Module 4 · Intraoperative Procedures I: The Sterile Team
Lesson 4.2 — Draping the Patient
Draping converts the OR table into a sterile field. The moment the first drape goes down, every action the scrubbed team takes — and cannot take — is governed by what is and is not sterile. The CST exam tests drape selection, placement sequence, technique rules, and what to do when something goes wrong.
📋 NBSTSA Blueprint: Domain I-B · Intraoperative Procedures · Tasks: Drape Mayo stand and back table · Drape patient · Secure cords and tubing to drapes
🎯 High-Yield Topics — What Gets Tested
Draping incision-site first, then periphery outward · Skin prep must be DRY before draping · Cuffing hands — how and why · Once placed, a drape cannot be moved · Drapes held high during placement · Drape falls below table level = contaminated · Four-towel squaring sequence · Which drape for which procedure · Fenestrated vs. non-fenestrated · Incise drape — when and how applied · Perforating vs. non-perforating towel clips · Hole in a drape after placement — cover or remove · Unprepped skin exposed — remove and re-prep · Draping furniture and equipment · Cords and tubing secured with non-perforating clips
1. Purpose of Surgical Drapes
Sterile surgical drapes serve three functions simultaneously: they establish the sterile field around the operative site, they protect the patient from microorganisms on the OR table and team members’ non-sterile areas, and they protect the team from the patient’s non-sterile skin and body fluids. Every draping decision — material choice, placement order, how the drape is handled — serves one or more of these functions.
Drapes must be impervious to fluid — strike-through contamination occurs when fluid soaks through the drape barrier, creating a path for microorganisms from the non-sterile underside to the sterile top surface. All drapes used in contact with the wound must meet fluid-resistance standards.
2. Before Draping — Prerequisites That Must Be Met
The CST exam consistently tests the conditions that must exist before draping begins. Skipping any of these is a patient safety violation.
Skin prep solution must be completely dry
Draping over wet prep solution traps moisture under the drape, which degrades the barrier and can cause chemical burns under some prep agents. The circulator confirms the prep has dried before handing off to the scrub team. This is a direct exam question — draping begins only after the prep is dry.
Patient is positioned and the surgical site is confirmed
The Universal Protocol time out is completed, the marked operative site is verified, and the patient is in final position. Draping locks in the site — a misplaced drape that exposes the wrong anatomy will require removal and re-prep.
The scrub tech is gowned and gloved
Only scrubbed personnel handle sterile drapes. The circulating nurse never touches the sterile draping surface. The anesthesia provider may receive the head end of the body drape by clipping it to an IV pole — the scrub tech cuffs their gloved hand in the drape before extending it toward the non-sterile anesthesia area.
Drapes are stacked in order of use on the back table
The draping items are organized so the first drape needed is on top. Towels go first, then the fenestrated sheet. Fumbling through the back table mid-drape breaks the flow and risks contamination.
3. The Universal Draping Principles — Applied to Every Procedure
These rules apply regardless of the procedure, position, or drape type. The CST exam presents scenarios that violate one of these and asks the student to identify the error or the correct response.
📝 Knowledge Check 1: A laparotomy drape has been placed on the patient. The surgeon notices unprepped skin is exposed at the edge of the fenestration. What is the correct action?
A. Apply additional drapes over the exposed unprepped skin to cover it
B. Reposition the laparotomy drape closer to cover the unprepped skin
C. Remove all drapes, re-prep the skin, allow it to dry, and re-drape
D. Apply an adhesive incise drape over the exposed skin to seal it
Reveal Answer
✅ Correct Answer: C
Unprepped skin must never be within or immediately adjacent to the operative field — it is a source of skin flora that can cause surgical site infection. The drapes must be removed, the skin prepped and allowed to dry, and the patient re-draped from scratch. Option B (repositioning a placed drape) violates the core rule that drapes cannot be moved once placed. Option A (draping over unprepped skin) does not solve the contamination risk — skin must be prepped, not simply covered. Option D is the trickiest distractor — an incise drape does not substitute for antiseptic skin prep. This is a NBSTSA practice exam question with option C as the confirmed correct answer.
4. The Four-Towel Squaring Sequence — Abdominal Draping
The four-towel technique is the foundation of abdominal draping and the exam’s most-tested draping sequence. Four sterile towels are placed to square off the incision site before the fenestrated sheet is applied. The sequence and direction matter.
Four-Towel Placement — Order and Orientation
Near side (closest to the scrub tech) — folded edge toward the incision line. The cuffed edge of the towel is placed along the incision border on the scrub tech’s side of the table. The scrub tech does not cross to the other side.
Bottom (toward feet) — folded edge toward incision, placed on the inferior border of the incision site.
Top (toward head) — folded edge toward incision, placed on the superior border. These three towels are cuffed toward the scrub tech (fold faces the scrub tech’s side).
Far side (toward surgeon) — passed to the surgeon or first assistant; cuffed toward the surgeon’s side. The folded edge goes adjacent to the incision line on the far side.
After all four towels are placed, the fenestrated (laparotomy) sheet is applied over them — opening centered precisely over the incision square. Towels remain permanently beneath the laparotomy sheet throughout the case.
