Port cleaning methods

Three previously reported port cleaning methods with surgical gauze already were selected in this study. The first method uses a 30 × 30 cm large surgical gauze (sterilized opegauze G; Hakuzo Medical, Osaka, Japan) wrapped around the 180-mm surgical forceps, and the second method is a 30 × 30 cm large surgical gauze wrapped around the laparoscopic forceps (CLICK line, K33310CC; Karl Storz, Tuttlingen, Germany), and the third method uses a 3 × 15 cm small laparoscopic gauze (laparogauze G; Hakuzo Medical, Osaka, Japan) wrapped around the laparoscopic forceps (Fig. 1a). Two dedicated cleaning devices, a cylinder-type cleaner and a swab-type cleaner, were used (Fig. 1b, c).

Fig. 1

Port cleaning methods. a Three cleaning methods with surgical gauze. b Dedicated cleaning devices for 12-mm port. c Dedicated cleaning devices for 5-mm port

The standard 12-mm and 5-mm laparoscopic ports (Versa One; Covidien) were used in this study. To simulate the surgical environment, we used pseudo-blood (Mock Blood Venous; Limbs&Things, Bristol, UK) to smudge the port as reported in the past [5]. The pseudo-blood was injected into the tip of the port sleeve using 0.2 ml for the 12-mm port and 0.08 ml for the 5-mm port, and then it was turned sideways. The port was then tilted and pseudo-blood was extended to the sleeve, 10 cm from the port tip for the 12-mm port, and 7 cm for the 5-mm port. Finally, the port was rotated 2.5 times to create uniform smudge. The cleaning was then attempted by passing the gauze/forceps through and out of the port three times.

Quantification of port cleanings test using UV spectrophotometer

We quantified the amount of pseudo-blood remaining in the port after cleaning by measuring the absorbance of the pseudo-blood using a UV spectrophotometer (V-630UV spectrophotometer; JASCO, Tokyo, Japan). First, the absorbance of adhering to the ports was measured before cleaning as a control. The ports with adherent pseudo-blood were immersed in pure water (12-mm port: 50 mL pure water, 5-mm port: 20 mL pure water) and the absorbance of this solution was measured (500 nm). This procedure was repeated five times and the median value was defined as the control for the absorbance of the pseudo-blood on a pre-cleaning port. The same procedure was performed after the above five different methods of port cleaning and the absorbance was measured. Finally, the ‘port cleaning rate’ was calculated using the following formula.

$$Port\;cleaning\;rate\left( \% \right) = \frac \right) - \left( \right)}}} \times 100$$

At each typical port cleaning rate after port cleaning (95%, 90%, 80%, 60%), how the laparoscopic image would look clinically was evaluated when the laparoscope was actually used in live swine models under general anesthesia.

Comparison of port cleaning rates by single use

To compare single-use port cleaning rates, all five methods described above were performed five times each for cleaning the 12-mm port. For cleaning the 5-mm port, a 30 × 30 cm large surgical gauze could not be used, so only three other methods (small laparoscopic gauze + laparoscopic forceps, a cylinder-type cleaner, and a swab-type cleaner) were used five times each.

Comparison of port cleaning durability by multiple use

The durability of the dedicated cleaning devices was assessed after continuous use. The port cleaning rates were calculated after the first, third, and fifth use of the same device, respectively. This series of procedures was performed five times and the degree of reduction in the cleaning rate was compared between the two devices.

Assessment for the contact of dedicated cleaning devices with port sleeves during cleaning

Contact load tests and the microfocus CT were performed to confirm the contact between the two dedicated devices and the port sleeve during cleaning procedures. The contact load was measured using a tension and compression testing machine. (SVZ-50NB-20R1; Imada Corporation, Aichi, Japan) (Fig. 2). The port was set in the fixture and the cleaning device was attached to the load cell straight on the movable axis. The port valve was removed, since this study was to measure the contact load between the device and the port sleeve. The tension and compression testing machine was moved at a constant speed (100 mm/min), and the maximum contact load (N) when the device was inserted/extracted was measured five times.

Fig. 2

The method of contact load test. The port was set in the fixture and the cleaning device was attached to the load cell straight on the movable axis. The tension and compression testing machine (SVZ-50NB-20R1; Imada Corporation, Aichi, Japan) was moved at a constant speed (100 mm/min), and the maximum contact load (N) when the device was inserted/extracted was measured

Non-destructive CT imaging was also performed using MCT225 micro-CT scanner (NIKON SOLUTIONS CO., LTD., Tokyo, Japan) to visualize the contact area when the device was inserted into the port.

Water absorption measurement of dedicated cleaning devices

To assess the blood absorption capacity of the two dedicated cleaning devices, water absorption measurements were performed on each device. The water absorption was measured only on the part of cotton swab for a swab-type cleaner. For a cylinder-type cleaner, it was measured on the identical portion to the cotton swab portion (3.3 cm for the 12-mm port and 1.2 cm for the 5-mm port). The water absorption was simply calculated as the increase in weight when the cleaning part of the device was immersed in water.

Statistical analysis

Statistical analyses were performed using a dedicated statistical software package (JMP version 17.0.0; SAS Institute, Cary, NC, USA) on a universal personal computer. Data were given as the mean ± standard error (SE). Statistical differences for comparison of port cleaning rates by single use, the contact loads, and water absorption were calculated by using the t-test. Comparison of port cleaning durability by multiple use between one time and five times was analyzed using paired t-test. A p-value of < 0.05 was considered statistically significant.