by Noelle La Croix, DVM, Dip. ACVO
The Art of Aseptic Technique in Ophthalmic Surgery
Postoperative endophthalmitis and corneal infection are rare but serious complications of intraocular surgery. Postsurgical infection of periocular tissues (eyelids, conjunctiva, and/or third eyelid) can result in significant visual impairment (Figure 1).Subsequent corrective surgery may significantly increase the morbidity, and even the mortality, of veterinary patients.
Prevention of a postoperative ocular infection begins and ends with an aseptic surgical site. Peri- and postoperative courses of antibiotics are not alternatives to aseptic techniques. Antibiotics may encourage the postoperative growth of resistant bacteria following non-aseptic procedures. Proper aseptic technique prevents subsequent infection and does not require the total elimination of bacteria within a surgical wound.
The terminology of bacterial control is often misunderstood and can lead to inappropriate behavior by a veterinary surgeon. Sterilization is defined as the total inactivation of all microbial reproduction on, or within, a material. Although ideal, sterilization is not routinely attained at any surgical site. Disinfectants are chemical agents applied to inanimate objects that kill microbes capable of producing infections. Antiseptics are chemical agents applied to living tissues that prevent sepsis (or putrefaction) by killing or inhibiting the growth of microbes. Many disinfectants cannot be used as antiseptics as they damage living tissue. Unfortunately, antiseptics are generally more expensive than, and not as effective as, most disinfectants. Asepsis implies a site free of pathogenic organisms, whereas aseptic technique refers to procedures designed to reduce the number of pathogenic organisms and prevent their reproduction. A surgical or sterile asepsis therefore refers to the elimination of pathogenic organisms from a surgical area.
Bacteria colonizing the epidermis are the primary source of infection of a surgical wound. Ocular infections are generally derived from the epidermal Staphylococci of a patient. Direct contact between the cornea and skin (especially in cases where ocular and/or systemic conditions increase the number of epidermal bacteria) predispose patients to postoperative infection. Predisposing conditions include, but are not limited to, blepharitis, conjunctivitis, canaliculitis, lachrymal duct obstruction, dry eye syndrome, prosthesis in the fellow orbit, entropion, immunosuppression, Cushing-like syndrome, and diabetes. Ideally, these disorders should be corrected or controlled prior to non-emergency surgery to prevent postoperative infection. Appropriate blood testing (including a CBC, chemistry panel, urinalysis, and urine culture) and physical examination will reveal established infections and determine the risk of subsequent infection in the patient. Routine ocular surgery should be avoided in cases with active or acute infections. Pre-existing disorders and infections cannot typically be controlled in cases requiring emergency ocular surgery (i.e.; eyelid laceration, corneal rupture, or lens luxation). These emergency procedures are therefore typically associated with higher rates of postoperative infection. Infected enucleated eyes should be cultured to guide appropriate courses of postoperative antibiotics.
Ocular surgical asepsis of the veterinary patient begins at home. A client’s bathing of their pet can significantly reduce bacteria-laden debris if performed within a day of surgery. Preoperative examination for corneal ulceration, skin infection, ear infection, and respiratory disease, will determine if surgical postponement is warranted. Pre-surgical anesthesia, shaving, and antiseptic cleansing should be performed in a designated area that is not the surgical suite. Clipper blades should be pre-sterilized as they can generate epidermal microabrasions that can be colonized with the bacteria of a prior patient. Similarly, all antiseptic bowls and applicators should be sterilized between patients. Shaving and cleansing should delineate a wide surgical field free of any hair and other organic material that can absorb and diminish the effectiveness of an aseptic compound. These techniques are designed to decrease a patient’s bacterial contamination prior to entering a surgical suite.
A solution of povidone-iodine (a complex of polyvinylpyrrolidone and elemental iodine) is the standard preoperative antiseptic for ocular and periocular surgery. The bactericidal effect of povidone-iodine is due to soluble iodine’s oxidation of bacterial proteins (primarily in cell walls and enzymes of the respiratory chain). Povidone-iodine’s ability to kill a broad spectrum of microbes, and even microbial spores, increases with its surface contact time while aqueous. However, some epidermal bacteria will survive in a bottle of povidone-iodine and cross-contamination between patients is possible. Single-use bottles of povidone-iodine solution are therefore ideal for ocular surgery. Povidone-iodine scrubs cannot be used as they contain additional detergents which can cause corneal and/or conjunctival ulceration.
High concentrations of, and increased contact time with, povidone-iodine can also oxidize and damage both corneal and conjunctival proteins. Povidone-iodine is therefore routinely diluted to between 5 and 10% for eyelid applications and to 0.2% for corneal and conjunctival tissue. A typical pre-surgical ocular application begins with 10 concentric gauze-based scrubs of the eyelids and surrounding skin with 5% povidone-iodine. The scrubbing increases contact time of the aqueous iodine with the skin and produces shearing forces that destroy biofilms (microbial aggregates). The conjunctival sac and cornea are then flushed with 150 ml of sterile saline to further dislodge bacteria and other organic material. A further 5 ml of 0.2 % povidone-iodine is then applied to the conjunctival sac for 5 minutes. The conjunctival fornix and cornea are then prepared with 10 concentric individual sterile swabs of 0.2% povidone-iodine. After the patient is transferred to a surgical suite, the eyelids are re-scrubbed with 5% povidone-iodine, and a drop of sterile hyaluronate solution is placed in the eye before draping. Intraocular surgery (cataract surgery and lens extraction) requires copious volumes of sterile saline, necessitating waterproof adhesive draping that prevents the wicking of epidermal bacteria back towards the eye.
The microsurgical instruments of ocular surgery are very delicate and can easily warp in temperatures that exceed 60° C. Chemical sterilization with ethylene oxide is therefore preferable. All ocular instrumentation must also be cleansed thoroughly prior to sterilization to eliminate organic debris. Regular magnified inspections of instruments can reveal pitting, cracking, and/or rust that can shelter organic debris, and thus prevent complete sterilization. Damaged instruments should be repaired or retired.
Ocular surgeons follow routine scrubbing, capping, gowning, masking, and gloving procedures to promote asepsis in the surgical suite. However, the greatest impediment to surgical asepsis may be the false sense of security in the mind of a surgeon following multiple procedures without subsequent infection. In reality, decreased diligence in aseptic techniques raises the frequency of postoperative infection that can lead to dire consequences for the veterinary patient.
Noelle La Croix, DVM, Dip. ACVO
Veterinary Medical Center of Long Island
75 Sunrise Highway
West Islip, New York 11795
(631) 587-0800; fax (631) 587-2006
Figure 1: A postoperative infection secondary to entropion surgery in a 3 year old pit bull canine.