💡 Towel Clip Rule: Towels are secured with non-perforating towel clips (e.g., Backhaus clamp used carefully, or specialty non-penetrating clips) wherever possible. Perforating towel clips that penetrate both the towel and the patient’s skin create a hole through the sterile barrier. If a perforating towel clip must be used and is subsequently removed mid-case, it is taken off the sterile field — the hole in the drape must be covered with additional sterile material.
⚠️ Cords and Tubing: Electrosurgical cords, suction tubing, irrigation tubing, camera cables, and other cords are passed off the sterile field to the circulator using sterile technique, then secured to the drapes with non-perforating towel clips. Perforating clips through a cord opening create a hole in the barrier. Cords that pass under the Mayo stand are considered sterile on the underside of the draped Mayo stand — the Mayo stand drape encloses both the top and sides.
📝 Knowledge Check 2: During draping of the abdomen, a towel is incorrectly placed and part of the fenestrated laparotomy sheet now covers the wrong area. The surgeon asks the scrub tech to pull the laparotomy sheet 2 inches toward the head. What should happen?
A. Move the laparotomy sheet as requested — 2 inches is a minor adjustment
B. Ask the circulator to move the sheet from the non-sterile side underneath
C. Inform the surgeon that once placed, the drape cannot be repositioned — the drape must be removed and re-draping performed if the placement is clinically unacceptable
D. Cover the incorrectly placed area with an additional sterile drape and continue
Reveal Answer
✅ Correct Answer: C
Once a drape is placed, it cannot be repositioned under any circumstances — not even a small adjustment. Moving the drape would drag the contaminated underside across the prepped sterile area, defeating the purpose of draping. The scrub tech respectfully informs the surgeon of this principle. If the placement is truly unacceptable for surgical access, the drapes must be removed (by the circulator removing contaminated drapes), the patient re-prepped if indicated, and new sterile drapes applied from scratch. Option D (covering with another drape) addresses the cosmetic appearance of the problem but does not correct the underlying issue of the incorrectly positioned fenestration.
5. Drape Types — Match the Drape to the Procedure
The CST exam tests drape selection directly — students must know which drape is used for which procedure and why the specific design of each drape serves that procedure’s anatomical requirements.
Fenestrated Drapes — Opening Exposes the Operative Site
| Drape | Fenestration | Used For |
|---|---|---|
| Laparotomy Sheet | Longitudinal (lengthwise) opening, center of sheet | Abdominal, back, thoracic procedures — the most common fenestrated drape |
| Thyroid Sheet | Transverse (horizontal) fenestration near the top of the sheet | Neck procedures: thyroidectomy, parathyroidectomy, carotid endarterectomy |
| Breast Sheet | Larger fenestration than laparotomy sheet | Breast and chest procedures requiring wider exposure |
| Kidney Sheet | Transverse fenestration to accommodate lateral flank access | Kidney and retroperitoneal procedures in the lateral position |
| Hip Sheet | Longer version of laparotomy sheet | Orthopedic procedures on fracture tables requiring extra coverage |
| Craniotomy Sheet | Round or oval fenestration near the head end | Cranial neurosurgical procedures |
| Eye / Ear Sheet | Small fenestration for the single operative eye or ear | Ophthalmic, otologic procedures — small, precise field |
| Shoulder Sheet | Round or oval opening for operative arm/shoulder | Shoulder arthroscopy and arthroplasty in beach chair position |
Non-Fenestrated and Specialty Drapes
| Drape | Description & Use |
|---|---|
| Split Sheet | Same size as laparotomy sheet but cut longitudinally from one end to the center, creating a U-shape. Used to wrap around an extremity or the neck; allows the extremity to be free while maintaining a sterile field around it. |
| Perineal / Lithotomy Sheet | T-shaped full-body drape designed for lithotomy position. May have leggings incorporated to cover each leg in the stirrups. Used for GYN, urological, rectal, and perineal procedures. |
| Combined Sheet | Combination of laparotomy and perineal sheet — two fenestrations. Used for abdominoperineal resection (APR) of the rectum, where both the abdominal and perineal fields must be sterile simultaneously. |
| Extremity (Stockinette) Drape | Tubular impervious drape closed at one end. Rolled up the arm or leg to allow the extremity to remain a working part of the sterile field during limb surgery. An impervious sheet also covers the arm board. |
| Medium / Half Sheet | Non-fenestrated plain sheet used to add coverage above or below the main fenestrated drape, extend the sterile field, or use when an odd anatomical area makes a fenestrated drape impractical. |
| ENT / Head Drape | Full-body sheet with a small split at one end that wraps at the chin or below the nose. Used for procedures of the nose, throat, ear, face. |
| Leggings | Supplied in pairs; cover each leg in lithotomy position. May be incorporated into the perineal sheet or used separately when legs require individual coverage. |
💡 Exam Shortcut — Matching Drapes: The exam asks “which drape for which procedure?” Fenestrated drapes match the anatomical shape of the operative field. Laparotomy = abdomen (longitudinal). Thyroid = neck (transverse, at the top). Kidney = flank (transverse). Perineal = lithotomy (T-shape with leggings). Combined = APR (two fenestrations). Split = extremity or neck wrapping. When in doubt, match the drape shape to the surgical site’s orientation and exposure needs.
