Distention Media Selection & Management

Malcolm G. Munro MD, FRCSC, FACOG
KEY POINTS
  • Distention media are needed for hysteroscopy for the purpose of converting the potential space of the endometrial cavity to a real space 
  • Options for uterine distention include CO2 and fluid media. CO2 is not suitable for operative procedures
  • Hypotonic, non electrolytic fluids solutions containing glycine, sorbitol and mannitol are required for the use of RF electrosurgery with monopolar instrumentation
  • Excessive absorption of hypotonic fluids can result in fluid overload and hypotonic hyponatremia, causing permanent neurological complications or death.
  • Normal saline is a safer media because, even with moderate levels of absorption, electrolyte levels are normal
  • Bipolar RF instrumentation require saline media, a circumstance that makes them safer than monopolar instrumentation when excess media is absorbed into the systemic circulation. 
  • Distention media management systems that control infusion pressure and monitor systemic absorption are recommended when it is known or suspected that the integrity of the myometrium will be breached during the procedure. 
  • The maximum allowable absorption of electrolyte free media ranges from 500 mL to a maximum of 1,000 mL
  • The maximum allowable absorption of normal saline ranges from 1,500 to 2,500 mL depending in large part on their baseline cardiopulmonary function
  • Hysteroscopic programs should have protocols that guide the termination of procedures when the preset thresholds are met
BACKGROUND
Hysteroscopy and hysteroscopic surgery require that the endometrial cavity be distended with a clear medium to create a viewing space. While a variety of media have been used over the decades the realistic options include gaseous CO2 and a spectrum of low-viscosity fluids that include non-electrolyte containing solutions of glycine, sorbitol, mannitol and dextrose in water, and electrolyte containing isotonic solutions such as normal saline. Should any of these substances reach the systemic circulation in a threshold volume, significant adverse events may result that are typified by fluid and electrolyte disturbances. Consequently, the hysteroscopic surgeon must be intimately aware of the appropriate use of these agents and of the measures necessary to limit the risk of related adverse events. 
Many are surprised at how quickly large volumes of distending media can leave the endometrial cavity and enter either the peritoneal cavity or the systemic circulation – or both. When sufficient intrauterine pressure is achieved, the loss through the fallopian tubes is understandable. But it takes relatively little pressure for the media to ender the systemic circulation should myometrial dissection result in the transection of endometrial and myometrial veins. If electrolyte free media are used, the patients can develop severe hyponatremia, right heart failure, and pulmonary and cerebral edema with resulting neurologic injury and even death. Available evidence suggests that that cerebral edema may be first identified following the absorption of as little as 500 mL of electrolyte free media (1, 2). If normal saline is used, electrolyte disturbances are essentially absent limiting the risk to fluid overload. Regardless, it is critical that the surgical team have the systems and protocols necessary to reduce the risk of systemic absorption, to monitor the fluid deficit and to appropriately and promptly manage the patient if excess absorption is suspected or detected.
CARBON DIOXIDE MEDIA
While CO2 distention media had a significant presence in the middle of the 20th century, its value and use has precipitously declined in the past 20 years. The use of gaseous CO2 for endometrial distension was introduced by Rubin almost 100 years ago, and it still can be used as a distending medium for diagnostic hysteroscopy. For instillation of gas CO2 media, the insufflator must be especially designed for hysteroscopy; the use of laparoscopic insufflators should be absolutely avoided. Laparoscopic insufflators used for hysteroscopy have been associated with massive CO2 embolism and death since gas flow rates cannot be reliably adjusted below 1 L/min. For hysteroscopy, the hysteroscopic insufflator is attached both to a pressurized CO2 tank and to the inflow channel of the hysteroscope system whereby it is transmitted to the endometrial cavity. While as long as the patient is not bleeding, the view is excellent, there exists high quality evidence from randomized trials that CO2 is associated with increased patient discomfort, reduced patient satisfaction and procedural times compared to the fluid media(3, 4). Furthermore, bleeding substantially interferes with evaluation, and transaction of vessels risks CO2 embolus, circumstances that limit the use of CO2 as a medium for most hysteroscopic surgical centers. 
FLUID MEDIA
Media delivery systems generally refer to the method whereby the distending media are delivered from the container or reservoir to the endometrial cavity. There exist a number of media delivery systems ranging from simple syringes to gravity-based infusion to automated pumps designed to maintain a preset pressure and systems for the estimation of the amount of fluid absorbed into the systemic circulation. 
