Assessment of Workload Using NASA TaskLoad Index in Perianesthesia Nursing

Gloria Young, MSN, CRNA, Lyubov Zavelina, MSN, CRNA,Vallire Hooper, MSN, RN, CPAN, FAAN

According to the Institute of Medicine (IOM), as many as 44,000 to98,000 people in the United States die in hospitals every year due tomedical errors. Multiple physiological and psychological factors canimpact the health care provider’s attention span, making medicalerrors more likely. Some of these factors include increased work-load, fatigue, cognitive overload, ineffective interpersonal commu-nications, and faulty information processing. Postanesthesianurses, responsible for providing care to unstable patients emergingfrom anesthesia with multiple life-threatening conditions, mustmake critical decisions on a minute-by-minute basis. The currentASPAN Patient Classification/Recommended Staffing Guidelinesdoes not adequately take into account varying care requirementsamong the patients. If a tool could be found that effectively evalu-ated staff’s workload, ongoing assessment would be enhancedand resources better used. The National Aeronautics and Space Ad-ministration–Task Load Index (NASA-TLX), a multifaceted tool forevaluating perceptual (subjective) workload, has seen extensive ap-plications and is widely regarded as the strongest tool available forreporting perceptions of workload. This article will survey varioususes of the NASA-TLX and consider the potential uses for this toolin perianesthesia nursing.

Keywords: NASA-TLX, workload measurement, perianesthesianursing.

� 2008 by American Society of PeriAnesthesia Nurses.

Vallire Hooper, who is coeditor of Journal of PeriAnesthesia

Nursing, was not involved in the editorial review or decision

to publish this article. The entire process from submission, ref-

eree assignment, and editorial decisions was handled by Jan

Odom-Forren, the other coeditor of this journal.

Gloria Young, MSN, CRNA, is a CRNA at the Medical College of

Georgia Hospital and Clinics, Augusta, GA; Lyubov Zavelina,

MSN, CRNA, is a CRNA at the Medical Center of Central Georgia,

Macon, GA; and Vallire D. Hooper, MSN, RN, CPAN, is a peri-

anesthesia consultant, PhD candidate, and Clinical Assistant

Professor, School of Nursing, Medical College of Georgia,

Augusta, GA.

Address correspondence to Gloria Young, MSN, CRNA;

e-mail address: gyoung@mail.mcg.edu.

� 2008 by American Society of PeriAnesthesia Nurses.

1089-9472/08/2302-0005$34.00/0

doi:10.1016/j.jopan.2008.01.008

102

‘‘TO ERR IS HUMAN,’’ a report by the Insti-tute of Medicine (IOM), stated that as manyas 44,000 to 98,000 people die in US hospitalsevery year because of medical errors.1 Deathsfrom avertable events in hospitals surpass thenumber of deaths attributed to motor vehicleaccidents each year.1 Furthermore, nonfataladverse events related to preventable medi-cation errors increase hospital costs by about$2 billion a year. According to the IOM re-port, higher error rates are particularly com-mon in intensive care units (ICUs), ORs, andemergency departments (EDs). For example,82% of preventable incidents were caused

Journal of PeriAnesthesia Nursing, Vol 23, No 2 (April), 2008; pp 102-110

ASSESSING WORKLOAD USING THE NASA TASK LOAD INDEX 103

by human errors during anesthesia adminis-tration.1 A study of patients in ICUs showedthat they were subjected to an average of1.7 errors per day, indicating that medical per-sonnel were functioning at a 99% level of pro-ficiency.2 Although seemingly insignificant,comparing this 1% failure rate with other in-dustries may help put it into perspective.Such a failure rate would mean 32,000 bankchecks charged to the wrong accounts eachhour, or two unsafe plane landings per day,or 16,000 pieces of misplaced mail per hour.2

