Anesthesia in Colonoscopy

Overview

• Yamada's Textbook of Gastroenterology, 7e
• Miller's Anesthesia, 10e

Continuum of Sedation Depth (ASA Definitions)

Pre-procedure Assessment

• NPO: 6 hours for a light meal, 8 hours for a full meal, 2 hours for clear liquids (in patients without aspiration risk factors such as GERD, gastric dysmotility, DM, bowel obstruction)
• ASA classification and comorbidities guide drug choice and monitoring level
• Patients with OSA, obesity, extreme anxiety, mental disability, movement disorders, or chronic pain may need deeper sedation or GA even for routine procedures
• Anticoagulation status must be reviewed

Pharmacology of Agents Used

Benzodiazepines

Opioids

Propofol

• Mechanism: Hindered phenolic compound with general anesthetic properties
• Onset: 30-60 seconds
• Duration: 3-10 minutes (rapid recovery)
• Dosing: IV: 20-40 mg slow injection; incremental boluses 10-20 mg every 20 seconds; smaller doses required when combined with opioids or benzodiazepines
• No analgesic effect; weak amnesic effect
• Advantages: Rapid onset, titratable, fast recovery - superior for outpatient colonoscopy throughput
• Disadvantages: Apnea, hypotension, injection-site pain; requires vigilant monitoring
• Administration by non-anesthesiologists (NAPS - nurse-administered propofol sedation) is used in some centers but remains controversial

Safety and efficacy of propofol have been well demonstrated for colonoscopy and EGD. Increasingly, US colonoscopies use propofol, and propofol administration is nearly synonymous with anesthesiologist involvement. - Yamada's Textbook of Gastroenterology, 7e

Remifentanil

• Ultra-short-acting opioid; patients recover earlier than with propofol
• However: more nausea and respiratory depression than propofol groups
• Less commonly used as sole agent

Inhalational Agents (Sevoflurane / Nitrous Oxide)

• When compared with TIVA (propofol + fentanyl + midazolam), inhalational anesthesia patients recovered slower but had less psychomotor impairment at discharge
• TIVA group emerged faster but had longer-lasting psychomotor impairment

Monitoring

• Pulse oximetry (SpO2) - continuous
• Capnography (ETCO2) - recommended; reduces incidence of O2 desaturation and hypoxemia during propofol sedation for colonoscopy (the ColoCap study)
• Blood pressure (NIBP) - intermittent or continuous
• ECG - especially in cardiac patients
• BIS monitoring - useful to titrate depth, particularly when propofol is used

Stimulating Events During Colonoscopy

1. Introduction of the endoscope
2. Colonic insufflation (with CO2 preferred over air)
3. Advancement of scope around flexures
4. Biopsy, polypectomy, stenting, dilation, and mucosal resection (endoscopic mucosal resection / ESD) - these require increased analgesia

Reversal Agents

Role of the Anesthesiologist vs. Non-Anesthesiologist

Complications

2025 Evidence Updates

1. Intravenous lidocaine + propofol for colonoscopy (2025, PMID 40102176): Meta-analysis in Anaesthesia examining whether adding IV lidocaine to propofol-based sedation improves outcomes - currently under evaluation.
2. Ciprofol vs. propofol for GI endoscopy (2025, PMID 40033212 & 40636379): Ciprofol (a novel propofol analogue with less injection pain and more stable hemodynamics) shows comparable safety and efficacy to propofol for colonoscopy and EGD in Chinese patient populations - a potential emerging alternative.

Summary

Levels of Lymph Nodes in the Neck

Bailey and Love's Short Practice of Surgery, 28th Edition

Figure 53.3 - Cervical Lymph Node Levels (Bailey & Love 28th Ed.)

Figure 55.4 - Detailed Anatomical Relationships

Figure 52.9 - The Level System (All Seven Levels)

The Seven Levels - Detailed Description

Metastatic Patterns by Primary Site

Types of Neck Dissection (based on Levels)

"Bulky nodal disease may dictate the need for a radical neck dissection, but this operation is less commonly performed owing to a better understanding of the lymphatic drainage of primary sites."

• Bailey and Love's Short Practice of Surgery, 28th Edition

N-Stage (AJCC 8th Edition TNM) - as in Bailey & Love Table 53.2

Sources: Campbell's Operative Orthopaedics (15th Ed, 2026), Miller's Review of Orthopaedics (9th Ed), + Current Meta-Analyses

1. Background: Two Alignment Philosophies

"Kinematic alignment philosophy is to maintain native limb alignment because knee ligaments and capsule have developed to function in current limb alignment and should not be adjusted."