Electrolyte Free Fluids
Low viscosity media without electrolytes include 3% sorbitol, 1.5% glycine, 5% mannitol and combined solutions of sorbitol and mannitol. These media are necessary when RF electrosurgery is to be performed using monopolar instruments. Should monopolar RF instruments be used in saline, the entire volume in the uterus becomes the electrode, a circumstance that prevents any thermal and therefore surgical effect on tissue. 
 Theoretically, 5% mannitol (osmolality 274 mOsmol/liter)) is a safer choice than either 1.5% glycine (200 mOsmol/liter) or 3% sorbitol (179) mOsmol/liter) because of its near normal osmolality. Indeed, one group of investigators have shown this to be the case in a comparative study(10). However, in a Korean comparative study of 2.7%sorbitol-0.54%mannitol and 5% glucose distending media there were no differences in intraoperative and postoperative levels of serum sodium, potassium, chloride, glucose and osmolality between groups (11). Consequently, available evidence is not consistent regarding the relative safety of 5% mannitol. 
The major disadvantage of hypoosmolar, electrolyte free media is the potential for fluid and electrolyte disturbances when there is excess media absorption (2, 5). There are related adverse neurologic events, including hypotonic encephalopathy, that appear to be more common in reproductive aged women than in those who are postmenopausal (6). Premenopausal women have a sodium-potassium adenosine triphosphatase (ATP-ase) pump that is inhibited by female sex steroids, a circumstance that impairs the shunting of sodium, and, indirectly, water, out of the cell, an effect that appears to be reversed by the administration of GnRH agonists (7). This circumstance makes hyponatremia even more problematic for premenopausal women who undergo hysteroscopic surgery without the use of GnRH agonists (8). Several deaths have been reported to be associated with the use of glycine or sorbitol for operative hysteroscopic surgery (9). 
Normal Saline
The most commonly available “physiologic” solution is 0.9% Normal saline, a uterine distension medium that is safer for patients and one that allows for more extensive procedures because there is greater tolerance of systemic absorption. These features also make normal saline a good choice for minor procedures performed in the office. The advent of bipolar RF instrumentation has allowed surgeons to use saline as a distending medium even for electrosurgical procedures. Ringer’s lactate has properties similar to those of normal saline however, there has been no published investigation of Ringer’s lactate for hysteroscopic applications(6).
MEDIA DELIVERY AND MANAGEMENT SYSTEMS
There are essentially three components of fluid management – infusion into the endometrial cavity, removal from the endometrial cavity and estimation or quantification of the amount of fluid that might be transferred to the systemic circulation through the fallopian tubes into the peritoneal cavity or via intravasation through breaches in endometrial or myometrial vascular integrity. There exist a number of media delivery systems, ranging from simple syringes, to gravity-based infusion to automated pumps designed to maintain a preset pressure and systems for the estimation of the amount of fluid absorbed into the systemic circulation.
Syringes
Relatively large-capacity syringes (30 – 50 mL) can be used for office diagnostic procedures for visualization only, and in the absence of bleeding. The syringe can be operated by either the surgeon or an assistant and is either connected directly to the sheath or attached by connecting tubing. 
Gravity-based Systems
Continuous hydrostatic pressure is can be created by using an IV pole or other suitable adjustable device to elevate the container of distention media to a height that is above the level of the patient’s uterus. The intrauterine pressure achieved by this approach is the product of the width of the connecting tubing and the elevation. With 10-mm diameter tubing he intrauterine pressure ranges from 70 - 100 mm Hg when the container is positioned from 1¬ to 1.5 m above the uterine cavity. The wide caliber tubing is connected to the inflow port of the system or sheath using equally wide connector tubing that allows maintenance of adequate pressure. 
Pressurized Delivery Systems
In some instances, and often transiently, gravity-based systems are inadequate for distension of the endometrial cavity. Circumstances that contribute to this situation include leakage around the cervix, a corpus encumbered with adenomyosis or leiomyomas or the absence of the wide diameter tubing (called “C-Tubing”) necessary to optimize flow to the endometrial cavity. In such instances, increased infusion pressure may be desirable. The simplest pressurized delivery system can be created by positioning a large pressure cuff around the bag of distension media. It should be remembered that this pressurized approach does not allow precise control of the pressure, so that in long cases, or those associated with dissection into the myometrium, excessive systemic extravasation could occur, especially if the intrauterine pressure is sustained for a considerable amount of time.
