Bursting pressures of CO2 laser-welded rabbit ileum

Bowel welding technique in dogs and cats using a diode laser: an experimental study

A laser bowel welding technique for dogs and cats was developed. The bowel was pinched using a special clamp having an opening on the body developed for this experiment (LW clamp). Using the 2 different types of contact probe (blunt tip: Laser Bipolar Dissector (LBD); sharp tip: Super Scalpel Dissector (SSD)), the laser passed through the hole in the LW clamp to cut the bowels, while at the same time, sealing the cut portion. The results obtained in this study showed that the optimum laser output using LBD was 6-10 W in dog and cat ileum, and 8-10 W in dog and cat colon. Optimum laser output using SSD was 6-8 W in dog ileum, 8-10 W in dog colon, 10 W in cat ileum and 6-8 W in cat colon. No marked differences were observed between ileum and colon when using either LBD or SSD. At the same power, burst pressure tended to be slightly higher with LBD than with SSD, although there were not significant differences between them. Histologically, complete sealing of the welded site was seen. Welding and cutting of bowel in dogs and cats was thus confirmed to be possible using the LW clamp in combination with LBD or SSD probes under a diode laser output of approximately 8 W for 50-80 s (400-640 J/cm). Thus, we can expect that this method is applicable to clinical veterinary medicine.

Carbon dioxide laser tissue welding: an alternative technique for tubal anastomosis?

Microsurgical tubal anastomosis is the gold standard for treatment of tubal occlusion. The present study was performed to establish the feasibility of tubal anastomosis by welding tissue with a defocused CO2-laser beam during laparotomy and with an endoscope. In an animal experiment, 70 white New Zealand rabbits were randomized in 2 study groups (E1, E2) and 3 control groups (C1, C2, C3) as follows: C1, 10 animals, no operation, as controls for the efficiency of the insemination technique; C2, 5 animals, spontaneous healing after tubal segment resection, to quantify spontaneous recanalization of the tube; C3, 15 animals, microsurgical end-to-end adaption after tubal segment resection; E1, 20 animals, laser welded anastomosis after segment resection via laparotomy; E2, 20 animals, laparoscopic laser welded anastomosis after segment resection. The pregnancy rate in C1 was 80%. None of the animals in C2 but 60% of the rabbits in C3 conceived. After sutureless anastomosis by laser welding 50% of the laparotomized, and 40% of the laparoscopically operated group became pregnant. Morphological examination of the oviducts after relaparotomy showed comparable patency rates of 70% in C3, 70% in E1, and 65% in E2. Whereas no dehiscence of anastomoses was observed in C3, 20% of the welded tubes in E1 and 22.5% in E2 were dehiscent. Tubal anastomosis took approximately three times as long laparoscopically as during laparotomy. Thus, laser welding as a sutureless alternative technique of tubal anastomosis should be viewed critically. A reduction of sutures through laser-assisted anastomosis might, however, be considered.

Collagen shortening. An experimental approach with heat

Decreasing joint laxity is a clinical goal of ligament reconstructions. This in vitro study examined the structural and histologic effects of heat shrinkage of human collagen. Two preliminary studies were performed to assess the effect of heat on fresh frozen human tendons obtained from a local tissue bank. As heat was applied to tissue in a saline solution, the percent shrinkage was plotted against temperature. A second study used a freebeam Nd:YAG laser to maximally shrink patellar tendons measuring percent shrinkage versus energy applied. Finally, the effects of 10% shrinkage of fresh frozen human patellar tendons were analyzed mechanically and histologically. Consistent tendon shrinkage curves were found with increasing temperatures in a saline solution. A sharp increase in shrinkage to approximately 70% of resting length was noted around 70 degrees C. Tendon shrinkage by laser induced heat was precise and dose related. Tensile testing of the tendons shortened 10% of their resting length showed a decrease in load to failure to approximately 1/3 compared with that of historical control specimens. Histologic sections showed a well demarcated site of diffuse denaturation and degeneration of collagenous elements. Normal collagen was present adjacent to these thermal changes. These experiments showed that collagen tissue can be shortened precisely by the application of heat. Future studies need to examine the in vivo biologic response of shortened collagen tissue with time, especially recollagenization, restoration of length, and the long term biomechanical effects.

