chapter 26. alarm devices

8/11/2019 Chapter 26. Alarm Devices

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Chapter 26

Alarm DevicesThe purposes of an alarm are to transfer information, enhance vigilance, and warnof a potential or actual abnormal or unusual condit ion (1,2,3,4). I t is essential that

there be a means of alert ing personnel to a change or potential change in

equipment function or the patient, for there wil l always be occasions when operator

vigilance wil l be lowered or attention reduced while performing other tasks.

The number of alarms in anesthetizing areas has increased greatly. To add further

confusion, alarm sounds may come from sources o ther than from anesthesia

apparatus, including electrosurgical equipment, lasers, hearing aids, and beepers

(5,6 ,7). The J oint Commission on the Accreditation of Healthcare Organizations has

made it a goal to improve the effect iveness of alarm systems (8,9).

Standards

An internati on al stan da rd for al arm systems was pu bl ishe d in 200 3 (10 ).

Terminology (10)

Alarm Con di t ion Delay: Time from the occurrence of a tr iggering event to

when the alarm system d etermines that a n alarm condit ion exists.

Alarm Signa l Generatio n Dela y: Time from the onset of an alarm condit ion to

the generation of i ts alarm signals.

Alarm Limi t: Threshold used by an ala rm system to determine an alarm

condit ion.

Alarm Off: State of indefinite durat ion in which an alarm system or part of an

alarm system does not generate alarm signals.

Alarm Pau sed: State of l imited durat ion in which the alarm system or part of

the alarm system does not generate alarm signals.

Alarm Pres et: Set of stored configurat ion parameters, including select ion of

algorithms and init ial values for use.

Alarm Res et: Operator action that causes the cessation of an alarm signal for

which no associated alarm c ondit ion currently exists.

Alarm Setti ng s : Alarm system configurat ion, including but not l imited to alarm

limits, the characterist ics of any alarm signal inact ivat ion states, and the

values of variables or parameters that determine the function of the alarm

system.


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Alarm Signa l: Signal generated by the alarm system to indicate the presence

of an alarm condit ion.

Alarm Sys te m: Parts of medical electrical equipment that detect alarm

condit ions and, as appropriate, generate alarm signals.

Au dio Off: State of indefinite durat ion in which the alarm system or part of

the alarm system does not generate an auditory alarm signal.

Au dio Paused: State of l imited durat ion in which the alarm system or part of

the alarm system does not generate an auditory alarm signal.

Default Alarm Preset: Alarm preset that can be act ivated by the alarm system

without operator act ion.

False-negative Alarm Condit ion : Absence of an alarm condit ion when a valid

tr iggering event has occurred.

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False-positive Alarm Condition : Presence of an alarm condit ion when no

valid tr iggering event has occurred.

High Priority: Indicates that immediate operator response is required.

Information Signal: Any signal that is not an alarm signal or a reminder

signal. Examples include the tone of the pulse oximeter or

electrocardiograph, the waveform of the electrocardiograph, and the heart

rate numeric.

Intell igent Alarm System: Alarm system that makes logical decisions based

on monitored information without operator intervention. Intell igent alarm

system methodologies include analysis of trends, l imit comparisons, data

redundancy, data fusion, rules, fuzzy logic controllers, and neural networks.

Latching Alarm Signal: Alarm signal that continues to be generated after its

tr iggering event no longer exists unti l stopped by deliberate operator act ion.

Low Priority: Indicates that operator awareness is required.

Medium Priority: Indicates that prompt operator response is required.

Reminder Signal: Periodic signal that reminds the operator that the alarm

system is in an alarm signal inact ivat ion state.


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Inhibit , silence , and suspendhave been used in past terminology for alarms.

Unfortunately, different meanings were attributed to these terms. For this reason,

these terms wil l not be used.

Alarm Prioritization

All alarms are no t eq ua ll y import an t. Th e inf orma ti on th at an alarm conveys ma y

represent an emergency, the potential for an emergency, or just an unusual

condit ion. Priorit ized alarms help to dif ferentiate l i fe-threatening si tuat ions f rom

those that are less urgent. Alarm condit ions priorit ies are shown in Table 26.1. It

may be possible to increase the prio rity of an alarm, but the priority cannot be

decreased.

