A spectrophotometric method for determining residual protein levels on reusable surgical instruments: a comparison of six washing methods of instruments with an internal lumen.

Aim: Washing is a multistep process and a critical step in the sterilization of reusable instruments used in surgery. The complexity of the design of some types of instruments, such as those with a lumen, is a major challenge, both in terms of cleaning and of checking their cleanliness.The aim of this study was to validate a new approach to compare washing methods of reusable instruments with internal lumen. This approach was then tested to compare six methods for washing reamers. Methods: The proposed method was based on detection by Soiltest®, a commercially available soiling test, using ninhydrin in a spectrophotometric approach at 570 nm. To increase the sampling yield of conventional swabbing, we used new wash brushes for each sampling. Results: Soiltest® results were linearly quantified with a quantitative and reproducible method. The equation of calibration curve was Y=0.2043X-0.03489, the coefficient of determination was 0.9926, and the slope was significantly different from zero (p<0.0001, F-test). The optimal cleaning method for reamers was a combination of chemical detergents, manual cleaning ensuring that no obstruction is present in the instrument, and mechanical washing in a washer-disinfector with a system of continuous irrigation of the lumen of the instrument. Conclusion: This study validated a new approach to evaluate the cleanliness of critical reusable surgical instruments with lumen based on the detection of protein residues using Soiltest®, by means of a colorimetric method using ninhydrin.