Archives of Physical Medicine and Rehabilitation
Volume 90, Issue 1 , Pages 17-19, January 2009

Classification Schema of Posttraumatic Amnesia Duration-Based Injury Severity Relative to 1-Year Outcome: Analysis of Individuals with Moderate and Severe Traumatic Brain Injury

Presented to the International Neuropsychological Society in February, 2008, Honolulu, HI.

  • Risa Nakase-Richardson, PhD

      Affiliations

    • James A. Haley Veterans Affairs Medical Center, Tampa, Florida
    • Corresponding Author InformationReprint requests to Risa Nakase-Richardson, PhD, James A. Haley Veterans Hospital, Psychology Service (116B), 13000 Bruce B. Downs Blvd, Tampa, FL 33612
    • ,
  • Arash Sepehri, MA

      Affiliations

    • Methodist Rehabilitation Center, Jackson, MS
    • University of Mississippi Medical Center, Jackson, MS
    • ,
  • Mark Sherer, PhD

      Affiliations

    • TIRR Memorial Hermann, Houston, TX
    • Baylor College of Medicine, Houston, TX
    • ,
  • Stuart A. Yablon, MD

      Affiliations

    • Methodist Rehabilitation Center, Jackson, MS
    • University of Mississippi Medical Center, Jackson, MS
    • ,
  • Clea Evans, PhD

      Affiliations

    • Methodist Rehabilitation Center, Jackson, MS
    • University of Mississippi Medical Center, Jackson, MS
    • ,
  • Tanja Mani, PhD

      Affiliations

    • Methodist Rehabilitation Center, Jackson, MS
    • University of Mississippi Medical Center, Jackson, MS

Article Outline

Abstract 

Nakase-Richardson R, Sepehri A, Sherer M, Yablon SA, Evans C, Mani T. Classification schema of posttraumatic amnesia duration-based injury severity relative to 1-year outcome: analysis of individuals with moderate and severe traumatic brain injury.

Objective

Early investigations classified traumatic brain injury (TBI) severity according to posttraumatic amnesia (PTA) duration, designating “greater than 7 days” as the most severe. PTA durations of more than 7 days are common in neurorehabilitation populations. Moreover, no study has derived a PTA severity schema anchored to late outcome. The purpose of this study was to develop a PTA severity classification schema.

Design

Prospective observational study.

Setting

Rehabilitation hospital.

Participants

Sample included TBI Model System participants (N=280) with known or imputed PTA duration during acute hospitalization and 1-year productivity status. Participants were primarily male (70%), median age of 27 years; and the most common mechanism of injury was motor vehicle collisions (79%). For study purposes, 4 injury severity groups were identified by observing differences in productivity associated with different PTA durations.

Interventions

None.

Main Outcome Measure

Productivity status at 1 year postinjury.

Results

Fisher exact test comparisons revealed significant differences among 3 of the groups. Most individuals with PTA fewer than 14 days had favorable 1-year outcome (68% productive), whereas worse outcomes were associated with PTA more than 28 days (18% productive).

Conclusions

If validated by other investigators, the proposed schema will be useful in determining prognosis for late functional status based on PTA duration.

Key Words: Brain injuries, Classification, Rehabilitation

List of Abbreviations: GCS, Glasgow Coma Scale, GOAT, Galveston Orientation and Amnesia Test, PTA, posttraumatic amnesia, TBI, traumatic brain injury

 

POSTTRAUMATIC AMNESIA, defined as the period from injury until resumption of the ability to store new memories early after a TBI, remains an important index for classification of injury severity.1, 2, 3 PTA duration is more predictive of outcome than other early injury indices, such as GCS score.4, 5, 6 It is also related to the extent of atrophy after TBI.7 In general, more severe brain injury is associated with longer duration of PTA.

Russell's original schema1, 2, 3 of PTA duration classified TBI severity into 4 groups (mild, <1h; moderate, 1–24h; severe, 1–7d; very severe, >7d). At the time1, 2, 3 (approximately 1932-61), there was no other type of severity rating for brain injury such as GCS. Russell's initial studies with military personnel derived PTA duration from patient report of preinjury and postinjury recall of memories. He later reported that longer duration is associated with poorer outcome, including return to service duty.8 His proposed schema continues to be commonly used by clinicians and in the scientific literature. Using PTA as a continuous variable, more recent studies have also confirmed that longer PTA duration is associated with greater disability and handicap.6, 9, 10, 11