A high-pri ority alarm ind icates a condit ion th at re qu ire s immedi ate ac t io n. Ex ampl es

include asystole, ventricular f ibri l lat ion, cardiac support device (intra-aort ic balloon

pump, cardiopulmonary bypass machine) fai lure, high airway pressure, extreme

hypoxemia, and sustained high-energy radiation beam.

Medium priority implies a potential ly dangerous situat ion that requires a prompt

response. Examples i nclude many cardiac arrhythmias, high or low b lood pressure,

apnea (unless prolonged or associated with extreme hypoxia), mild hypoxemia, and

high or l ow part ial pressure of carbon dioxide (pCO2).

A lo w priori ty a la rm ind ic ate s tha t on ly opera tor awa re ness is requi red. Exam ples

include failure of an i nfusion pump for maintenance intravenous f luids and failure of

an enteral feeding pump.

The object of p riorit izat ion is to minimize distract ion from less important alarms

during an emergency. It has been suggested that only the alarm sound

corresponding to the most urgent of the prevail ing alarm condit ions should be

annunciated; all other sounds s hould be temporari ly audio paused (2). Once the

most urgent alarm condit ion is resolved, the sound corresponding to the

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next highest priority condit ion would then be init iated. This priority interlock should

be l imited to audible annunciat ion; lower priority visual signals need not be

suppressed because they are relat ively unobtrusive.

TABLE 26.1 Alarm Condition Priorities


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Onset of Potential HarmaPotential Resul t of

Fai lure to

Response to the

Cause of A larm

Condition

Immediateb Promptc Delayedd

Death orirreversible

injury

HIGHPRIORITY

HIGHPRIORITY

MEDIUMPRIORITY

Reversible injury HIGH

PRIORITY

MEDIUM

PRIORITY

LOW PRIORITY

Minor injury ordiscomfort

MEDIUMPRIORITY

LOWPRIORITY

LOW PRIORITYor no alarm signal

An information signal may be used to indicate the potential for delayed minor injuryor discomfortaOnset of potential harm refers to when an injury occurs and not to when it is

manifested.bHaving the potential for the event to developed within a period of time not usually

sufficient for manual corrective action.cHaving the potential for the event to develop within a period of time that is usually

sufficient for manual corrective action.dHaving the potential for the event to develop within an unspecified time that is greater

than that given under prompt.From International Standards Organization. Medical electrical equipment-Part 18:general requirements for safety. Collateral standard: general requirements, tests andguidelines for alarm systems in medical electrical equipment and in medical electricalsystems (ISO-IEC 60601-1-8). Geneva, Switzerland: Author, 2003.

Audible Signals

The primary purpose of auditory alarm signals is to get the operator's attention. In

addit ion, they should help the operator to identify the onset of alarm condit ions, the

urgency of the required operator response and the l ocation of the device generating

alarm signals.

An aud ib le s ign al wi l l a tt ra ct at te nti on fas ter and mo re reli ab ly tha n one tha t is

visual (11). Ideally, i t should do this in a t imely, non-startl ing, and non-irr itat ing


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fashion (12 ). Unfortunately, the qualit ies that cause sounds to attract attention also

tend to make them intrusive or s tart l ing. Some are so unpleasant that the response

may be to inappropriately disable or deactivate the alarm s ystem.

There are a number of available options in alarm sound technology, including

variat ions in pattern, pitch, tone, frequency, and loudness. The international alarm

standard specif ies the characterist ics of auditory alarm signals (10 ).

One problem associated with alarm sounds is that clinicians may not hear them.

Background noise and other alarms can i nterfere with hearing an audible alarm

signal (13). I f an a udible signal is allowed to continue to sound, other audible

signals may not be noticed (14 ,15). An anesthesia provider with a hearing deficit

may have dif f iculty determining the source of a sound. One s tudy found that many

anesthesiologists have an abnormal audiogram and that 7% had one or more alarm

intensit ies below the detectabil i ty threshold (16). Audible alarms should be a djusted

so that the si gnal wil l be perceived despite background noise.

Once an audible signal has been perceived, the next step is to identify its origin.

This is important because many monitors are not in the clinician's immediate f ield

of view, and the operator cannot always turn around to view them. Many anesthesia

providers have trouble identifying audible alarms (13 ,17 ,18,19 ). Inabil i ty to identify

an alarm may delay or prevent the appropriate remedial act ion (15,20).

