Visual Occlusion During Minimally Invasive Surgery: A Contemporary Review of Methods to Reduce Laparoscopic and Robotic Lens Fogging and Other Sources of Optical Loss

Abstract

Background:

Maintenance of optimal vision during minimally invasive surgery is crucial to maintaining operative awareness, efficiency, and safety. Hampered vision is commonly caused by laparoscopic lens fogging (LLF), which has prompted the development of various antifogging fluids and warming devices. However, limited comparative evidence exists in contemporary literature. Despite technologic advancements there remains no consensus as to superior methods to prevent LLF or restore visual acuity once LLF has occurred. We performed a review of literature to present the current body of evidence supporting the use of numerous techniques.

Methods:

A standardized Preferred Reporting Items for Systematic Reviews and Meta-Analysis review was performed, and PubMed, Embase, Web of Science, and Google Scholar were searched. Articles pertaining to mechanisms and prevention of LLF were reviewed. We applied no limit to year of publication or publication type and all articles encountered were included in final review. Limited original research and heterogenous outcome measures precluded meta-analytical assessment.

Results:

Vision loss has a multitude of causes and although scientific theory can be applied to in vivo environments, no authors have completely characterized this complex problem. No method to prevent or correct LLF was identified as superior to others and comparative evidence is minimal. Robotic LLF was poorly investigated and aside from a single analysis has not been directly compared to standard laparoscopic fogging in any capacity.

Conclusions:

Obscured vision during surgery is hazardous and typically caused by LLF. The etiology of LLF despite application of scientific theory is yet to be definitively proven in the in vivo environment. Common methods of prevention of LLF or restoration of vision due to LLF have little evidence-based data to support their use. A multiarm comparative in vivo analysis is required to formally assess these commonly used techniques in both standard and robotic laparoscopes.

Introduction

Laparoscopic procedures have become commonplace among multiple surgical specialties and in many areas are considered a surgically superior option compared to open approaches. Safety and operative efficiency in these procedures is dependent on many factors, but few (if any) are deemed more important than the maintenance of pristine visual acuity^1,2 especially with limited or absent tactile feedback.³ The need for clarity of vision has driven the production of many preventative and restorative adjuncts and methods to prevent vision reduction. Despite this, given a dearth of evidence in the medical literature, there remains significant uncertainty over which methods are superior. This scarcity of clear and concise advice on the management of loss of image clarity has led many surgeons to utilize those methods most readily available to them or to operate in suboptimal operative conditions.

Among the most common cause of vision loss is laparoscopic lens fogging (LLF), caused by a discrepancy in temperature of laparoscopic lens and environment in which it resides.^1,4
–6 This problem is compounded further by the humidity of the cavity in which the lens is placed.⁷ Conceivably the difficulty of a universal resolution is dependent on the multifactorial nature of LLF and the variability in environments and equipment utilized. Other causes of visual acuity loss are similarly common, including physical contamination, plume from cauterization, and fluid accumulation from wash within the cavity.^2,8

A number of agents and protective measures have been proposed to limit the development and progression of LLF intraoperatively. Subsequently the objective of this updated review is to summarize contemporary literature on management of LLF and other sources of visual acuity loss, while also providing a scientific analysis and explanation of its etiology.

Etiology of LLF

Psychrometry, dew point, and surface condensation

Psychrometry is the scientific field relating to the determination of physical and thermodynamic properties of gas–vapor mixtures. Currently it is nearly exclusively used for the air–water mixtures because of its applications in air conditioning and meteorology. An essential tool in these fields is the “psychrometric chart,” which plots the moisture content of the air against dry atmospheric temperature, with curves for various relative humidities from dry to complete saturation in normal air. These instruments aid in the eventual calculation of the dew point temperature, which can be defined simply as: the temperature at which air becomes saturated, when cooled isobarically.⁹ Essentially this is the temperature at which (at a given humidity) condensation will form on objects within that atmospheric environment. These two concepts although complex and perhaps seemingly irrelevant to clinical practice are undeniably the basis behind the formation of lens condensation and, subsequently, the cause of LLF.

However, we suggest that the understanding of the underlying scientific phenomenon of LLF is further complicated by three particular notions. None of which has been addressed before in medical literature.

