Bipolar coagulation with small diameter forceps in animal models for in-utero cord obliteration

N. Yesildaglar1, L. Zikulnig3, E. Gratacós1,2, R. Devlieger1,2, H.J. Schröder4, J. Deprest1,2,5 and K. Hecher3

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
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 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
The objective of this study was to evaluate the feasibility, efficacy and safety of bipolar coagulation using endoscopic forceps of diameters of 2.7 mm and less in animal models mimicking in-utero conditions. Forceps of 2.2, 2.3, 2.5 and 2.7 mm were tested in rabbits (n = 36). Vessel pairs were dissected and coagulated in a fluid environment under endoscopic vision at 15 and 25 W. The main outcome measure was the perforation rate. In fetal lambs (n = 25), umbilical cords were coagulated under sono-endoscopic control with power settings from 10 to 35 W. Main outcome measures were the duration of coagulation, perforation rate, change in the temperature of the amniotic fluid and efficacy of vessel occlusion rate. At 20–25 W, all cords were coagulated successfully without any perforation using 2.3, 2.5 or 2.7 mm forceps. Coagulation with the 2.2 mm forceps was associated with a high perforation rate, although the design rather than the diameter of the forceps may have influenced this outcome. Bipolar coagulation with forceps between 2.3 and 2.7 mm and appropriate power settings achieves efficacious and safe coagulation in animal models for umbilical cord occlusion.

Key words: bipolar coagulation/monochorionic twins/rabbit/sheep/umbilical cord


    Introduction
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
Cord occlusion is one of the current techniques to perform selective feticide in complicated monochorionic pregnancies. Conventional feticide with intracardiac injection of potassium chloride cannot be considered, as the substance could embolize to the other fetus over the virtually ever-present placental vascular anastomoses (Machin et al., 1996Go). Appropriate techniques for arresting blood flow at the level of the umbilical cord should aim to stop flow completely and permanently (Deprest et al., 1998Go). Fetoscopic cord ligation achieves these goals, but remains a complex procedure and carries a high risk for preterm premature rupture of membranes (PPROM) (Quintero et al., 1996Go; Deprest et al., 1998Go). Alternatively, Nd:YAG laser coagulation of the umbilical cord has been carried out, but this technique is limited by gestational age (Ville et al., 1994Go; Hecher et al., 1996Go). We recently suggested using bipolar coagulation to occlude the umbilical cord with instruments of an outer diameter of >=2.7 mm (Deprest et al., 1999Go). Smaller diameter forceps are now available on the market and it is tempting to consider their use for cord coagulation. However, some concerns regarding safety and particularly the risk of perforation may arise. Perforation of umbilical cord vessels leads to fetal haemorrhage, which, even if limited, can lead to in-utero death of both fetuses. Therefore, any new instrument should first be assessed in experimental conditions. In the present pre-clinical study, we evaluated those smaller diameter forceps with respect to their efficacy, safety and complication rate in animal models mimicking in-utero conditions.


    Materials and methods
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
The forceps tested in this study were of an outer diameter of: 2.7 mm (Imagyn, Laguna Nigel, CA, USA); 2.5 mm (prototype, Karl Storz, Tuttlingen, Germany); 2.3 mm (Auto Suture, Mechelen, Belgium); 2.2 mm (Imagyn); and 2.7 mm (prototype; Karl Storz), connected to a conventional electrogenerator (Autocon, Karl Storz). All these forceps open not by articulation but by advancing the jaws, which are partially retracted within the sheath in the closed position. Features of the instruments tested regarding maximum opening of the jaws, angle of opening and forward displacement of the jaws (the distance the jaws move forward while opening) are displayed in Table IGo.


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Table I. Features of the bipolar forceps tested in this study
 
Studies in the rabbit
The 2.7 and 2.2 mm (Imagyn), 2.3 mm (Autosuture), and 2.5 mm prototype (Storz) were used for these experiments. In a preliminary study, adult New Zealand rabbits (n = 3, data not shown) were dissected to determine which vessels could serve as a model for cord coagulation. Criteria were that (i) vessels ran in pairs, to mimic the flow system of an umbilical cord, (ii) they could be dissected en bloc, i.e. with some perivascular tissue, to mimic the embedding of umbilical cord vessels in Wharton's jelly and (iii) their diameter was >1.0 mm, as above this diameter laser coagulation may be difficult or associated with perforation (Evrard et al., 1996Go). The only vessels meeting these criteria were the renal vessels and the combination of the abdominal aorta and cava vein, hereafter referred to as aorta-cava package. Various power settings, duration of coagulation, as well as continuous versus intermittent coagulation were tested. In these experiments we observed that with continuous and prolonged coagulation the blades tended to stick to the perivascular tissues and vessel wall, increasing the risk of tearing and perforation while removing the instrument.