Multiple physiological and psychological fac-tors impact attention spans and make medicalerrors more likely to happen.3 Some causes in-clude increased workload, fatigue, cognitiveoverload, ineffective interpersonal communi-cations, and faulty information processing.3

Like pilots, physicians and nurses function intechnologically-oriented and complex envi-ronments. In aviation, where critical deci-sion-making calls for high mental acuity, anaccurate assessment of workload is necessaryto make decisions about crew size, safety,and the effects of cockpit automation.4 Gabaand Lee4 point out that assessing the workloadof health care providers is just as essential, be-cause various stressors may affect the pro-viders’ ability to manage heavy workloads.Moreover, increases in workload because ofeither additional tasks or monitoring require-ments decreases the health care provider’sability to detect and react to emergencies.

PACU nurses, responsible for providing care tounstable patients emerging from anesthesiawith multiple life-threatening conditions,must make critical decisions on a minute-by-minute basis.5 These nurses are also expectedto be experts in airway management andadvanced cardiac life support, as well as pos-sess a variety of skills to care for patientswhose final destination will, in many cases,be an ICU.5 Although more procedures arehandled on a same-day basis with shorter-acting anesthesia, the number of patientsand their level of acuity has continued to

increase, pressing nursing resources to thelimit.6 There are also growing concerns re-garding use of the Phase I PACU, as well asthe Phase II Ambulatory Care Unit (ACU) asa temporary location for overflow ICU andmedical-surgical patients.7-8 Caring for acutelyill ICU patients increases the perianesthesianurse’s workload5 and may interfere with theability to attend to traditional postoperativepatients, thus potentially disrupting the sur-gery schedule flow and admissions to thePACU. Also, as PACU nurse–patient ratios in-crease because of this overflow, the qualityof health services suffers and negatively im-pacts patient outcome. A study by Kiekkasand colleagues5 demonstrated that one ICUoverflow patient necessitated an additional0.3 PACU nurses per shift. Although that num-ber may appear deceptively small at firstglance, over an 18-month period it translatesinto 106 more 8-hour shifts without extrapersonnel to cover this need. The lack of addi-tional staff may compromise care to post-anesthesia patients, increase workload, causefatigue, and weaken staff morale.5 A positionstatement by ASPAN7 encourages manage-ment to ‘‘develop a comprehensive resourceutilization plan with ongoing assessment thatsupports the staffing needs for both thePACU/ASU patients and overflow patientpopulation.’’ Ongoing assessment could beenhanced and resources better used if man-agement had access to a tool that could effec-tively evaluate the staff’s workload.

The National Aeronautics and Space Adminis-tration–Task Load Index (NASA-TLX) may pro-vide just such a tool. A multifaceted tool forevaluating perceptual (subjective) workloaddeveloped by the Human Performance Groupat the NASA Ames Research Laboratory,9

NASA-TLX is widely regarded as the strongesttool available for reporting perceptions ofworkload.10 It has seen extensive use andbeen judged to be reliable and valid for a vari-ety of tasks.11 This article will survey varioususes of the NASA-TLX and consider the poten-tial uses for this tool in perianesthesia nursing.

104 YOUNG, ZAVELINA, AND HOOPER

Definition of Workload

Workload is commonly defined as ‘‘the degreeof processing capacity that is expended duringtask performance,’’ and it reflects a relationshipbetween resource supply and task demand.12

The NASA-TLX, however, defines the work-load experience in terms of ‘‘the sources ofloading imposed by different tasks.’’9 Weingerand colleagues13 report three principalmethods for measuring workload: physiologi-cal, procedural, and perceptual (subjective).Examples of physiological measures includerecording of heart rate and blood pressure asresponses to stress such as that induced byphysical activities. The procedural methodlargely measures time spent on secondarytasks. Perceptual (or subjective) workloadmeasurement uses rating scales to evaluateparticipants’ perceived workload. Althoughphysiological and procedural measurementsmay appear to be more accurate and objective,subjective measurement of workload has beenreported to be less invasive, easier and lessexpensive to obtain, more easily reproduced,and of higher face validity. A pilot workload as-sessment study found subjective measures tobe sensitive enough to produce meaningfuldata.13 The focus of this discussion, therefore,will be on perceptual (subjective) workload.