1. Use of existing “psychrometric charts” and the subsequent calculation of dew point are currently almost exclusively limited to air–water environments as opposed to the CO₂ enriched environments in laparoscopic insufflation.

2. Remarkably, calculations and the subsequent “psychrometric charts” for CO₂ atmospheres have only been constructed for the analysis of other planetary weather systems, most notably using fundamental equations of state for the Martian atmosphere, which is 95.5% CO₂.¹⁰ Importantly, according to these charts CO₂ saturated environments subsequently contain 2/3rd the concentration of water than air at a given temperature.

3. Although laparoscopic environments are CO₂ enriched ( using insufflation), they are unlikely to contain the significant CO₂ concentrations used in those “psychrometric charts” that do assess CO₂ (close to 100%). In addition, it must be said that no evidence does exist regarding the exact gas–vapor makeup of the “generic” laparoscopic atmosphere.

Fogging

Despite this, if we do accept these current limitations and utilize an air–water model, widely accepted scientific theory suggests that vision in a lens is obscured when small water droplets form from condensation in the setting of both heat and moisture.^7,8 This “condensation” forms when the temperature of an object is at or below the dew point temperature of the air surrounding the object. Dew point is consequently altered with different environmental temperatures and humidity and can be calculated utilizing “psychrometric charts” and the hygrometers (humidity measurement devices) they calibrate. More specifically in lens (including laparoscopes), vision is obscured when this “condensation” takes the form of accumulated droplets with a size larger than 190 nm in diameter.¹¹ It can then be extrapolated that the most significant contributing factor to LLF is moisture accumulation on the lens from the environment in which it is placed, followed by subsequent droplet formation of the threshold size, caused by a temperature differential at the external lens at a given humidity. Figure 1 illustrates the progression of vision loss during LLF during an operative case.

FIG. 1.

An example of the progression of vision loss due to laparoscopic lens fogging.

The science of heat and humidity in LLF and clinical practice

Two basic determinant variables subsequently influence the formation of “condensation” on a lens: temperature and humidity. Yet, once again little evidence of specific peritoneal temperatures and water saturation has been published to date. One study to date has stated an intraperitoneal humidity of >85% after insufflations;⁴ however, descriptions of how these values were obtained is not clearly provided. Interestingly, no further studies have reported on this measurement in humans and there are no other published data on other types of body cavities (retroperitoneal, inguinal, and the like). In addition, no study has recorded intraperitoneal temperatures in humans. Despite this, data in porcine and canine models suggest that insufflated gas ultimately equilibrates with core body temperature and as such it may be reasonable to suggest that in human subjects this would not be dissimilar.^7,12 Standard dry CO₂ insufflation, however, has been shown by some to decrease body core temperature, an effect which has a more incremental impact the longer the surgical procedure lasts.^1,13

Aside from the absence of medical evidence, scientific theory would suggest that surface condensation of liquid on the lens would require the temperature of any cavity to be above dew point and the lens to be below dew point. This is a likely scenario when an unheated laparoscope is inserted into the warm and humidified cavity. This is commonly experienced by surgeons when removal of the scope is required for cleaning of lens contaminant. This results in heat loss when exposed to surroundings of the cooler operative environment.¹⁴ The subsequent reinsertion of a cool scope into the warmed and humidified cavity induces almost instantaneous loss of vision from fog. Intuitively, the solution to this may be to insert a preheated scope as the lens' would persistently be warmer than the dew point of the atmosphere. Yet, this alone is often ineffective and as such other factors must be present.

The explanation for fogging in the presence of preheated scopes then seems to lie in another source of heat transfer from the scope. This can theoretically come in many forms (or a combination of them); yet three particular sources seem to be most obvious in port site surgery.

1. Convection loss to the atmosphere in the cavity causing the scope to cool to no less than the surrounding temperature. However, in theory this should not cause condensation on the lens unless another source of heat sink is present.

2. Conduction losses up the stem of the laparoscope, out of the cavity, and then subsequent convection to the cooler surrounding air of the operating room (i.e., port site leak). However, this is not likely to be rapid.

