Effectiveness of Heated Sterile Water vs ResoClear ® for Prevention of Laparoscopic Lens Fogging in a Randomized Comparative Trial

Abstract

Background:

Laparoscopic surgery may be complicated by visual disturbances, including lens fogging. Several techniques have been developed to prevent laparoscopic lens fogging (LLF). We aim to compare the effectiveness of two commonly available techniques in prevention of LLF: heated sterile water in a thermos flask and ResoClear^® impregnation wipes.

Materials and Methods:

In this single-center prospective randomized study, 50 patients underwent an elective laparoscopic donor nephrectomy and were allocated to either heated sterile water or ResoClear^® impregnation wipes as the antifogging method. The primary outcome was the number of fogging events during the first 30 minutes of the operation, whereas secondary outcomes were operating time, number of cleaning events because of other causes, cost differences, and assessment of predicting factors for fogging events.

Results:

In 50 patients, the outcomes were analyzed. The number of fogging events was significantly lower when using heated sterile water (median = 0, interquartile range [IQR]: 0–0) compared to ResoClear^® (median 1.0, IQR: 0.5–3.0), p < 0.001. There were no significant differences in operating time, number of cleaning events because of other causes, and costs. No predictors of fogging events were found.

Conclusion:

The use of heated sterile water leads to significantly less fogging events than the use of ResoClear^® impregnation wipes, resulting in an improved continuity of the surgery without differences in operating time and costs.

Introduction

Minimal invasive surgery has gradually become the standard in several surgical specialties.¹ The transition from open to laparoscopic surgery has resulted in decreased postoperative pain, less wound infections, and minimized recovery time.² However, because of the absence of tactile feedback, visual acuity during the procedure is of utmost importance for the surgeon.³ Although clear vision is necessary for perioperative safety and efficiency,^4,5 it is often disturbed in clinical practice. These visual disturbances have different origins, for example, condensation of the lens, debris caused by coagulation of tissue, or blood contamination. The most common issue is condensation, which leads to laparoscopic lens fogging (LLF).

The widely accepted scientific theory concerning condensation states that condensation occurs when the temperature of an object is at, or below, the dew point temperature of the air surrounding the object. The dew point temperature is dependent on the temperature and the humidity of that environment.⁶ To prevent LLF and maintain clear vision, various techniques have been developed. Heating of the camera lens, by either using heated sterile water in a thermos flask or a warm water bath (continuous heating system), is frequently used.^7,8 Other methods include antifogging solutions and even modifications to the laparoscopic device itself.^9
–11 The working mechanism and reasoning behind the use of heated sterile water are to ensure that the temperature of the camera lens rises and remains above the aforementioned dew point temperature, thus preventing condensation. The antifogging solutions use a surfactant to lower the surface tension. When surface tension is lowered, condensation does not form single droplets that distort vision, but rather forms a nonscattering film of water that does not jeopardize the visual acuity. Although both techniques are potentially effective, data on their effectiveness are scarce. In a recently published review by Manning et al., the authors addressed the current absence of comparative analysis on this subject.¹²

The aim of this study is to evaluate the effectiveness of two commonly used techniques to prevent LLF. The use of heated sterile water vs ResoClear^® impregnation wipes was compared during a standardized laparoscopic procedure (laparoscopic donor nephrectomy [LDN]). To our best knowledge, comparison of these techniques has not been previously studied.

Materials and Methods

Design

In this prospective randomized study, we compared the number of fogging events between heated sterile water and ResoClear^® impregnation wipes during the first 30 minutes of LDNs that were performed in a single center from November 2016 to June 2017. The study was approved by the institutional review board (CMO Arnhem-Nijmegen).

Patients

All patients scheduled for an elective LDN were considered eligible for this study. No exclusion criteria were defined.

