Alcohols

Alcohols have rapid bactericidal activity but have variable efficacy against viruses and are generally ineffective against spores.22,93,94 Alcohols likely exert their bactericidal effects by denaturing proteins, a process that occurs more readily in the presence of water; they also exert some effect through interference with metabolism and lysis of cells.⁷¹ The efficacy of alcohols is decreased substantially in the presence of organic debris. Ethyl alcohol is commonly used in hand sanitizers and may have some sporicidal value at higher temperatures.¹⁴⁸ The most effective concentration is reported to be 60% to 70%, with effectiveness diminishing rapidly at concentrations below 50%, depending on the organism.^123,139 Isopropyl alcohol is an alternative to ethyl alcohol with greater bactericidal efficacy but less virucidal activity.^7,22 Unfortunately, because isopropyl alcohol is a more effective fat solvent, its use on skin should be limited.⁷

Iodophors

Iodophors are iodine-containing compounds in which the iodine is complexed to a high-molecular-weight carrier such as polyvinyl pyrrolidone (a polymer similar to dextran).22,179 Iodine is found in various forms in aqueous solutions, but its antimicrobial efficacy is largely due to molecular iodine (I₂) and hypoiodic acid.⁹³ Iodide (I⁻) has no antimicrobial value.^51,150 The mechanism of action is incompletely understood but involves disordering protein structure, blocking protein synthesis, and altering the cell membrane.⁵⁰ The use of a carrier serves to cause a slow continuous release of free iodine, while limiting undesirable properties such as staining and local toxicity.^50,51 Rodeheaver and colleagues challenged the antibacterial efficacy of iodophors compared with noncomplexed aqueous iodine, but supported the idea that iodophors have fewer undesirable side effects.¹³⁴ One of the most common iodophors is povidone-iodine. The concentration of free iodine increases as 10% povidone-iodine is diluted, reaching maximal concentration at about a 0.1% solution.^17,93 One author has reported that iodine-alcohol preparations are more effective than aqueous-based versions, but this has not been widely supported by the general literature.¹⁹

Iodine, in its active forms, has rapid efficacy in killing bacteria, spores, viruses, and fungi.⁸² Efficacy against spores is dependent on prolonged contact time, but is still better than that of many other agents.¹⁵⁴ As of 1993, no resistance to iodine had been noted, and the spectrum of activity was broad.⁴⁹ Its activity is decreased in the presence of organic debris and blood,^80,145 although possibly to a lesser extent than other agents.^50,179 Caution should be used around open wounds because systemic iodine toxicity can result from absorption of iodine.²² Although the length of time that iodine maintains an effect after application is controversial, some persistence of its antimicrobial activity is likely because of elution from deeper skin layers to which it initially diffused.⁵⁰ In dogs, povidone-iodine caused adverse skin reactions (erythema, edema, papules, wheals, or weeping) in almost 50% of animals—a higher rate than is observed with chlorhexidine gluconate.¹¹⁰ Povidone-iodine is lethal to canine embryonic fibroblasts at concentrations of 0.5% or greater, but concentrations of 1.0% or greater are necessary for bactericidal activity.¹⁴⁰ Studies by Lineaweaver and others found that concentrations of .001% povidone-iodine maintained bacterial toxicity while sparing human fibroblasts.^77,78 These investigations suggest that povidone-iodine should be used with caution around wounds or exposed tissues. A thorough review of the toxicity of povidone-iodine solutions has been published.¹⁷⁹

Chlorhexidine

The cationic bisbiguanide chlorhexidine is commonly used in veterinary medicine as chlorhexidine gluconate (a scrub preparation) or chlorhexidine diacetate (a solution).²² It is not considered to be sporicidal at normal temperatures, although sporicidal activity has been reported at higher temperatures (60° to 70° C).^67,93,149 Chlorhexidine has variable efficacy against viruses and fungi.³⁴ Recent research has confirmed that chlorhexidine is effective against multiple-drug-resistant strains of bacteria and methicillin-resistant Staphylococcus aureus.³³ Its activity is reportedly reduced in the presence of organic debris and soaps,^34,93 although chlorhexidine was not inhibited by organic debris (blood) when compared with povidone-iodine in at least one study.⁸⁰ The activity of chlorhexidine varies with concentration: At lower concentration, it exerts a bacteriostatic effect by interfering with the cell membrane and causing leakage of cell contents; at higher concentrations, it has a bactericidal effect caused by coagulation of cellular contents.^34,93 The specific concentration at which a given effect is observed varies with the bacterial species, as well as with duration of exposure.³⁴ Surgical scrub formulations are recommended to be 2.0% to 4.0%, whereas wound treatment formulations are typically 0.05% or less, and disinfectant formulations are 0.5% to 2.0%.⁷³

A benefit often attributed to chlorhexidine as a surgical preparation agent is residual activity.70,111,152 It is interesting to note that this claim is difficult to document well in the literature and to separate from the prolonged effects of thorough initial antiseptic preparation (independent of a true residual antimicrobial effect).^{76,82,119,156} Residual activity can result from a cumulative effect of multiple applications. Although definitive answers are elusive, it appears that some residual effect is seen with the use of chlorhexidine, and this effect is superior to any observed with povidone-iodine.