Controlled temperature tissue fusion: argon laser welding of canine intestine in vitro

BACKGROUND AND OBJECTIVE

Thermal denaturation of proteins is recognized as a rate process governed by the local temperature-time response and is believed to be the principal mechanism for photothermal tissue welding. Since rate processes are exponential with temperature, feedback control of tissue surface temperature is hypothesized to create a quasi-constant rate of denaturation that will enhance the tissue welding process.

STUDY DESIGN, MATERIALS AND METHODS

Controlled temperature tissue welding of severed edges of fresh canine jejunum was performed in vitro by remote sensing of tissue surface temperature with an infrared sensor. A hardware controlled temperature feedback system opened and closed a shutter located in the beam path of an argon ion laser to provide constant temperature welding.

RESULTS

Strong tissue fusion was not possible at or below a surface temperature of 70 degrees C, but was accomplished at 80 degrees, 90 degrees, and 95 degrees, and 100 degrees C. Fusion was achieved with thermal coagulation of the collagenous submucosa and mucosal tissues. The bursting strength of welds created at 90 degrees C and 95 degrees C were significantly stronger than those performed at 80 degrees C.

CONCLUSION

Laser-assisted intestinal anastomoses created in vitro are optimally strong at 90-95 degrees C feedback control temperatures.

Prevention of pharyngocutaneous fistulas by means of laser-weld techniques

Although much has been written on methods of dealing with pharyngocutaneous fistulas once they have formed, there are few reports of methods of preventing fistula formation from occurring. We examined the use of laser-weld techniques with the neodymium:yttrium aluminum garnet (Nd:YAG) and diode lasers to seal pharyngotomy closures. Laser-weld techniques have been used successfully in many other tissues, but reports documenting use in the upper aerodigestive tract are minimal. Indocyanine-green dye-enhanced collagen and fibrinogen were studied as laser solder materials for the diode laser. Twenty-nine experimental animals were studied. Neither the Nd:YAG nor the diode laser was successful in preventing fistula formation. Tensiometric studies documented significant strength of the laser welds ex vivo, but this finding was not clinically significant.

Experimental laser anastomosis of the colon. Long-term results and histologic findings after laser closure of colotomies

PURPOSE

Our previous experimental work showed the feasibility of colon anastomosis using laser; however, it also revealed a narrowing tendency after laser anastomosis. Long-term observation of the postoperative course of laser anastomosis was planned to assess this point.

METHODS

Clinical observation and histologic examination of transverse colotomies (average, 21.2 mm) in New Zealand white rabbits (n = 12) closed with a 1,064-nm neodymiumyttrium aluminum garnet (Nd:YAG) laser were carried out up to the third postoperative month, compared with closure of colotomies using a single layer of interrupted sutures of 5-0 Maxon (Davis & Geck, Pearl River, NY) in a control group (n = 12).

RESULTS

Whereas the narrowing tendency was observed up to one month after the operation in the laser group (P < 0.05), it disappeared at three months following the operation without causing abnormal weight loss during the experiment. Simultaneously, there was again a marked decrease in adhesion formation following laser anastomosis (P < 0.01). Collagen fibers were observed earlier in the laser group.

CONCLUSIONS

An earlier commencement of collagen synthesis after laser anastomosis was proved. A narrowing tendency, which was observed from seven days to one month postoperatively, disappeared at three months after laser anastomosis without exerting any effect on growth.

Healing process of laser-welded intestinal anastomosis

Intestinal welding by means of low-power laser has been reported as an efficient method for intestinal anastomosis. We designed an experimental model in rats to investigate collagen and DNA concentrations in CO2 laser-welded anastomoses as compared with those in sutured anastomoses on the 4th, 7th, and 10th postoperative days. The results revealed that DNA, total collagen, and insoluble collagen concentrations were significantly lower in the lased anastomoses than in the sutured anastomoses on the 4th postanastomotic day. On the 7th and 10th postanastomotic days, collagen concentrations increased in the laser-treated group attaining significantly higher levels than in the sutured group at that time. These findings are compatible with other studies demonstrating that laser-welded intestinal anastomoses are more prone to dehiscence during the first 4 postanastomotic days, but become at least as effective as the sutured ones with passage of time.