Clinical experience and several recent investigations call Russell's injury severity intervals into question.8, 12, 13 Very severe TBI (PTA duration>7d) is commonly observed among patients in neurorehabilitation settings and encompasses a broad range of potential late outcomes.6, 11, 12, 13, 14 Ideally, classification of patients into severity-based categories would confer better prognostic specificity for persons with more severe TBI. Accordingly, Jennett and Teasdale15 proposed classifying prolonged PTA durations of 1 to 4 weeks as “very severe” and more than 4 weeks as “extremely severe.” Although widely cited, these PTA severity classification schemas have not been validated by other investigators. Although studies have found relationships between cut-points of PTA and outcomes, no attempts have been made to examine intervals for the purpose of developing a classification schema using PTA duration.13, 16, 17 Thus, the purpose of this study was to empirically derive a TBI severity classification schema based on PTA duration by examining productivity outcomes at 1 year postinjury.

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Methods 

Participants 

The study population consisted of all TBI Model Systems participants admitted to a freestanding neurorehabilitation hospital from January 1999 through December 2006 (see Gordon et al18 for TBI Model System inclusion and exclusion criteria). Of 404 qualified participants, persons who were nonproductive prior to injury (n=79), had missing follow-up data (n=42), or who emerged from PTA prior to rehabilitation admission with missing PTA data (n=3) were excluded, resulting in a final study sample of 280. The study sample was primarily male (n=196; 70%), median age of 27 years (range, 16–82y) and most had completed high school (n=169, 60.4%). Severe TBI, as classified by emergency department GCS score, composed most of the sample (n=184, 65.7%), with fewer moderate (n=57, 20.4%) and mild (n=39, 13.9%) injuries. Median time from injury to rehabilitation admission was 20 days (range, 5–91d). Primary mode of injury was motor vehicle–related (n=220, 78.6%).

Measure 

Galveston Orientation and Amnesia Test.19 

The GOAT is a 10-item measure that assesses orientation as well as memory for events before and after TBI. Areas of orientation include biographical information, place, time, and current circumstances. Error points are assigned for incorrect responses. Total error scores can range from 0 to 108, with higher error scores indicating poorer orientation. Error scores are subtracted from 100 to determine a GOAT score. Inter-rater reliability has been found to be excellent (correlation coefficient=.99).9 The GOAT has been used to determine the duration of PTA in numerous studies of TBI. PTA duration was defined as the interval from injury until 2 consecutive observations were obtained within a period of 24 to 72 hours in which a patient scored in the target range on the GOAT (≥76).

Procedure 

Trained TBI Model System research assistants collected information from hospital and emergency medical service records about injury severity (GCS scores, time to follow commands) and medical course. Demographic information such as date of birth, education, and employment were collected in interview with the subjects or family/significant others. Emergence from PTA was assessed prospectively by repeated GOAT until 2 consecutive nonconfused scores were achieved (score≥76). For persons who were admitted to rehabilitation having already emerged from PTA, a chart review procedure that documented 2 days of consistent orientation was used.20, 21 Using these procedures, 74% (n=206) of cases had observed PTA durations, with 18% using the chart-review procedure. For all remaining participants 82% (n=169), PTA duration was prospectively monitored using the GOAT procedure, with 74 (26%) being discharged from inpatient rehabilitation in PTA. To minimize missing data, length of PTA was calculated as the length of stay plus 1 day for persons discharged from inpatient rehabilitation still with PTA.13 Although this procedure underestimates true PTA duration for many participants, it permits inclusion of participants with the most severe injuries and has been used in previous research.13 Exclusion of persons whose PTA did not resolve by rehabilitation discharge would bias the sample to those with less severe injuries. Subjects were contacted 1 year postinjury to assess their current level of functioning, including productivity status (ie, full- or part-time competitive employment); full- or part-time school enrollment; homemaker status as previously defined in TBI Model System outcomes research.9, 10

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Results 

Of 280 eligible participants, 74 were discharged from inpatient rehabilitation still in PTA and thus had PTA imputed using length of stay (acute and rehabilitation) plus 1 day. Of 280 participants, 93 (33%) were productive at 1 year postinjury. Injury severity groups were created by selecting PTA cut-points that resulted in a moderately injured group with approximately twice the likelihood of being employed at follow-up as the overall sample, a moderately severely injured group with approximately one third greater likelihood than the overall group of being employed at follow-up, a severely injured group with approximately one third less likelihood of being employed, and an extremely severely injured group with very low likelihood of being employed at follow-up.

