In order to overcome the risks of bowel or vascular injury during blind entrance to the Pouch of Douglas (POD), ultrasound and other imaging modalities have been investigated and the ultrasound technique can be easily learned by surgeons.  In this study we hypothesized that in patients without suspected history of POD obliteration, blind POD entry for the purposes of creating a surgical port using a transvaginal trocar can be feasible. This concept has previously been tested in an Ovine Model. As such we chose to test our hypothesis on female frozen cadavers to demonstrate safe angles for entry of the trocar into POD.

Four fresh frozen cadaveric specimens with an intact uterus were identified.  Laparotomy incisions were made and the abdominal content was packed cephalad in the upper abdomen.  Posterior fornix was grasped 3 cm posterior to the cervix with an Alice clamp.  The distance between S2 and POD was measured. The Alice clamp effectively provided traction and kept the rectum posterior to the entry point.  A 2 cm incision was made between the posterior cervix and the Alice clamp.  An 11 mm trocar (Ethicon ENDOPATH Excel) was placed at the incision site and maximum pressure was exerted, horizontal to the axis of the bed, to the extent that the tip of the trocar tented the peritoneum. The distance between the S2 and the trocar tip under the peritoneum was measured.  The S2 was designated at zero centimeters. The trocar tip movement of POD with pressure was: Difference = (sacrum to POD with pressure) - (Sacrum to POD).   At this point, the trocar was advanced to puncture the peritoneum and pointed anteriorly to clear the sacrum and the bifurcation of the major vessels.  The angle required to safely clear the sacral blood vessels was measured. 
The trocar insert was removed and passing the measuring tape through the trocar, the distance between S2 and the hymen was measured as a direct line. The POD distensibility was calculated as % Change = Difference / Sacrum to the hymen.  The mean of these measurements was calculated.  The above procedure was repeated with robotic trocars (Memic Innovative Surgery, Israel) and measurements were obtained.  The Memic trocar is a specialized trocar that has a needle tip that engages to prevent movement of the peritoneum.

The average age of cadavers was 60.  With the full deployment of the trocar in the POD, the tip of neither trocar was less than 2 cm away from the sacrum before it had to be curved anteriorly to clear the sacrum.  With removal of the trocar insert at full deployment and pressure, this distance increased to 4 cm.   The average distance for sacrum to the hymen, sacrum to cul de sac, and sacrum to POD with pressure were respectively, 18.75, 9.75, and 7.25 cm respectively. After the deployment of the trocar, the tip was 2 cm below the cervix at the POD (Table 1).  The distance between the sacrum and the POD with the application of trocar pressure was reduced on 35% on average. The mean trocar angle to clear the sacral promontory and neurovascular structures without injury to the uterus was 25-40 degrees from the horizontal plane, and 15-30 degrees from the mid-sagittal plane (Fig 1).

In this fresh-frozen cadaveric study, the technique for direct laparoscopic trocar entry into the POD is validated.  It is shown that with appropriate technique and angulation of the trocar, the rectum and sacral vascular structures can be avoided.  This technique needs to be authenticated in the clinical setting for patients undergoing laparoscopic or robotic vNOTES surgeries.

The aim of the current study was to investigate if transvaginal direct pouch of Douglas entry using a laparoscopic trocar.   This concept is important as the use of the POD as surgical port access has gained popularity for both vNOTES surgeries [10-13] and vaginal robotic surgery.   This is particularly important as POD port of entry affords enlargement of the port for primary surgeries such as hysterectomy, bladder repair, ureteroneocystostomy or adnexectomy, or large tissue extraction without the need for additional abdominal incisions.

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Sheth, S.S., K.P. Paghdiwalla, and A.R. Hajari, Vaginal route: a gynaecological route for much more than hysterectomy. Best Pract Res Clin Obstet Gynaecol, 2011. 25(2): p. 115-32.
Bernhardt, J., et al., Update in natural orifice translumenal endoscopic surgery. Current opinion in gastroenterology, 2017. 33(5): p. 346-351.