Af ter an aud ibl e sign al has succee de d in cap turing atte nti on, aud io paus ing

(muting, si lencing) wil l provide t ime to correct the situat ion. The continuous

presence of an audible s ignal can degrade task p erformance and impair detect ion

of new alarm condit ions and the abil i ty to dist inguish between exist ing and new

alarm condit ions. The visual co mponent of the alarm indicator and associated

functions should stay act ivated unti l the condit ion that tr iggered the alarm is

corrected. If another alarm condition occurs while an alarm is audio paused, the

addit ional alarm should have both audible and visual indicat ions.

Most manufacturers provide a means of audio pausing. The t ime varies with the

instrument and can sometimes be varied. Some monitors i ndicate elapsed t ime. The

alarm standard requires that there be a visual indicat ion that any a larm signal has

been inactivated (10 ).

Some alarms can be turned to AUDIO OFF (defeated, disabled) for an unlimited

time. The volume of some alarms can b e decreased to a point where the audible

signal cannot be heard (21 ). Using AUDIO OFF or low volume is dangerous, as

either can lead to a false-negative alarm.


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Alarm Category I ndicator Color F lashing Fr equency

HIGH PRIORITY Red 1.4 Hz to 2.8 Hz

MEDIUM PRIORITY Yellow 0.4 Hz to 0.8 Hz

LOW PRIORITY Cyan or yellow Constant

View Figure

Figure 26.1Graphic symbols for alarm systems. (FromISO IEC 60601-1-8,Medical electrical equipmentPart1-8: general requirements for safetycollateralstandard general requirements, tests and guidelines foralarm systems in medical electrical equipment and inmedical electrical systems, 2003

).

Alarm Limits

An al arm l imi t (set poin t, threshold valu e, thresho ld, sett ing ) ma y be non-

adjustable, operator-adjustable, or an algorithmically determined criterion (12). The


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alarm standard requires that if an operator-adjustable alarm limit is provided, the

limit shall be indicated continuously or by operator act ion so that it c an be

determined if the set values are appropriate for the patient and procedure (10)

(Figs. 26.2, 26.3).

Default alarm limits can be set by the manufacturer, the health care facil i ty, or the

operator. Those set by the manufacturer may be default values or may be bracketed

around the value of a monitored variable at a point in t ime, recent values of a

monitored variable, or a current control sett ing (10 ). Most monitors allow the

operator to alter the default sett ings.

Realist ic alarm limits need to be set. Wide l imits result in fewer false alarms but

increase the risk of missing a true alarm (good specif icity but poor sensit ivity) ( 12 ).

With pressure and volume alarms during art if icial venti lat ion, a low s ett ing may

result in a part ial disconnection or small leak being missed. Constrict ions in the

breathing system that increase resistance can cause the airway pressure to remain

above a low alarm set point although a total disconnection would probably not be

missed (23).

Ensuring that an alarm is act ivated before a d angerous condit ion has occurred

without creating frequent spurious alarms requires intell igence on the part of both

the alarm system and the operator. Some operators set limits to extremes unlikely

to be encountered clinically. The farther thresholds are from normal values, the

greater the probability that a dangerous condition will occur without activating the

alarm. Others simply use the l imits se t by the last person who used the device.

Others keep the thresholds close to the manufacturer-preset l imits.

I t is good pract ice to record alarm limits on the anesthesia record. This provides

evidence that the alarms were act ivated. I t may also i ncrease the operator's

awareness of the alarms and/or make it more l ikely that appropriate values wil l be

used. I t is possible that the set alarm limits may be recorded in the electronic

record.

False Alarms

Actu al al arm ma lfu nction s are rare (24 ,25). The anesthesia provider can reduce the

number of false-posit ive and false-negative alarms by carefully preparing the

patient interface, securely a ttaching probes, select ing monitors with art ifact

reject ion capabil i t ies, using wider l imi ts, increasing the alarm signal generation

delay, and tailoring the alarms to the patient or operat ion (25 ,26 ,27,28 ,29 ).

Posit ioning the pulse oximeter probe away from electrosurgery


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wires may also help, as may locating the electrosurgery grounding pad far away

from the pulse oximeter probe and electrocardiogram electrodes (30).

View Figure

Figure 26.2Alarms limits are displayed continuously to theright of the values for the parameters. (Picture courtesy ofDraeger Medical, Inc.)

View Figure

Figure 26.3The complete set of alarm values is displayed.