A few studies indicate that chlorhexidine preparations with alcohol have improved efficacy compared with saline or aqueous solutions.10,11,118 The clinical significance of this difference may be questionable because of the magnitude of the effect.¹¹¹ When chlorhexidine is combined with saline or lactated Ringer’s solution at certain concentrations, it forms a precipitate that does not diminish its antimicrobial activity.⁸⁴

Chlorhexidine does not typically produce skin irritation, but is noted to be neurotoxic and ototoxic (in the middle ear).³⁴ Additionally, at concentrations higher than 0.05%, and in certain formulations such as hand wash solutions or products with detergents, chlorhexidine can cause ocular damage.³⁴ One investigator reported that at minimum bactericidal concentrations of 0.05%, chlorhexidine is lethal to canine embryonic fibroblasts.¹⁴⁰ Even at these concentrations, the clinical effect on wound healing may not be significant.¹⁴¹ This and other work suggests that chlorhexidine, although of low overall toxicity, should be used with caution around wounds or exposed tissues.^58,136

Triclosan

Triclosan is a derivative of hydroxydiphenylether, which is a member of the phenol family. The primary mechanism of action is cell wall destruction.⁷⁰ It has broad bacteriostatic properties and can be combined with soaps without losing efficacy.^43,93 Triclosan is less effective than chlorhexidine or povidone-iodine in terms of antibacterial activity and is intermediate in its residual effect.^43,70,101 Little information is available on comparison of its antiviral activity. Its low toxicity allows its use in products from deodorants and toothpastes to hand washes. The concentration contained in some of these products may not yield efficacy that exceeds that of common soap.^24,137 Widespread use has prompted debate about the development of strains of bacteria resistant to triclosan.⁸⁸

Other Agents

Other agents such as hexachlorophene, parachlorometaxylenol (PCMX), and glutaraldehyde have been used as antiseptics. They are less effective than the iodophors or chlorhexidine, and their use is not recommended.

Draping

Numerous protocols and variations have been used for draping patients for aseptic surgery after they have been clipped and scrubbed. The goal is to create a barrier that prevents microbial spread from the patient into the surgical field or onto surgical personnel. This barrier should be resistant to penetration by fluids, should not tear with normal use, and should be secured in such a way as to remain effectively in position during the surgery. Typically, the area draped off for veterinary surgery will extend to the limits of the clipped hair and will include the area of the expected incision along with enough exposed skin to allow for extending the incision, placing drains, and gaining access to implants (e.g., intramedullary pins). A smaller area may be exposed by the most superficial draping layer.

The initial layer of draping usually consists of four drapes placed evenly around the clipped and scrubbed area. These drapes may be disposable paper drapes with adhesive strips or may be secured to the patient with penetrating towel clamps that secure the drapes to the skin. Towel clamps should not penetrate subsequent layers of draping. As the first four drapes are placed, care is taken to protect the fingers and hands of the surgeon from contact with the patient. Typically, this is done by grasping the drape in such a manner as to have a portion of the drape folded and covering the fingers.

A second layer of draping consists of a larger sheet that covers all exposed portions of the patient and surgical table. This drape may be extended onto the instrument table to create a continuous barrier. The instrument table should be covered first with an initial sterile drape, so that ultimately each draped item consists of two layers. The outer patient drape may be secured to the towel clamps underneath with nonpenetrating clamps if needed to maintain its position. The outer drape should be suspended at the cranial aspect of the patient to shield anesthetic personnel from the surgical field. This may involve a suspending framework such as an ether stand, or the drape could be taped to fluid poles next to the table.

Draping of a limb for orthopedic surgery is slightly different, and the approach will vary depending on the portion of the limb to be treated and the planned procedure. The limb should be positioned on the surgery table suspended in air by tape or rope attached to the toes or foot, and then should be secured to a hook or fluid stand next to the table. The final scrub is performed, then the four drapes are placed. When the surgeon has grasped the foot using a sterile towel as a barrier, an assistant releases the suspended limb, and the surgeon can proceed to cover the foot with sterile material (sterile towels, bandage material, or foil). A sterile stockinette then is used to cover the limb and is secured to the towel clamps by holding the four boundary drapes. Finally, a fenestrated superficial patient drape is positioned over the limb in a manner similar to that previously described.

Scrub Suits

Standard surgical scrub suits are worn to decrease dissemination of bacteria into the operating room environment and to promote a clean surface on clothing. Shedding from operating room personnel is the primary source of contamination in the operating room environment; men are worse shedders than women.18,125 Closely weaved fabric decreases the degree of bacterial dissemination, but the overall effect of scrub suits on the environment is questionable.^18,90,126 Routine surgical scrub suits do little to limit the dispersion of bacteria, so suits of tighter weave and better design should be sought.¹⁸ The use of such suits is preferable to the use of street clothes, and scrub suits with elastic cuffs or other occlusive seals are better yet.¹⁴ Routine laundering does little to decrease pathogenic bacteria on scrub suits.⁹⁶