Implications of Increased Workload

Work overload and long hours of continuouswork are key factors that result in fatigue.14

Fatigue is defined as ‘‘a state of increased dis-comfort and decreased efficiency resultingfrom prolonged exertion; a generalized feelingof tiredness or exhaustion; loss of power orcapacity to respond to stimulation.’’15 Symp-toms of exhaustion and psychological repug-nance to additional work are objective signsof extreme fatigue and can be measured.14

Although fatigued individuals can continue tofunction, the quality of their continued workis likely to suffer, which is especially problem-atic when human lives are at stake. Studieshave shown that professionals exposed to

excessive workload, fatigue, and badly sched-uled work hours show degraded performance,memory deficits, impaired thought processes,irritability, and lack of learning.14 Also, fa-tigued subjects are more likely to select risky al-ternative behaviors like taking shortcuts whenperforming a task. For example, 61% of anes-thesiologists in the United States and 86% inAustralia have admitted to making fatigue-re-lated medical errors.16 Furthermore, a surveyof 254 internal medicine residents revealedthat fatigue contributed to their most signifi-cant medical mistakes.16 From these studies,it can be surmised that fatigued, overworkednurses would have shorter attention spansand be less likely to exercise sound judgmentand detect and react appropriately to criticalevents, all of which translate into decreasedvigilance.

Workload vs Acuity

Although there is no standardized definitionfor acuity, multiple tools are used to measureit in health care facilities across the UnitedStates. For nurses, patient acuity is used tohelp predict workload by assigning scoresbased on the needs of patients so the numberof nursing hours required to attend to theneeds of a specified number of patients canbe calculated.17,18 Graf and colleagues17 de-scribe daily workload as the sum of these ‘‘acu-ity values’’ for each of the patients on the unit,providing a basis for nursing care require-ments. Nursing workload can thus be quanti-fied, but such scoring should be used only asa general means of predicting future work-load, not as a means of labeling the complexityof given patients.

Perhaps because the patient acuity systemdoes not very subtly register differences incare requirements among patients,18 thescores it predicts often vary widely from actualscores.19 Patient care scores have been under-estimated by 8 to 33 minutes per patient perday, resulting in a deficit of 0.24 to 2.99 full-time equivalent employees. When Yurko and

ASSESSING WORKLOAD USING THE NASA TASK LOAD INDEX 105

colleagues20 surveyed 133 burn centers, theyfound that 69% of the units were dissatisfiedwith the acuity system because of its failureto take into consideration the complexityand labor-intensiveness of nursing care,a drawback that made it difficult to use ina burn center. This study clearly identifiedthe limitations of traditional acuity systems.

In a report on the safety of health care, theIOM provided evidence that better nursingstaff levels result in better patient care.21

This organization recommends schedulingadditional staff to each shift to compensatefor unpredicted variations in patient volumethat may push the actual workload higherthan predicted. According to ASPAN, adequatestaffing is necessary to deliver quality careand maintain a safe environment. ASPANreports that 21 states are reviewing their staff-ing guidelines and mandatory staffing levels,and that further research is needed in thisarea.7,8

Introduction to the NASA-TLX

The NASA-TLX, an instrument providing themost widely accepted subjective measure ofhuman workload in various industries, mayalso be applicable to nursing (Table 1).22 Thistool defines individual workload componentsthat are task specific. It does so by asking

respondents to rate the mental, physical, andtemporal demands made by the task, as well

as the level of frustration they feel, number

of performance concerns they have, and level

of effort they must exert in completing it.

Mental demand is described as the mental

and perceptual activity required by a task.

