Gas embolism during hysteroscopic surgery using bipolar or monopolar diathermia: a randomized controlled trial




Objective


The objective of the study was to determine the incidence and amount of gas embolism during hysteroscopic surgery using either monopolar or bipolar diathermia and to investigate the relationship between the severity of gas embolism and the amount of intravasation of distension fluid.


Study Design


This was a randomized, observer-blinded trial. Fifty patients, scheduled for hysteroscopic surgery, were assigned to either monopolar or bipolar diathermia. Transesophageal echocardiography was used to detect and classify gas embolism (grade 0-IV). Intravasation of distension fluid was measured.


Results


Venous gas embolism was observed in all but 1 patient. A higher incidence of more extensive (grade IV) was seen during bipolar diathermia (42% vs 13%; P = .031). Paradoxical embolism was observed in 2 patients. When intravasation exceeded 1000 mL, significantly more grade IV venous gas embolism was seen ( P = .049).


Conclusion


During hysteroscopic surgery, gas embolism was equally observed irrespective of the type of diathermia. However, more extensive embolism was observed when intravasation of distension fluid exceeded 1 L. These results question the acceptance of up to 2500 mL intravasation of distension fluid if bipolar diathermia is used.


Transcervical resection of myoma (TCR-M) and transcervical resection of endometrium (TCR-E) are established and safe minimal invasive hysteroscopic procedures. However, potentially life-threatening venous gas emboli (VGE) and paradoxical embolism have been described. It is thought that during hysteroscopic surgery, exposed uterine veins may allow gas to enter the circulation. These emboli most likely originate from the products of electrosurgical vaporization. They consist of hydrogen, carbon monoxide, and carbon dioxide, and their slow rate of absorption from the circulation allows them to reach the heart.


When monopolar diathermia is used during hysteroscopic procedures, electrolyte free medium (eg, sorbitol 2%) is used for uterine distension. More recently, bipolar diathermia was introduced in hysteroscopic surgery, which allows for the use of an isotonic distension medium (NaCl 0.9%). Consequently, dilutional hyponatremia can be avoided and intravasation of up to 2500 mL is considered to be safe. This provides more time to complete the hysteroscopic myomectomy. However, this higher limit of intravasation may not be as safe as has hitherto been thought because a recent retrospective analysis showed that 43% of patients who had intravasation between 1000 and 2500 mL experienced clinical symptoms that result from the formation of gaseous emboli.


The gaseous particles produced by monopolar electrodes are smaller and might be more likely to enter the circulation. In addition, in vitro experimental studies have shown that monopolar diathermia is associated with more gas production compared with bipolar diathermia. Whether this leads to more intravascular gas embolism is not yet known. No studies are available that compare monopolar and bipolar instruments on the incidence and grade of venous gas VGE during operative hysteroscopy. Therefore, in the present study, the difference between monopolar and bipolar diathermia with respect to the incidence and grade of VGE was determined by using transesophageal echocardiography (TEE).


The primary objective of our study was to investigate the prevalence of VGE between monopolar and bipolar diathermia. In addition, the incidence and grade of VGE were related to the amount of intravasation of distension fluid.


Materials and Methods


Trial design


We conducted a single-center, randomized, semiblinded study. The study was approved by the appropriate ethics committee (Verenigde Commissies Mensgebonden Onderzoek, St Antonius Ziekenhuis, Nieuwegein, The Netherlands) and was registered at the Dutch organization for registration of human research (Centrale Commissie Mensgebonden Onderzoek) under no. 1357. Informed consent was obtained from each patient before inclusion in the study.


Patients


Patients, scheduled for TCR-M because of intracavitary myomas or TCR-E because of medication resistant menorrhagia, were studied. Myomas were measured by transvaginal ultrasound, and the intra cavitary extension of the myomas was determined by saline infusion sonography and consequently graded in type 0-3 according to the Wamsteker classification.


Exclusion criteria were age younger than 18 years or older than 70 years, a history of pulmonary embolism, cardiac disease or any contraindication for TEE (esophageal disease), and American Society of Anesthesiologists (ASA) classification III or higher. Non–Dutch-speaking patients were also excluded. Only patients with an expected operating time that exceeded 0.5 hours were included.


The study protocol was approved by the hospital medical ethical committee, and each participant provided informed, written consent. Patients were randomized by envelopes, designating either monopolar or bipolar diathermia. The study was open by its nature to the principal investigator and the operating gynecologist. The cardiologist who reviewed the TEE images was blinded for both diathermia groups.


