Continuous controllable balloon dilation: a novel approach for cervix dilation

Abstract

Background: Cervical dilation using mechanical dilators is associated with various complications, such as uterine perforation, cervical laceration, infections and intraperitoneal hemorrhage. To achieve safe and painless cervical dilation, we constructed a new medical device to achieve confident mechanical cervical dilation: a continuous controllable balloon dilator (CCBD).

Methods: Controlled pumping of incompressible fluid into the CCBD increases the pressure and outer diameter of the CCBD, continuously dilating the cervical canal. The reliability of the CCBD was confirmed in vitro (testing for consistency and endurance, with no detected risk for breakage) and in vivo. A multi-center clinical study was conducted,with 120 pregnant women randomly assigned to one of three groups: Group I,control group, no dilation;Group II,mechanical dilation, Hegar dilator (HeD); and Group III,CCBD. The tissue material for histological evaluation was obtained from the endocervical mucosa before and after dilation using the HeD or CCBD.

Results: The CCBD dilations were successful and had no complications in all 40 patients of Group III. The cervical tissue was markedly less damaged after CCBD dilation compared with HeD dilation (epithelium damage: 95% (HeD) vs. 45% (CCBD), P <0.001; basal membrane damage: 82.5% (HeD) vs. 27.5% (CCBD), P <0.001; stromal damage: 62.5% (HeD) vs. 37.5% (CCBD), P <0.01). Cervical hemorrhagia was observed in 90% of the patients after HeD dilation versus in 32.5% of the patients after CCBD dilation.

Conclusions: The CCBD should be used as a replacement for mechanical dilators to prevent uterine and cervical injury during cervical dilation.

Trial registration: ISRCTN54007498.

Figure 1

System for continuous controllable balloon dilation. (A)The continuous controllable balloon dilator (CCBD) system for cervical dilation. (B) Image of the CCBD. (C) CCBD with an uninflated BD (a) and an inflated BD (b). (D) The calculation of cervical resistance during cervical dilation using the CCBD: line 1, change in pressure during in vitro balloon dilation; line 2, change in pressure during in vivo cervical dilation using the CCBD; line 3,difference in the change in pressure between the in vivo and in vitro experiments, which represents the resistance of the cervical tissue to CCBD dilation. (E) Pictures of the phases of in vivo cervical dilation using the CCBD (after 10, 15, 20 and 25 seconds). (F) The comparative results of CCBD cervical dilations for three representative patients: P1, the cervical resistance of Patient 1 was depressed after 23 seconds with a pressure of 3.8 bars; P2, the cervical resistance of Patient 2 was depressed after 22 seconds with a pressure of 1.4 bars; P3, the cervical resistance of Patient 3 was depressed after 21 seconds with a pressure of 1.1 bars.

Figure 2

Biophysical phenomena during cervical dilations. (A) Biophysical model of Hegar dilator (HeD) dilatation. Under external force F_e (required to dilate the cervix at each stage of dilation), the dilator of diameter D_i moves at speed v through the cervical canal having length L. F_e must overcome the resultant sum of forces that appeared in the direction of HeD movement. During dilation with the N⁰9 HeD (diameter D_i = 9 mm) the mean recorded value of external force ${\bar{F}}_e$was 11 N (with vaginal sodium nitroprusside (SNP) gel) and 17 N (with vaginal misoprostol) [A]. The mean recorded ${\bar{F}}_e$ during dilation with the N⁰10 HeD (diameter D_i = 10 mm)was 13 N [B]. The mean ${\bar{F}}_e$ required to complete cervical canal dilation points to the complex biophysics of processes in the contact zone of tissue and the HeD. HeD motion along the cervical canal (length L) in the direction of the internal uterine os leads to changes in geometry of the cervical canal. Tissue, in different ways, opposes this change of geometry in contact with the HeD, characterized by the pressure distribution p(x). (B) Biophysical model of balloon dilatation (BD) by continuous controllable balloon dilator (CCBD). (a) Initial BD form diameter is approximatelyD_i ≈ 4.5 mm,enabling insertion into the cervical canal with very low resistance to penetration. (b) Pumping of incompressible fluid in the BD leads to increased pressure and outer diameter of the BD, causing dilatation of the cervical canal. The dilatation process is performed simultaneously on the entire length (L) of the cervical canal, where relative movement (sliding) between the tissue/BD contact pair is almost reduced to zero. In this case the cervix tissue opposes less the change in geometry characterized by p(x).

Figure 3

Cervical tissue damage after Hegar dilator and continuous controllable balloon dilator dilation. (A) Percentage of patients with cervical epithelial damage. There was a statistically significant difference in the percentage of epithelial damage between the cervices dilated using the Hegar dilator (HeD) and the cervices dilated using the continuous controllable balloon dilator (CCBD). Mean ± standard error, n = 40 per group, P <0.001. (B) Percentage of patients with cervical basal membrane damage. There was a statistically significant difference in the percentage of basal membrane damage between the cervices dilated using the HeD and the cervices dilated using the CCBD. Mean ± standard error, n = 40 per group, P <0.001). (C) Percentage of patients with cervical stromal damage. There was a statistically significant difference in the percentage of stromal damage between the cervices dilated using the HeD and the cervices dilated using the CCBD. Mean ± standard error, n = 40 per group, P < 0.001).

Figure 4

Extent of cervical hemorrhagia after Hegar dilatorand continuous controllable balloon dilator dilation. (A) A semiquantitative determination of representative samples. Intraepithelial, subepithelial and stromal bleeding was observed after Hegar dilator (HeD) dilation (a) compared with intraepithelial hemorrhagia observed after continuous controllable balloon dilator (CCBD) dilation (b). (B) Percentage of patients with cervical hemorrhagia after HeD and CCBD dilation. A significant difference in the extent of cervical hemorrhagia was observed between the nondilated and HeD-dilated patients. Mean ± standard error, n = 40 per group, P <0.01. There was no significant difference in the extent of cervical bleeding observed between the nondilated and CCBD-dilated patients. The extent of cervical hemorrhagia was significantly lower after CCBD dilation compared with HeD dilation. Mean ± standard error, n = 40 per group, P <0.01.