Currently, most available infusion pumps are those included in the media management systems designed specifically for operative hysteroscopic procedures. However, there exist a variety of isolated infusion pumps that range from simple pressurized devices to those that maintain a preset intrauterine pressure. However – and this is important – such simple pump devices continue to press fluid into the uterine cavity regardless of resistance, a circumstance that facilitates excess systemic absorption (12). As a result, a general recommendation is that the use of such pumps should only be undertaken in the context of an efficient and effective method for measuring fluid deficit. 
Measurement of Systemic Absorption
Quantification of systemic absorption of distension media requires that a system accurately measure four parameters: 1. Volumetric inflow into the endometrial cavity; 2, Volumetric outflow from the resectoscope; 3. Fluid captured by the perineal collection drape; and 4. Otherwise uncaptured fluid from other sources such as the drapes or that which has escaped to the floor. Unfortunately, manual measurement of these parameters is severely impaired by the variable volume present in media containers. For example, sorbitol and glycine containers have been reported to contain fluid volumes that range from 3 to 5% higher than that indicated on the label (13). It can be difficult to capture of all the media that exits the uterus, including that which may saturate the sterile drapes and/or fall on the floor of the procedure or operating room. There do exist floor suction systems that can be attached to the fluid collection and therefore can be included in the calculation of fluid deficit.
The preferred approach to hysteroscopic media management, particularly in higher risk procedures, is the use of an automated fluid measurement system that considers the media delivered to the uterus and the continuous retrieval and measurement of the fluid returned to the system from the hysteroscope or resectoscope, from the under buttocks collection drape and from other sites such as the floor. Collectively these real time data allow continuous calculation of an imputed volume of systemic absorption of the distending media. Such systems compensate for the variable volume in the infusion bags by either measuring the weight or quantifying the volume of infused media to calculate the amount of fluid delivered to the endometrial cavity. Collection of all the fluid either escaping or removed from the endometrial cavity optimizes the chance that total weight or volume can be subtracted from infused volume allowing for calculation of systemic absorption. Most contemporary systems provide a digital display of simultaneous real-time intravasation rate and the running fluid deficit. This allows the surgeon to essentially eliminate the complications associated with excess absorption of distending media (14).
When automated systems are not available, a manual measurement protocol can be considered, but there exist several pitfalls to this approach. Manual monitoring protocols require that systemic “absorption” be estimated frequently – at least every 10 minutes. To do this, the team must attempt to quantify both the total volume of inflow and outflow to determine the total infused volume, an issue discussed previously. One option is to weigh fluid containers prior to the procedure and then stop the procedure intermittently while a more careful estimate of fluid absorption status is obtained, including measuring the weight of the “returned” media. Additional safety measures could include reducing the maximum threshold for measured fluid loss and careful cardiovascular evaluation frequently during the procedure.
ESTABLISH DISTENTION MEDIA GUIDELINES AND PROTOCOLS
It is critically important that any hysteroscopy program have clearly defined guidelines, and, in some instances, protocols, that govern the use of distension media. Part of any protocol is surgeon and staff familiarity with the systems in use. The surgeon must be familiar with the function, assembly and management of the system that should collect not only fluid from the outflow port of the sheath, the underbuttock collection drape, and, ideally, that which spills onto the floor beneath the foot of the operating table
The major consideration is the prevention of systemic overload and electrolyte disturbances. Bipolar instrumentation is recommended wherever RF based procedures are performed. If only monopolar RF instrumentation is available, an automated fluid management system should be used because of the risk and consequences if substantial amounts of electrolyte free fluid are absorbed into the systemic circulation. For these reasons, it is also reasonable to state that such procedures are best performed in an environment where both rapid assessment of electrolytes and intensive care facilities are available should overload be suspected. 
There are several measures that can be adopted that may reduce the risk of fluid overload. The first is judicious restriction of intravenous fluid by the anesthesiologist (if there is one), an approach that must be done carefully, but which may provide a greater “buffer” for systemic absorption. The second is surgeon management of the infusion pressure of the distending media. The amount of distending media absorbed is related to the intracavitary pressure; exceeding the mean arterial pressure may facilitate absorption into the systemic circulation (15). Consequently, the intrauterine pressure used should be the minimum that creates distention adequate to safely perform and complete the procedure(16). With a gravity-based system, hydrostatic pressure in mm Hg can be estimated by calculating the product of the width of the connecting tubing and the elevation. For operative hysteroscopy with 10-mm tubing, intrauterine pressure is about 80 to 120 mm Hg when the bag is between 1 and 1.5 meters above the endometrial cavity.