Anaesthesia and operative procedure


All patients received propofol-based total intravenous general anesthesia. Monitoring during this procedure included 3-lead electrocardiography with ST-II segment analysis (ST-II), noninvasive blood pressure measurement, pulse oximetry, infrared CO 2 analysis, inspired oxygen fraction, nasopharyngeal temperature, and minute ventilation. Ventilation was controlled to maintain a normal end-tidal CO 2 . A data management system (MetaVision Anaesthesia Information Management System; iMDsoft, Needham, MA) collected all hemodynamic (including ST-segment changes) and ventilatory and respiratory data during the operation with a sample frequency of 1 per minute. Data were stored in the hospital’s central MSQL client/server database.


The operative procedures were performed by 3 experienced gynecologists. Monopolar diathermia (Olympus resectoscope, loop diameter 6.5 mm [Olympus Medical Systems Europa, Hamburg, Germany], connected to Erbe VIO generator (Erbe Elektromedicin, Tübingen, Germany), power setting for cutting: mode dry cut, effect 4, maximum 200 W, for coagulation: mode spray coagulation, effect 1, maximum 75 W) was used in combination with electrolyte-free, 2% sorbitol containing distension fluid. During bipolar diathermia (Olympus resectoscope, loop diameter 5 mm, connected to Erbe VIO generator, power setting for cutting: mode bipolar cut plus, effect 4, maximum 250 W, power setting for coagulation mode: mode bipolar soft plus, effect 4, maximum 250 W), normal saline was used as distension medium. To obtain a clear operating field, gas air bubbles and debris are actively removed from the uterine cavity by a continuous in- and outflow system (Olympus Uteromat, inflow pressure 80 mm Hg, flow 400 mL/min). To minimize the chance of air entrance in the uterus, the surgeon purged the air from all lines and hysteroscopic instruments before starting the resection, and after the change of every fluid bag. Following cervical dilation, the open cervix was minimally exposed to room air and the cervix was kept closed at all times, using a tenaculum forceps. The removal of tissue chips from the uterine cavity with reintroduction of the hysteroscopic instruments followed by accidental introduction of air was minimized.


Outcomes


Intraoperative characteristics including operating time, amount of intravasation, ST-II segment changes, end-tidal CO 2 , peripheral oxygen saturation, and extremes in blood pressure and pulse-rate were retrieved from the data management system.


After the induction and placement of an oropharyngeal tube, an anesthesiologist qualified for TEE inserted an A 5 mHz multiplanar probe (Vivid-i GE Healthcare, Cardiovascular Ultrasound System; GE Medical Systems, Tirat Carmel, Israel). Because air bubbles dissolved in the intravenous fluid disturb the TEE imaging, no intravenous fluids were administered during anesthesia to avoid artifacts.


Before the start of surgery, the gain setting was adjusted to minimize artifact and the midesophageal 4-chamber view was continuously monitored. The first recording was made before the start of surgery. Thereafter a loop of 3 heart cycles was recorded every 2 minutes. A final recording was made at the end of surgery, after the uterus distension was terminated. Because surgery lasted longer than 30 minutes in all patients, each patient had at least 15 recordings. A cardiologist, blinded for the study groups, reviewed the TEE loops.


To quantify the degree of embolism by TEE, a 5-stage classification was used ( Figure ). Grade 0 was defined as the absence of emboli passing through the heart. Grade I embolization was defined as the presence of a limited number (<10 per field of view) of small particles in the right atrium (RA), right ventricle (RV), and right ventricular outflow tract (RVOT). Grade II included moderate amount of small particles (10-20 per field of view). Grade III included many small particles (>20 per field of view), and grade IV included many small and large particles (>20 per field of view), completely filling the diameter of RA, RV, and RVOT.




FIGURE


Degree of embolism

Embolic events observed and graded on transesophageal echocardiography. A, Grade 0 embolization and absence of emboli passing through the heart. B, Grade I embolization and a limited number (<10 per field of view) of small particles in the RA, RV, and RVOT. C, Grade II embolization and moderate amount of small particles (10-20 per field of view). D, Grade III embolization and many small particles (>20 per field of view). E, Grade IV embolization and many small and large particles (>20 per field of view) completely filling the diameter of RA, RV, and RVOT.

RA, right atrium; RV, right ventricle; RVOT, right ventricular outflow tract.