3. Cooling by convection to the cold insufflation gas caused by the proximity of the injection port to the laparoscope. This seems to be the most likely rapid causative factor in the presence of a prewarmed scope.

Flemming and colleagues⁷ and Tittel and colleagues¹² suggested this when testing theories regarding lens fogging in surgical procedures on their porcine models. Their subsequent recommendations included insufflation through an alternative port site with warmed insufflation gas.

Misting

The presence of a mist consisting of fine droplets of water within the cavity could also increase the propensity of LLF. Movement of the gas within the cavity will cause the mist to impact the lens and deposit droplets, thereby fogging the lens. Three possible mechanisms for creating a mist are:

1. Entrainment of liquid droplets in the circulating gas caused by high velocity insufflation gas impacting a wet surface to create fine droplets of liquid.

2. General condensation of the atmosphere caused by the temperature of the atmosphere in the cavity dropping to below its dew point. Certainly with current operative apparatus the only way this cooling could occur is by the introduction of cold insufflation gas (which is used in standard laparoscopic insufflation). The propensity for condensation to occur would then become a complex problem of the effects of the temperature drop, the change to the humidity in the cavity caused by the mixing of the dryer insufflation gas, and the effectiveness of the mixing.

3. High frequency electrocautery and subsequent steam production from superheating moisture within the peritoneum.⁴

Translation of scientific theory

Clearly LLF is a complex problem with a multitude of contributing factors each with different means of prevention or reversal. This convoluted mix perhaps explains why a seemingly simple but critically important problem is yet to be completely solved by surgeons, scientist, and the like. It can certainly be determined that according to heat and mass transfer theory, direct condensation onto the lens should not occur if the laparoscope is preheated, unless the scope lens is subsequently cooled below the dew point of the environment in which it is placed.

The consequences of LLF

Although common sense dictates that any operative hurdle has the possibility to affect patient outcomes, fogging is often regarded as an aggravation rather than a significant obstruction to the operative course. The dangers of poor visual field have been well documented with regards to the loss of detailed focus on critical tasks,¹⁵ in addition to the delay in operative efficiency and the immeasurable effect of surgeon frustration. In addition, the absence of tactile feedback³ and the subsequent reliance on singular visual sense for operative safety are enough to stress concern of the gravity of this common problem and its potential to cause serious or even fatal operative events.

Current Antifogging Methods

Surfactants

Surfactants minimize overall surface tension at the lens to create a uniform nonscattering film of water as opposed to separate distorting droplets as previously described. Examples of readily available surfactants include: FRED™ (Covidien Ltd., Mansfield, MA), Resoclear™ (RESORBA Wundversorgung GmbH & Co. KG, Nürnberg, Germany), chlorhexidine, Povidone-iodine and its commercial formulas, standard soaps, and saliva. Surfactants are cheap (Table 1) and when present in low concentrations they adsorb onto surfaces and markedly alter the interfacial free energies of that surface. This subsequently reduces the “surface tension” and creates a uniform film, which does not distort the image.⁹ Surfactants are applied topically intraoperatively as required and are proposed to reduce the propensity of LLF.

Table 1.

The Cost Associated with the Single Use of Various Antifogging Methods (US Dollar)

Antifog	Manufacturer	Single use cost (US Dollar)
Resoclear™	RESORBA Medical GmbH	$2.23
FRED™	Covidien Ltd.	$4.71
Betadine™	Sanofi Aventis Pty Ltd.	$5.40
Chlorhexidine/Cetrimide	Baxter International, Inc.	$5.04
FloShield™	Minimally Invasive Devices, Inc.	$78
Insuflow™	Lexion Medical	$40
Scope Warmer	Various	Wide variety and dependent on manufacturer

These products theoretically prevent the formation of fog; however, variation in performance is common. This is likely due to challenges in long-term compound stability, variable adherence to the underlying substrate, and inability to resist additional cleaning procedures.¹⁶ In addition, current theory states that different types of surfactants display different properties at differing temperatures, including drastic changes in solubilization.¹⁷ Given that these products are often applied to prewarmed scopes that additionally fluctuate in temperature variance at the external lens,⁷ it is not irrational to imply that this should also alter ultimate effectiveness.

