Roberto J. Manson

Readily Available Tissue-Engineered Vascular Grafts

Nonimmunogenic, tissue-engineered vascular grafts stored long-term maintain their patency, strength, and function after transplant in large-animal models. Grow Your Own Blood Vessels Growing your own vegetables may be a well-established approach for a healthier life, but growing blood vessels for surgical transplantation is a more unusual pastime. But the idea of growing a readily available supply of blood vessels for surgical transplant into patients requiring, for example, a cardiac bypass or dialysis is not as far-fetched as it sounds. Although a patient’s own blood vessels can sometimes be used for the graft, often this is not possible. Engineered autologous blood vessels can be grown from endothelial cells taken from the patient and cultured on scaffolds, but this process takes 9 months or more, and often the patients cannot wait that long for surgery. Enter Dahl and her team with a new approach that provides readily available, off-the-shelf vascular grafts that retain their strength and patency during long-term storage and function successfully after vascular surgery in baboon and dog animal models. The authors grew their human vascular grafts by culturing smooth muscle cells from human cadavers (that is, allogeneic cells) on tubular scaffolds made from a biodegradable polymer called polyglycolic acid (PGA). The smooth muscle cells produced collagen and other molecules that formed an extracellular matrix. When the scaffold degraded, fully formed vascular grafts were left behind. The investigators then stripped the cells from the grafts, using detergent to make sure the grafts would not elicit an immune response when transplanted. These human vascular grafts were 6 mm or greater in diameter and retained their strength, elasticity, and patency even after storage in phosphate-buffered saline solution for a year. The human vascular grafts were tested in a baboon model of arteriovenous bypass in which the graft formed a direct conduit between an artery and a vein (an approach that enables human patients with kidney disease to undergo dialysis). The authors showed that the grafts in baboons restored blood flow and retained their patency and strength for up to 6 months. When the grafts were removed and examined histologically, they did not show evidence of fibrosis, calcification, or thickening of the vessel wall intima. But the authors wanted to test engineered vascular grafts with smaller diameters, which are often plagued by thrombi (blood clots) after transplant. To do this, they turned to a dog model of peripheral and coronary artery bypass, surgeries that require smaller-diameter vascular grafts. Using dog smooth muscle cells cultured on PGA scaffolds, they created canine vascular grafts with small diameters (3 to 4 mm). They then seeded these grafts with endothelial cells (from the dogs due to be recipients) because an endothelial cell lining helps to prevent blood clot formation. Using the engineered grafts, the investigators then conducted either peripheral or coronary artery bypass in the dog recipients and showed that they functioned effectively for at least 1 month. Together, these results demonstrate that durable vascular grafts derived from allogeneic donors and rendered nonimmunogenic by removal of donor cells are suitable for surgical transplant. The added advantage of being able to store these off-the-shelf vascular grafts long-term in a simple saline solution means that these can be made ahead of time and then are ready to go whenever they are needed. Growing blood vessels for a healthier life is as real as the home-grown asparagus in your garden. Autologous or synthetic vascular grafts are used routinely for providing access in hemodialysis or for arterial bypass in patients with cardiovascular disease. However, some patients either lack suitable autologous tissue or cannot receive synthetic grafts. Such patients could benefit from a vascular graft produced by tissue engineering. Here, we engineer vascular grafts using human allogeneic or canine smooth muscle cells grown on a tubular polyglycolic acid scaffold. Cellular material was removed with detergents to render the grafts nonimmunogenic. Mechanical properties of the human vascular grafts were similar to native human blood vessels, and the grafts could withstand long-term storage at 4°C. Human engineered grafts were tested in a baboon model of arteriovenous access for hemodialysis. Canine grafts were tested in a dog model of peripheral and coronary artery bypass. Grafts demonstrated excellent patency and resisted dilatation, calcification, and intimal hyperplasia. Such tissue-engineered vascular grafts may provide a readily available option for patients without suitable autologous tissue or for those who are not candidates for synthetic grafts.

Decellularized tissue-engineered blood vessel as an arterial conduit

Arterial tissue-engineering techniques that have been reported previously typically involve long waiting times of several months while cells from the recipient are cultured to create the engineered vessel. In this study, we developed a different approach to arterial tissue engineering that can substantially reduce the waiting time for a graft. Tissue-engineered vessels (TEVs) were grown from banked porcine smooth muscle cells that were allogeneic to the intended recipient, using a biomimetic perfusion system. The engineered vessels were then decellularized, leaving behind the mechanically robust extracellular matrix of the graft wall. The acellular grafts were then seeded with cells that were derived from the intended recipient—either endothelial progenitor cells (EPC) or endothelial cell (EC)—on the graft lumen. TEV were then implanted as end-to-side grafts in the porcine carotid artery, which is a rigorous testbed due to its tendency for graft occlusion. The EPC- and EC-seeded TEV all remained patent for 30 d in this study, whereas the contralateral control vein grafts were patent in only 3/8 implants. Going along with the improved patency, the cell-seeded TEV demonstrated less neointimal hyperplasia and fewer proliferating cells than did the vein grafts. Proteins in the mammalian target of rapamycin signaling pathway tended to be decreased in TEV compared with vein grafts, implicating this pathway in the TEVs resistance to occlusion from intimal hyperplasia. These results indicate that a readily available, decellularized tissue-engineered vessel can be seeded with autologous endothelial progenitor cells to provide a biological vascular graft that resists both clotting and intimal hyperplasia. In addition, these results show that engineered connective tissues can be grown from banked cells, rendered acellular, and then used for tissue regeneration in vivo.

