Medicine is full of rituals based on tradition rather than clinical evidence. Take surgical skin preps. Povidone-iodine has long been considered the standard of care, but do you still prep with it because of its clinical efficacy or because it's what you've always used? Since two-thirds of surgical-site infections occur at the point of incision, and there's no arguing that using the most effective agent is essential to protecting your patients, perhaps it's time to reassess your prepping habits.

The evidence mounts
Povidone-iodine has been widely used even though there's been little clinical evidence showing it's any more effective in preventing SSIs than other available skin preps. At the same time, surgeons and other healthcare providers believe SSI rates are too high — each year 300,000 to 500,000 patients develop infections following surgery — so the pendulum is starting to swing away from povidone-iodine as the prepping agent of choice. In 2002, the CDC recommended 2% chlorhexidine-alcohol as a skin preparation for vascular catheter insertion based on a meta-analysis of a number of clinical studies. Chlorhexidene gluconate possesses broad-spectrum antimicrobial activity, provides residual activity on the skin for days after application and, unlike povidone-iodine, remains active upon exposure to blood. Couple these properties with alcohol's fast and broad kill rate, and you have a very effective agent against infection.

Because most SSIs occur at the incision site, my colleagues and I hypothesized that chlorhexidene-alcohol was a good candidate for a head-to-head comparison with povidone-iodine. We jumped at the chance to perform a study that had the possibility of changing the standard of care. Several studies had already looked at the effectiveness of each prepping product in killing bacteria or reducing the bacterial load on the patient's skin, but no studies had compared the efficacy of different skin preps in preventing infections.

So in 2004, we organized a large, randomized and controlled clinical trial of the 2 preps. Over 4 years in 6 hospitals, we followed 849 patients for 30 days after surgery who had received chlorhexidine-alcohol or povidone-iodine preps.

What we learned confirmed our hypothesis. Chlorhexidine-alcohol protected patients better than povidone-iodine did. Chlorhexidine-alcohol was associated with an overall rate of infection of 9.5% compared to 16.1% for povidone-iodine. And chlorhexidine-alcohol was particularly protective against incisional infections (4.2% vs. 8.6%).

By making the switch to chlorhexidine-alcohol, the average facility can prevent an infection that statistically would have occurred with povidone-iodine after prepping 17 patients. Is the approximate $8 more per patient that chlorhexidine-alcohol costs worth the expense? It probably is ($8 x 17= $136 to prevent 1 infection). Also consider the huge potential savings you'd realize by not having to treat an infection acquired at your facility.

More than a year after we published our findings in the New England Journal of Medicine (see "Surgical Prep Comparison Touts Chlorhexidine-Alcohol"), the CDC has yet to issue new guidelines for surgical skin prepping. But the National Quality Forum's 2010 Safe Practices #22 for Surgical Site Infection Prevention calls for using alcohol-based preps. Additionally, hospitals across the country have been switching in large numbers to chlorhexidine-alcohol and updating their protocols.

Not the only choice
Regardless of the evidence supporting the use of chlorhexidine-alcohol as your default surgical skin prep, other choices still play important roles in your infection control efforts. Here's what you need to know about the most common agents.

• Chlorhexidine kills bacteria by disrupting cell membranes. Besides its broad-spectrum antimicrobial activity, it has a long residual effect, up to days after application. When exposed to blood or other bodily fluids, chlorhexidine maintains its antiseptic properties. There are, however, situations where the agent is contraindicated, such as procedures near mucous membranes and the meninges. Chlorhexidine can cause corneal damage if it enters the eye and deafness if it reaches the inner ear. This makes chlorhexidine-alcohol inappropriate for ophthalmic, neurologic, ENT and some plastic surgery procedures. This prep also should also not be used on patients with tender skin or on premature infants.

A chlorhexidine-alcohol solution dries in about 3 minutes. But it's important to remember that because of its alcohol content, the solution is flammable. Let the prep dry completely before starting any procedure, especially one that calls for the use of electrocautery. Avoid letting the prep pool under patients. Also avoid applying it near patients' hair, as would be the case with head and neck surgery, since hair still damp with prepping solution is extremely flammable.

• Iodine kills bacteria by oxidation and the substitution of free iodine in cells. According to the CDC, povidone-iodine rates excellent for killing gram-positive bacteria and good for killing gram-negative bacteria. It takes longer to dry and to begin its killing action than alcohol-based preps and has a shorter residual activity than chlorhexidine. However, povidone-iodine can be used on mucous membranes, making it the prep of choice for ENT, ophthalmic and gynecologic procedures. This agent is also best suited for patients with a known sensitivity to chlorhexidine.

Iodine povacrylex-alcohol is a prepping solution with broad-spectrum and rapid antimicrobial activities. However, a large, randomized and controlled clinical trial has yet to assess its capacity to protect against SSI. In situations where a patient has a known allergy to chlorhexidine, iodine povacrylex-alcohol can be used.

• Parachlorometaxylenol (PCMX) is an alternative skin prep intended for use on patients who are sensitive to iodine, alcohol or chlorhexidine. It's safe for use prior to surgery in the eye or ear or near mucous membranes. It kills bacteria by disrupting cell membranes. The solution is rated good against gram-positive bacteria, fair against gram-negative bacteria and has moderate residual activity.

Stay tuned
Having established that chlorhexidine-alcohol protects patients better than povidone-iodine, my research colleagues and I are setting our sights on assessing the sources of pathogens that cause SSIs and the best way to treat them. Our prepping study will surely not be our last, so check back with us to keep your skin antiseptic practices up to date.