP referral
80 - Outpatient visit 75 - Surgery 12 - Follow Up 50 - Discharge 100

In this example, the bottleneck, or rate limiting step, is surgery. Only 12 patients can be dealt with per week. To increase overall throughput, you must first increase throughput at this step by identifying the constraint.
Just as the strength of a chain is determined by its weakest link, the limiting step and its constraint determines the throughput or work rate of a team, process or hospital, eg the number of patients that can be seen per day.

In complex systems like healthcare, there is always going to be a rate limiting step along pathways. Knowing where the constraints are makes it possible to  focus improvement effort and allows specific operational management effort in order to increase and maintain throughput.

When does it work best?

There is national information on known ‘hot spots'. These include:

  • Diagnostic capacity for some diagnostic tests
  • Theatre capacity

It is important to make sure that you identify the real constraint. For example, assumptions are often made about a surgeon's time being the most expensive resource, or about a specific piece of kit. Increasing capacity for the wrong thing will make the processes much worse, as well as making things harder for staff or worse at other steps in the patient pathway.

How to use it

The Theory of Constraints identifies a five step process to achieve continuous flow and improve throughput:

  1. Identify the system's constraint
  2. Get the most out of the constraint - exploit it
  3. Support the system's constraint - subordinate everything else to it
  4. Elevate the system's constraint
  5. Go back to step one, don't allow inertia to become the system's constraint

1. Identify the system's constraint (this limits throughput)

Map out the processes or patient pathways at a high level (see process mapping).

Identify the steps or parts of the process where there are the longest delays for patients. 

Then map this part of the process or the patient journey in more detail so you really understand what is going on. Do this to the level of what one person does, in one place, with one piece of equipment, at one time. Look at the process templates tool at this stage, in conjunction with capacity and demand analysis.

Look carefully for the true constraint. The constraint is often a lack of availability of a specific skill or piece of equipment. Waiting lists or backlog of work tends to occur before the bottleneck in the patient journey, and clear after the patient has gone past the stage with the constraint.

Keep asking 'why' to try to discover the real reason for the delay (see five whys).

For example, 'the clinic always overruns and patients have to wait for a long time'.

 - Why? The consultant does not have time to see all her patients in clinic.

 - Why? She has to see everyone who attends
    (including first visit assessments and follow-up patients).

 - Why? It is what she has always done.

Now you have a good idea about the location of the constraint and some of its measures of demand, capacity, backlog and activity.

2. Get the most out of the constraint - exploit it

The constraint must always be managed, as it determines the rate at which patients go through the system. It is therefore important to ensure that there is no idle or wasted time at this point in the process. For example, if a radiologist is found to be the constraint in a given process, any time the radiologist is waiting for patients or equipment would be considered wasted time and this in turn affects the overall throughput. 
It is also important to always work this part of the process. First see if time can be released by improving the organisation of work processes and work environments. See sort and shine  and make niggles in your workspace visible .

Other examples that may help to ensure maximum utilisation are multi-skilling staff, as well as assisting with set up and paperwork activities to enable trained staff to concentrate on the use of the machinery itself.

Where the constraint is equipment, it is important to ensure that it is always in use.  Routine servicing of radiotherapy machines (a frequent constraint in the radiotherapy process) during the working week, will impact on throughput.

At the same time, see if processes can be improved. For example, prepping patients outside of the theatre to release theatre time, if theatres are the constraint. Detailed process templates will help to identify opportunities and help the operational management of constraints. This information will help you develop careful schedules around the constraint. This is important, as every minute that is not used at the constraint is a minute lost to the whole process.

Once you get the most out of a constraint, the bottleneck may move to another step in the process.

3. Support the system's constraint - subordinate everything else to it

It is here that the organisation needs to ensure that its own policies, resources, behaviours, measurements etc support the constraint to ensure that it is always working. This may require behaviour change in the organisation.

To protect inevitable variation at the constraint, see demand and capacity. Theory of Constraints recommends putting a ‘buffer' (a small queue) in front of the constraint to ensure it is always fed and there is no ‘down time'. An example might be that patients are scheduled to arrive at a time so there are an average of two or three patients in the waiting room.

