Dealing with surgical smoke

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by Lisa B. Samalonis Contributing Editor

	The Mastel Clean Room System

During the surgery, when a laser or electrosurgical unit is used, thermal destruction of tissue creates a smoke byproduct (plume). In ophthalmology, when the excimer laser strikes the cornea, a thin layer of corneal cells is released. These cells create a plume of tissue that scatters into the air seconds after the laser strikes.

Steven J. Dell, MD, of Austin, Texas, clinical instructor of ophthalmology, Tulane University, New Orleans, said that aspirating this cloud away as rapidly as possible will produce a more uniform ablation pattern. "Additionally, most proposed culprits in diffuse lamellar keratitis [DLK], such as Betadine [povidone-iodine, Purdue Frederick], bacterial endotoxins, or polishing compounds, can be aspirated. Removing these substances from the stromal bed seems prudent," he said.

Another concern is that the laser plume may transport infectious diseases or viruses, such as HIV-AIDS or hepatitis. He said that it might take years to definitively determine if the laser plume is dangerous to the surgical staff. However, the dangers of breathing plume smoke from CO2 lasers are documented in dermatology literature. "The typical particle size in the plume of an excimer laser is on the order of 120 nm, which is in the general range of coal dust and several compounds in cigarette smoke. It is conceivable that the plume might also contain prions, and the consequences of breathing this material are totally unknown," Dell said.

Ophthalmology research

Research on the subject dates to the mid-1980s. Recent studies show conflicting results. Michael J. Taravella, MD, associate professor, University of Colorado, Denver, and colleagues published a study in the August 1999 Ophthalmology concluding that the oral polio vaccine virus could survive excimer laser ablation. The live virus was shown in the material trapped from the laser plume. Whether another, more clinically relevant virus, such as HIV, can withstand ablation and remain infectious is yet to be determined, he said.

This study followed a previous study Taravella and colleagues published in the August 1997 issue of Archives of Ophthalmology, in which they examined excimer laser ablation of fibroblasts infected with attenuated varicella-zoster virus. In the study, viral DNA was detected in the material trapped from the laser plume, although live virus could not be demonstrated to have survived the ablation. The researchers recommended that although attenuated varicella-zoster virus did not seem to survive ablation, safety precautions such as wearing a surgical mask during the procedure are warranted.

A study by Kerry Brent Hagan, MD, clinical instructor at Oregon Health Sciences University, Portland, published in the August 1997 American Journal of Ophthalmology, was conducted to test the possibility of pathogenic virus transmission into the operating suite during excimer laser treatment of corneal tissue.

Hagan said that even under conditions designed to maximize the likelihood of virus transmission, the excimer laser plume did not appear capable of transmitting the pseudorabies virus, the study-designated live enveloped virus. The researchers concluded that excimer laser ablation of the cornea of an HIV- or herpes-infected patient is unlikely to pose a health hazard to the surgeon.

The plume may cause other problems, however. A study by J. Noack and colleagues in Germany, published in the May 1997 Ophthalmology, analyzed the dynamics of ablation products during excimer laser photorefractive keratectomy and their influence on the formation of central islands. The researchers concluded that a major cause of central island formation is particle redisposition at the center of the ablation zone. They concluded that the dynamics of the ablation plume led to a concentration of airborne particles over the center of the ablation zone, which may contribute to the creation of central islands by partial absorption of the next laser pulse.

Physician recommendations

While it is impossible to eliminate exposure to plume smoke, Dell advocates the use of 0.1-µm plume-filtering operating room masks during excimer surgery. "To truly be effective, however, the mask would need to be taped securely on all sides to the surgeon's face. This is simply not practical. Additionally, moisture from the surgeon's breath rapidly degrades the efficacy of the filter. ... These masks filter down only to 0.1 µm, which is equivalent to 100 nm. Many viruses, such as hepatitis A, echovirus, and enterovirus, are smaller. ... All prions are much smaller than this," he said.

To provide additional protection, he routinely uses the Mastel Clean Room System. This system consists of a fixation ring coupled to a vacuum system with a series of high-performance filters. He said that one could clearly observe the plume being aspirated from the surface of the eye during the ablation.

According to Dale Hughes-Hargraves, Mastel vice president of administration, Rapid City, S.D., the system employs a surgical handpiece that removes the smoke directly at the level of the eye. It removes the plume in four directions away from the stromal bed. "The filters on the system trap particles and stops odorous hydrocarbons, which are responsible for the offensive smell emitted during the procedure," he said.

Accommodating the system

A filtration system usually requires some adaptations to the surgical procedure. "When using the Mastel system, it is necessary to deduct about 10% from your usual treatment, as the quick removal of the plume causes you to ablate deeper than you would without the system. However, one should bear in mind that the laser is actually cutting as deeply as though you had not deducted this 10% factor. For the purposes of calculating the true ablation depth achieved, the 10% factor must be added back in," Dell said.

"Postoperative topographies have been uniform with the system, and we have observed a slight increase in the number of patients achieving uncorrected 20/15 acuity on the first postoperative day. It remains to be seen whether this will translate into any long-term advantage in visual acuity," Dell said.

In OSHA's Laser/
Electrosurgery Bulletin (revised March 2000), surgical plumes have contents similar to other smoke plumes, including carbon monoxide, polyaromatic hydrocarbons, and a variety of trace toxic gases. According to the bulletin, plumes can produce upper-respiratory irritation and have in-vitro mutagenic potential. Although there has been no documented transmission of infectious disease through surgical smoke, the potential for generating infectious viral fragments may exist.

OSHA noted that local smoke evacuation systems may improve the quality of the operating field and are recommended by various organizations whose members use laser technology.

The National Institute for Occupational Safety and Health also has a statement on the control of smoke from laser/electric surgical procedures. This statement, updated in 1998, states that the institute's research has shown airborne contaminants generated by these surgical devices can be effectively controlled by ventilation methods. These include a combination of general room and local exhaust ventilation. Two major approaches used to reduce surgical smoke levels for healthcare personnel are portable smoke evacuators and room suction systems.

For more information, check out www.osha.gov and www.cdc.gov/
niosh.