When barrier fabrics, whether scrub suits, gowns, or drapes, are discussed, it is common to refer to them without fully describing their material construction, likely because a large array of materials are currently used, and relevant data are not always readily available. The material originally used with any frequency was cotton muslin woven with 140 threads per inch. This material (after being wetted) is quickly penetrated by moisture and bacteria.12,13 Later, nonwoven materials formed from nonwicking fibers were found to be resistant to water, except under significant pressure. These paper-like products are not launderable. Additionally, launderable, tightly woven material with 280 threads per inch and treated to be water resistant has become available (e.g., Quarpel). Although the 140-count material is not suitable as a barrier material, the latter two products are suitable. Treated 280-count materials have been shown to lose their barrier properties after 75 laundry cycles.¹⁴⁴

Scrubbing Hands

A bewildering amount of literature describes investigations into the effects and value of various components of surgical personnel preparation. In the end, it is difficult to cite specific evidence for the efficacy of many of the aseptic techniques routinely used in the operating theater. Surgeons must consider the evidence and must use common sense when developing an aseptic protocol for their specific situation. It seems likely that many procedures, for which value may not be statistically verifiable, may contribute to an overall reduction in surgical site infections.

Preparation of the surgeon’s hands has changed greatly over the course of surgical history, and excellent reviews have been published.23,157,160 Typically, the hands have high concentrations of unique bacteria.^11,166 The area around and under the fingernails typically has the highest bacterial numbers, even after scrubbing.¹⁰¹ Use of an antiseptic and an ethanol cleanser will dramatically decrease bacterial counts, but these numbers will rebound to prescrub levels within 8 hours, and even the population distribution will return to normal within 2 to 3 days.^11,85

The ideal method of hand preparation is quick, effective, nonirritating, and cost-effective, and has residual action. Recommendations vary, but trends toward hand rubbing as opposed to scrubbing and the use of quick alcohol-based methods predominate. The traditional use of a scrub brush was shown in several studies to have little significance.79,106,170 Even the use of nail picks or bushes has been questioned, despite higher bacterial counts in those areas.¹⁵⁸ Surgeons should be aware that some evidence suggests that frequent surgical scrubbing of the hands may alter normal flora or epidermal integrity to the extent of creating a state whereby higher numbers of pathogenic and nonpathogenic bacteria may be found on the skin.²⁸ Additional research is needed to definitively explore the effects of various scrub protocols on the skin flora of surgeons and the significance of any changes.

Chlorhexidine-containing preparations have been shown to be more effective than povidone-iodine products, although both formulations significantly decrease bacterial numbers.116,119 Although povidone-iodine and chlorhexidine solutions continue to be commonly used, their use in an aqueous vehicle offers disadvantages and is waning compared with the use of an alcohol-based preparation. Several studies support the contention that chlorhexidine is more effective than povidone-iodine in reducing bacterial counts and in maintaining that reduction.⁶⁹ This difference has not been universally noted and may be more prevalent in testing for residual effect.¹⁰⁶ Some evidence suggests that avoiding a final rinse when using chlorhexidine increases its effectiveness.³²

As early as the 1960s, the value of shorter scrub times was recognized and investigated. Initial scrub times of 10 minutes or longer were reduced to 5 minutes when equal efficacy was demonstrated.³⁶ The development of alcohol-based scrub solutions has shown that scrub times of 2 minutes, or even 1.5 minutes, can be as effective as traditional 3 or 5 minute scrubs, depending on the agent used.^{60,64,107,173} The ability to shorten scrub times in such a manner is dependent on the newer alcohol-based agents. The efficacy of these agents has been demonstrated satisfactorily in many studies.^25,66,72,160 Although these products tend to combine an alcohol with a traditional antiseptic, the alcohol seems to be the key to their effectiveness.¹³⁸ Despite this observation, it has been noted that the combination of alcohol and antiseptic (ethanol and chlorhexidine) is more effective than either agent alone.⁹⁹

Romatowski noted that the value of a short surgical scrub depends on whether the scrub is performed correctly.¹³⁵ Additionally, surgeons should be cautious when changing scrub products because the efficacy of these agents varies.⁶⁵ Surgeons should search the literature pertaining to the specific product they intend to use, because following the manufacturer’s instructions regarding scrub time, volume, and method of application is important.¹¹³ Surgeons with larger hands may require greater volumes of solution, and precise guidelines may not be available.⁶⁵

Despite these limitations, the quick alcohol-based solutions are effective and desirable. Somewhat counterintuitively, they are less drying to the skin than traditional products.¹¹⁸ One study showed that their overall effect on skin dryness, erythema, and roughness was less when compared with conventional scrubbing.⁵² This fact, in combination with their ease of application, has led to greater compliance with appropriate use.¹¹⁴

Although traditional protocols call for removal of rings and nail polish before scrubbing for surgery, these recommendations have not been well researched. Recent studies found no effect on bacterial counts when rings were removed before scrubbing.3,8,177 No note was made of the style or size of rings worn in most of these studies, although this is likely to influence findings. Wedding bands have been associated with higher incidences of glove perforations.¹⁰⁵ Until additional studies have been conducted, removal of rings with all but the simplest designs is recommended.