Laparoscopic donor nephrectomy

All procedures were performed by a team of an experienced urologist and vascular surgeon. By working with fixed surgical teams, the effectiveness of LDN is optimized.¹³ Perioperative settings were predefined, but adapted if deemed necessary by the operating surgeon or anesthesiologist. CO₂ insufflation pressure was set at 12 mm Hg, the D-Light C light source from Storz^® (Karl Storz GmbH & Co. KG, Tuttlingen, Germany) was used and set at 30%, and a Bair-Hugger™ (3M™ Science, Delft, The Netherlands) heating blanket was used and set at 43°C. The temperature of the operating room was set at 20°C. The standard laparoscopic camera system from Storz was used in all procedures. The LDN was performed as described by Ratner et al.¹⁴

Antifogging method

Fifty consecutive patients were randomly assigned after an envelope randomization procedure in a 1:1 ratio. One randomly picked envelope was opened and announced at each preoperative briefing.

Before this study, an experimental study (unpublished data) was performed to gain insight into the temperature of the water as well as of the scope itself, when using heated sterile water. For this, an infrared thermometer and a probe thermometer were used. It was found that the water reached an average temperature of 74.6°C after being heated in the microwave for 3 minutes. The water maintained its temperature as much as 65°C after 90 minutes, although residing inside the thermos flask. The scope itself reached an average temperature of 44°C after 15 minutes inside the thermos flask containing heated sterile water.

In the heated sterile water group, a thermos flask (Applied Medical, Rancho Santa Margarita, CA) was used in the following manner: a 500-mL bottle of sterile water was heated in a microwave for 3 minutes. The thermos flask was filled with heated sterile water, which was then sealed before the laparoscopic scope was inserted for at least 15 minutes preoperatively.

ResoClear^® (Resorba Wundversorgung GmbH & Co. KG, Nürnberg, Germany) is a commercially available impregnation wipe that utilizes a surfactant to minimize surface tension on the laparoscopic lens. In this study, ResoClear^® was used as follows: wiping the optic and allowing the surfactant to act for 10 seconds before use of the camera system.

After each visual disturbance, the scope was removed from the abdomen and cleaned using the same corresponding method. For the heated sterile water group, the scope was briefly inserted into the thermos flask before abdominal reinsertion. For the ResoClear^® group, the scope was manually cleaned and ResoClear^® was reapplied for 10 seconds.

Outcome measures

All measurements were conducted by an independent trained observer during the first 30 minutes of the operation starting with the laparoscopic camera insertion. The primary outcome of this study was to assess the number of fogging events during the initial 30 minutes. Using a fixed time frame of 30 minutes creates homogeneity between the groups, enabling excellent comparison of absolute numbers between both study groups.

Secondary outcomes were the number of other events causing visual disturbance that needs cleaning of the laparoscopic lens in the same time frame, operating time, cost difference, and assessment of possible predicting factors of the primary outcome.

Statistical analysis

Sample size calculation was performed. Since no data on number of fogging events using heated sterile water or ResoClear^® were available, means were estimated using the surgeons' experiences, that is, two events for the heated sterile water and three events for ResoClear^®. For α = 0.05 and β = 0.10, the result was 21 patients per arm. To account for unforeseen circumstances, 50 patients were enrolled.

Continuous variables were tested on normal distribution using the Kolmogorov-Smirnov test. In case of normal distribution, two means were compared using the independent t-test and expressed in mean ± standard deviation. In case of non-normal distribution, the Mann–Whitney U test was used and expressed as median and interquartile range (IQR). Categorical variables were expressed using percentages and analyzed using the Pearson chi-square test or the Fisher's exact test.

We performed an intention-to-treat analysis. Statistical analyses were performed using SPSS 22.0 (IBM, Chicago, IL).

Results

Study population

Fifty consecutive patients were analyzed. The mean patient age was 53.8 years (28–76 range) and the mean body mass index was 26.5 kg/m² (21.5–35.5 range). Forty-five procedures involved transplantation of the left kidney (90%), and 5 of the right kidney. Baseline demographics and clinical characteristics were similar in both groups (Table 1). Operating room temperature (20°C) and CO₂ pressure (12 mm Hg) were used as predefined in all procedures. A Bair-Hugger set at 43°C was used in all procedures, except for one in which it was set at 38°C. Light source was set at 30% in 44 procedures (88%), whereas in 6 procedures, it varied from 20% to 60%.

Table 1.

