1 Center for Surgical Technologies, Faculty of Medicine and 2 Department of Obstetrics and Gynaecology, University Hospital Gasthuisberg, Katholieke Universiteit Leuven, Leuven, Belgium, 3 Department of Prenatal Medicine and Therapy, Allgemeines Krankenhaus Barmbek and 4 Universitäts-Krankenhaus Eppendorf, Hamburg, Germany
![]() |
Abstract |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Key words: bipolar coagulation/monochorionic twins/rabbit/sheep/umbilical cord
![]() |
Introduction |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
![]() |
Materials and methods |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
|
Then the formal rabbit experiment was set up to determine the safety of bipolar coagulation under water in terms of vessel perforation. Thirty-six does were used for this purpose. After pre-medication with ketamine 50 mg/kg i.m. (Ketalin®; Apharmo, Arnhem, The Netherlands) and promazinum hydrochloridium 5 mg/kg i.m. (Prazine®; Libamedi, Brussels, Belgium), animals were placed under general anaesthesia using halothane (23%) in oxygen 1 l/min. The animals were positioned in a supine position and the abdomen was shaved under continuous aspiration. A midline abdominal incision was made and the uterus, bladder and bowels were displaced. An endotrainer (Ethicon Endosurgery, Dilbeek, Belgium) was placed over the rabbit, to stabilize a 5 mm endoscope connected to a light cable, light fountain and videocamera (Karl Storz). The animal's abdominal wall was suspended with six stay sutures to the top of the endotrainer. As a result, the peritoneal cavity could be filled with 500 ml of Hartmann's solution, warmed up to 37°C. Whenever needed to improve vision, fluid was replaced using a prototype irrigator (Amniomat; Karl Storz).
For this part of the study, power was pre-set either to 15 or 25 W and bipolar coagulation was applied for time intervals of 15 s with pauses of 10 s. The effect of coagulation was assessed by visual control: a vessel was considered to be coagulated when blanching and shrinking occurred, and, in the case of an artery, if no pulsations could be seen distal to the impact site. The main outcome measure of this study was the occurrence of vessel perforation.
Studies in the fetal lamb
Two series of experiments were conducted in fetal lambs. In the first one, several forceps were tested with a fixed power setting, and in the second the same forceps was tested with variable power settings.
For the first experiment, the 2.7 and 2.2 mm (Imagyn), 2.3 mm (Autosuture), and 2.5 mm prototype (Storz) were used. Eleven pregnant ewes with a total number of 15 fetuses and gestational ages ranging from 120 to 140 days (term = 145 days) were used. Pre-operative sedation consisted of xylazine 0.4 mg/kg and atropine 10 µg/kg i.m. After induction with ketamine 15 mg/kg i.v., general endotracheal anaesthesia was maintained with halothane 1.53.0% in 100% oxygen under maternal monitoring (heart rate, temperature and ventilatory parameters). Prior to the procedure 1 l pre-load of Hartmann's solution was given i.v. A lower midline laparotomy was performed, the number and position of the fetuses were assessed by ultrasound, and one pregnant uterine horn was partly exteriorized. Two purpose-designed 5 mm ports were placed, the first one for a 5 mm fetoscope and the second allowing the use of 3 mm instruments, both being inserted through mini-hysterotomy as previously described (Deprest et al., 1995). A temperature probe (Tissue Implantable Thermocouple Microprobe IT-18; Physitemp Instruments Inc., Clifton, NJ, USA) was inserted into the amniotic cavity through a 14-gauge angiocatheter to monitor the temperature of the amniotic fluid at 1 and 4 cm from the site of coagulation. The umbilical cord was grasped at about 5 cm from its fetal insertion. A power setting of 25 W for coagulation was applied during 30 s with pauses of 15 s. Cessation of flow was assessed by colour Doppler (Aspen®; Acuson, Erlangen, Germany). Main outcome measures were total duration of coagulation needed for effective occlusion as evaluated by colour Doppler, increase in temperature of the amniotic fluid at 1 cm and 4 cm from the coagulation site, measured at the end of each coagulation attempt and perforation rate. Effective occlusion was later confirmed by flushing the coagulated cord after delivery.
In the second experiment, the 2.7 mm prototype (Storz) was used. Eight pregnant ewes with a total number of 10 fetuses, with gestational age ranging from 88 to 120 days, were used. Pre-operative sedation consisted of xylazine 0.2 mg/kg and atropine 1 mg i.m. After induction with barbiturate, general endotracheal anaesthesia was maintained with isoflurane 11.5% in 100% oxygen under maternal monitoring using an arterial catheter (tibial artery: heart rate, blood pressure, blood gases). Prior to the procedure, 0.5 l pre-load of 5% glucose solution was given i.v. Surgical exposure of the uterus and introduction of trocars, endoscope and forceps was performed as detailed above, but in these experiments no temperature probe was used. After grasping the cord, bipolar coagulation with power settings of either 10, 20 or 35 W was applied for periods of 120180 s with pauses of 15 s. Cessation of flow was assessed by colour Doppler and by cutting the cord after coagulation. Main outcome measures were total duration of coagulation needed for effective occlusion as evaluated by colour Doppler and perforation rate.
Animals were treated in accordance with current guidelines on animal well-being, and the experiments were approved by the Ethical Committees for Animal Experimentation of the Faculty of Medicine of the Katholieke Universiteit Leuven and the Public Health Institution of the State of Hamburg.