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 (2–3%) 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 1.5–3.0% 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., 1995Go). 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 1–1.5% 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 120–180 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
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 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
In the rabbits, the renal vascular pedicle, including artery and vein, measured on average 5 mm, whereas the package of abdominal aorta and vena cava was 10–11 mm. No perforations occurred when coagulation was performed either in both renal pedicles or aorta-cava package with forceps of 2.3 mm (n = 10), 2.5 mm (n = 8) and 2.7 mm (n = 8). The 2.2 mm forceps (n = 10) tended to stick to the tissues, even in the absence of obvious carbonization. On removal, this resulted in perforation and major haemorrhage in 30% (3/10) of cases in the aorta-cava package and 5% (1/20) in the renal vessels.

Results of bipolar cord coagulation in fetal lambs using several forceps and with power set at 25 W are displayed in Table IIGo. The mean diameter of the cords was 13 mm (range 10–16). 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 5.4–21.4) at 1 cm from the coagulation site and 3.4°C (range 0.2–6.4) 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.


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Table II. Experiments in fetal lambs with a fixed power setting of 25 W
 
Results of bipolar cord coagulation with variable power settings in fetal lambs are displayed in Table IIIGo. At a power setting of 10 W, coagulation was not completely effective in two cases, as part of the umbilical vessels were still patent, but no perforations occurred. At 35 W, in three out of four cases the coagulation was effective, whereas in one case perforation and bleeding occurred.


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Table III. Experiments in fetal lamb with 2.7 mm forceps and variable power settings
 

    Discussion
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 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
During bipolar coagulation, electrical current is applied to the portion of tissue that is grasped between the forceps blades. The electrical current is mainly restricted to the tissue between those blades. At that time, the tissue is heated up and `cooked' within its own fluid. In the first phase, the intracellular temperature rises and cellular water leaves the cell, making it shrink and retract, with associated denaturation of the cellular proteins. Tissue proteins become denatured at a temperature of 55–80°C to form a quasi-glutinous white coagulum. The effect on tissue was linear in relation to the exposure time and exponential in relation to the temperature generated by the forceps. Appropriate duration of application and correct energy lead to coagulation, while excessive heat leads to dehydration and carbonization of the tissue. The tissue close to the active electrode is heated the most, and at a given time cellular water is converted into steam, creating a vapour layer between the electrode and the tissue. If energy at a low voltage is further applied, the tissue near the electrode will dry out, and no further electrical current flows into the tissue. At a higher voltage, arches of current will puncture the dried out tissues, and deeper tissue can be coagulated. This goes on until the electrogenerator is switched off or if the dried tissue layer is so thick that no arches can puncture it any more. However, arching is associated with tissue carbonization, which makes the blades stick to the tissue. This not only decreases efficacy and contaminates the blades, but may also cause tearing away of the coagulum at the time of removal of the blades. This, in its turn, results in haemorrhage as blood vessels may be torn. In summary, for specific haemostatic denaturation, no more tissue is coagulated than needed for the purpose of the procedure. Coagulation should be ended as soon as vapour emerges from the coagulation area, in order to avoid carbonization.

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
 
Supported by the Biomed Programme of the European Commission (Eurofoetus, PL 962383). E.G. and L.Z. are recipients of a research fellowship of the European Commission.


    Notes
 
5 To whom correspondence should be addressed at: Centre for Surgical Technologies, Minderbroedersstraat 17, 3000 Leuven, Belgium Back


    References
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
Deprest, J.A., Luks, F.I., Peers, K.H.E. et al. (1995) Intrauterine endoscopic creation of urinary tract obstruction in the fetal lamb: a model for fetal surgery. Am. J. Obstet. Gynecol., 172, 1422–1426.[ISI][Medline]

Deprest, J.A., Evrard, V.A., Van Ballaer, P.P. et al. (1998) Fetoscopic cord ligation. Eur. J. Obstet. Gynecol. Reprod. Biol., 81, 157–164.[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, 422–426.[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, 97–100.[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, 229–236.[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, 16–22.[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, 396–398.[ISI][Medline]

Submitted on July 28, 1999; accepted on December 15, 1999.





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