• Miller's Review of Orthopaedics, 9th Edition

2. Key Anatomical Concepts

Mechanical Axis Femur (MAF) and Tibia (MAT)

Important Angular Measurements

Coronal Plane Alignment of the Knee (CPAK) Classification

3. Three Variants of Kinematic Alignment

a) Unrestricted KA (True KA)

• Bone cuts set exactly to native LDFA and MPTA without any limit
• Fully restores the patient's native anatomy, including pathological variants
• Risk: extreme outliers (e.g., tibial varus >3-4°) are associated with higher failure rates

b) Restricted KA (rKA / "Bounded" KA)

• Native anatomy is restored within defined safety limits
• Tibial component: kept within 0-3° varus (never >3° beyond neutral)
• Femoral component: kept within 0-3° valgus of neutral
• Most commonly used clinical variant; provides balance between native feel and implant longevity

c) Adjusted MA with Kinematic Principles ("Kinematic Mechanical")

• Primarily MA framework, but with attention to joint line preservation and phenotype
• Not a distinct technique but rather a surgeon preference applied within MA

4. Obtaining KA Using Conventional Instrumentation (Step-by-Step)

Step 1: Preoperative Planning (Critical)

• Measure the native mLDFA (lateral distal femoral angle referenced to mechanical axis)
• Measure the native mPTA (medial proximal tibial angle)
• Calculate the arithmetic HKA = mPTA - mLDFA
• Classify the CPAK phenotype (varus/neutral/valgus + apex distal/proximal)
• Measure the posterior tibial slope on lateral radiograph
• Measure the sagittal femoral flexion (posterior condylar offset)

Two dedicated RCTs (Smolle et al., Arch Orthop Trauma Surg 2023; Sadoghi et al., J Knee Surg 2024) confirmed that conventional instrumentation achieves adequate restoration of native tibial obliquity and tibial slope in KA TKA when measurements are properly planned preoperatively.

Step 2: Distal Femoral Cut - Setting the Valgus Cut Angle for KA

• Calculate the patient-specific valgus cut angle = (native mLDFA - 90°)
  • If native mLDFA = 87°, the valgus cut = 3° (less than typical MA 5-7°)
  • If native mLDFA = 92°, the valgus cut = 2° of varus cut (an apex proximal phenotype)
• Insert the IM rod into the femoral canal; adjust the IM cutting jig to the calculated valgus angle
• This produces a distal femoral cut that restores native joint line obliquity on the femoral side

"A kinematic alignment with a 3-degree varus joint line at the tibia and an increased distal valgus cut on the femur may improve functional results after TKA." - Campbell's Operative Orthopaedics, 15th Ed (2026)

• Most standard IM femoral cutting jigs allow adjustment from 0-9° valgus
• The surgeon dials in the patient-specific angle rather than a population-average 5-7°
• Use a preoperative full-length HKA radiograph to determine accurate entry point

Step 3: Proximal Tibial Cut - Restoring Native MPTA

• Native mPTA is typically 85-88° (3-5° varus)
• The tibial cutting jig (EM or IM) must be angled to match native obliquity
• For EM jigs: adjust the coronal angle to match native MPTA
• For IM jigs: the rod is angled within the medullary canal

• Native posterior tibial slope (average ~7°) must also be restored
• Sadoghi et al. RCT (2024) found that CI achieved exact tibial slope in 86% of cases vs. 56% with PSI
• The conventional IM tibial guide must be adjusted to avoid over-flexing the tibial cut

• 78% had tibial obliquity restored exactly (0° deviation)
• 21.3% had a 0-1° deviation
• Only 0.7% had 1-2° deviation
• No case exceeded 2° deviation - confirming conventional instrumentation is adequate for KA

Step 4: Femoral Rotation and Flexion

• In MA: femoral component is externally rotated ~3° relative to the posterior condylar axis (PCA) to form a rectangular flexion gap after the perpendicular tibial cut
• In KA: because the tibial cut is not perpendicular to the mechanical axis but follows native MPTA, the required femoral external rotation is different and must be recalculated
• The gap-balancing approach (tensioning) or measured resection are both used
• Posterior condylar axis, transepicondylar axis (TEA), and Whiteside's AP axis are all reference options

• The IM rod must be angled appropriately to avoid hyperflexion of the femoral component
• Sadoghi et al. (2024): both CI and PSI showed no deviation >1° in sagittal femoral alignment

Step 5: Gap Balancing vs. Measured Resection in KA

Step 6: Ligament Balancing (or Avoiding It)

• Cuts are made to match the joint line that the native ligaments are adapted to
• The medial and lateral compartments are balanced by the anatomy, not by sequential releases

• Minor releases may still be needed for soft tissue contracture
• In severe preoperative deformity (e.g., varus >15°), true KA may not be achievable without extensive releases - this is when restricted KA limits apply