Dyrbye. Gas embolism and intravasation during hysteroscopic surgery uses either monopolar or bipolar diathermia. Am J Obstet Gynecol 2012.


To assess a relationship between the amount of intravasation and the grade of VGE, both monopolar and bipolar groups were brought together and analyzed according to the amount of intravasation. A cutoff point of 1000 mL of intravasation was chosen because this is considered the safe upper limit of intravasation when monopolar diathermia is used.


During the operative hysteroscopy, cardiovascular disturbances that might be the result of VGE are as follows: a drop in end-tidal CO 2 more than 20% of baseline, a blood pressure drop of more than 25% (not explained by hypovolemia), ventricular arrhythmias or electrocardiographic changes (defined as an ST-segment change of more than 2 mm from baseline). Cardiovascular instability was defined when at least 2 of these clinical signs were present.


Statistical and power analysis


The sample size was calculated by a priori power analysis. A target alpha of 0.05 and a beta of 0.8 and a 30% increase in the occurrence of venous emboli using monopolar diathermia compared with bipolar diathermia resulted in a group size of 21 patients.


To correct for a possible loss of patients during follow-up, 25 patients were included in both groups. Data are presented as totals, means, and percentages when indicated. Continuous variables were analyzed using unpaired Student t test or Mann-Whitney U test, whereas categorical variables were analyzed using a χ 2 test. Grading of the embolic events and possible confounders were analyzed using a multivariate analysis of variance for repeated measures. A P ≤ .05 was considered statistically significant. All statistical analyses were performed using SPPS version 17.0 (SPSS Inc, Chicago, IL).




Results


A total of 50 women were included: 40 patients scheduled for TCR-M and 10 patients scheduled for TCR-E. Four patients (3 bipolar, 1 monopolar) were excluded in the final analysis, 2 because of loss of the TEE-images and 2 because no abnormalities were observed during the procedure, and only a diagnostic hysteroscopy was performed.


There were no statistically significant differences with respect to the patient demographic, obstetric, relevant gynecological, and intraoperative characteristics between the study groups ( Table 1 ). One patient in the monopolar and 2 patients in the bipolar group underwent a TCR-M as well as a TCR-E procedure.



TABLE 1

Demographic, clinical and intraoperative characteristics
















































Variable Monopolar group (n = 24) Bipolar group (n = 22)
Age, y 45.5 ± 7.0 43.7 ± 7.4
Weight, kg 73.0 ± 14.2 71.4 ± 13.2
Height, cm 168.9 ± 6.4 166.1 ± 5.9
ASA (1/2) 16/8 17/5
Para status 0/1/2/3 or more 12/2/7/3 10/4/6/2
Hormonal therapy 6 (25%) 8 (36%)
TCR-M/TCR-E 15/10 19/5
Myoma, cm 2.9 (0–5) ± 1.2 2.5 (1–4) ± 0.8
Myoma class (0/1/2/3) 3/11/3/0 3/11/2/0
Surgery, min 49.4 (24–180) ± 29.4 50.8 (30–90) ± 15.1

Data are mean (range) ± SD or number (percentage).

ASA , American Society of Anesthesiologists; TCR-M/TCR-E , transcervical resection of myoma/transcervical resection of endometrium.

Dyrbye. Gas embolism and intravasation during hysteroscopic surgery uses either monopolar or bipolar diathermia. Am J Obstet Gynecol 2012.


VGE were observed in all but 1 patient. Significantly more grade IV VGE was observed during bipolar diathermia (*, P = .05). The total number and percentage of patients experiencing different grades of VGE are shown in Table 2 . In addition, the different grades of VGE were associated with the amount of intravasation in each group. No VGE was observed at levels of intravasation below 240 mL.



TABLE 2

Distribution of venous gas embolism (grade 0-IV) among patients and related amount of intravasation







































Variable Grade 0 Grade I Grade II Grade III Grade IV
Monopolar, n (%) 1 (4) 7 (29) 7 (29) 6 (25) 3 (12)
Intravasation, mL a 240 (–) 378 (0–1400) 620 (250–800) 967 (600–1200) 1215 (30–1700)
Bipolar, n (%) 0 (–) 1 (4) 6 (27) 5 (23) 10 (45) b
Intravasation, mL a 500 (–) 474 (100–670) 833 (200–2300) 950 (200–2000)

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May 15, 2017 | Posted by in GYNECOLOGY | Comments Off on Gas embolism during hysteroscopic surgery using bipolar or monopolar diathermia: a randomized controlled trial

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