CO2 laser nerve welding: optimal laser parameters and the use of solders in vitro

To improve the welding strength, an in vitro study was performed to investigate the bonding strength of CO2 laser nerve welding (LNW), with and without the use of human albumin solution, dried albumin solution, egg white, fibrinogen solution, fibrin glue, and red blood cells as a solder. Fifteen different combinations of laser power (50, 100, and 150 mW) and pulse duration (0.1 to 3 s) were used with a spot size of 320 microns. The results have been compared to suture, fibrin glue, and laser-assisted nerve repair (LANR). The strongest welds (associated with whitening and caramelization of tissue) were produced at 100 mW with pulses of 1.0 s and at 50 mW with pulses of 3 s. The use of a dried albumin solution as a solder at 100 mW with pulses of 1 s increased the bonding strength 9-fold as compared to LNW (bonding strength 21.0 +/- 8.6 g and 2.4 +/- 0.9 g, respectively). However, positioning the nerves between cottons soaked in saline for 20 minutes resulted in a decrease of the bonding strength (9.8 +/- 4.5 g). The use of a 20% albumin solution and egg white, both at 50 mW with pulses of 3 s, resulted in a bonding strength of, respectively, 5.7 +/- 2.1 g and 7.7 +/- 2.4 g. Other solders did not increase the bonding strength in comparison to LNW. The substantial increase in bonding strength for some solders suggests that it is worthwhile to investigate the dehiscence rate and nerve regeneration of solder enhanced LNW in an in vivo study.

Lasers in neurosurgery

Lasers have been used in neurosurgery for the past 25 years, undergoing modifications to suit the specific needs of this medical discipline. The present report reviews the current use of lasers in neurosurgical practice and examines the pros and cons of lasers in specific neurosurgical applications. In spite of their advantages, laser use is still not widespread in neurosurgery. One reason is the continued lack of complete control over real-time laser interactions with neural tissue. A greater acceptance and use of lasers by neurosurgeons will depend upon automated control over defined specific parameters for laser applications based upon the type of tissue, the desired effect on tissue, and application to the clinical situation without loss of precision and a lot of expense. This will require the integration of newer lasers, computers, robotics, stereotaxy, and concepts of minimally invasive surgery into the routine management of neurosurgical problems.

Primary closure of choledochotomy using CO2 laser: comparison with suture closure

This study was designed to compare laser welding to suture closure of the common bile duct (CBD). A 12 mm linear choledochotomy was closed in 12 mongrel dogs using tissue welding low-energy CO2 laser. Tissue welding was accomplished at 5.0 w/cm2 for 120 sec. Twelve similar mongrel dogs (control) were treated with CBD closure using 5/0 Vicryl (polyglactin 910, Ethicon, Inc., Somerville, NJ) interrupted simple stitches. All animals were sacrificed at six weeks. Gross and histologic evaluation of the choledochotomy site were performed. There were no statistical differences in parameters of comparison in the two groups. These parameters were pre- and post-treatment measurements of liver function tests, stenosis, and dehiscence. However, it must be noted that there was a 33% (4/12) incidence of dehiscence and death in the CO2 laser welded choledochorrhaphy. This result, although not statistically significant, is clinically significant. We conclude that the tensile strength of CO2 laser welded CBDs must be optimized and that these results are preliminary and still unreliable to recommend for clinical adaptability.