Step 7: Implant Sizing and Patellofemoral Considerations

• Femoral component size: Must restore distal condylar offset; avoid overstuffing or understuffing
• Patellofemoral joint: KA may alter trochlear groove orientation; studies (Blakeney 2019) showed KA better reproduces normal gait but does not always restore native trochlear anatomy
• Tibial sizing: Posterior tibial slope restoration affects PCL tension and flexion ROM

5. How KA is Achieved with Conventional vs. Other Technologies

6. Current Evidence: KA vs. MA - Clinical Outcomes

Meta-Analysis Evidence (2022-2026)

RCT on Conventional Instrumentation Specifically (2026)

• KA showed significantly better KSS Pain, WOMAC total, and FJS-12 at 2 years
• Patients with varus alignment showed the greatest benefit from KA
• Most differences did not exceed MCID thresholds
• ROM did not differ significantly between groups

Overall consensus: KA is at least equivalent to MA, with modest but statistically significant early functional and patient satisfaction advantages. Long-term survivorship data remain essential.

7. Outlier Risk and the "Safe Zone" Concept

• Tibial varus >3° (mPTA >3° from neutral = <87°): associated with significantly higher short- and mid-term failure rates
• Femoral varus >3°: similarly at risk
• Campbell's 15th Ed: "Opponents of KA point to the fact that if outliers on the tibia reach 4 or more degrees varus, the rate of short-term and midterm failures is much higher."

rKA Safe Zone:
   Femur:  mLDFA 85-90° (0-5° valgus from neutral)
   Tibia:  mPTA 87-90° (0-3° varus from neutral)
   Coronal limb: mHKA ±3° from neutral

8. Advantages and Disadvantages of KA in Conventional TKA

Advantages

• No (or minimal) ligament releases required in most cases
• Preserves native kinematics - tibiofemoral contact points and rotational arc maintained
• Better gait pattern (closer to native) shown in gait analysis studies
• Potentially higher patient satisfaction and joint awareness (FJS)
• Eliminates "soft tissue balancing" challenge in two planes

Disadvantages

• Requires meticulous preoperative planning and measurement of native angles
• Risk of implant overload if outliers are not controlled (>3-4° tibial varus)
• May not be suitable for severe coronal deformity (>15° varus/valgus)
• Some increased complexity with conventional instrumentation vs. navigation/robotics
• Long-term survivorship data are still limited compared to MA

9. Step-by-Step Summary: Conventional KA Technique

1. PREOPERATIVE
   └── Full-length HKA radiograph
   └── Measure native mLDFA, mPTA, HKA, tibial slope, femoral flexion
   └── Classify CPAK phenotype
   └── Plan restricted KA limits (rKA: tibia ≤3° varus, femur ≤3° valgus)

2. FEMORAL SIDE (Distal Cut)
   └── Insert femoral IM guide
   └── Set valgus cut angle = (native mLDFA - 90°), patient-specific
   └── Make distal femoral cut at native LDFA

3. TIBIAL SIDE (Proximal Cut)
   └── Set tibial cutting jig obliquity to match native mPTA (usually 2-3° varus)
   └── Set posterior tibial slope to match native (usually 5-9°)
   └── Make proximal tibial cut at native MPTA and slope

4. FEMORAL ROTATION (AP Cut)
   └── Reference: TEA, AP axis, or gap balancing
   └── Adjust ER relative to PCA based on the non-perpendicular tibial cut
   └── Create symmetric (or intentionally asymmetric) flexion gap per native anatomy

5. TRIAL REDUCTION
   └── Assess gap balance in extension and flexion
   └── Verify patellofemoral tracking
   └── Minor soft tissue adjustment if needed (should be minimal in true KA)

6. FINAL IMPLANTATION
   └── Cement components at verified native orientations
   └── Check ROM, stability, and patella tracking

Inlay and Onlay Mesh Repair

Sources: Fischer's Mastery of Surgery (8th Ed), Bailey & Love's (28th Ed), Current Surgical Therapy (14th Ed), Sabiston Textbook of Surgery

Overview: Mesh Placement Positions

Bailey & Love's Fig 64.8 - Layers for Mesh Placement

Fischer's Fig 216.5 - ICAP Classification (Onlay, Inlay, Sublay)

Five-Plane PMC Schematic (a-e)

1. ONLAY MESH REPAIR

Definition

"Mesh placed underneath the subcutaneous tissues on top of the anterior rectus sheath and/or external oblique aponeurosis"

• Fischer's Mastery of Surgery, 8th Ed

Technique (Step-by-Step)

