Transdermal patches: high-yield perioperative guide

1. Scopolamine: the main anesthesia patch

• Prevention of PONV, particularly in patients with high baseline risk, motion sickness history, or anticipated post-discharge nausea.
• It is an adjunct, not a replacement for risk-stratified multimodal PONV prophylaxis.

• Central muscarinic antagonism, mainly vestibular and vomiting-pathway effects.

• Common adult system: 1 mg delivered over 3 days.
• Best placed sufficiently before surgery to allow absorption. The product label supports use for PONV, and clinical studies included application about 11 hours before anesthetic/opioid exposure. Current scopolamine labeling lists it as 1 mg/3 days for adults.

• Dry mouth, blurred vision, mydriasis, dizziness, sedation, urinary retention, agitation, confusion, and delirium.
• Avoid or use great caution in older adults with delirium risk.
• Avoid in angle-closure glaucoma. Morgan and Mikhail's Clinical Anesthesiology, 7e, p. 435.
• Wash hands after handling. Accidental ocular transfer can cause unilateral mydriasis and trigger an unnecessary neurologic workup.
• Additive sedation/anticholinergic toxicity with opioids, benzodiazepines, antihistamines, TCAs, and other antimuscarinics.
• Consider removal after the highest-risk PONV window if adverse effects occur, remembering that clinical effects may not end instantly.

2. Fentanyl patch: the dangerous one to miss

• Intraoperative analgesia.
• Acute postoperative pain.
• Opioid-naive patients.
• Rapid opioid conversion without expertise.

• Treat the patient as opioid tolerant, but do not presume the patch covers surgical pain.
• Removing the patch does not immediately eliminate fentanyl effect because of a skin depot. Residual absorption can continue for many hours.
• Document patch location, strength, and time of placement/removal.
• Avoid external heat over or near the patch: forced-air warming, warming blankets, heating pads, hot baths, fever, and possibly major temperature changes can increase fentanyl exposure.
• Maintain heightened vigilance for delayed respiratory depression, particularly with additional opioids, sedatives, OSA, obesity hypoventilation, renal/hepatic dysfunction, or postoperative warming.

3. Clonidine patch

• Usually indicates chronic antihypertensive therapy rather than a drug to begin on the day of surgery.
• It has a slow onset, commonly several days, so a new patch will not reliably manage acute perioperative hypertension or withdrawal.
• If chronic clonidine is stopped abruptly, sympathetic rebound can occur: hypertension, tachycardia, agitation, and headache.
• Intraoperatively anticipate lower HR/BP and possible additive sedative effects. Use direct-acting vasoactive drugs as clinically indicated.

4. Nitroglycerin patch

• Active nitroglycerin may lower preload and BP, especially during induction, neuraxial anesthesia, hypovolemia, or with other vasodilators.
• Ask specifically about PDE-5 inhibitors. The nitrate-PDE-5 inhibitor combination can produce severe hypotension.
• A patch on the chest can be overlooked under ECG leads, forced-air warming, or surgical drapes. Document it and decide deliberately whether to continue or remove it.

5. Lidocaine patch and EMLA

• Lidocaine 5% patch: provides local analgesia for selected superficial focal pain syndromes. It does not generate a dense surgical anesthetic block.
• EMLA cream is a eutectic mixture of lidocaine-prilocaine and is often confused with a patch. It is a topical anesthetic cream used under occlusion for needle procedures or superficial skin anesthesia, with a delayed onset.
• In infants, large applications, prolonged application, or susceptible patients, prilocaine-containing preparations raise concern for methemoglobinemia.

Pre-op patch checklist

1. Look for patches. Examine behind ears, upper arm, chest, back, abdomen, and lower torso.
2. Identify drug, strength, placement time, and indication.
3. Record exact location in the anesthetic chart.
4. Remove or protect when appropriate, particularly fentanyl from heat sources and any patch interfering with the surgical field.
5. Avoid doubling patches. A replacement may be applied before the prior patch is recognized.
6. Dispose safely. Fold adhesive sides together. Fentanyl patches retain substantial drug after use and can harm children, pets, staff, or family members.
7. Reconcile at discharge. Specify which patches were continued, removed, replaced, or need reapplication.

One-line oral-exam summary

Transdermal systems bypass first-pass metabolism and provide sustained drug delivery, but their slow onset, delayed offset, variable absorption, and susceptibility to heat make them inappropriate for acute anesthetic titration. In anesthesia, scopolamine is mainly a PONV adjunct, while fentanyl patches signal chronic opioid therapy and require heat avoidance plus careful respiratory-risk management.

Local anesthetic transdermal systems

EMLA: the resident-level essentials

• A eutectic mixture allows lidocaine and prilocaine to penetrate intact skin because the drugs are predominantly non-ionized in the formulation.
• Apply a thick layer to intact skin and cover with an occlusive dressing. The anesthetic effect is delayed, so it must be placed well before cannulation or the procedure.
• It produces skin anesthesia, but does not reliably anesthetize deeper structures. For example, a ring block or dorsal penile block is more effective than EMLA for neonatal circumcision.
• Main toxicity is methemoglobinemia from prilocaine. Be cautious in premature neonates, infants, patients with G6PD deficiency or significant anemia, and when using oxidant medications.
• Do not apply to large areas, inflamed/broken skin, or use for an extended time without following product-specific limits.

Practical anesthesia uses

• Pediatric IV cannulation or venepuncture
• Arterial blood gas sampling
• Superficial dermatologic procedures
• Needle phobia or difficult IV access, when time permits
• Occasionally before intramuscular injection or minor superficial infiltration

Important distinction

• EMLA / lidocaine-tetracaine patch: intended for pre-procedure dermal anesthesia.
• Lidocaine 5% patch: intended for localized neuropathic pain, not acute procedural anesthesia. The approved indication for a lidocaine 1.8% topical system is postherpetic neuralgia, per current DailyMed labeling.
• Iontophoresis: not a passive patch. Electrical current drives lidocaine, often with epinephrine, through skin and can provide relatively rapid cutaneous anesthesia before pediatric venepuncture. Roberts and Hedges’ Clinical Procedures in Emergency Medicine, “Iontophoresis.”

The main transdermal preparations used for local anesthesia are EMLA, a lidocaine-prilocaine eutectic cream under occlusion, and lidocaine-tetracaine heat-assisted patches. They are useful for intact-skin anesthesia before venepuncture and superficial procedures, but have delayed onset, limited depth, and risk of local reactions and systemic local-anesthetic toxicity, particularly prilocaine-related methemoglobinemia.