![]() |
Results |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Results of bipolar cord coagulation in fetal lambs using several forceps and with power set at 25 W are displayed in Table II. The mean diameter of the cords was 13 mm (range 1016). Successful interruption of flow was achieved in all cases and no perforations occurred with 2.7, 2.5 or 2.3 mm forceps. However, coagulation with the 2.2 mm forceps caused perforation at the time of removal of the blades in the first two cases. Further experiments with this size forceps were therefore abandoned. The mean increase in temperature with respect to basal values at the end of a 30 s interval was 12.9°C (range 5.421.4) at 1 cm from the coagulation site and 3.4°C (range 0.26.4) at 4 cm. Temperature changes were very similar irrespective of the forceps used. The temperature returned to the initial value within 5 s after the peak in all cases.
|
|
![]() |
Discussion |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Bipolar coagulation of the umbilical cord represents an alternative technique to fetoscopic cord ligation. It requires less operation time and manipulation, and can be carried out under ultrasound guidance through a single port. Small diameter forceps now available may represent the possibility to further reduce the invasiveness of the procedure by reducing the port size, but safety concerns should first be addressed. Ideally, coagulation should seal the cord vessels but carbonization must be avoided as well as sticking of the blades to the cord tissue. This may lead to vessel perforation during coagulation or at the time of removal, which is by definition associated with fetal haemorrhage. Small volumes of blood loss early in gestation may be fatal for the fetus, and as both circulations are connected in twin gestations, even more so for the second fetus. Another point of concern is the heat production and subsequent elevation of fetal temperature, neither of which has yet been assessed in experimental conditions.
This study provides evidence that an endoscopic bipolar forceps with an outer diameter between 2.3 and 2.7 mm can be used safely and reliably in underwater conditions. Power setting, duration of coagulation and pauses between coagulation in sheep were established according to preliminary data obtained in the rabbit model. Results from the sheep experiments suggest that the use of a moderately low power setting with pauses between coagulation intervals avoids the risk of too high temperatures at the coagulation site, resulting in tissue protein denaturation rather than carbonization, and makes perforation extremely unlikely. On the other hand, too high power settings are likely to increase the likelihood of perforation. Reducing considerably the power setting (i.e. 10 W) resulted in ineffective permanent occlusion in spite of apparent interruption of flow by Doppler ultrasound. The coagulation time required to achieve effective cord occlusion was variable but usually >10 min. Considering the pauses between coagulation, the duration of the procedure may extend to >15 min. The study was conducted under direct endoscopic vision, and it is likely that the total procedure time is longer when it is performed under ultrasound guidance only, where grasping can occasionally be more difficult and time consuming.
The study addresses another common concern about the use of bipolar coagulation in a fluid environment, i.e. the possible temperature changes in the surrounding fluid. The data demonstrated that bipolar coagulation for the durations used in this study was associated with a localized modest increase in the surrounding amniotic fluid temperature, which decreased with increasing distance from the coagulation site. Furthermore, the temperature normalized within a few seconds after the peak in all cases. It is therefore very unlikely that the temperature changes associated with the power settings used in this study are of clinical relevance.
In this study, bipolar coagulation with the currently commercially available 2.2 mm forceps was associated with a high risk of perforation. However, any potential interpretation regarding the influence of forceps diameter should be made with caution. The forceps used were obviously not designed for umbilical cord coagulation. Excessive forward displacement of the blades at opening, the presence of a prominent tooth at the tip of the blades and very narrow conducting surfaces of the blades may have contributed to the risk of perforation. Also, power settings other than those used in this study might reduce the perforation rate. Given the risk, however, we do not consider this forceps suitable for current clinical use. Additional work on its design may render it more effective and safe.
In summary, our data provide evidence that bipolar cord coagulation, using available endoscopic forceps with diameters from 2.3 to 2.7 mm, is safe and efficacious in the ovine model. Low power and prolonged application with pauses between coagulation intervals make the risk of perforation unlikely.
![]() |
Acknowledgments |
---|
![]() |
Notes |
---|
![]() |
References |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Deprest, J.A., Evrard, V.A., Van Ballaer, P.P. et al. (1998) Fetoscopic cord ligation. Eur. J. Obstet. Gynecol. Reprod. Biol., 81, 157164.[ISI][Medline]
Deprest, J.A., Audibert, F., Van Schoubroeck, D. et al. (1999) Bipolar coagulation of the umbilical cord in complicated monochorial twin pregnancy. Am. J. Obstet. Gynecol., 192, (in press).
Evrard, V.A.C., Deprest, J.A., Van Ballaer, P. et al. (1996) Underwater Nd:YAG laser coagulation of blood vessels in a rat model. Fetal Diagn. Ther., 11, 422426.[ISI][Medline]
Hecher, K., Reinhold, U., Gbur, K. et al. (1996) Interruption of umbilical blood flow in an acardiac twin by endoscopic laser coagulation. Geburtshilfe Frauenheilkd., 56, 97100.[ISI][Medline]
Machin, G., Still, K. and Lalani, T. (1996) Correlations of placental vascular anatomy and clinical outcomes in 69 monochorionic twin pregnancies. Am. J. Med. Gen., 61, 229236.[ISI][Medline]
Quintero, R.A., Romero, R., Reich, H.L. et al. (1996) In utero percutaneous umbilical cord ligation in the management of complicated monochorionic multiple gestations. Ultrasound Obstet. Gynecol., 8, 1622.[ISI][Medline]
Ville, Y., Hyett, J., Vandenbussche, F.P.H.A. et al. (1994) Endoscopic laser coagulation of umbilical cord vessels in twin reversed arterial perfusion sequence. Ultrasound Obstet. Gynecol., 4, 396398.[ISI][Medline]
Submitted on July 28, 1999; accepted on December 15, 1999.