A plethora of topical preparations have been used since the advent of laparoscopic surgery to counter LLF. These include commercial antifogging products, either liquids or impregnated wipes, and solutions commonly found in theatre. Most frequently mentioned in the literature are Fog Reduction and Elimination Device or FRED (Covidien)¹⁸ and Ultra-Stop™ (Sigmapharm, Vienna, Austria).¹⁹ Both are commercial solutions of alcohol, surfactant, and water. Authors frequently state their use or preference for these products, but without supporting data.^5,20,21

A small number of studies, however, have attempted to objectively compare available agents. Recently, Manning and colleagues constructed a model peritoneum to assess the effect on LLF of different substances.²² This group illustrated that FRED resulted in the least LLF compared to cetrimide solution or a scope warmer, which were in turn equivalent and both superior to Betadine™ solution or Resoclear surfactant wipes. However, this assessment was limited to a select few techniques and did not include more modern technologies, including FloShield™ (Minimally Invasive Devices, Inc., Columbus, OH) and Insuflow™ (Lexion Medical, St. Paul, MN). Similarly, Knauth and colleagues constructed an artificial airway to assess bronchoscopic fogging rates with various agents.²³ Their results varied depending on whether flexible or rigid bronchoscope was used, but generally showed superiority of surfactant preparations, either liquid (Ultra-Stop, Fog Free™²⁴) or impregnated wipes (LiNA Clear Sight Wipe™,²⁵ Resoclear) compared to scope heater systems or additional oxygen insufflation. However, the performance of these substances during laparoscopy remains unclear. Conversely, other studies suggest that Ultra-Stop may have no advantage over chlorhexine or infant's shampoo.^26,27

Many other commercial liquids exist, such as Dr. Fog™ and Elvis Anti-Fog™ (both Aspen Surgical, Caledonia, MI²⁸), but are not supported by robust evidence. Commercial impregnated wipes include Resoclear and LiNA Clear Sight Wipe. Standard noncommercialized theatre solutions commonly used to combat LLF include warmed saline,²⁹ cetrimide,²² povidine-iodine,^29,30 and chlorhexidine.²⁶ These are typically much cheaper than other options. Compared with commercial surfactants in preventing LLF, results of the limited studies to date differ between inferiority and equivalence.

Mechanical and material technologies

Mechanical and material based antifogging techniques have also been utilized and these apparatuses draw upon scientific theory to maximize their effectiveness. Understandably these devices have a single use cost, which is much higher than surfactant products (Table 1). Some manufacturers suggest that this cost is counterbalanced by an overall reduction in operative time (no time loss to scope removal and cleaning).³¹ Insuflow is a modification applied to current CO₂ insufflators to supply heated and humidified gas according to the manufacturer to 95°F and 95% humidity.³² Through a self-funded investigation there is some evidence to support its usefulness in reducing intraoperative hypothermia and pain.¹³ However there still remains little evidence proposing its use as a solitary antifog technique, with reports of no statistical difference to a standard insufflated control in a single surgeon rated fogging scale.³³

Differing materials compared with those in conventional laparoscopes have also been described, including adaptation of titanium oxide coated glass, which has been utilized in the motor vehicle industry with some effectiveness.³⁴ Ohdaira and colleagues composed a well-designed study, which compared a self-designed laparoscopic lens coated with titanium oxide to other more conventional methods. While superiority was achieved with regards to LLF, the authors did report on possible structural instabilities (lens cracking) during the testing and conceded that further durability testing was required of the “Pyrex” glass utilized and are currently designing a new prototype.³⁵

More modernized apparatus are in production to prevent LLF and also clean lenses actively without removal of the scope while inside the peritoneum. FloShield is one such device that provides the ability to clean the lens without scope removal. It involves the production of a CO₂ barrier, which is constantly applied to the lens through an over tube. Thus, in addition to reducing LLF, it has the ability to shield the lens from smoke and debris. Published literature supporting its use is absent; however, comparative studies are currently in recruitment stages or awaiting formal publication.^36,37

