Logic tree can get to real cause of a systemic error

Robert Latino, vice president of The Reliability Center, a risk management consulting firm in Hopewell, VA, recommends a tool developed by his firm calls the "logic tree" for investigating chronic problems or adverse events. The logic tree is a tool specifically designed for use within root-cause analysis, showing cause and effect relationships that queued up in a particular sequence to cause an undesirable outcome to occur. These cause and effect relationships are validated with hard evidence as opposed to hearsay.

"The data lead the analysis, not the loudest expert in the room," Latino explains.

A logic tree starts off with a description of the facts associated with an event, then you work your way down by asking how that event could have happened. A key part of this tool that makes it different from others is that you must ask "how could this specific step have happened" instead of simply "why" it happened.

"We find that when simply asking why, we are connoting a singular answer and to a point, an opinion," Latino explains. "When asking how could, we are seeking all the possibilities, not only the most likely, and evidence to back up what did and did not occur."

Latino offers an example of using a logic tree to investigate an endobronchial fire during surgery using a laser. (Click here for this example in a logic tree.) The logic tree begins with the sentinel event and then works down by asking what could have happened. The first line of answers is it could have happened before, during, or after the procedure. Before and after are eliminated, and then the next question is how the fire began — inside or outside the right bronchus. Then the next question is how oxygen, fuel, and ignition source were all present.

Must explore all options

By exploring all the possible answers to each of those questions and eliminating those that don't apply, you end up with a more reliable, thorough answer than simply charting the one answer that everyone thinks is correct, Latino says. In this example, the logic tree leads to two conclusions: First, an operating channel in the bronchoscope was contaminated with a flammable cleaning agent, which was used because financial concerns led to inadequate procedures. The hospital switched to using a less expensive solution for cleaning the bronchoscopes, and the hospital had no system in place for assessing the potential implications on patient safety of such a change. Second, anesthetic gas was mismanaged because there was no quality control inspection.

"I could have done a '5 Whys' and easily concluded that the anesthesiologist mismanaged the gasses, or I could have used a fishbone and never gotten to the fact about inappropriate cleaning of the instruments. There wouldn't be a category for that because it's not something you immediately think of," he explains. (To see a comparison how different tools can lead to different conclusions, see chart below.)

Latino says the logic tree helps show how much seemingly unrelated issues and actions can combine to threaten patient safety or otherwise cause a problem for the organization.

"The failure of a process to achieve its designed objective has to do with the design of the linkages between steps in the process, how the steps relate to one another, the hand-offs," he says. "It is the interrelationships that are themselves prone to failure and that propagate the effects of a failure to other parts of the process, often in ways that are unexpected or not immediately evident."