To display the alarm limits menu, the alarm limits soft key(1)is pressed. The menu (2)lists the parameters, their

current measured values (larger numbers), and the currentlow and high alarm limits. The alarm limits also appear on

the curves as dashed lines (3). (Picture courtesy of DraegerMedical, Inc.)

Fa ls e - p o s i t i v e A l a rm s

Many alarms are spurious. Only a small number indicate actual r isk

(31,32,33,34 ,35 ,36,37 ,38 ,39,40 ).


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An al arm ac tivated wi th ou t prop er cause requi res t ime an d eff ort to chec k the

actual condit ions. This wil l result in less attention to other tasks and may lead to an

inappropriate act ion. False-posit ive alarms are a source of irr i tat ion and distract ion

and are a threat to patient care, because the anesthesia provider becomes

increasingly l ikely to ignore the signals, lower the alarm volume, turn OFF the

entire alarm system, use the AUDIO OFF or AUDIO PAUSE without looking for the

cause, or set the alarm limits at such extremes that the ala rm system is effect ively

disabled (12 ,41 ,42 ,43,44,45 ). False-posit ive alarms may fr ighten patients and

relat ives.

False-posit ive alarms a re a fact of l i fe. While there are s trategies for minimizing

them, they cannot be entirely eliminated.

False-posit ive alarms may be caused by alarm malfunction, art ifacts, extraneous

sounds being mistaken for a larm signals, and inappropriate set points.

The start-up sequence on equipment can prevent false-posit ive alarms. Medical

equipment that automatically enables the alarm system when a patient is connected

to the equipment when a valid physiologic signal is f irst detected, or through an

admit new patient function act ivated by the operator wil l decrease the number of

such alarms.

False alarms may be reduced by changing alarm limits at certain t imes, since

clinical ranges vary during dif ferent phases of anesthesia (46 ). For example, the

high heart rate alarm limit might be set higher during intubation than during

maintenance.

The ALARM PAUSED state can be used to avoid nuisance alarm signals before

performing an act ion that is l ikely to cause an alarm condit ion (10 ,38). Examples of

such act ions are intentional breathing system disconnection to perform airway

suctioning, opening a transducer to air for zero cal ibrat ion, intubation, and trying to

restore spontaneous breathing at the end of a case.

Monitors with art ifact reject ion such as pulse oximeters with motion-resistant

algorithms can decrease the

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number of false-posit ive alarms (47,48 ,49 ,50 ). Filtering in the algorithm that is

monitoring for an alarm condit ion often causes alarm condit ion delay (10). For

instance, a heart rate monitor can average the R-R interval f or several heartbeats.

An ab rupt cha nge in R-R interv al s wi l l no t im me dia te ly cause an alarm condi ti on,

because it wil l take several consecutive heartbeats for the calculated heart rate to


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exceed the alarm limit. Some electrocardiogram monitors have automatic lead

switching so that monitoring can continue even if one or two electrodes come OFF.

This can d ecrease false-posit ive alarms.

False alarms can be reduced by integrat ing monitors (38,51 ). An example is

synchronizing the pulse oximeter and noninvasive blood pressure monitor. I f the

oximeter probe is on the same arm as the blood pressure cuff, no alarm wil l sound

if no pulse is detected when the cuff is inf lated. Another example is the pulse

oximeter and electrocardiogram (ECG). SpO 2values are rejected unless the pulse

rate measured on the oximeter matches that on the ECG.

Fa ls e - n e ga t iv e A l a rms

I f an alarm s ystem fails to generate a signal when it should (false negative), the

patient 's s afety may be threatened. An alarm condit ion may be rejected or missed

because of spurious information produced by the patient, the patient-equipment

interface, other equipment, or the equipment itself.

Another cau se is the alarm be ing turn ed OFF . Su bseq uen t users may no t be aware

that it has been turned OFF. Automatic enabling is present on many newer

monitors. Once a monitored parameter is s ensed, the alarm becomes active. This

eliminates the problem of forgetting to turn an alarm ON or not being aware that an

alarm has been turned OFF by a previous user. Appropriate application of reminder

signals should reduce the chance that the alarm system is unintentionally left in an

alarm signal inact ivat ion state (10).

Speaker failure, sett ing the audible volume too low, and sett ing the alarm limits too

widely may also cause false-negative alarms (52).

False-negative alarms may be reduced by not s ett ing the l imits too widely, using

the AUDIO PAUSE rather than the AUDIO OFF state, and checking alarm systems

at regular intervals to detect problems such as a faulty loudspeaker or low audible

volume that can result in a n audible signal not being heard.

