Interact CardioVasc Thorac Surg 2009;9:399-401. doi:10.1510/icvts.2009.206706
© 2009 European Association of Cardio-Thoracic Surgery
Work in progress report - Experimental |
Ultrasonic scalpel for sealing of the thoracic duct: evaluation of effectiveness in an animal model
Haruhiko Nakayama*,
Hiroyuki Ito,
Yasufumi Kato and
Masahiro Tsuboi
Division of Thoracic Surgery, Kanagawa Cancer Center, 1-1-2, Nakao, Asahi-Ku, Yokohama, 241-0815, Japan
Received 7 March 2009;
received in revised form 18 May 2009;
accepted 20 May 2009
*Corresponding author. Tel.: +81-45-391-5761; fax:+81-45-361-4692.
E-mail address: nakayama-h{at}kcch.jp (H. Nakayama).
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Abstract
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To verify the usefulness of an ultrasonic scalpel for the sealing of lymphatic ducts, a Harmonic Ace scalpel (Ethicon Endo-Surgery, Inc, Cincinnati, OH) was tested, using the thoracic ducts in pigs. Indocyanine green was injected into the abdominal lymphatic ducts in two pigs, and the stained thoracic ducts were identified. The thoracic ducts were then divided and sealed into seven sections with a Harmonic Ace scalpel, used at a power setting of level 3. The cut ends of the thoracic ducts were evaluated macroscopically, histologically, and by measuring bursting pressure. The whole length of thoracic duct of each pig was clearly imaged by pigment. Each stump divided by the ultrasonic scalpel was completely sealed, and there was no pigment leakage from the cut end macroscopically. Histologic examination revealed that the cut end was sealed by homogenous degenerative coagulation. Bursting pressures could be determined at three cut ends of thoracic ducts and were 195 mmHg, 188 mmHg, and 203 mmHg, respectively. The thoracic ducts were reliably divided and sealed by an ultrasonic scalpel in pigs. This device is expected to be a useful tool for the surgical treatment of chylothorax.
Key Words: Lung cancer surgery; Ultrasonic scalpel; Thoracic duct; Chylothorax; Postoperative complications; Lymph node dissection
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1. Introduction
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Injury to the thoracic ducts or large lymphatic vessels caused by trauma, pulmonary resection, or cardiovascular surgery can lead to chylothorax [1]. Mediastinal lymph node dissection is the leading cause of chylothorax in patients with lung cancer who undergo pulmonary resection [2]. Persistent lymph leakage can prolong the duration of chest-tube placement, leading to prolonged hospitalization and an increased risk of infections such as empyema. Electric coagulation devices are well suited for the division and hemostasis of small blood vessels, but are not useful for the occlusion of lymphatic vessels larger than collecting lymphatic vessels because of the much thinner walls and lower density of collagen fibers as compared with blood vessels [3]. Ultrasonic scalpels have been reported to be useful for dividing small and medium blood vessels, and the mechanism of vessel closure has been proposed [4, 5]. However, few studies have divided the lymphatic ducts with an ultrasonic scalpel [6, 7]. We, therefore, investigated whether an ultrasonic scalpel was useful for the sealing of lymphatic vessels in an animal model.
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2. Materials and methods
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2.1. Identification of thoracic duct in animals
All experimental procedures were performed in accordance with ‘Guidelines for proper conduct of animal experiments,’ prepared by the Science Council of Japan. Two healthy male pigs, weighing 42 kg each, were studied. Anesthesia was induced with medetomidine hydrochloride, butorphanol tartrate, and midazolam and was maintained with isoflurane. Animals underwent surgical intervention in a horizontal supine position. After making a median incision in the lower abdomen, a 20-G angiocatheter was inserted and retained in a lymph duct between the abdominal aorta and posterior vena cava (Fig. 1). Subsequently, a median sternotomy was made to permit exploration of the right thoracic cavity. Indocyanine green was injected into the abdominal lymph duct. Several minutes later, the stained thoracic duct was clearly and easily identified behind the esophagus (Fig. 2).
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Fig. 1. Cannulation of the lymphatic duct between the abdominal aorta and posterior vena cava (arrow head).
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Fig. 2. The thoracic duct stained green with indocyanine green is clearly depicted (arrow head) behind the esophagus (asterisk).
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2.2. Division and sealing of the thoracic duct
A 5-mm handheld ultrasonic scalpel, Harmonic Ace (Ethicon Endo-Surgery, Inc; Cincinnati, OH), was used to divide and seal the thoracic duct. Seals were created in cranial to caudal fashion. Electrical energy is passed into the handpiece from a power source and converted to vibrations by the delivery of high-frequency ultrasound waves (55,000 cycles per second). The vibrations denature hydrogen bonds and form a coagulum, which seals vessels [http://www.jnjgateway.com/home.jhtml?page=viewContent&contentId=09008b9880a2d37a&loc=USENG. Accessed February 18, 2009]. We used a Harmonic Ace scalpel with the power set at level 3 in variable mode.