Neoadjuvant Chemoradiation for Rectal Cancer Reduces Lymph Node Harvest in Proctectomy Specimens

PurposeThe purpose of this study was to compare the number of lymph nodes retrieved following proctectomy for rectal cancer in patients either receiving no neoadjuvant therapy versus those treated with standard preoperative chemoradiation.MethodsA retrospective review was performed of all consecutive patients that underwent proctectomy for rectal cancer from 1997–2006. Specimens from patients that received neoadjuvant therapy were compared to patients that did not receive preoperative chemoradiation.ResultsOf a total of 286 patients, 188 received neoadjuvant therapy and 88 did not. More patients with stage II or higher cancers received neoadjuvant therapy. Overall, fewer neoadjuvant patients underwent an anastomotic procedure than the no neoadjuvant group (17% vs. 7% APR). Significantly fewer total lymph nodes were retrieved in the neoadjuvant therapy patients compared to those who did not receive preoperatively therapy (Neo 14.6 ± 0.6 vs. No-Neo 17.2 ± 1.1, p < 0.029).ConclusionsStandard neoadjuvant therapy significantly decreases the number of lymph nodes retrieved following proctectomy for patients with rectal cancers. Quality initiatives or performance measures evaluating lymph node harvest following proctectomy should reflect the use of preoperative chemoradiation.

Laparoscopic Nissen fundoplication for treating reflux in lung transplant recipients

Gastroesophageal reflux disease may contribute to pulmonary injury and the development of bronchiolitis obliterans syndrome in lung transplant patients. As a result, such individuals are increasingly likely to undergo corrective gastrointestinal surgery. The present study collected outcome data for 28 lung transplant patients with documented reflux who underwent an uncomplicated laparoscopic Nissen fundoplication at our institution. The results were compared to data from 63 nontransplant reflux patients who had undergone the procedure over the same time period. All Nissen fundoplications were conducted by the same surgeon. There were no intraoperative or perioperative deaths in either patient group. Operative parameters did not differ but the postoperative hospital stay was significantly greater for the lung transplant patients (P < 0.05). Seven transplant patients (25%) were readmitted within 30 days compared to two readmissions (3.2%) in the reflux group. Five transplant patients (17.9%) have died, all from pulmonary complications; on average, death occurred 15.5 months after the Nissen surgery. There have been no deaths in the reflux group. These data indicate that laparoscopic Nissen fundoplication can be performed on lung transplant recipients to treat reflux. The average hospital stay is longer and there are more frequent readmissions in this population, but this does not appear to be due to any Nissen-related morbidity.

Arteriovenous Fistula Creation using the Optiflow Vascular Anastomosis Device: A First in Man Pilot Study

Although arteriovenous fistulae are the preferred form of dialysis vascular access they continue to have significant problems with maturation failure. The Optiflow device is a sutureless anastomotic conduit which could potentially reduce surgical time and also standardize the surgical procedure. We report herein on the “First in Man” experience with the Optiflow device.

Tissue engineered vascular grafts: Origins, development, and current strategies for clinical application

Since the development of a dependable and durable synthetic non-autogenous vascular conduit in the mid-twentieth century, the field of vascular surgery has experienced tremendous growth. Concomitant with this growth, development in the field of bioengineering and the development of different tissue engineering techniques have expanded the armamentarium of the surgeon for treating a variety of complex cardiovascular diseases. The recent development of completely tissue engineered vascular conduits that can be implanted for clinical application is a particularly exciting development in this field. With the rapid advances in the field of tissue engineering, the great hope of the surgeon remains that this conduit will function like a true blood vessel with an intact endothelial layer, with the ability to respond to endogenous vasoactive compounds. Eventually, these engineered tissues may have the potential to supplant older organic but not truly biologic technologies, which are used currently.