Experimental carcinogenesis at sutured and sutureless colonic anastomoses

This study explores the role of sutures and the healing colonic wound in experimental carcinogenesis. One hundred sixty rats underwent surgery with colotomy and repair using silk, steel, or Vicryl (Ethicon, Somerville, NJ) sutures or a sutureless technique. Forty rats had a sham procedure. All animals received azoxymethane for 12 weeks at a dose of 10 mg/kg/week. Half the rats commenced carcinogen before surgery, and half commenced it eight weeks after surgery. Animals with anastomotic tumors were found in 46 percent of the sham group (P less than 0.05 cf. sutured), 41 percent of the sutureless group (P less than 0.02 cf. sutured), and 68 percent of the sutured group. The corresponding figures for anastomotic carcinoma were 9 percent (P less than 0.001 cf. sutured), 22 percent, and 38 percent. No significant differences in tumor yield were noted among the different sutures. However, several differences were noted between the two carcinogen models. In those animals that received surgery first, there was a higher incidence of anastomotic tumors (P less than 0.002) and cancers (P less than 0.0001) in the sutured and sutureless groups, and those tumors that occurred in the sutured group were considerably larger than in those that had carcinogen first (15.9 mm cf. 4.9 mm; P less than 0.0001). Overall, all sutures seem to enhance anastomotic tumor formation, and we would suggest that a sutureless anastomosis may diminish this risk.

First experimental sutureless end-to-end laser anastomosis of the large bowel. Short-term results

Completely sutureless end-to-end large bowel anastomoses were successfully created in New Zealand white rabbits (n = 26) by using a low-energy (0.4-W wave of power) Nd:YAG laser to produce welded anastomoses. In this study, the short-term integrity, degree of narrowing, macroscopic appearance, and microscopic findings were compared with those of the conventional interrupted one-layer anastomosis (n = 24) at zero, one, four, and seven days after surgery. Two rabbits in the laser group died from leakage. All remaining animals had an uneventful postoperative course. The bursting pressures in the laser group at zero, one, and four days were lower than those in the control group. The narrowing index of the laser anastomosis was higher than that of the suture anastomosis at four and seven days. However, the laser anastomoses showed fewer adhesions, no instances of bowel obstruction, and histologic healing with less fibrosis. The technique of laser anastomosis presents a promising alternative to suturing in reconstitution of the large bowel.

First sutureless closure of a colotomy: short-term results of experimental laser anastomosis of the colon

To assess the possibility of laser anastomosis of the colon, experimental laser closure of colotomies was performed. Transverse colotomies (average 20.7 mm) in New Zealand white rabbits (n = 20) were closed with a 1,064-nm Nd:YAG laser at a pulsating 0.5-W wave of power, using guy sutures to approximate the tissue edges. The laser energy was applied through a specially designed hand piece and hand-held 600-microns gas-cooled noncontact quartz fiber to produce a satisfactory tissue welding. Similar colotomies were closed using a single layer of interrupted sutures of 5-0 Maxon (Davis & Geck, Pearl River, NY) in a control group (n = 20). Bursting pressure and index of narrowing were recorded immediately after anastomosis and at 1, 4, and 7 days following surgery. Bursting pressure of the laser-welded closure at 1 day was significantly lower than that of the sutured controls (P less than 0.01); however, all rabbits recovered uneventfully. There was a marked decrease in adhesion formation following laser anastomosis (P less than 0.05). Conversely, one control rabbit showed functional stenosis at 4 days. Histologic study revealed an accelerated healing in the laser group. The index of narrowing was significantly higher in the laser group than in the control group (P less than 0.05). The completely water-sealed laser anastomosis reduces adhesions and is comparable to conventional suture anastomosis of the colon.

Sutureless intestinal anastomoses

Sutureless intestinal anastomoses can be achieved either by compression, where two inverted rings of bowel are compressed by a hollow circular device that subsequently sloughs away and is passed anally, or by the use of tissue glues or laser welding. Compression devices used clinically with success are the Valtrac biofragmentable anastomotic ring, the polypropylene rings described by Rosati and the AKA guns. Glued anastomoses have only been used in animals and seem to be unsafe. However, laser-welded intestinal anastomoses appear highly promising in experimental studies and further development of this technique is warranted.

