Why changing the ‘knife-to-skin’ time doesn’t affect theatre efficiency, and what to do instead.

Productivity (activity / unit cost) continues to fall throughout the NHS and, operating theatre (room) productivity is no exception.  This does not mean that people are not working hard; indeed, they may be working harder than ever.  But, it does mean that everyone has an interest in improving the system to increase the NHS’s value for money in general, and the financial survival of your own hospital in particular.

What’s gone wrong?

Using the Theory of Constraints (see below if you’re interested), we know that the ‘constraint’ in theatre throughput is the surgeon.  In other words, actually doing the surgery is the rate-limiting step.  All other resources in theatre should be focused on how best to ‘exploit’ the surgeon’s time fully.  Put another way, any time the surgeon spends not cutting is wasted time.

So, it’s not difficult to see what’s wrong in theatre, is it?  A surgeon hanging around waiting to operate gets us nowhere.

A lesson from aviation

A good analogy is the airline industry.  The surgeon is like the engine of an aeroplane.  Any time the engine is off, the plane is going nowhere.  Everything should be geared towards getting the plane moving.  The time spent on the ground, loading the plane, refuelling and cleaning the toilets out, must be reduced to the absolute minimum.  This time is called the ‘turnaround’ time; it is literally, the time taken to turn the plane around and send it on its way.  For planes with similar engines, turnaround time is the key.

Before ‘low-cost’ airlines came on the scene, a good, highly-efficient turnaround time was 45 minutes.  Nowadays, the best can do it in 15 minutes!

Avoid the simplistic, embrace the simple!

You have heard it said that bringing forward the ‘knife-to-skin’ time to 09:00 will improve theatre efficiency.  This is like saying bringing forward the take-off time will improve the efficiency of the plane’s engines because we’ll get to our destination earlier!  You will indeed get there earlier, but not quicker!  You haven’t affected the constraint in the system at all.

Let’s take some concrete examples.  A single, long operation requiring invasive anaesthetic procedures (intravenous lines, arterial lines, epidurals, etc), may not achieve a knife-to-skin time till, say 10:30.  But, the operation will go on till it finishes, which could be 13:30 or later.  Using our analogy, the ‘flight-time’ is unaffected, though the arrival time may seem late.  The efficiency is the same regardless of what time we ‘take-off’.  The opportunity for efficiency is absent because there is no turnaround time available to reduce.

On the other hand, think about multiple, short procedures, say, an ENT list with lots of tonsillectomies.  Here, the turnaround time is crucial.  If you can reduce delay between knife-to-skin times, you can do more procedures with the operating time available.  One extra short-haul flight can make the difference between profit and loss for Easyjet!   For a surgical service provider (e.g. a hospital), it could make the difference between keeping a service or not.

Simple (not necessarily easy) solutions

In our analogy, the surgeon is represented by the engine.  The anaesthetist must be the pilot.  He/she is the one who does the clever take off and landing bits.  You shouldn’t be using the pilot to refuel the aircraft or clean the toilets!  The operation is represented by the flight and the patient by the passengers (you can have fun trying to allocate roles – I haven’t worked out who provides the in-flight entertainment yet!).

So, we reduce turnaround time by ensuring a ‘ready-to-go’ patient is always available as soon as the surgeon finishes one operation. 

Here are some examples; you will be able to think of more yourself:

  • Have a local anaesthetic patient on the table whilst another is being put to sleep.  To this end, ensure that all patients are strongly offered LA in outpatients/pre-assessment clinics, and make sure surgeons are trained in these techniques
  • Perform invasive anaesthetic procedures before the previous operation has finished.  These could be done by other anaesthetists in separate areas, e.g. epidurals could be sited in Recovery (or some other appropriate place)
  • Double-up anaesthetists and ODPs, and/or make use of Anaesthetic Practitioners
  • Use Dual-Operating, where a surgeon shuttles from one anaesthetised patient to another in adjoining theatres
  • Designate a buffer area where ‘stand-by’ patients can be waiting, rather than have to fetch them from remote areas (i.e. wards)
  • Don’t insist on an Escort nurse for every patient

All these solutions are simple and easy to monitor, most are evidence-based from elsewhere in the NHS, private medicine or other countries.  They may not be cost-neutral, but in fact, most merely require a change to the way we organise ourselves.  They will improve theatre efficiency.


By using a well-established theory and borrowing useful analogies from the airline industry, I hope I have shown that simply shifting start times in isolation will not achieve greater theatre efficiency.

But, there are efficiency gains to be had, which must be achieved.  They involve the way we organise, not how fast we work.  I would emphasise that none of what I propose means cutting corners or jeopardising patient safety (which, in my book, is paramount).

Further reading:

Dettmer H W (1998) Goldratt’s Theory of Constraints: A Systems Approach to Continuous Improvement   McGraw-Hill Education, ISBN: 0873893700

Step guide to improving operating theatre efficiency


One thought on “Why changing the ‘knife-to-skin’ time doesn’t affect theatre efficiency, and what to do instead.

  1. I have to say I think the solution is easy. Invest in anaesthetists to save money via more efficient throughput. More anaesthetists would allow more patients to be ‘in the loop’ rather than waiting for the whole cycle to finish before introducing another widget into the front end. We work like a bottling plant where only one bottle is in the factory at a time. JB

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