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Intern: 胡學錦 , 葉力仁學號 : 9200011, 9200040

日期 : 09/11指導醫師 : 陳昭文醫師

Poor Test Characteristics for the Digital Rectal

Examination in Trauma Patients

Annals of Emergency Medicine July 2007, Volume 50, NO.1 25-33

From the Department of Emergency Medicine (Shlamovitz, Mower, Crisp, DeVore, Shroff, Snyder, Morgan) and the Department of Urology (Bergman), UCLA Medical Center, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, CA; the Department of Emergency Medicine, Cedars-Sinai Medical Center, Los Angeles, CA (Hardy); and the Department of Emergency Medicine, Highland General Hospital, Oakland, CA (Sargent).

Study objective

• ATLS guidelines: DRE as part of the initial evaluation of all trauma patients.

• Our goal is to estimate the test characteristics of the DRE in trauma patients.

Methods

• A retrospective medical record review study of consecutive trauma patients treated in our ED from January 2003 to February 2005 for whom the trauma team was activated and who had a documented DRE.

Results

• 1401 p’ts met the selection criteria • Composite sensitivity of the DRE (any abnormal

finding) for detecting any of the index injuries to be 22.9% and the specificity to be 94.7%.

• The calculated sensitivity and specificity for the DRE :(1) spinal cord injury: 37% and 96% (2) bowel injury: 5.7% and 98.9% (3) rectal injury: 33.3% and 99.8% (4) pelvic fracture: 0% and 99.8% (5) urethral disruption: 20% and 99%

Conclusion

• The DRE has poor sensitivity for the diagnosis of spinal cord, bowel, rectal, bony pelvis, and urethral injuries.

• Our findings suggest that the DRE should not be used as a screening tool for detecting injuries in trauma patients.

1. INTRODUCTION: Background and Importance

• Current ATLS, emergency medicine and trauma surgery textbooks recommend DRE be performed on every trauma patient.

• Recommendations are to look for the following potential findings of the DRE:

(1) Decreased or absent anal sphincter tone as a sign of spinal cord injury

(2) Presence of rectal blood => intestinal injury(3) Disruption of the rectal wall integrity => rectal

injury(4) Palpation of bony fragments => pelvic fracture(5) Abnormal position of the prostate (high-riding)

=> urethral disruption.

Goals of This Investigation

• To estimate the test characteristics (sensitivity and specificity) of the DRE in trauma patients for the following injuries: spinal cord injury, bowel injury, rectal injury, pelvic fracture, and urethral disruption.

• Also estimated the test characteristics of the DRE (any abnormality) for detection of any of the above-listed index injuries (composite outcome).

2. MATERIALS AND METHODSStudy Design

• A retrospective medical record review study of consecutive trauma patients.

• The study protocol was approved by the institutional review board.

Setting (1)

• This study was conducted at an academic, university-based, Level I (adult and pediatric) trauma center.

• Once the trauma team is activated, the assessment and treatment of the trauma patient are provided by emergency physicians and trauma surgeons (trauma surgery history ).

• A nurse: clinical information on a preprinted trauma flow sheet.

Setting (2)

• The DRE was typically performed by a surgery resident.

• No member of the trauma surgery team or the emergency medicine staff knew about this study at trauma patient evaluation.

Selection of Participants

• All trauma patients treated in our ED from January 2003 to February 2005, for whom the trauma team was activated.

• Patients who were pharmacologically paralyzed before the DRE or who had previous spinal cord injury were excluded from the test characteristics calculation for digital rectal examination in spinal cord injuries. (Figure 1).

Data Collection and Processing

• Data abstraction methodology followed previously published guidelines include: (1) Training of data abstractors, (2) Clear def. of case selection criteria and study variables, (3) Use of a standardized abstraction form, (4) Monitoring of abstractors’ performance, (5) Blinding of data abstractors to hypothesis, (6) Calculation of interabstractor reliability,(7) Identification of the database and medical records, (8) Identification of the sampling method and missing data management plan,(9) Approval of the study by the institutional review board.

• The data abstractors were all resident physicians. Table 1. Definitions of key study variables

Primary Data Analysis

• SPSS 13.0 for Windows (SPSS Inc., Chicago, IL) was used for data analysis.

• We classified a patient as having an unknown physical examination finding when the patient underwent a DRE but had incomplete documentation of the findings.

• We performed 3 separate calculations of test characteristics:

(1) calculation based solely on recorded digital rectal examination findings (2) worst estimate (3) best estimate

3. RESULTS Characteristics of Study Subjects

• 1401 patients met our selection criteria and were included in the analysis

• Study group: 72% male patients, mean age of 36.2 years and an age range of 1 month to 94 years.

• Blunt trauma injuries: 91% of all trauma team activations, with the leading mechanism being motor vehicle collisions (40%).

• Mean Champion Trauma Score was 10.6 (range 1 to 11). and the mean Glasgow Coma Scale score was 14 (range 3 to 15).

Table 2: Demographic and clinical characteristics of study patients.

Main Results (1)• We identified:

(1) 47 patients with spinal cord injuries (3% prevalence), (2) 35 patients with bowel injuries (2%), (3) 7 patients with rectal injuries (0.5%), (4) 67 patients with pelvic fractures (5%), (5) 5 patients with urethral disruptions (0.4%).

• The composite sensitivity of the DRE (any abnormal finding) for detecting any of the index injuries to be 22.9% (95% confidence interval [CI] 16% to 30%) and the specificity to be 94.7% (95% CI 93% to 96%).

Main Results (2)

• The DRE missed (false-negative rates) 63% of spinal cord injuries, 94% of bowel injuries, 67% of rectal wall injuries, 100% of pelvic fractures, 80% of urethral disruption injuries. Figure 2 for detailed findings and calculations of test characteristics

• 243 random study subjects (17%) were independently reviewed by another data abstractor for estimation of abstractor agreement.

