Friday, 3 October 2014

Sound the alarm!

US Secret Service under scrutiny

On 19th September 2014, an intruder armed with a knife scaled a fence surrounding the White House in Washington, DC. He managed to run across the North lawn, past a guard posted in the entrance hall and the stairs to the living quarters, before being tackled in the East Room. There were a number of factors involved in his success in accessing one of the most iconic buildings in the world, as detailed in this Washington Post article

One suggested contributing factor was the muting of an intruder alarm which would have alerted the guard in the entrance hall that the perimeter had been breached. According to the Washington Post, "White House usher staff, whose office is near the front door, complained that they were noisy" and "were frequently malfunctioning and unnecessarily sounding off."

Alarms, or their equivalents, have a number of everyday uses such as waking us up in the morning, telling us we've left the car headlights on, or informing us that we've burned the toast again. In healthcare, alarms are meant to draw our attention to occurrences which need to be acknowledged or require action. However, just as happened with the Secret Service, alarms (and their misuse) can cause their own problems.

The 4 most common abuses of alarms

(This is a list derived from personal experience and observations in the simulation centre, it is not definitive)

1) Alarm not switched on
Some healthcare devices allow alarms to be set but these are not the default option. For example the "low anaesthetic gas" alarm is often switched off by default by the manufacturer of the anaesthetic machine. Their reasoning may be that the alarm will sound inappropriately during the wash-in phase of anaesthesia as the anaesthetic gas increases from 0% to the set concentration. The down-side is that inattention by the anaesthetist may lead to patient awareness under anaesthesia if the anaesthetic gas falls below an appropriate level. A contributing factor to the lack of attention paid to the anaesthetic gas level may be a (not unreasonable) assumption that the machine would warn the anaesthetist of low anaesthetic level as the machine does alarm for most other variables if they are below a safe level.

2) Inappropriate alarm limits
Most alarms have default limits set by the manufacturer of the device. A pump may alarm if a given pressure is exceeded or an ECG machine may alarm if a given heart rate is not achieved. Some default limits are however outside safe levels. For example, some oxygen saturation monitors will not alarm until the saturation falls below 90%. With normal saturations of 99-100%, many healthcare personnel would prefer to be alerted at a higher level in order to begin countermeasures. 

3) Alarm not muted
One consequence of not muting an alarm is that the noise may be "tuned out" and therefore ignored. Another consequence is that some healthcare devices do not change tone as alarms stack up, i.e. if a second variable, such as heart rate, causes another alarm to trigger when the first alarm is still sounding, the original alarm masks the new alarm.

4) Alarm muted inappropriately
This was the case with the White House intruder and the ushers did not feel it was inappropriate at the time. The decision as to whether an alarm was muted inappropriately is often one taken in hindsight. The consequences are obvious, an alarm does not sound when it is supposed to. In addition, a false sense of security may occur, especially if not everyone is aware that the alarm is muted. In the White House example, the guards on the North Lawn pursuing the intruder may have believed that he would not gain access to the entrance hall as the guard inside is meant to lock the door if the alarm sounds.


Intruder alarms tend to have low specificity and high sensitivity which may lead to repeated activation. In the White House case, with the wonderful retrospectoscope, the muting of the intruder alarm should have triggered an investigation and a search for alternative solutions. Perhaps the alarm could be a visual rather than auditory one, or perhaps the alarm could be relayed to an earpiece carried by the guard.

As always there is not one but many "solutions". Device users should be trained to know what the alarm settings are, how to alter them and the possible consequences of alarm (mis)use. Organisations should be aware of how their devices are being used, should set standards for critical alarm defaults and examine near-misses and critical events where alarms were contributory factors. Device manufacturers should involve end-users from the design stage of the equipment, should test their devices under realistic conditions (e.g. in a simulator) and should act on feedback from end-users to modify their devices.

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