The first sutureless, laser-welded, end-to-end bowel anastomosis

The use of laser energy to weld together tissue offers great promise in the expanding field of laser surgery. The published results of laser welding intestinal tissue have, to date, been limited to the successful laser closures of small enterotomies. This is the first report of using laser energy alone to create an end-to-end small bowel anastomosis. A biocompatible, water-soluble, intraluminal stent was employed during the laser welding of this sutureless, stapleless ileal anastomosis in a rabbit model. Excellent recovery and healing were observed. The rapidity, ease, and potential for full precision automation of laser welding mandates further research.

Enterotomy fusion with laser energy: preliminary results in rabbit ileum

The utility of enterotomy closure with the argon and CO2 lasers was examined in New Zealand white rabbit ileum. Thermal properties of 10 argon (0.5 W power for 30 s, energy fluence 230 J/cm2) and 10 CO2 (1.0 W power for 30 s, energy fluence 2700 J/cm2) laser-fused enterotomies were determined during acute fusion experiments using an AGA 782 digital thermographic camera. Healing of the fusions created by the two lasers was subsequently assessed in an additional group of 28 rabbits by comparing three 1.0-cm longitudinal ileal enterotomies, with each rabbit having both types of laser-welded closures and a sutured control. Thermal measurements made from the 10 closures with each laser revealed that the CO2 fusions generated significantly higher temperatures (max. 198 degrees C, mean 106 +/- 37 degrees C, n = 100) than argon (max. 85.2 degrees C, mean 60.5 + 8.1 degrees C, n = 100) p less than 0.001. In the healing studies, four rabbits died from weld failures (one argon and one CO2 disruption, two rabbits with both welds disrupted). Two additional rabbits died at 1 day and one at 10 days for undetermined reasons. The remainder of the animals were sacrificed at 1 (n = 11), 2 (n = 2) and 4 (n = 9) weeks postoperatively. Sutured closures exhibited more granulation tissue and adhesions surrounding the wounds than did welded closures and seven microabscesses were noted adjacent to sutured repairs. One of the CO2 repairs had an abscess at 4 weeks and none of the argon laser fusions had evidence of disruption or abscess.(ABSTRACT TRUNCATED AT 250 WORDS)

Laser-assisted intestinal anastomosis

Laser-assisted tissue fusion has been investigated as a new technology to enhance the healing of soft tissues. Laser fusion of intestinal anastomoses shows promise as a method to obtain primary healing while eliminating a foreign-body reaction associated with the sutures. This paper reviews the experimental data that are available regarding laser-assisted intestinal anastomoses and summarizes our experience using the CO2, Nd:YAG, and argon lasers to form fusions in small bowel.

Plaque-media rewelding with reversible tissue optical property changes during receptive cw Nd:YAG laser exposure

Laser dosimetry for thermal fusion of plaque-wall separations during laser balloon angioplasty (LBA) is dependent upon the optical properties of the atheromatous arterial wall during one or more exposures to cw Nd:YAG laser radiation. An integrating sphere technique was used to measure relative transmission and reflection continuously during irradiation of human postmortem atheromatous aortic sections. Tissue luminal surface temperature was recorded continuously with a thermographic video imager during repetitive 20-30-sec, 8-15-watt exposure of a 3-mm nominal spot. In all specimens, transmission fell progressively during each exposure by 10-70% of baseline values. This effect was reversible with normalization of transmission during the initial phase of each subsequent exposure. Changes in transmission were inversely related to temperature over a 50-170 degrees C range, whereas relative reflection remained constant. Accompanying reversible transmission changes was the observation that the weld strength of plaque-aortic wall separations was unchanged by repetitive laser welding and tissue separation of individual sections. In conclusion, temperature-dependent reversible optical and physical properties of plaque occur during exposure to 1.06 microns cw laser radiation.