• The proportion of agreement between data abstractors was 0.86, and the interrater reliability of the data abstraction for DRE as measured by the k value was 0.8, suggesting excellent abstractor agreement.

To Be Continued…

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6 index injury

• 1. Spinal cord injury

• 2. Bowel injury

• 3. Rectal injury

• 4. Pelvic facture

• 5. Urethral disruption

• Composite: Any injury

DREas a screening tool

Poor !!

1. Spinal Cord injury

Poor sensitivity Poor screening tool

63 % missed!!

當 DRE 不正常時只能增加 Spinal

cord injury 的可能性 8.5 倍

當 DRE 正常時只能降低 spinal

cord injury的可能性 0.66 倍

2. Bowel injury

Poor sensitivity Poor screening tool

95 % missed!!

當 DRE 不正常時只能增加 Bowel

injury 的可能性 5 倍

當 DRE 正常時只能降低 Bowel

injury的可能性 0.95 倍

3. Rectal injury

Poor sensitivity Poor screening tool

67 % missed!!

Wide CI Because the low

prevalence of rectal injury

4. Pelvic Fracture

Poor sensitivity Poor screening tool

100 % missed!!

seems unlikely physician would document only the tone or gross blood but fail to document the palpation of bony fragments.

Therefore, the true sensitivity DRE is close to our estimation of 0% despite that 53 (79%)

5. Urethral disruption

Poor sensitivity Poor screening tool

80 % missed!!

當 DRE 不正常時中度地增加

可能性 19.4 倍

當 DRE 正常時只能降低

可能性 0.8 倍

Any injury

Poor sensitivity Poor screening tool

77 % missed!!

當 DRE 不正常時只能增加 any injury

的可能性 4.36 倍

當 DRE 正常時只能降低 any injury

的可能性 0.81 倍

無尾熊

Limiations (1/4)• The record is vulnerable to missing data.

– For example: rectal mucosal defect, palpable bony fragments, or abnormal position of the prostate was not routinely recorded.

• 補救方法 : – We perform 3 calculations of test characteristics (best

estimate, worst estimate, and estimate based on available data)

• Large changes in test performance characteristics depending on how missing data are handled.

Limiations (2/4)• Criterion standards are less than ideal.

– In an ideal study, all patients diagnosis of – spinal cord injury :C to L spine MRI– bowel and rectal injuries (endoscopy or

laparotomy)– pelvic fracture (pelvic CT)– urethral disruption (retrograde urethrogram).

• However, because these index injuries are typically symptomatic

• we believe the number of missed injuries is likely to be low.

• Such an ideal study is unlikely • The evaluation missed some injuries may

have

Limiations (3/4)

Falsely increase estimated sensitivities

• Physicians not blinded to DRE • Because DRE was not performed in isolation• Physicians more likely to record a positive

DRE in the presence of other physical findings that support the presence of an index injury

• falsely increasing our estimated sensitivities of the digital rectal examination.

Limiations (4/4)• The missing data• DRE was deferred or not recorded in 371 patients of the

1,820 trauma team activations during the study period (20%).

• 20 index injuries among those 371 excluded patients: – 6 spinal cord injury– 8 bowel injury– 6 pelvic fracture– 0 rectal injury or urethral disruption.

• Given the small number of index injuries in the excluded group

• we believe that the missing data are unlikely to alter the calculated test characteristics.

Conclusion1. Although the various limitations , we

have created a “best-case scenario” for estimating DRE

DRE

4. Our findings suggest DRE should not be used as a screening tool for detecting injuries in trauma patients.

3.DRE has poor sensitivity for the diagnosis of spinal cord, bowel, rectal, bony pelvis, and urethral injuries.

2. The true sensitivity and specificity of DRE are probably lower than we reported in this study.

Thanks for your attention!!

Unknown

• incomplete documentation of the findings

• for example: • a patient with “normal rectal tone and no

gross blood” was considered “unknown” for the presence of palpable bony fragments.

Worst and Best estimatatioons

• Worst estimations • add “unknown” cases to “normal”

group• Best estimations • add the “unknown” cases to “abnormal”

group• For example• best estimate of the sensitivity of the

DRE for diagnosing spinal cord injury• Add the single spinal cord injury patient

that was classified as “unknown” anal tone to the “decreased tone” group (considered him as a true positive).

Likelihood ratio• A likelihood-ratio test, also called LR test, is a statistical test in which

the ratio is computed between the maximum of the likelihood function under the null hypothesis and the maximum with that constraint relaxed.

• 18 歲以下小孩盲腸炎的報告所得到的幾個關鍵症狀，用概度比 (LR, likelihood ratio) 表示出來

• 反彈壓痛 (LR=3.0) ：在右下腹按壓後快速放開，如果會痛，也明顯提高可能是盲腸炎的機會﹔

• 腹痛由肚臍附近轉移到右下腹 (LR=1.9-3.1) ：這種疼痛轉移比單純右下腹疼痛更可能是盲腸炎﹔

• 概度比是一種診斷功效的表示法，在數學上的意義簡單講就是小孩盲腸炎有這個症狀與小孩盲腸炎沒有這個症狀的比例，數字越大，通常必須大於 10 ，表示越能夠當作診斷的指標。

• 譬如，在這些盲腸炎的症狀裏，腹膜炎 (diffuse peritonitis) 的蓋度比就高達 25 ，也就是說到了這個地步才診斷是盲腸炎可以說有相當高的機率不會誤診。

• Ref: http://en.wikipedia.org/wiki/Likelihood-ratio_test#Technical_introduction