These outcome categories were selected because they are clinically meaningful and because they roughly compare with outcome groupings found by Dikmen et al22 in a study examining the association between time to follow commands and employment outcome. Using this methodology, persons with PTA durations of 0 to 14 days were classified as moderate, 15 to 28 days were classified as moderately severe, 29 to 70 days were classified as severe, and more than 70 days were classified as extremely severe. Table 1 shows age, years of education, GCS, time to follow commands, and number (percent) productive at 1 year for each of these 4 severity groups. Using Fisher's exact test, significant differences were found in productivity status except between groups 3 and 4. Kruskal-Wallis comparisons found significant differences among groups for education, GCS, and time to follow commands. Post hoc comparisons found that all groups differed significantly on time to follow commands. GCS was not significantly different between groups 2 and 3. Finally, education was only significantly different between groups 1 and 3.

Table 1. Description of PTA Classification Intervals, Group Demographics and Injury Severity, and FET Comparisons
GroupsnPTA (d)AgeEDUGCSTFCPRO P (%)Group Comparison PClassification
1234
1520–1432±1413±0211±0302±0236(68)—.006⁎.000⁎.000⁎Moderate
27015–2831±1412±0208±0405±0429(41)——.004⁎.000⁎Moderate severe
311329–7034±1511±0307±0313±1024(21)———.103Severe
445>7028±1212±0305±0234±3004(9)————Extremely severe

NOTE. P denotes FET P for PTA duration group comparison. Values for age, EDU, GCS, and TFC are means ± SDs.

Abbreviations: EDU, years of education; PRO, productivity rates (number productive and percent for subgroup); FET, Fisher exact test; GCS, Glasgow Coma Scale score on emergency room admission; TFC, time until patient consistently followed commands.

⁎Significant.

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Discussion 

The purpose of this study was to empirically derive a TBI severity classification schema based on PTA duration. Results of this study and others indicate that the schema proposed by Russell et al1, 2, 3 that collapsed all persons with PTA more than 7 days into a single category as very severe does not reflect important variations in outcomes for those with longer PTA durations. For brain injury survivors with 15 to 28 days of PTA, 41% were able to return to productivity at 1 year postinjury. More recent classification schemas group all persons with PTA more than 28 days.15 Accordingly, we did not find statistically significant differences between the severely injured group (29–70d of PTA) and the extremely severely injured group (>70d of PTA). Perhaps the relative differences in group sizes may have contributed to the lack of a statistical difference because the last interval only included 45 subjects. However, there were clinically meaningful differences between these 2 groups. Specifically, patients with PTA durations of 29 to 70 days returned to work by 1 year at the rate of 21%, whereas only 9% with PTA more than 70 days returned to productivity. Replication studies may help distinguish the relative distinction of the latter 2 proposed PTA intervals.

Although productive employment outcome at 1 year postinjury is highest (69% productive) for those in the moderate group (<14d of PTA), not all persons in this group returned to productive status at 1 year. This is similar to studies using older classification schema.8, 23, 24 Injury severity along with other factors influences employment outcome after TBI.9, 10, 11, 25 Although this study restricted the sample to persons who were productive before injury, other variables such as preinjury demographics (ie, education) and environmental support likely influenced employment outcome, as has been demonstrated in previous studies.11, 22

Study Limitations 

Injury severity cut-points are notorious for being sample-specific. Although other severity indices distinguished the groups as expected (ie, time to follow commands and GCS). The current study only included persons admitted for inpatient rehabilitation, who are likely to have more severe injuries and poorer outcomes than those not requiring this intensity of therapy after TBI. Actual PTA durations were missing for 26% of the sample because they were still in PTA at rehabilitation discharge. The impact of estimating PTA for these persons as total hospital length of stay plus 1 day was moderated to some degree by the fact that 73 (97%) of those discharged in PTA were in the severe or extremely severe categories, with 36 (48%) in the extremely severe category. Even if actual PTA durations had been obtained, many of these participants would have remained in the same severity category, and only 2 could have changed by more than 1 category.

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Conclusions 

The cut-points proposed by this investigation require validation in independent samples.

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References 

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 Supported by the National Institute on Disability Rehabilitation and Research (grant no. H133A020514).

 No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit on the authors or on any organization with which the authors are associated.

PII: S0003-9993(08)01542-6

doi:10.1016/j.apmr.2008.06.030

Archives of Physical Medicine and Rehabilitation
Volume 90, Issue 1 , Pages 17-19, January 2009

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