Vasovasostomy in the murine vas deferens: comparison of the Nd:YAG laser at 1.06 microns and 1.318 microns to the CO2 laser

A comparison is made of laser anastomoses of the murine vas deferens at different energies with the neodymium (Nd):YAG laser at 1.06 micron and 1.318 micron and with the CO2 laser. A total of 28 welds were performed with a free-hand technique employing a 600-micron silicon fiber with the Nd:YAG and a hand piece with a 500-micron spot size for the CO2. After 6 weeks, all animals were sacrificed and the vasa evaluated for patency. Fifteen out of 28 controls repaired with microsurgical techniques were found to be patent; 4/10 vasa were patent with use of the Nd:YAG at 1.318 micron at laser energies of 300 mW and 500 mW. At 1.06 micron, only 1/4 anastomoses was patent at a power setting of 1 W. None of the anastomoses performed with the CO2 laser was patent. Histologic study revealed intense fibrosis in all the lasered vasa, with sperm granuloma formation associated with most anastomoses. Although this is a preliminary study, it appears that the Nd:YAG laser at 1.318 micron and a power setting of 300-500 mW provides patency rates superior to the Nd:YAG at 1.06 micron and to the CO2 lasers and is equivalent to standard micro-surgical techniques in the murine vas deferens.

Closure of rabbit ileum enterotomies with the argon and CO2 lasers: bursting pressures and histology

In this study, we examined short-term strength and histology of experimental argon and CO2 laser-welded and control-sutured enterotomies in a rabbit model. Longitudinal 1.0-cm enterotomies were closed with the argon laser at 0.5 (n = 10) or 1.0 (n = 10) W power and a spot diameter of 2.8 mm resulting in energy fluences of 230 and 450 J/cm2, respectively. Similar enterotomies were closed using the CO2 laser at 0.5 (n = 10) or 1.0 (n = 10) W power and a spot diameter of 1.2 mm, resulting in energy fluences of 1,360 and 2,730 J/cm2. In all closures, continuous wave laser was delivered for 30 seconds. Using a pressure-monitored infusion system with normal saline, the pressure required to burst each weld as well as sutured controls (n = 10) was recorded approximately 1 minute following fusion. Mean bursting pressures for the argon laser at 0.5 W and 1.0 W were 34.1 +/- 19.4 mm Hg (mean +/- SD) and 17.3 +/- 8.3 mm Hg, respectively, and for the CO2 laser were 23.5 +/- 12.0 mm Hg and 31.8 +/- 15.6 mm Hg, respectively. Sutured controls leaked at 45.2 +/- 12.0 mm Hg. With the exception of argon-laser welds at an energy fluence of 450 J/cm2, which were less than sutured repairs, the bursting pressures for welded closures were not significantly different from the sutured controls (Student's t distribution, P less than .05). Histologic examination of both types of welds demonstrated a fibrin and red blood cell coagulum bridging the anastomosis, with some evidence of mild thermal injury at the mucosa.(ABSTRACT TRUNCATED AT 250 WORDS)

The Nd:YAG laser 1.3 u wavelength: in vitro effects on ocular structures

We evaluated the in vitro effects of the 1.3 u wavelength of a Nd:YAG laser using a fiberoptic delivery system, with or without sapphire tips on ocular tissue. Conjunctival and retinal adhesions were achieved best with a noncontact technique compared with a contact method.

Effects of electrocautery, CO2 laser, and contact Nd:YAG laser scalpel on the healing of intestinal incision

Leakage after intestinal resection is a serious complication with a high mortality rate. A recent study claims that cutting the intestine with the CO2 laser improves the healing of intestinal anastomoses (Ferulano et al: Eur Surg Res 16:127-130, 1984). The present study was undertaken to analyze the effects of electrocautery, CO2 laser, and contact Nd:YAG laser on the healing of intestinal incisions. Fifteen piglets were used and the cutting and reanastomosing were performed by using all cutting methods in each animal in randomized order. Resection sites were 50 cm, 100 cm, and 150 cm distal to the ligament of Treitz. On the seventh day the bursting pressures were measured for each anastomosis. They were 172 +/- 17 mmHg for normal bowel segment and 133 +/- 12, 135 +/- 40, and 139 +/- 17 mmHg for electrocautery, CO2 laser, and Nd:YAG laser, respectively. There were no mortality, no anastomotic leaks, and no statistically significant differences in the bursting pressures, in histology, or in the healing of anastomotic sites, indicating that electrocautery, CO2 laser, and contact Nd:YAG laser scalpel can safely be used in the surgery of small intestine.