📝 Knowledge Check 3: Which drape would the scrub tech select for a laparoscopic-assisted vaginal hysterectomy (LAVH)?
A. Laparotomy sheet — to cover the abdominal access sites
B. Split sheet — to wrap around the operative leg
C. Perineal sheet with leggings — the patient is in lithotomy position requiring perineal and vaginal access
D. Thyroid sheet — for access to the lower pelvis
Reveal Answer
✅ Correct Answer: C
An LAVH is performed with the patient in lithotomy position, requiring both perineal (vaginal) access and laparoscopic abdominal port sites. The perineal sheet with leggings is designed specifically for this position — it accommodates both legs in stirrups and provides access to the perineum. The LAVH may also require a separate abdominal/laparotomy component depending on the extent of laparoscopic work, but the primary draping consideration is the lithotomy position, making the perineal sheet the correct answer. This is one of the most frequently tested drape-to-procedure matching questions on the CST exam.
6. The Incise Drape — What It Is and What It Is Not
The incise drape (also called an adhesive or plastic drape) is a clear, sterile, adhesive-backed film applied directly to the prepped skin over the operative site. The surgeon makes the incision through the drape — the film remains adhered to the wound edges throughout the case, theoretically preventing skin flora migration into the wound.
How It Is Applied
Applied after the towels and body drape are placed, after prep solution is completely dry. Two-person application is optimal — one on each side of the table. The backing is peeled away while both persons hold the edges, and the drape is applied smoothly without wrinkles to ensure adhesion. Iodophor-impregnated incise drapes (e.g., Ioban) release iodine continuously throughout the case for antimicrobial effect.
What the Incise Drape Does NOT Do
The incise drape is not a substitute for skin prep. It cannot be applied to unprepped skin as a shortcut. It is applied after antiseptic prep and draping — it is an adjunct, not a replacement. Also: evidence is mixed on whether plain (non-iodophor) incise drapes reduce SSI — some studies suggest non-impregnated drapes may actually increase infection risk by trapping moisture under the film. If used, iodophor-impregnated is preferred — unless the patient has an iodine allergy.
Aperture Drape vs. Incise Drape — Know the Difference
An aperture drape is a small self-adhering fenestrated drape (often called a “sticky drape” or “isolating drape”) used to wall off a contaminated area — like a stoma or the anus — from the clean surgical field. It is not the same as an incise drape. The aperture drape seals off contamination; the incise drape seals the wound site to the skin. Both are tested on the CST exam.
7. Holes, Tears, and Drape Integrity Problems
Drape integrity problems can occur at any point — during unfolding, from instrument puncture, from towel clip placement, or from strike-through. The exam tests the correct response to each scenario.
Hole found before drape is placed → Discard and use a new drape
A drape with a pre-existing hole is contaminated and cannot be used. Discard immediately and open a new sterile drape.
Hole discovered after drape is placed → Cover immediately with additional impervious sterile material
If the hole is small, it can be covered with an additional sterile impervious drape or adhesive-edged towel placed over it. If the hole is large or at the fenestration, the entire drape must be replaced.
Strike-through (wet drape) → Contaminated at that area — cover or replace
A wet area on a drape has wicked through the barrier. Cover with additional impervious sterile material immediately. If the strike-through involves the fenestration or wound area, the drape and prep may need to be redone.
Perforating towel clip removed mid-case → Remove from sterile field; cover the hole
Once a perforating clip is removed from the drape, the clip itself is contaminated (it penetrated the barrier) and must come off the sterile field. The hole it created must be covered with additional sterile material immediately.
📝 Knowledge Check 4: Immediately after the laparotomy sheet is placed, the scrub tech notices a small 1-cm tear in the drape about 8 inches from the fenestration. The prep site and wound area are not involved. What is the correct action?
A. Remove all drapes, re-prep, and start over — any hole in any drape invalidates the entire sterile field
B. Leave the hole — it is small and far from the operative site
C. Cover the hole immediately with an additional sterile impervious drape or adhesive-edged sterile towel
D. Ask the circulator to place a piece of tape over the hole from the non-sterile side
Reveal Answer
✅ Correct Answer: C
When a hole or tear is discovered after a drape has been placed, the response is proportional to the location and size. A small tear 8 inches from the operative site that does not involve the wound area or fenestration can be managed by covering it immediately with an additional sterile impervious drape or adhesive-edged sterile towel. This restores the barrier at that point. Option A is an overreaction for a small, peripherally located hole — total removal and re-draping is indicated only when the integrity at the operative site itself is compromised. Option B is never acceptable — no hole is ignored. Option D involves the circulator (non-sterile) reaching over the sterile field, which itself would contaminate the drape.
⚡ Rapid Review — Draping High-Yield Facts
Lesson 4.2 Complete
Draping converts positioning into surgery. Know the seven universal rules cold, match every drape to its procedure, and you will not lose points on this category — it tests consistently across the intraoperative domain.
Next: Lesson 4.3 — Surgical Instruments