Improving the Measurement of Surgical Site Infection Risk Stratification/Outcome Detection

Exhibits 8 to 10

Exhibit 8. Distribution of SSI among surgeries in VASQIP data

  CABG   HERNIA   KNEE   HIP   TOTAL  
Total Procedures 4525   19692   7467   3867   35551  
Surgical Site Infections #SSI % Total #SSI % Total #SSI % Total #SSI % Total #SSI % Total
sSSI 108 93.1 165 74.7 61 59.2 40 51.3 374 72.2
dSSI 8 6.9 36 16.3 29 28.2 33 42.3 106 20.5
oSSI 0 0.0 20 9.0 13 12.6 5 6.4 38 7.3
Total 116   221   103   78   518  

SSI = surgical site infections, VASQIP = Veterans Affairs-Surgical Quality Improvement Program, CABG = coronary artery bypass grafting, HERNIA = herniorraphy, KNEE = total knee arthroplasty, HIP = total hip arthroplasty, #SSI = number of SSI, % Total = percent of all SSI, sSSI = superficial SSI, dSSI = deep SSI, oSSI = organ space SSI

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Exhibit 9. Preliminary performance on VASQIP training set

  CABG HERNIA KNEE HIP
Total Cases 4525 19692 7467 3867
Positive SSI TP8 FN0 TP52 FN4 TP39 FN3 TP36 FN2
Negative SSI FP402 TN4115 FP1004 TN18632 FP873 TN6552 FP295 TN3534
ID by Alg 410 4115 1056 18636 912 6555 331 3536
% Excluded by Alg 90.94 94.64 87.79 91.44
Diagnostic Accuracy
Sensitivity 100.00% 92.86% 92.86% 94.74%
Specificity 91.10% 94.89% 88.24% 92.30%
PPV 1.95% 4.92% 4.28% 10.88%
NPV 100.00% 99.98% 99.95% 99.94%
AUROC 95.60% 93.90% 90.50% 93.50%
Time Saving
NNR w/Alg 51.25 20.31 23.38 9.19
NNR s/Alg 555.56 357.14 178.57 102.04

Alg = algorithm, AUROC = area under receiver-operator curve, CABG = coronary artery bypass grafting, HERNIA = herniorraphy, ID = identified, KNEE = total knee arthroplasty, HIP = total hip arthroplasty, NNR= number needed to read, NPV = negative predictive value, PPV = positive predictive value.

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Exhibit 10. Performance of different algorithms by SSI type on the training set

  Total Surgeries sSSI dSSI oSSI
Total 35551 374 106 38
  Surgeries Flagged # Caught (Sensitivity)
Rpart Algorithm 2709 (7.6%) 156 (41.7%) 101 (95.3%) 34 (89.5%)
Inclusive Algorithm 7961 (22.4%) 328 (87.7%) 104 (98.1%) 35 (92.1%)
Simple 6939 (19.5%) 318 (85.0%) 103 (97.2%) 34 (89.5%)

SSI = surgical site infection. sSSI = superficial SSI. dSSI = deep SSI. oSSI = organ-space SSI. Inclusive algorithm looks for any high-normal value. Rpart algorithm refers to the algorithm derived using the Rpart procedure. ( ) = percentage of total

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Page last reviewed December 2012
Internet Citation: Exhibits 8 to 10. December 2012. Agency for Healthcare Research and Quality, Rockville, MD. http://www.ahrq.gov/research/findings/final-reports/ssi/ssiexh8-10.html