Furthermore, Calhoun and colleagues independently investigated the use of directional flow CO₂ in prevention of LLF with a self-made device mechanically similar to FloShield. This group reported that it effectively prevented LLF and removed existing LLF in extensive multifaceted testing.³⁸ Another unnamed system also utilized a similar concept, with the aid of small rinsing and drying nozzles at the tip of the over tube instead of directional CO₂ flow, as well as an inbuilt smoke evacuation system. This device was tested in both animal and clinical scenarios with good results in the authors' single analysis, but unfortunately involved no comparative arm.³⁹ Unfortunately, an obvious limitation for both of these over tube based devices is the requirement for specialized 12 mm trocars, which considering the minimalistic approach to laparoscopic surgery may be considered significant for some surgeons, as well as additional equipment, which can add to operative set up time and become cumbersome throughout the operation. Other mechanical apparatus with differing methods to reduce LLF has been described but most are limited to conference presentations and are in early stages of development and testing.⁴⁰

Warmers

Given widely accepted scientific theory of dew point temperature, scope warming has become a common antifogging preventative method in standard surgical practice. Although the intended outcome is common to all techniques, the method of warming is extensively diverse with many different technologies available. Heating systems are most commonly small over sheaths that heat the tip of the scope and shaft to safe levels and are commonly utilized in combination with developed topical agents.

More recently however combination systems, which heat and clean the lens and apply antifog, have become available. The Clearify™ Visualization System (Covidien), formerly known as D-HELP™ (New Wave Surgical, Coral Springs, FL), is a disposable battery operated plastic unit with a heated well for antifogging solution.⁴¹ The laparoscope lens is inserted into the well for both cleaning and application of their proprietary antifog agent.

Alternatively, more generic hardware may be used to heat the surgeon's preferred antifog agent rather than the scope itself. This may be a simple sterile thermos flask⁶ or an electrically heated basin such as the ORS Fluid Warming System™ (Ecolab, St Paul, MN; previously of O.R. Solutions, Chantilly, VA).^42,43 A recent study suggests that this technology may result in less fogging events than the Clearify Visualization System.⁴⁴ Yet, despite all of these different apparatus, once again little comparative evidence exists regarding superiority of any singular device.

Robotic Scopes and Comparative Analysis

To date limited comparative evidence exists between laparoscopic and robotic scopes regarding the production of LLF. Manning and colleagues²² demonstrated superior vision when robotic scopes were assessed without the aid of any antifog apparatus. This was plausibly explained by the increased temperature of the external lens, as well as time limitations in their own experimental analysis. Furthermore, limited evidence exists regarding the management of LLF in robotic lenses with manufacturers advising against the application of topical antifog solutions instead recommending that self-supplied scope warmers be utilized.⁴⁵

Despite these recommendations, attempts have been made to address fogging in these more specialized scopes. FloShield has an adapted model for robotic lenses (FloShield Plus™)³¹ but to date, limited evidence supporting its use in robotic lenses has been published.⁴⁶ Insuflow has also been utilized by some, combining the Insuflow technology with an infusion of a modified solution of physiologic saline and FRED.²¹

Future Directions

Future directions in the area of antifogging products and techniques in the field of surgery are unclear, mainly because of the multifactorial nature of the presenting problem. Certainly, what is clear is the need for a large comparative analysis of the major methods utilized in LLF management, especially given the multitude of different techniques and technologies elucidated in this review all of which are accompanied by limited supportive evidence. However, simple plausible future techniques exposed by this review and an analysis of the underlying scientific theory could include heated insufflation, self-heating scopes, and ports with directional insufflation flow.

Conclusion

Obfuscated vision in laparoscopic and robotic surgery is a frustrating, dangerous, and common problem, which still remains poorly investigated despite its hazardous implications. LLF is among the commonest causes of this vision loss. Despite technologic developments aided by the use of scientific theories by surgeons and medical technology companies alike, it remains a persistent entity with a significantly limited evidence base to support the use of developed preventative measures. Although the nature of the problem is clearly multifaceted, a well-designed multiarm analysis in vivo is possible and could possibly elucidate a solitary superior method. This would have significant implications in the continued practice of minimally invasive surgery.

Footnotes

Author Disclosure Statement

No competing financial interests exist.

Abbreviation Used

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