2.3. Evaluation of division margin of thoracic duct
The division margin of the thoracic duct was evaluated by three methods: macroscopic examination after sealing of the thoracic duct, microscopic examination of the thoracic duct, and measurement of the bursting pressure. Macroscopic evidence of pigment leakage was considered to indicate incomplete ligation. Cross-sections of the divided thoracic duct were prepared, mounted on slides, and stained with hematoxylin and eosin for histologic examination. The bursting pressure of the thoracic duct was measured as described by Kanehira, with minor modifications [8]. Briefly, a 20-G angiocatheter was inserted into the cut end of the thoracic duct, and the duct was ligated with 3-0 silk. The other end of the duct had been already sealed by the Harmonic Ace scalpel. The catheter was connected to both a syringe and a digital manometer (PG-100, Copal Electronics Co, Ltd, Tokyo, Japan). The removed thoracic duct was gradually filled with saline until the sealed duct burst. The pressure at this point was recorded as the bursting pressure.
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3. Results
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The thoracic ducts were divided into seven sections and sealed with a Harmonic Ace scalpel. No pigment leak was detected from any of the cut ends, indicating that sealing was complete (Fig. 3). Histological examination confirmed that the cut ends of the thoracic ducts were completely sealed by degenerative coagulation (Fig. 4). The bursting pressures were measured for three sections of thoracic ducts and were 195 mmHg, 188 mmHg, and 203 mmHg, respectively.
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Fig. 3. Macroscopic findings after division and ligation of the thoracic duct with a Harmonic Ace scalpel. There was no pigment leakage from the sealed margin (arrow head).
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Fig. 4. Histologic findings of the cut end of the thoracic duct. The duct was completely sealed by degenerative coagulation tissue (hematoxylin and eosin, x100).
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4. Discussion
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Persistent lymph leakage from lymphatic ducts injured during lymph node dissection for lung cancer can lead to postoperative chylothorax or prolong chest-tube drainage and hospitalization. The incidence of chylothorax after lung cancer surgery is <1% in most recent reports [9, 10]. The incidence, however, may be increasing due to the higher chance of more extensive, radical lymph node dissection. Moreover, prolonged chest-tube drainage may increase risk of retrograde infections such as empyema. Electric coagulation is an excellent technique for the hemostasis of small divided blood vessels, but is not useful for the occlusion of lymphatic vessels larger than collecting vessels.
A prospective randomized trial has compared the advantages and disadvantages of an ultrasonic scalpel with those of an electronic scalpel in patients who underwent lymph node dissection for gastric cancer [11]. The use of an ultrasonic scalpel was associated with a significantly lower incidence of postoperative lymphorrhea and a significantly shorter drainage period than an electronic scalpel. An ultrasonic scalpel was thus considered useful for preventing lymphorrhea after lymph node dissection. Kajiyama et al. used an ultrasonic scalpel to seal the human thoracic duct and reported that it was effective on the basis of bursting pressure and histologic findings [7].
An important feature of our experiment was that indocyanine green was used to stain the thoracic duct. It is very difficult to macroscopically detect leakage of colorless and transparent lymph fluid. In contrast, the use of indocyanine green enables the macroscopic detection of even small amounts of stained lymph leakage if sealing by the ultrasonic scalpel is inadequate. Histologic examination also revealed that the cut ends of the duct were sealed by degenerative coagulation tissue, similar to the sealing of blood vessels [4, 5]. Furthermore, the firmly sealed cut ends could withstand pressures up to 188 mmHg. The intraductal pressure of the thoracic duct ranges from 10 to 25 cm H2O and may rise to 50 cm H2O with obstruction, as demonstrated by Shafiroff and Kau [12]. Olszewski and Engeset reported that the lymphatic pressure ranges from 5 to 30 mmHg and can rise to 100 mmHg if the proximal vessels are occluded [13]. Therefore, the cut end of the thoracic duct sealed by an ultrasonic scalpel is not expected to rupture, even if the intraductal pressure is increased by occlusion.
Ligation of the thoracic duct or direct ligation of the fistula site is a widely accepted standard procedure for the treatment of chylothorax [1]. To our knowledge, only two reports have documented the use of an ultrasonic scalpel for the surgical treatment of chylothorax [14, 15]. Khelif et al. successfully reported two cases of persistent chylothorax after cardiac surgery that were successfully managed by thoracoscopic thoracic duct coagulation with an ultrasonic scalpel [14]. Takeo et al. succeeded in controlling the vigorous flow of chylous fluid by coagulation of the fistula site, using an ultrasonic scalpel without clipping or ligation in a patient with chylothorax after aortic replacement for an aneurysm of the descending aorta [15]. Our animal model clarified the fundamental principles of using an ultrasonic scalpel to treatment chylothorax, however, our study had some weaknesses. In this study, we did not compare the use of ultrasonic scalpel to electric coagulation, and we did not evaluate the efficacy of ultrasonic scalpel at the late phase after sealing.
In conclusion, our animal experiment suggested that an ultrasonic scalpel can be a useful tool for division and sealing of the thoracic duct. Sealing of the thoracic duct with an ultrasonic scalpel may also be a promising surgical approach for the treatment of chylothorax. Also, careful dissection techniques using ultrasonic scalpels may be useful for preventing the occurrence of chylothorax complicating pulmonary resections. However, further clinical experience and additional animal experiments should be necessary before drawing firm conclusions.
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Abstract
1. Introduction