Physical demands may include pushing, pull-

ing, lifting, or other activities, depending on

the task. The temporal demand assesses the

time pressure to complete the task. The effort

component assesses how much mental and

physical work was required to perform at a cer-

tain level. The frustration component evalu-

ates how the continuum of stress and

contentment correlate with task completion.

The endpoints used to evaluate these five sub-

scales are low and high. The sixth subscale,

performance, was developed to measure the

degree of success or satisfaction felt upon the

performance or completion of a given task.

The endpoints of the performance subscale

are good and poor.23 Each of these subscales

describes certain traits used to illustrate gen-

eral aspects of workload. As a result, the

NASA-TLX, initially developed for use in flight

simulation, has been extrapolated and/or

modified over many disciplines outside of the

aeronautical arena. NASA-TLX is one of the

strongest tools available for reporting percep-

tions of workload.10

Table 1. NASA-TLX Rating Scale and Definitions

Workload Component Endpoints Definitions

Mental demand Low to high The mental and perceptual activity required by a task

Physical demand Low to high The physical activity associated with a task

Temporal demand Low to high The time pressure associated with the rate or pace required

to complete the task

Effort Low to high The mental and physical work required to perform the task

at a certain level

Frustration level Low to high Refers to the continuum of stress and/or contentment associated

with task completion

Performance Good to poor The degree of success or satisfaction felt upon the performance

or completion of a given task

Data from reference 23.

Use of the NASA-TLX

Aeronautics

Used alone, in conjunction with other mea-sures of workload, or in combination withphysiologic factors, the NASA-TLX has provedto be a reliable tool for assessing workload ina variety of industries. Because the field of avi-ation fosters such close communicationamong governmental agencies and between

governmental agencies and similar industriesin the civilian sector, it is not surprising thatmany reports published in aviation researchrely on the NASA-TLX. For example, Beckerand colleagues10 used the NASA-TLX to evalu-ate the effects of jet noise and performancefeedback on perceived workload in a monitor-ing task with specific implications for air traf-fic controllers and persons handling flightdeck operations, where vigilance is a require-ment for safety. They introduced three levelsof jet noise and evaluated the impact of each

on signal detection, which was used as a meansto measure vigilance. Performance was nega-tively affected by the introduction of noise,and it worsened as the noise level wasincreased. Of the six subscales, frustrationand mental demand contributed the most toperceived workload, and physical demandthe least. When subjects were given positivefeedback by being notified of correct re-sponses to the signal detection exercise, theirperception of perceived workload decreased.

Metzger and Parasuraman24 evaluated theperformance of air traffic controllers in sixpossible conflict scenarios and a variety of traf-

fic conditions, using the controllers’ memoryof aircraft positions as a criterion. As trafficincreased, so did perceived workload. In addi-tion to using the NASA-TLX, these researchersintroduced heart rate variability (HRV). Theyfound no appreciable change in heart rate var-iability in varying traffic conditions, or duringpassive monitoring or free-flight conditions.Using heart rate, altitude deviation, NASA–TLX, and personality, Jo and Sohn25 attemptedto provide a theoretical basis on which flight

106

crew combinations could be determined andthe efficacy of flight training optimized. Theyfound that NASA-TLX increased as altitude de-viation and personality harmony increased.

In a study of communications between pilotsand air traffic controllers, Rantanen and col-leagues26 examined the assumption that audiodelays contribute to delays in pilot responsetime. Through the use of NASA-TLX, theseresearchers found that audio delay did notcorrelate with pilot delay and had no effecton the NASA-TLX frustration ratings. Becausenurses and physicians also perform vigilancetasks, it may be presumed that the NASA-TLXwould also prove valuable in estimating theirworkloads.

Computer Systems

Mayes et al27 used the NASA-TLX to assessworkload, reading times, and comprehensionafter computer and paper-based reading.These researchers speculated that scores onthe NASA-TLX would reveal an increased per-ception of workload associated with video-displayed information, and that subscales ofthe NASA-TLX might help determine whichaspects of reading information from a videodisplay proved the most taxing.

