Hysteroscopic Fluid Management

Hysteroscopy performed with liquid media at a sufficient pressure, usually between 70 mm and 90 mm Hg of true intrauterine pressure, will bring about satisfactory uterine distention, but not necessarily adequate visualization. Depending on the amount of intraoperative bleeding, an adequate flow rate of the media with separate channels of entry and egress is necessary to have a clear operative field.

Balanced against these prerequisites are fluid overload and/or electrolyte imbalance as a consequence of intravasation of the media via the uterine vasculature. When arterial bleeding is encountered, a simple consequence of pressure relationships occurs. If arterial pressure exceeds that within the cavity, blood flow hinders visualization; when pressure relationships are reversed, media flows into the arterial tree, sometimes quite rapidly. Ideally, intracavitary pressure should just equal mean arterial pressure. Transducers mounted anywhere on the operating instrument or pump do not measure true uterine pressure, unless the tip of the sensor is in the uterine cavity.

Unlike laparoscopy, one is not dealing with an essentially closed system in which pressure is equal throughout. In the case of hysteroscopy, fluid can pass through the tubes, into the uterine vessels, around the sheath in the cervix, and out via the outflow channel resulting in a pressure gradient. The differential between true cavity pressure and the transducer pressure readings is minimal (about 10 mm Hg) when the flow valve on the outflow tract is closed. The differential increases to about 40 mm when the flow valve is completely open. This gives the operator full control of the situation at all times by manipulating the valve to obtain satisfactory distention and visualization, assuming that the pressure head for delivery is adequate.

Use of Distending Medium

Generally, when the venous system is at low pressure, inflow of medium should be more of a problem than is actually the case. The myometrial fibers surrounding these soft-walled vessels control menstrual blood loss to a great extent, and function similarly in a situation when the uterus is distended, although the presence of venous lakes beneath the endometrium can be a problem.

In a randomized, prospective double-blinded study, our research has demonstrated that prophylactic use of dilute vasopressin (10 units in 50 ml saline) injected as 3 or 4 ml into the stroma of the cervix, affords protection against both intraoperative bleeding and intravasation by causing intense myometrial and arterial wall contraction for 20-30 minutes, after which another injection can be made as needed. However, intravasation is still dependent on the duration of the operation, the total volume of fluid used, intrauterine pressure, and the extent to which vascular channels are invaded.

When non-electrosurgical procedures are performed, the distending medium should be a physiologic one of saline or lactated Ringer's solution. This avoids the potential problem of electrolyte disturbance, but does not guard against fluid overload, which can be lethal under extreme circumstances. Some authors advocate using a chilled medium to reduce bleeding, and others have opined that a medium containing mannitol as a “built-in” diuretic is useful. At our institution, we routinely have the anesthesia team limit the amount of intravenous fluids in order to provide the surgical team an extra margin of safety.

There are available systems that allow for electrosurgery and the use of saline as the medium. However, most of these procedures are performed with dilute sorbitol or glycine as the electrolyte-free medium, although the dangers of hyponatremia and hypervolemia exist. Even at low pressure, a prolonged operation with large volumes of inflow will cause a reduction of serum sodium, since the endometrium functions as a dialysing membrane against the medium.

Volume Measurement

In addition to pressure considerations, it is necessary to measure volume instilled/volume collected to calculate the fluid deficit (that amount assumed to have entered the patient¹s vascular system). Estimating the pressure with gravity-fed systems is inherently inaccurate, taking into account the height of the table and other variables. No matter how assiduously the nurses attempt to monitor fluid volumes, the fact that the 3-liter bags used for delivery come as plus or minus 10% precludes volumetric estimation as a reliable technique.

What is needed is a systems approach to instrumentation that will address the issues of patient safety, provide accurate real time access of information for the operator, and give warning signals to the nurses that the reservoir is near empty and that the collecting canister is almost full. The Dolphin® Fluid Management System (Figure 1), which was designed with the engineers of CIRCON, satisfies these prerequisites. This fluid management system works on the principle of measuring the mass of the reservoir 3-liter bag versus the increasing mass of the collecting vessel so that a real-time fluid deficit volume appears on the pump or video screen. An audible and visual alarm system is usually set at 1000 ml. The DOLPHIN also allows for presetting and measurement of fluid pressure at the pump.

Summary

Ideally, devices such as these will greatly lessen the incidence of surgical fluid overload during operative hysteroscopy, provided that the surgeons pay attention to the information available to them. However, an additional early warning system is provided by the anesthesia team. It is also important to note that an increase of 15 mm Hg or more in diastolic pressure compared with baseline is usually an indication of impending pulmonary edema. Under these circumstances, the surgery should be halted, electrolytes checked, and intravenous diuretics, such as 10-20 mg of furosemide should be given. Urinary output and serial electrolytes are monitored. Use of hypertonic saline to correct extreme hyponatremia is controversial, but may be considered if the degree of abnormality gives rise to EKG changes, or if there is a risk of cerebral damage.

Operative hysteroscopy should be a safe procedure. Problems of fluid management constitute a serious risk factor, but can be readily controlled with currently available systems of fluid delivery and measurement. At our institution we have seen sudden jumps in fluid deficit attributable to entry into vascular channels not apparent to the operator, so the take-home message is to pay attention to what your monitors tell you.

Dr. Corson is a clinical professor of obstetrics and gynecology, and section head, reproductive endocrinology, at Thomas Jefferson University School of Medicine. He is director of the In Vitro Fertilization Program, Pennsylvania Reproductive Associates at Thomas Jefferson University Hospital, and director of the Women's Institute for Fertility, Endocrinology, and Menopause, in Philadelphia, PA.