Baseline Characteristics, Perioperative and Postoperative Parameters

	Heated sterile water (n = 25)	ResoClear^® (n = 25)	p
Demographic/clinical
Age	51.5 ± 13.2	56.0 ± 9.2	0.168
BMI, kg/m²	26.5 ± 4.2	26.5 ± 3.1	0.982
Gender
Male	15 (60%)	14 (56%)	1.000
Female	10 (40%)	11 (44%)	1.000
No history of abdominal surgery	21 (84%)	19 (76%)	0.725
Temperature patient at start surgery, °C	35.8 ± 0.5	35.8 ± 0.4	1.000
Surgical
Donor kidney
Left	23 (92%)	22 (88%)	1.000
Right	2 (8%)	3 (12%)	1.000
CO₂ used, L	18.9 ± 7.5	18.5 ± 9.2	0.867
Total blood loss, mL	46.8 ± 40.0	58.2 ± 49.2	0.375
Environmental/laparoscopic
CO₂ pressure, 12 mm Hg	25	25	^a
Operating room temperature, 20°C	25	25	^a
Bair-Hugger heating blanket used	25	25	^a

All continuous variables are expressed in mean ± SD and categorical variables are expressed in frequency (%). p Values are calculated by the independent t-test for continuous variables and the Fisher's exact test for categorical variables.

These values are constants and thus have no relevant p values.

BMI = body mass index; SD = standard deviation.

Visual disturbances

The number of fogging events was significantly lower when using heated sterile water compared to ResoClear^® impregnation wipes (p ≤ 0.001) (Table 2). Furthermore, the number of fogging events ranged from 0 to 2 using heating sterile water and ranged from 0 to 14 using ResoClear^® impregnation wipes. In addition, in 20 procedures (80%) using heated sterile water, no LLF was reported compared to 6 (24%) using ResoClear^®. There was no difference in number of cleaning events caused by other visual disturbances between the two groups (p = n.s.).

Table 2.

Comparison of Fogging Events, Other Events, and Operating Time Between the Two Groups

	Heated sterile water (n = 25)	ResoClear^® (n = 25)	U	p
Number of fogging events	0 (0–0)	1 (0.5–3.0)	121	<0.001
Number of other events causing visual disturbances	1 (0–1)	1 (0–1)	303	0.857
Operating time	131 minutes (116, 147)	132 minutes (115, 149)	^a	0.951

Number of fogging events and number of other events are expressed in median (IQR). Operating time is expressed in mean (95% CI). p Values are calculated by the Mann–Whitney U test for number of fogging events and number of other events, and with the independent t-test for operating time.

U-value is a test outcome in the Mann–Whitney U test.

CI = confidence interval; IQR = interquartile range.

The total operating time (skin-to-skin) did not differ significantly between the heated sterile water group and the ResoClear^® group (131 minutes (95% confidence interval [CI] 116, 147) and 132 minutes (95% CI 115, 149), respectively, p = n.s.) (Table 2).

Secondary outcome

To assess predicting factors for fogging events, univariate analysis was performed, which showed that there was no evidence that patient demographic characteristics or perioperative settings were predictive for fogging events. No post hoc analysis was performed.

Costs equipment

The procedural costs of both groups differed minimally. The ResoClear^® method costs € 1.09 per impregnation wipe (one wipe per procedure). For the heated sterile water group, costs were as follows: sterile water, € 0.89 per bottle, and the seal on the thermos flask, € 3.73. Sterilization of the thermos flask is performed within the standard equipment and thus no additional costs are accounted for. In total, the cost for the use of heated sterile water is € 4.62 per procedure. Additional to the procedural costs is the initial purchase of the thermos flask at € 165. Taking the operating room cost of € 700 per hour into account, the difference in costs for ResoClear^® and heated sterile water were not considered clinically relevant.