4. Elevate the system's constraint

If the constraint still exists after exploiting and subordinating everything else to  it, then during this step the constraint is elevated and ‘broken' by investing resources in it. This may require capital expenditure, overtime and increased bed or theatre capacity. This step is only necessary if the constraint is a true bottleneck. If you break the bottleneck, the constraint will move - and it is often not easy to predict where to.

However, knowing the constraint may be sufficient to help improve the process and to help its operational management.

5. Go back to step one, don't allow inertia to become the system's constraint

When the constraint is broken, go back to step one. This step highlights the need to focus on continuous improvement.


Oxford Radcliffe Hospitals Case Study - ‘A Story of Success'
‘Hitting the Bottom' - Health Management Feb 1999

Staff at the Radcliffe Infirmary carried out a Theory of Constraints workshop, prompted by 64 elective neuro-surgical cancellations in a three month period combined with increased sickness levels. The neurosurgeon and the anaesthetists all believed they were the constraint in the process, however on examination the problem was found to be bed capacity. Changes introduced included one member of staff being given the role of bed manager whilst the maximum daily number of elective patients was reduced from eleven to six. Although initially these changes seemed counterproductive, the overall impact included reductions in patient cancellations, a drastic cut in out of hours operations and an increase in throughput of 16 per cent.

‘The Impact of Theory of Constraints in an NHS Trust'  - Journal of Management Development Vol. 24  No 2, 2005

This study investigated the impact of Theory of Constraints on three NHS trust departments, Neurosurgery, Opthalmology and Ear, Nose and Throat (ENT), in relation to reducing waiting lists and improving throughput of patients. Significant improvements were made in ENT and Opthalmology, but not in Neurology due to the size of the system, its complexity and its heavy reliance on support services. The authors of this study recommend that an organisation's social environment is taken in account in order to maximise the benefits of Theory of Constraints.

Goldratt's Dice Game

Outlined in Dr Eli Goldratt's book ‘The Goal'.  It highlights how systems work where dependencies exist (for example assessment cannot happen until referral has taken place) and there is statistical variation. See ‘Improvement Leaders Guide Matching Demand and Capacity'.

There will always be a bottleneck

"An interesting strategic perspective is that there will always be a bottleneck; the decision is where you want it. The idea of designing a system with the bottleneck placed where it can best be managed or responded to is powerful." 
Young T et al 

What next?

Theory of Constraints is an overall approach that will help to improve patient flow. This guide describes how you can use this approach from an organisational perspective. It is an approach that has an overlap with Lean Thinking .

Whichever approach is the main driving philosophy of your organisation, understanding where the rate limingstep in the processes exist along an 18 week pathway and post-treatment can help you to understand how to improve throughput. This understanding will complement other improvement strategies.

Leadership, engaging staff  and using project planning  will support your improvement efforts. A structured approach applying small tests of change (plan, do, study, act ) with measurement will help you to make sure that any change results in an improvement.

Other useful tools and techniques on this website

The following links may be useful: 
Process mapping
Process templates
Five whys
Statistical process control
Variation: How to manage and reduce
Comprehensive guide to demand and capacity

Additional resources

‘The Goal: A Process of Ongoing Improvement' Goldratt Eliyahu M and Cox Jeff (Gower 1993)

Improvement Leaders Guide Matching Demand and Capacity

'Using Industrial Processes to Improve Patient Care' - Young T et al


Theory of Constraints began with a simple concept about production lines, similar to the idea that a chain is only as strong as its weakest link (in Dr Eliyahu Goldratt's book). It can also be used to describe a business philosophy and an improvement methodology. Theory of Constraints has been developed over the last 20 years, predominately in the manufacturing industry. It has most recently been applied to healthcare with regard to reducing waiting times and increasing throughput.  Its application alongside Lean Thinking is now well recognised in the NHS.

Acknowledgements / sources

Bicheno J (2004) ‘The New Lean Tool Box', PICSIE Books, Buckingham
Goldratt E (1990) ‘The Theory of Constraints', North River Press, New York
Hopp W and Spearman M (2000) ‘Factory Physics', McGraw Hill, Boston

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