INSUFFLATORS

Laparoscopy is endoscopic visualization of the peritoneal cavity usually assisted by a pneumoperitoneum that distends and separates the abdominal wall from its contents.  Visual clarity, space to perform diagnostic and therapeutic procedures and maintenance of a normal physiologic state is required for safe effective surgery.  To perform laparoscopic procedures the abdominal cavity is inflated with gas to create the pneumoperitoneum. Gases used for pneumoperitoneum include carbon dioxide (CO2), air, oxygen, nitrous oxide (N2O), argon, helium and mixtures of these gases. Gas delivery systems are composed of a containment cylinder, insufflator (gas throttling down pressure regulating unit), tubing, filter and abdominal entry device or port. Gas cylinders are made of ferrous alloy. The cylinders contain the gas as a liquid under pressure (57 atmospheres).  Over time, the cylinders build up inorganic and organic contamination.  This occurrence requires filtration of the gas prior to insufflation of a patient’s abdomen. The pressure change from the containment cylinder to insufflator and into the patient’s abdomen causes cooling by the Jewel-Thompson effect. When the laparoscope is first introduced into the abdominal cavity lens fogging often occurs.  This phenomenon is due to the relatively cold dry lens being introduced into a warm moist environment causing the dew point to be reached.  This results in condensation forming on the internal lens surface.  When the insufflation gas is heated and hydrated or a surface wetting agent is used, no lens fogging occurs and the visual field is clear.The gases used for pneumoperitoneum have low water content.  CO2 has less than 200 parts per million of water.  Dry insufflation gases cause drying of the peritoneum and result in intact mesothelial cells being lost or desiccated from the peritoneum surface.  To preserve peritoneal surface integrity and decrease the tendency to adhesion formation continuous or intermittent moistening should be performed.All mechanical systems have inherent weaknesses.  Insufflators require proper calibration and maintenance.  Insufflator pressure accuracy depends on the quality of the gauges used in the insufflator.  Wide ranges of variation are seen due to gauge inaccuracy. Pressure testing should be done regularly to assure proper readings. Over time, insufflators become contaminated on their internal and external surfaces.  Germicidal cleaning of external ports is important.  Gas filtration to 0.3 microns prior to abdominal entry assures reduction of quantitative exposure of the peritoneal cavity from these organic and inorganic materials.Initial abdominal entry pressure readings should be low—less than 2-3 mm Hg.  Elevated initial pressures indicate improper placement.  Increased intra-abdominal pressures after proper access can impede venous return and result in potential anesthesia complications.  Pressure on intra-abdominal surfaces due to the pneumoperitoneum can inhibit bleeding.Gas embolism is of particular concern when using insufflators because these devices introduce gas into the body at pressures that can exceed vascular pressure. For example, during hysteroscopic insufflation, insufflators designed to deliver gas at pressures up to 150 mm Hg (a pressure of 100 mm Hg is usually sufficient to distend the uterus for hysteroscopic observation) and flow rates up to 100 mL/min are typically used. If open vessels (primarily veins) are pre-existing or caused by cervical dilation or distention of the uterus, the pressure can force gas into the uterine vessels, where the blood flow can eventually carry any undissolved gas to the heart. false sense of security regarding hemostasis.  Prior to concluding any procedure, surgical sites need to be observed with reduced pressure to assure appropriate hemostasis. To minimize the risks of undissolved gas traveling to the heart when insufflating various body cavities, a highly soluble gas—CO2—is used in most cases. Using an animal model, Corson et al. (1988) examined the safety of using this gas as a uterine insufflant. CO2 was infused at flow rates up to 90 mL/min directly into the femoral vein of several female sheep for prolonged periods. Although some hemodynamic changes occurred at the higher flows used, the sheep tolerated the direct continuous infusion of CO2. This study showed that, because of the high solubility of this gas in blood (54 mL/dL), CO2 bubbles entering from uterine vessels were sufficiently dissolved during transit from the pelvic region before reaching the heart.

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