Discussion

In this study, two widely used antifogging techniques were compared. The results show that the use of heated sterile water is superior to the use of ResoClear^® in preventing LLF during the first 30 minutes of LDNs. Despite an equal operating time, heated sterile water has the potential to increase safety and effectiveness of the procedure. Having clear vision during several critical steps during LDNs, for example, clipping of the renal artery or vein, is of paramount importance in preventing complications.^4,5 Another interesting finding is the number of procedures in which no endoscope removal was necessary, specifically when using the thermos flask. This improves the continuity of the procedure and may further reduce complications caused by unnecessary distractions.^15,16 The costs of both methods are relatively low compared to other commercially available devices.^17,18

LLF remains a common issue of which the etiology has not been fully understood. The occurrence of LLF may lead to a decrease in perioperative safety and efficiency. Besides the methods used in our study, there are several other methods available in clinical practice, some of which have recently been compared in literature. Drysch and colleagues compared the Clearify Visual System with a Fluid Warming System, a heated warming bath, during urological operations.¹⁷ They reported superiority of the Fluid Warming system with an average of 0.7 fogging events per hour compared to 1.4 fogging events per hour for the Clearify Visual System. Bendifallah and colleagues compared the FloShield Air System^® with nonheated water combined with povidone-iodine solution during gynecological procedures. They observed an average of 2.8 endoscope removals per procedure when using FloShield Air System compared to 7.0 when using water with povidone-iodine, without further specifying the reason for removal.¹⁸ Furthermore, Brown and colleagues reported that one downside of using a thermos flask lies in the cooling down of the heated sterile water and subsequently requires refilling of the flask.⁸ As shown in methods, an analysis of the temperature was conducted in which it was found that temperature remained at >65°C during at least 90 minutes. After this trend, it is unlikely that the sterile water inside the thermos flask cools off to the extent that refilling is required. When comparing the results with current literature, most interesting is the low number of laparoscopic fogging events and endoscope removals during this study. This could partly be explained by study design in which we measured the fogging events during a fixed time frame. The decision to measure fogging events during the first 30 minutes after abdominal scope insertion was driven by the experiences of our surgeons with LLF. They reported that LLF is almost exclusively occurring at the beginning of the operation, which is in line with the theory presented by Lawrentschuck et al. and observed by Yong et al.^6,19

In this study, a high homogeneity in both groups is achieved by using a fixed time frame of 30 minutes as well as exclusively collecting data during LDN. This is a standardized procedure with very low complication risk.²⁰ In addition, perioperative settings were predefined as much as possible, such as light source, temperature of operating room, pressure of pneumoperitoneum, and patient heating elements. Most of the procedures were carried out with these predefined settings. Furthermore, randomization in our study prevented selection bias. This study also comes with potential limitations. The operating surgeons were not blinded. Therefore, a potential bias toward either technique cannot be excluded. Furthermore, since a total of six surgeons have performed the operations for this study, their definitions of visual disturbances may differ, thus potentially skewing the reported number of fogging events. On the other hand, if fogging was reported bothersome, it should be considered clinically relevant. The exact duration of cleaning events was not reported. By not reporting this, a potential influence of the cleaning events on total operating time could not be evaluated. Since similar duration of cleaning is advised for both methods, it is unlikely this would strongly influence the total operating time. The fogging events were measured during the first 30 minutes of the procedure, which makes it difficult to correlate our absolute numbers to the number of cleaning events reported in other studies, in which full procedures were observed. Finally, since only two techniques have been included in this study, comparison with other devices is impossible.

To fully assess which technique can be considered the standard, a multiarm study should be conducted, as previously suggested by Manning and colleagues.¹²

A possible explanation for the results in this study lies in the etiology of condensation. As stated before, the widely accepted scientific theory states that condensation occurs when the temperature of an object is at or below the dew point temperature of the air surrounding the object. In this study, the average scope temperature was considered to be around 44°C after residing inside the thermos flask. According to the article of Flemming and colleagues, this temperature would lead to clear vision in their model.²¹ To achieve this scope temperature, heating the scope for at least 15 minutes could be mandatory. The nonscattering film of water caused by ResoClear^® should theoretically prevent visual obscurity, but in clinical practice, this evidently does not always apply.^22,23

Although operating times did not differ significantly, the results show superior effectiveness in preventing LLF of heated sterile water when compared to ResoClear^® impregnation wipes. This has resulted in standard use of heated sterile water in our center.

Conclusion

In this study, the use of heated sterile water was shown to be superior in preventing LLF compared to ResoClear^® impregnation wipes with subsequent higher efficiency, although operating times did not decrease.

Footnotes

Acknowledgments

The authors thank the observers participating in this study as well as Jos Rutting for his assistance in providing and training these observers.

Author Disclosure Statement

No competing financial interests exist.

Abbreviations Used

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