An ultimate goal of surgery is “scarless” surgery, not only because of the improved cosmetic outcome but also because the “stress” of surgery appears to be less when it is possible to minimize or avoid incisions in the skin and body wall. Natural Orifice Translumenal Endoscopic Surgery (NOTES) involves performing surgical procedures using a flexible endoscope passed through a natural orifice (mouth, vulva, urethra, anus) and then through an opening in the trachea, esophagus, stomach, vagina, bladder, or colon.¹ When the surgical procedure is performed only with a single point of access and a flexible endoscope, it is considered “pure” NOTES. When the endoscope is through a natural orifice and combined with a laparoscopic approach, the surgical procedure is considered a “hybrid” NOTES technique.

NOTES grew out of the merger of two technologies in human medicine: laparoscopic surgery and interventional endoscopy. Surgeons performing less invasive surgery and gastroenterologists performing therapeutic endoscopic procedures (e.g., percutaneous endoscopic gastrotomy [PEG] tube placement, drainage of pancreatic cysts and necrosis, ultrasound-guided fine-needle aspirates) merged the tools and techniques to develop what is now known as NOTES. The first NOTES procedure was presented in 2000 at Digestive Disease Week by Dr. Anthony Kalloo, a gastroenterologist, and it involved a transgastric approach to the peritoneal cavity in swine to perform peritoneoscopy, obtain liver biopsy samples with a flexible endoscope, and close the gastrotomy with endoscopic clips.² Two years later, the first human case of transgastric NOTES appendectomy was presented at the same meeting by Drs. Rao and Reddy from India. Researchers around the world have performed experimental NOTES tubal ligation, cholecystectomy, splenectomy, intestinal anastomosis, gastrojejunostomy, nephrectomy, lymphadenectomy, thoracic access, and colon resection in swine³ and hybrid transvaginal ovariohysterectomy,^4,5 ovariectomy (OVE),⁶ cecectomy,⁷ inguinal hernia repair,⁸ thoracic surgery,^9,10 gastroenterostomy,¹¹ nephrectomy,¹² cholecystectomy,¹³ and prostatectomy¹⁴ in dogs. By these studies, NOTES instrumentation was developed, the safety of translumenal access and infection control methods were established, and the physiology of NOTES procedures and closure of the access means were investigated.2 These animal studies provided a strong foundation for clinical trials of NOTES procedures in humans.³ In recent years, the evolution of NOTES in human surgery has been away from transgastric approaches in favor of transvaginal and hybrid approaches.¹⁵

Theoretical advantages of NOTES over open and laparoscopic surgery include less postoperative pain, decreased wound complications, and fewer adhesions and faster recovery mediated through a decreased inflammatory reaction, as well as improved cosmesis.¹⁶ A recent review of experimental and clinical studies determined no significant advantage or disadvantage to NOTES over laparoscopy in regards to the pulmonary, cardiovascular, and immunologic systems.¹⁷ In animal and human studies, NOTES procedures appear to elicit less postoperative pain than laparoscopic or open surgery.^4,18-20 Although there have been no large studies of complication rates in animals, the German registry of NOTES observed that cholecystectomy performed via transvaginal or laparoscopic approaches in humans resulted in equivalent complication and conversion rates to open surgery.²¹

As for disadvantages, the availability and limitations of endoscopic equipment and lack of familiarity with therapeutic gastroenterology present challenges for wide utilization of NOTES in veterinary medicine. The natural orifice must be prepared properly to prevent infection and of sufficient diameter to accept the endoscope. Poor visualization and issues with navigation, maneuverability, grasping or tissue extraction, and lumen closure are additional issues that must be addressed. The learning curves for NOTES techniques in veterinary medicine are quite steep.²² The pure NOTES procedures nearly always result in longer operative times, and our studies have shown that transgastric access requires approximately 10 OVE procedures to be performed by the same team before approaching proficiency.²² This does not appear to be the case with hybrid transvaginal OVH procedures performed in dogs because operative times are relatively short.^5,23

One of the concerns with translumenal access is the potential for introduction of pathogenic microorganisms into the abdominal or thoracic cavity. When investigators first began to perform the transgastric NOTES procedures in swine, systemic antibiotics were administered.²⁷ Because infections were noted in early studies, efforts were then directed toward sterilizing the instruments that would be used during the procedure. It now appears that when sterile instruments are used, local lavage with povidone-iodine or systemic antibiotics is effective in addressing the potential for infection in NOTES procedures.²⁸ For transgastric procedures, cefazolin 1 g in 200 cc of saline is instilled into the stomach, allowed to dwell for 10 minutes, and then aspirated before the procedure.^6,18 For transvaginal approaches, the vagina is lavaged with povidone-iodine solution for 2 minutes followed by flushing with saline.⁵ In addition, a wide surgical prep is used, and the OR is prepared so that rapid conversion to an open or laparoscopic procedure is possible if needed.

Laparoscopic procedures and all endoscopic procedures in small animals are routinely performed under general inhalation anesthesia. This is necessary to minimize movement, ensure a patent airway, and assist with ventilation if necessary during the procedure. Because insufflation levels are generally lower than routine laparoscopy and procedures are thought to be less painful in NOTES procedures, the feasibility of using conscious sedation for NOTES procedures was investigated in dogs undergoing transgastric NOTES OVE.¹ There were no airway emergencies and no episodes of oxygen desaturation, and the outcomes were comparable to those of inhalant anesthesia.

Although there are many potential routes of access to the abdominal and thoracic cavity, the two most commonly used in small animals are the transgastric and transvaginal approaches.

In pure NOTES procedures, both working channels of the endoscope are used to introduce instruments to perform the procedure. Usually, the guidewire is left in place, and the endoscope is introduced into the abdominal cavity beside the guidewire. In hybrid procedures, visualization is provided by a laparoscope. If the cannula is used for insertion of an instrument (e.g., a stapler or clip applier), then visualization is provided by the endoscope. Procedures are technically much easier with a hybrid approach because rigid and larger diameter traditional laparoscopic instruments can be used. Similar to laparoscopy, additional exposure in NOTES procedures is gained by tilting the table to allow gravity retraction of internal structures.