# Early detection of deep pelvic surgical site infection by microdialysis after abdominoperineal resection for locally advanced rectal cancer

## TL;DR

This study shows that microdialysis can detect early signs of pelvic surgical infections in cancer patients, up to 9 days before diagnosis.

## Contribution

The study introduces microdialysis as a novel method for early detection of pelvic surgical site infections after rectal cancer surgery.

## Key findings

- Tissue lactate levels were significantly higher in patients who developed infections.
- The lactate-to-pyruvate ratio was 34 units higher in infected patients.
- Microdialysis detected infections with 92% sensitivity and 65% specificity.

## Abstract

Patients with locally advanced rectal cancer (LARC) treated with (chemo)-radiotherapy before abdominoperineal resection (APR) are at high risk of developing pelvic organ/space surgical site infection (O/S-SSI). This increases morbidity and prolongs length of stay. Vague symptoms delay diagnosis. In microdialysis, thin catheters are placed in tissue enabling monitoring of metabolism. We hypothesize that local metabolic changes related to O/S-SSI might be detected by microdialysis.

In a prospective observational study, 38 patients who underwent open APR for LARC were analysed. At the end of surgery microdialysis catheters were placed in remnant tissue of the pelvic floor. Postoperatively, metabolic parameters including lactate, pyruvate, glucose and glycerol were measured, and the lactate-to-pyruvate (L/P) ratio was calculated. Out of 38 patients, 12 (32%) developed O/S-SSI.

O/S-SSI was diagnosed median 9 (range 6–17) days after surgery. On the day of surgery, mean lactate in the O/S-SSI group was 6.0 mmol/L, whereas it was 3.6 mmol/L in the no-O/S-SSI group. ROC analysis (AUC = 0.73), with cut-point lactate 5.7, detected O/S-SSI with 92% sensitivity and 65% specificity. Overall mean lactate was 1.9 mmol/L higher in the O/S-SSI group than in the no-O/S-SSI group (P = 0.002). Overall mean L/P ratio was 34 units higher in the O/S-SSI group (P = 0.001).

In patients developing pelvic O/S-SSI, tissue lactate and L/P ratio measured by microdialysis were significantly higher and evident already from the day of surgery, 9 days prior to diagnosis, with high negative predictive value and moderate positive predictive value. Local monitoring using microdialysis may aid detection of O/S-SSI.