1. Incision and exposure: Midline incision; skin and subcutaneous tissue raised as lipocutaneous (skin) flaps off the anterior rectus sheath laterally - only as far as needed for adequate mesh overlap
2. Hernia reduction: Hernia contents reduced; hernia sac dealt with
3. Primary fascial closure: Anterior rectus sheath edges approximated with slowly absorbable or non-absorbable suture - this is mandatory before placing the onlay mesh
4. Mesh placement: Large mesh laid on top of the closed anterior rectus sheath, extending well beyond the defect in all directions (minimum 3-5 cm overlap)
5. Mesh fixation:
   • Transfascial U-stitches placed circumferentially - 12 o'clock and 6 o'clock first (vertical tension), then 3 and 9 o'clock (horizontal tension)
   • Additional interrupted sutures at 1-1.5 cm intervals
   • Optional: running suture around mesh edge to prevent irregular contouring
   • Fibrin glue (Chevrel technique) or self-gripping mesh (no sutures)
6. Dead space management: Progressive tension sutures (lateral-to-medial, through fascia and Scarpa's fascia of skin flap); closed-suction drains placed in subcutaneous space
7. Closure: Skin closed in layers

Advantages of Onlay

Disadvantages of Onlay

"Onlay meshes may become exposed in the event of wound breakdown, and the elevation of skin flaps to allow wide overlap can lead to skin ischaemia and/or seroma formation."

• Bailey & Love's Short Practice of Surgery, 28th Ed

Clinical Examples of Onlay Repair

• Chevrel repair: Classic onlay with fascial plication and fibrin glue mesh fixation (midline incisional hernia)
• Modified onlay: Mesh placed inferior to released external oblique - a hybrid between onlay and anterior component separation
• Open incisional hernia repair with anterior fascial reinforcement
• Parastomal hernia onlay (less common; higher recurrence)
• Inguinal hernia - Lichtenstein repair: Though inguinal, this is an "onlay" principle - mesh placed on top of the posterior inguinal wall (on the external oblique / inguinal floor) after primary repair

2. INLAY MESH REPAIR

Definition

"If placed between the muscles without any overlap to bridge the defect as an interposition mesh, this is defined as an inlay repair. Notably, this type of repair should be avoided during elective hernia repair."

• Fischer's Mastery of Surgery, 8th Ed

"Inlay meshes are not recommended as they are effectively no more than a suture repair at each mesh-tissue interface."

• Bailey & Love's Short Practice of Surgery, 28th Ed

Why It Is Inferior

• The mesh-tissue junction is under pure tension - the mesh is essentially treated like a suture
• No overlap means no margin for error - any edge failure = hernia recurrence
• Mesh is exposed to the peritoneal cavity (adhesion risk) AND to the subcutaneous space (infection risk)
• No tissue ingrowth from the deep muscular layers that reinforces the repair

When Inlay Is Used (Indications)

1. Non-closable defects: When fascial edges cannot be brought together, even after component separation - inlay is preferred over leaving the defect completely open
2. Contaminated/emergency fields: When the patient is too unstable for complex reconstruction and a temporary bridge is needed
3. Bridge repair in strangulation/bowel resection: Vicryl (absorbable) bridge mesh can be used if omentum is placed between mesh and intestines
4. Giant ventral hernias with loss of domain: Initial bridge in staged repair

Technique

1. Dissect edges of the fascial defect; open hernia sac; reduce contents
2. Close the peritoneum if possible (running absorbable suture) to separate mesh from bowel
3. Anchor the mesh to the lateral rectus sheath at the semilunar line (stronger than the defect edge alone) using interrupted permanent sutures
4. Alternatively: anchor at the fascial defect edges with interrupted full-thickness bites
5. Ensure mesh lies flat without tension or wrinkles
6. Mesh type required: Anti-adhesive barrier-coated composite mesh (since mesh faces peritoneal cavity); absorbable mesh (Vicryl) or biologic mesh preferred over permanent uncoated mesh in contaminated cases

Mesh Choice for Inlay

"Inlay mesh repairs are associated with higher recurrence and surgical site events than sublay or onlay meshes."

• Current Surgical Therapy, 14th Ed

3. Comparison: Onlay vs Inlay vs Other Positions

4. Named Procedures Using These Principles

Onlay-Principle Procedures

Inlay-Principle Procedures

Other Mesh Position Procedures (for context)

5. Why Sublay is Preferred over Onlay and Inlay

• Sublay (retromuscular): Intraabdominal pressure pushes the mesh against the abdominal wall = Pascal's principle - pressure reinforces the repair
• Onlay: Intraabdominal pressure acts against the mesh-fascial suture interface
• Inlay: Intraabdominal pressure acts to separate the mesh from the fascial edges - worst mechanical position

"Meshes placed deep to the abdominal wall muscle layers have a mechanical advantage over onlay positioning as the abdominal pressure helps to keep the mesh in place."

• Bailey & Love's Short Practice of Surgery, 28th Ed

Summary Box