Intelligent Alarm Systems

An inte ll ige nt (s ma rt, ex pert ) alarm system may do one or mo re of th e fol lowi ng

without operator intervention: determine an alarm co ndit ion on the basis of t ime,

weightings, mult iple variables, or other advanced processing; generate alarm

signals for two or more alarm condit ions of equal priority; change the previously

assigned priority or relat ive priorit izat ion of a part icular alarm condit ion; change the

alarm signal generation delay or alarm condit ion delay; change the characterist ics

of the generated alarm signals (e.g., to indicate a change in urgency); provide the


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operator with a l ist of c ondit ions that could have tr iggered the alarm(s); a nd present

information that is helpful in dealing with the c ondit ion that tr iggered the alarm

(36,46,53,54 ,55 ,56,57 ,58 ,59,60 ).

Smart alarms can reduce the number of false alarms by discriminating between

art ifacts and truly threatening condit ions. Human response t imes are longer and

have greater variabil i ty with c onventional alarms than intell igent alarms (61 ).

Alarm Condition Logging

Many modern monitors and l i fe-support ing equipment are equipped with alarm

condit ion logging. Logging can be used to determine the cause of a transient alarm

condit ion, for quality assurance purposes, to s tudy crit ical incidents, and to

determine when an alarm condit ion occurred. The log should include the value of

the variable that caused the alarm condit ion, the alarm limits, and the alarm status

(ON, Audio Paused, Paused, Audio Off, etc). This information can then be made

available if a problem occurs.

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P.836

QuestionsFor the following questions, answer

i f A, B, and C are correct

i f A and C a re correct

i f B and D a re correct

is D is correct

i f A, B, C, and D are correct.

1. Purposes of an alarm include

A. Warning of a potenti al or actu al abn orma l or un us ua l condi ti on

B. Gett ing attention

C. Transferring information

D. Transferring legal responsibil i ty from the manufacturer to the user

View Answer2. Problems associated with determining the source of an

alarm include

A. Th e hearin g of th e anes the sia prov id er

B. Dif f iculty in recognizing tone patterns

C. Noise levels in the operating room

D. Audible signals that do not sound continuously

View Answer3. Visual signals

A. Give less specif ic inf ormat ion than audi bl e s ig nals


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B. May go unrecognized for a longer period of t ime than audible signals

C. Use continuous l ights for more crucial information

D. Require the anesthesia provider to be looking at the monitor instead of the

patient

View Answer4. Causes of false-positive alarms include

A. Ac tivat ion by an inapp ro pri ate dev ice

B. Extraneous sounds that sound l ike an alarm signal

C. Alarm malfunction

D. Widely set l imits

View Answer5. Means to reduce the incidence of the false-positive alarms

include

A. Alteri ng al arm l im its duri ng the proced ure

B. Synchronizing monitors

C. Delaying the t ime between detect ion of an alarm condit ion and alarm ac tivat ion

D. Decreasing the averaging time

View Answer6. Concerning alarm prioritization, which of the following

are true?

A. Low-pri ori ty v is ua l s igna ls ne ed not be suppre ssed

B. With mult iple alarm condit ions, all alarms wil l be annunciated

C. All alarms are not equally important

D. Alarm priorit ies may be increased or decreased.

View Answer7. The purpose(s) of alarm signals include(s)

A. Gaini ng atte ntion

B. Notifying the operator of the alarm urgency

C. Identifying the onset of an alarm condit ion

D. Identifying the device that provides the alarm

View Answer8. The characteristics of a false-negative alarm include

A. Automa ti c enabling

B. The alarm may be turned OFF

C. Narrow alarm limit range

D. Failure to generate a signal when there is a threat to patient safety

View Answer9. Which are some of the functions that a smart alarm may

perform?

A. De termin in g th e alarm condi ti on on the bas is of mu lti pl e vari abl es

B. Changing the alarm s ignal generation delay

C. Presenting a l ist of condit ions that may have generated the alarm


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D. Changing the alarm priority

View Answer10. Alarm condition logging

A. Shou ld inc lu de th e val ue of the varia ble th at caused the alarm condi t io n

B. Can help to determine the cause of transient alarm condit ions

C. Is useful for quality assurance

D. Can d etermine when an alarm condit ion occurred

View Answer

chapter 26. alarm devices

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