Gastric Transmural Pressure Measurements In Vivo: Implications for Natural Orifice Transluminal Endoscopic Surgery (NOTES®)

Abstract

Introduction: There is currently no consensus on the best method of closing the gastrotomy in NOTES. One reason is that there is no agreement on the pressures acting on the gastric wall that might disrupt closure and result in leakage of gastric contents. Pressure measurements reported previously are relative intragastric pressures measured against ambient pressure in the lab, not versus intra-abdominal pressure, which is the true environment of the stomach. We hypothesized that forces acting on the stomach to promote disruption of a gastrotomy are much smaller than previously thought, and consist of the difference between the intragastric and extragastric pressures, that is, the gastric transmural pressure gradient. Methods: Twelve 35-45 kg swine were placed under general anesthesia. The pressures in the abdominal cavity and the gastric lumen were measured simultaneously. A high-resolution manometric catheter was inserted into the stomach through a gastroscope, and an identical catheter was placed in the abdominal cavity through an abdominal wall puncture. Pressures were measured under various conditions including rest, simulated cough, and Valsalva maneuver. These measurements were performed with the stomach and abdomen empty, stomach inflated / abdomen empty, stomach empty / abdomen inflated to 12 mm Hg, stomach filled with 1 liter of water (to simulate a liquid meal) / abdomen empty, and stomach filled with water / abdomen at 12 mm Hg. Tracings of pressure measurements were overlaid graphically and also subtracted in real time, yielding a continuous (difference) measurement of the gastric transmural pressure gradient. Results: Measurements where both the stomach and abdomen were empty were hampered by artifact due to the manometry catheter impacting against tissue. When there was air or water around the catheters, good quality tracings were obtained. The average peak pressure generated in the abdomen during simulated cough was 35.4 mm Hg (stdev14.3) and during Valsalva it was 30.7 mm Hg (stdev 11.5) for an average of 2.9 seconds (stdev 0.6). The mean gastric transmural pressure gradient during these conditions was only 0.7 mm Hg (stdev 0.9). Conclusion: Forces acting on the gastrotomy to induce disruption and leakage are much smaller than previously believed, with an average pressure gradient of only 0.7 mm Hg. This has bearing on the durability and method of gastrotomy closure in NOTES.