TLX analysis revealed that the group readingfrom the video display felt more confident intheir understanding but had lower actual com-prehension scores than did those reading thepaper assignment. When grade point average(GPA) was introduced as a covariant, it wasdemonstrated to have a high correlation withcomprehension. This study also showed thatin the presence of a workload, subjects gavehigher performance scale ratings when usinga video display than when using paper. How-ever, when no workload was present, partici-pants showed equal levels of confidence inthe computer and paper-based modes of infor-mation delivery. Based on their findings, theseauthors concluded that many variables mustbe taken into consideration when choosingthe best medium to disseminate information.

YOUNG, ZAVELINA, AND HOOPER

ASSESSING WORKLOAD USING THE NASA TASK LOAD INDEX 107

impacts safety. Harbuk and Noy30 studied theimpact of cognitive distraction on drivers’visual behavior and vehicle control. These re-searchers evaluated driver behavior duringhands-free cell phone use. Visual behavior,braking behavior, and perceived workloadwere assessed under easy conditions, difficultconditions, and conditions under which noadditional cognitive tasks were evaluated. Al-though results were not absolutely consistent,overall it was found that, as cognitive tasks in-creased, less attention was paid to peripheralevents and more hard-braking events oc-curred, showing that in this instance increaseddriver workload negatively impacted safety.Hubbard and colleagues31 evaluated driverperformance in several vehicles used in themining industry. Subjects were chosen to rep-resent the demographics of drivers in that in-dustry. No significant differences in skidlengths were reported for the different vehi-cles. However, the temporal demand sectionof the NASA-TLX did reveal that the vehiclepreferred by the participants was that whichwas perceived as the easiest to control.

Kaber and colleagues32 compared situationalawareness to perceived workload in a varietyof automation settings. They concluded thathuman–machine system performance wasgreater at higher levels of automation (levelsinvolving greater computer control of systemfunctions) and lower operator subjectiveworkload. Interestingly, reaction times re-vealed that operator situational awarenesswas substantially lower during certain typesof system problems or failures. In fact, thosewho performed best during automation failurewere those who had been functioning atlower and intermediate levels involvinggreater human control of system functions.

Use of the NASA-TLX in the HealthProfessions

Weinger33 used NASA-TLX along with othertools to compare anesthesia provider work-load in teaching and nonteaching cases at

Psychological Applications

Psychologists have also used the NASA-TLX tostudy the effects of task difficulty on mentalworkload.12 They reported that both time-on-task and task demand are important loadingfactors in industrial workload. These re-searchers developed a checklist of mental con-ditions (CLMC) which they used in this study.Event-related potentials (ERP) were recordedand the NASA-TLX was also used. They alsomonitored electrocardiography (ECG) to assessheart rate variability. ECG was monitored be-cause it reflected autonomic nervous systemchanges that occurred with time-on-task andtask difficulty. As expected, the NASA-TLXand ERP monitoring showed that mental work-load increased with task difficulty but not withtime-on-task. As the time-on-task increased,subjects felt more fatigued, but their heartrate actually went down. This study succeededin linking physiologic parameters to subjectivemeasures of workload assessment.

In 2002, Rose and colleagues28 used the NASA-TLX to assess the impact of personality onvigilance and workload. These researchers de-fined vigilance as the ability of observers tomaintain a high level of mental concentrationover extended periods of time. In this case, thetask itself was insignificant. Using the index todescribe how age differences reflect percep-tion of workload, Bunce and Sisa29 measuredvigilance in terms of mean performance acrossthe assignment and performance at the endcompared with the performance at the begin-ning. Although older workers performed com-parably with younger ones, they showeda greater increase in perceived workload, sug-gesting that a greater demand is placed on theattentional resources of older workers thanyounger ones in the completion of a task.