Maternal Insufflation during the Second Trimester Equivalent Produces Hypercapnia, Acidosis, and Prolonged Hypoxia in Fetal Sheep

Background:Anecdotal reports suggest that the second trimester is the safest time to conduct a laparoscopic procedure on a pregnant patient, but this supposition has not been tested empirically. Methods:Previously instrumented preterm sheep (total n = 8) at gestational day 90 (term, 145 days) were anesthetized and then insufflated with carbon dioxide for 60 min at a pressure of 15 mmHg. Cardiovascular parameters were continuously recorded while blood gas status was determined before and at 15-min intervals during and up to 2 h after insufflation. Results:Insufflation produced minimal maternal blood gas or cardiovascular changes except for a significant reduction in uterine blood flow. The decrease in perfusion increased fetal arterial blood partial pressure of carbon dioxide and decreased fetal pH, oxygen saturation, and oxygen content; there was also progressive fetal hypotension and bradycardia. After manually deflating the ewe, uterine blood flow returned to normal, and the fetal partial pressure of carbon dioxide and pH changes resolved within 1 h. However, fetal oxygen saturation and content remained depressed, and fetal cardiovascular status continued to decline during the 2-h postinsufflation monitoring period. Conclusion:Previous studies with near-term sheep determined that carbon dioxide pneumoperitoneum produces respiratory acidosis but does not decrease fetal oxygenation. In contrast, the current findings indicate that in the preterm fetus, insufflation-induced hypercapnia and acidosis are accompanied by prolonged fetal hypoxia and cardiovascular depression. This result suggests that additional work should be conducted to confirm the presumed safety of conducting minimally invasive procedures during the second trimester.

A Description of the Preterm Fetal Sheep Systemic and Central Responses to Maternal General Anesthesia

BACKGROUND: The second trimester is recommended as the optimal time to conduct a surgical procedure on pregnant patients, even though the fetal responses to anesthesia at this age are not known. Here we assessed the responses of preterm fetal sheep to a standard anesthetic regimen of midazolam, thiopental, and isoflurane. METHODS: Variables were monitored in previously instrumented preterm pregnant sheep before, during, and after 4 h of general anesthesia. Isoflurane produced moderate fetal hypotension and bradycardia, whereas extubation was accompanied by increases in fetal heart rate and mean arterial blood pressure. RESULTS: We observed an initial increase in fetal Sao2 followed by a gradual decline to baseline. Within the fetal brain, oxygenated hemoglobin changed by <10% (nonsignificant) and deoxygenated hemoglobin and total hemoglobin varied by <5%. Overall, although O2 levels within the preterm fetal brain were not independently enhanced by isoflurane (as occurs in the older fetus and in the adult), they did remain constant even as fetal mean arterial pressure decreased by more than 20%. By extension, we failed to identify changes in cerebral oxygenation that could be construed as injurious. CONCLUSION: Any adverse preterm fetal response to maternal surgery should not be attributed solely to the actions of general anesthesia upon the fetus.

Tissue-engineered vascular grafts: autologous off-the-shelf vascular access?

Dialysis grafts have provided reliable access for millions of patients in need of renal replacement therapy. However, regardless of the material used for artificial dialysis grafts their mean patency remains generally poor and infection rates are greater than native arteriovenous fistulas. The need for superior alternatives to conventional synthetic materials used for vascular access has been an area of investigation for more than 25 years and recently there has been a great deal of progress in the field of tissue-engineered vascular grafts. Many of these technologies are either commercially available or are now entering early phases of clinical trials. This review briefly covers the history, potential advantages, and disadvantages of these technologies, which are likely to create an impact in the field of vascular access surgery.

Maternal and preterm fetal sheep responses to dexmedetomidine.

BACKGROUND The α(2) adrenergic receptor agonist dexmedetomidine has some unique pharmacologic properties that could benefit pregnant patients (and their fetuses) when they require sedation, analgesia, and/or anesthesia during pregnancy. The purpose of the present study was to delineate maternal and fetal responses to an intravenous infusion of dexmedetomidine. METHODS This study was conducted on surgically-recovered preterm sheep instrumented for physiologic recording and blood sampling. Maternal and fetal cardiovascular and blood gas parameters and fetal cerebral oxygenation levels were recorded before, during, and after 3h of dexmedetomidine infusion to the ewe at a rate of 1 μg/kg/h. RESULTS Drug infusion produced overt sedation but no apparent respiratory depression as evidenced by stable maternal arterial blood gases; fetal blood gases were also stable. The one blood parameter to change was serum glucose, By the end of the 3-h infusion, glucose increased from 49±10 to 104±33mg/dL in the ewe and from 22±3 to 48±16mg/dL in the fetus; it declined post-drug exposure but remained elevated compared to the starting levels (maternal, 63±12mg/dL, P=0.0497; and fetal, 24±4mg/dL, P=0.012). With respect to cardiovascular status, dexmedetomidine produced a decrease in maternal blood pressure and heart rate with fluctuations in uterine blood flow but had no discernable effect on fetal heart rate or mean arterial pressure. Likewise, maternal drug infusion had no effect on fetal cerebral oxygenation, as measured by in utero near-infrared spectroscopy. CONCLUSIONS Using a clinically-relevant dosing regimen, intravenous infusion of dexmedetomidine produced significant maternal sedation without altering fetal physiologic status. Results from this initial acute assessment support the conduct of further studies to determine if dexmedetomidine has clinical utility for sedation and pain control during pregnancy.