Medical Error FMEA Risk Grids – why they are a problem

FMEA risk grids are presented as a small spreadsheet.  As an example, the VA HFMEA “scoring matrix” is shown below.

























This table is similar to those in the ISO standard on risk management, 14971. The idea is to classify all potential errors in a process as to their severity and probability of occurrence. Each potential error event will fall in one of the grid cells. Events that fall in the yellow cells (designated as number+”y”) are unacceptable and require action.

So what’s wrong with this? On the face of it, there is nothing wrong – it is a standard practice from other industries. The problems emerge as one looks into the details. Each of the row and column headings are defined by the VA as follows (for the sake of brevity – severity is limited to patient outcomes only):


Frequent -Likely to occur immediately or within a short period (may happen several times in one year)
Occasional -Probably will occur (may happen several times in 1 to 2 years)
Uncommon -Possible to occur (may happen sometime in 2 to 5 years)
Remote -Unlikely to occur (may happen sometime in 5 to 30 years) 


Catastrophic  – Death or major permanent loss of function (sensory, motor, physiologic, or intellectual), suicide, rape, hemolytic transfusion reaction, Surgery/procedure on the wrong patient or wrong body part, infant abduction or infant discharge to the wrong family
Major –
Permanent lessening of bodily functioning (sensory, motor, physiologic, or intellectual), disfigurement, surgical intervention required, increased length of stay for 3 or more patients, increased level of care for 3 or more patients
Moderate – Increased length of stay or increased level of care for 1 or 2 patients
Minor – No injury, nor increased length of stay nor increased level of care  

Now the problems can be seen:

If one focuses on catastrophic errors, almost all of them will be located in the remote cell – none will be in the frequent cell. The implication of the VA table is that one does not have to further examine a process that has remote catastrophic errors but this is clearly wrong. There are many examples of catastrophic errors whereby it is desired that they occur much less than once in 5 to 30 years. An example is the tragic case of the Mexican teenage girl, who was given organs with the wrong blood type and later died, a story which made the national news.

To understand what needs to be done, one must examine a potential error in more detail. For simplicity of this explanation, let’s eliminate human error and focus on machines. In the operating room, blood gas results are needed, so this hospital has a blood gas lab nearby with a blood gas system. But there is a possibility that this blood gas system will fail and blood gas results will be unavailable. One has reliable data from the manufacturer about the frequency of a blood gas system failing. The mitigation is to have a second blood gas system. Now, blood gas results will be available unless both blood gas systems fail simultaneously. So now the probability of unavailability of blood gas results is lower, but it is not zero. The hospital can keep on going and put in place as many blood gas systems as they see fit, with each additional system lowering the probability of this adverse event from occurring. From the standpoint of a risk grid, one will eventually arrive at a cell that has acceptable risk.

The point is that for many (all?) catastrophic errors, the desired goal is to never have them. Because one is dealing with probabilities, never is unattainable, so one must put in place mitigations which lower the probability to an acceptable level.

This also means that for each potential catastrophic error, one must quantify the probability of occurrence before and after any mitigations and this is the problem – this quantification is a monumental task and until it is tackled, one will have FMEAs performed to satisfy regulatory requirements, but with little improvement in reducing risk. 


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