Transportation

In North America, where transportation canalmost be regarded as a natural resource,much has been reported regarding driverworkload in a variety of industries, most of itsuggesting that increased workload negatively

108 YOUNG, ZAVELINA, AND HOOPER

various phases of anesthesia administration.Workload was assessed in real time and physi-ological measures such as heart rate, proce-dural measures such as response latency toan alarm, and psychological measures suchas self-assessment and observer ratings wereevaluated. These results revealed that clinicalinstructors perceived an increased workloadduring teaching cases, reducing their capacityfor vigilance during anesthesia administration.

The NASA-TLX was also used in a study thatevaluated the use of graphic monitors for thedetection, diagnosis, and treatment of pa-tients.34 The study concluded that the graphi-cally-designed display provided good clinicalinformation, without leading to an increasein perceived workload. In fact, the researchersconcluded that providing clinical informationgraphically can improve providers’ capabilityto detect, diagnose, manage, and treat criticalcardiovascular events.

Another study assessed the reliability of NASA-TLX in evaluating the subjective mental work-load of cardiovascular critical care nurses.35

Conducted across four medical centers inthe southeastern United States, the studyrevealed considerable correlation betweensubjective mental workload and patient diag-nosis, number of assigned patients, and num-bers of days off from work.

Recommendations

Workload assessment is intended to evaluatethe extent to which a worker has engaged thecognitive and physical resources necessary fortask completion.33 Workload, multidimen-sional and complex, is affected by external, or-ganizational, psychological, cognitive, andperceptual dimensions. Assessment of work-load is essential for evaluating perceptual (sub-jective) requirements of jobs and for calculatingworkers’ capacity for further tasks. Perceivedworkload evaluation is essential to prevent fa-tigue and human errors. Concerned that cur-rently used measures of nursing workload do

not take into consideration the cognitive de-mands of patient care, Gregg35 introduced theidea of studying subjective workload amongnurses.

Like pilots, nurses function in extremelystressful and technologically advanced envi-ronments. One difference, however, is thatthe aviation industry routinely evaluates stressand workload in various human–machine en-vironments. It may then be useful for hospitalsto examine and possibly adopt the policiesput into place by airlines to assist pilots withfatigue and workload management.36 Somepolicies that may be of particular interest toperianesthesia/perioperative nurses include:

Hour limitations. Daily working hours andrest time are specified and followed.Extensive retraining. Pilots fly one type ofaircraft and are required to take extensiveretraining before using any new equipment.‘‘Get off’’ policy. Should a pilot have anydoubt about his/her ability to fly safely, thepolicy is ‘‘get off’’ first and ask questionslater. The pilot is then later referred to theoccupational health department or to otherprofessional sources.Cockpit resource management. Pilots areencouraged to take courses in com-munication skills, teamwork, and stressmanagement.

Future studies on the use of the NASA-TLX ina perianesthesia setting could help with the as-sessment of perceptual (subjective) workload.

Conclusion

Ongoing nursing staff shortages and cutbacksin staffing have resulted in increased work-load, raising important concerns about thequality of care provided.37 Such shortagescould inevitably lead to staff frustration andto a dangerous increase in the risk of pro-fessional errors. Faced with this situation,hospitals should develop a method for measur-ing increases in errors in an effort to avoidthem, while also striving to provide safe and

Refe

ASSESSING WORKLOAD USING THE NASA TASK LOAD INDEX 109

pressure, decisions that could potentially belife threatening.11 The NASA-TLX could serveas a tool for registering the cognitive demandsof patient care, allowing for a better assess-ment of workload and guarding againstincreases in it that could have a deleteriouseffect on staff morale and the quality of patientcare.

cost-effective care. The NASA-TLX has beenused to evaluate workload data in the aeronau-tical and transportation industries, in psy-chology, and in technology-related fields.However, no studies have been reported onits daily use in the health professions. Healthcare professionals routinely make a high num-ber of critical, diagnostic decisions under high

rences

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