1.4 Surgical Skin Prep & Draping

Purpose and Antiseptic Agents

The surgical skin prep mechanically and chemically reduces the number of microorganisms on the patient's skin before incision, lowering the risk of a surgical site infection (SSI). It removes transient flora (loosely attached surface organisms) and reduces resident flora (organisms in deeper skin layers and follicles). The prep does not sterilize skin — that is impossible on living tissue — but it reduces the count to the lowest practical level.

The CST must know the common antiseptic agents, their actions, and their cautions:

Alcohol-based agents give the fastest and most durable kill, which is why CHG-alcohol combinations are widely preferred — but their flammability drives the dry-time rule below.

Prep Technique: Clean to Dirty

The defining principle is clean to dirty: begin at the planned incision site (the cleanest area) and move outward in a widening circular or back-and-forth motion, expanding the field well beyond the incision to allow for extension, drains, and draping.

Core rules tested on the exam:

• A prep sponge that has reached the outer (dirty) edge is discarded and never brought back toward the clean center — the motion is unidirectional.
• A contaminated area (stoma, open wound, sinus tract, vagina, anus) is prepped last, with a separate sponge, even when it lies within the field; the umbilicus is cleaned separately.
• The prep is wide enough to cover the incision plus a wide margin in every direction.
• Pooling of flammable prep solution under the patient, in the umbilicus, or in skin folds is wicked away, because pooled alcohol fuels surgical fires.

Hair removal, when required, is done immediately before surgery with electric clippers (single-use heads) or depilatory — never a razor, which creates microabrasions that increase SSI. Hair is removed only when it interferes with the procedure; routine shaving is avoided. The patient's skin is also assessed for breaks, rashes, or lesions before prepping.

Dry Time, Fire Safety, and Draping

Dry time is a non-negotiable safety step. Alcohol-based preps must be completely dry before draping — generally at least 3 minutes on hairless skin and up to an hour in hair. Draping over a wet prep traps flammable vapor under the drapes; combined with an ignition source (ESU, laser) and an oxygen-enriched atmosphere, this completes the fire triangle and is a leading cause of OR fires.

Draping establishes the sterile field around the prepped site. Principles:

• The scrubbed CST drapes the patient, beginning at the incision site and working outward.
• Hold drapes above waist level and cuff gloved hands under the drape edge to protect them.
• Once a drape is placed, it is not moved toward the field — it may be moved away from the site or discarded, but never repositioned closer to the incision (that would drag contamination inward).
• A drape that becomes contaminated or falls below the table edge is removed and replaced.

The sequence typically begins with four sterile towels squaring off the incision: the first three are cuffed toward the scrub and the fourth toward the surgeon, secured at the corners with towel clips (once placed, a clip's tips are considered contaminated and are not removed and reused on the field). A fenestrated drape — a large sheet with an opening — is then placed with the fenestration directly over the incision and oriented toward the head or foot of the table.

Self-adhering incise drapes (sometimes antimicrobial/iodophor-impregnated) may be applied directly to the skin so the incision passes through the adhesive film.

Special Preps, Drape Types, and Maintaining the Field

Different sites demand modified technique. For an eye, ear, or face prep, agents that are toxic to the cornea or middle ear (notably CHG) are avoided, and a diluted povidone-iodine is often used; the patient's eyes are protected during a facial prep. The vagina and rectum are considered contaminated and are prepped last. An umbilicus is cleaned with a separate applicator because it harbors debris, and a planned bowel stoma is isolated and prepped last. Skin prep always extends widely so additional sites (drain exits, a second incision) remain within the sterile margin.

Common drape types the CST handles:

• Towels — square off the incision; first three cuffed toward the scrub, the fourth toward the surgeon.
• Fenestrated sheet (laparotomy/lap drape) — single opening for general abdominal cases.
• Split / U-drape and extremity drape — wrap around an arm, leg, or specific anatomy.
• Incise (adhesive) drape — clear film placed over the skin; the incision goes through it.
• Mayo stand cover and back-table drape — establish the sterile equipment field.

Once draping is complete, sterile-field integrity is everyone's job. The field is monitored continuously, anything that drops below the table edge or table level is contaminated, and the field is never left unattended. Items are passed without reaching over the field, and only the top of a draped surface is considered sterile — the sides hanging below table level are not. If sterility is breached, the affected drape or item is removed and replaced before the procedure continues, keeping SSI risk as low as possible.