Guidelines for fluid management have been published by the AAGL based on the combination of available evidence and expert consensus (17). When electrolyte-free, low-viscosity fluids such as glycine, sorbitol, or mannitol are used and the estimated or measured systemic absorption reaches 1 L, the procedure should be stopped, and serum electrolyte levels measured. This threshold volume should be revised down to as low as 500 mL for those with cardiopulmonary compromise. If the maximum fluid absorption is reached, the administration of an appropriate dose of furosemide should be considered. When normal saline is used, hyponatremia is not a consideration, so the volume limit can be expanded to as high as 2.5 liters, again revised downward for those who are considered less tolerant of these levels of absorption(17).
PERIOPERATIVE MANAGEMENT 
Before the Procedure
Reducing the risk of media related complications begins well before the procedure starts. It is important to recognize the procedure types prone to excess media absorption. For such cases a number of risk reducing preoperative measures can be implemented. For example, diagnostic hysteroscopy and simple polypectomy and other procedures that do not involve the myometrium present a very low risk for media-related complications. Such procedures can be performed with gravity-based inflow and outflow systems. On the other hand, there are a number of procedures and techniques that place the patient at higher risk including those that are prolonged in time and operations that involve dissection into the myometrium. Such procedures include transcervical endometrial ablation with a loop electrode or resection of FIGO Type I or Type II leiomyomas. Available evidence suggests that the risk of resectoscopic myomectomy associated fluid overload is directly related to the duration of the procedure, the diameter of the lesion(s) and the proportion of the leiomyoma that is within the myometrium (18) – The FIGO Type.  
For premenopausal women, the volume of systemically absorbed distension media may be reduced with the preoperative use of GnRH analogs (7, 19). However, the actual value of routine GnRH analog administration prior to uterine resectoscopic surgery for this purpose has not been clearly determined, thus administration is left to the discretion of the surgeon considering anticipated complexity of the procedure(20). 
Another preventative strategy that can be used immediately prior to cervical dilation is the administration of dilute vasopressin 4 mL (total of 8 mL) of a dilute solution (0.01U/mL) injected deeply at 4 and 8 o’clock in the cervix. Vasopressin administration has been shown to significantly reduce systemic fluid absorption by up to 50% in the available studies (21-23). Incidentally this protocol has been demonstrated effective at reducing the force required for dilation of the cervix(24).
Well before the procedure begins the surgical team should determine which media and, if necessary, the monitoring system or methodology to use for a given case. It is recommended that the default media be normal saline unless monopolar RF instrumentation is to be used whereupon it will be necessary to select from 1.5% glycine, 3% sorbitol or 5.0% mannitol. 
An important part of the assessment is the patient herself. Those individuals who have cardiovascular compromise may well be best managed in an institutional environment, and if she is using diuretics for therapy, then baseline serum electrolytes should be obtained. For some, it will be appropriate to have medical and anesthetic consultations well before the procedure. With all but the simplest procedures, an accurate distending media monitoring system should be utilized, and it will be frequently necessary and appropriate to modify the threshold of systemic absorption that will trigger cessation of the procedure based upon the patient’s medical condition. As stated above, and restated here, quantification of systemic media absorption requires a media management protocol that preferably includes an automated fluid management system.
Management of Distention Media Overload
The management of recognized intraoperative excessive fluid intravasation will vary depending on the amount and type of media, the patient's medical condition, the surgeon’s intraoperative assessment, and the status of the procedure – in other words how far along is the case? How long will it be until it is done? As stated, a protocol should exist stating that when the deficit reaches a predetermined limit the procedure should be expeditiously terminated. As previously discussed, for electrolyte free media this threshold would range from 750 to 1000 mL while for normal saline the range is 1500 to 2500 mL, amounts that will vary to a degree depending on the patient’s baseline functional status(17).
If the predetermined deficit is approached or reached when using electrolyte-free media such as glycine, sorbitol or mannitol, measurement of serum electrolytes should be expeditiously accomplished and furosemide given intravenously, in a dose of 10 to 40mg depending on renal function. While measurement of electrolytes may not be necessary for women who approach the upper limit of saline media absorption, careful evaluation for signs of clinical overload will assist medical management. 
Should excess media be absorbed, and especially if it is electrolyte free fluid, postoperative management should include the support of a consultant with expertise in critical care. Patients with overload may experience one or a combination of cerebral edema, pulmonary edema and right heart failure and could require ventilatory support, the use of diuretics and inotropic agents, and the judicious use of hypertonic saline solutions.
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