- Clinical science
Local and regional anesthesia, in contrast to systemic, general anesthesia, involves the reversible numbing of a specific region of the body to prevent any sensation of pain. Pain may be blocked on different levels of its signal transduction pathway, e.g., at the site of origin, along the nerves, or in the brain. Accordingly, local and regional anesthesia can be divided into local topical and infiltration anesthesia, regional peripheral nerve blocks (PNB), and neuraxial anesthesia (e.g., spinal and epidural). Local anesthesia can be combined with general anesthesia, allowing the doses of anesthetic and analgesic drugs to be reduced during surgery, and may eliminate the need for other measures to achieve sufficient anesthesia (depending on the timeframe of surgery, risk profile, patient's consent). In general, local anesthesia carries less risk than general anesthesia, as essential body functions (e.g., respiration) are not affected. However, specific complications (e.g., bleeding, infection) and contraindications (e.g., patient's refusal, allergies) to local anesthesia must be considered. The drugs used for anesthesia can be found in the learning card .
Local and regional anesthesia are used prior to certain medical procedures to reduce pain; see “Indications” in .
- Types of anesthetic agents and their pharmacology: See “ L.
- Local anesthesia: topical or infiltrative
- Intravenous regional anesthesia (e.g., Bier block anesthesia): a local anesthetic is injected intravenously to perform surgery on the extremities ..
- Neuraxial: See and .
- Definition: : Local anesthesia reversibly blocks nerve endings and pain conduction near the site of administration (limited area).
- Indications: See .
- Topical anesthesia: application of gels, ointments, sprays, or patches → anesthetic agent gets absorbed through the skin or mucosa
Infiltration anesthesia: injection of local anesthetic directly into a painful area or one to be operated on
- Hygiene is crucial and depends on the specific intervention!
- Sufficient infiltration of the target area (e.g., wound margins of a cut) by injecting the local anesthetic drug from all sides with as few punctures as possible (avoid vascular infiltration by aspirating before injecting!)
- Injection site: injected locally subcutaneously and/or submucosally wherever required (e.g., wound margins of a cut)
The effect of local anesthetic drugs is very limited in inflamed tissues (e.g., abscess)! The acidic environment of inflamed tissues leads to protonation of the anesthetic drug, which in turn reduces its lipophilicity and prevents the spread of the drug to the site of action.
- Local anesthetic is injected near a specific nerve or nerve bundle.
- Surgery of the upper extremities
- Interscalene block
- Supraclavicular plexus block
- Vertical infraclavicular plexus block
- Axillary brachial plexus block
Surgery of the lower extremities
- Sciatic and femoral nerve block
- Lumbar plexus (psoas compartment) block
- Inguinal block and paravertebral plexus block
- Surgery of the scalp, neck, and trunk
- Block of selected peripheral nerves (e.g., digital nerve block): technique to anesthetize the digits to perform surgery on the fingers or toes.
- Injection site: depends on the nerves that need to be blocked
- The patient is placed in a position that is tolerable for him or her and allows the practitioner to access the relevant nerve easily (e.g., to apply an axillary plexus block, the hand is placed underneath the head with the arm abducted and bent.)
- Hygiene: hand disinfection, sterile gloves, sterile face mask, utensils for wipe disinfection of the puncture site afterward, (if catheter is inserted, also sterile gown and sterile fenestrated drape)
- Identification of the relevant nerve guided by specific landmarks and/or:
Ultrasound: ultrasound-guided needle advancement towards the target nerve
- Needle advancement towards the target nerve is vision-guided (the movement of the needle tip should always be monitored), aspiration tests should be performed continuously. The needle may be navigated, e.g., using the out-of-plane technique. or the inline technique
- Injection of the local anesthetic drug around the target nerve, no injection if high resistance is encountered, needle retraction if injection evokes pain or paresthesia!
- Nerve stimulation test
- Oriented approach: The needle is inserted and advanced towards the target nerve with high current intensity (standard values: amplitude: 1.0–1.5 mA, stimulus duration: 0.1 ms, frequency: 2 Hz) until a motoric nerve response becomes detectable in the desired innervation area.
- Precise approach: The intensity of the stimulus is reduced (e.g., to 0.5 mA) while the needle is repositioned to elicit a motoric nerve response just above the response threshold.
- Injection of the local anesthetic drug (during nerve stimulation) until the nerve response has subsided.
- Ultrasound: ultrasound-guided needle advancement towards the target nerve
- Two approaches to inject the local anesthetic drugs are available:
- Single-shot technique: A single dose of the local anesthetic drug is injected (e.g., bupivacaine).
- Catheter placement with the advantage of repeated/continuous administration of anesthetic drugs
Peripheral nerve blocks are preferred over general anesthesia in patients with respiratory problems and preferred over epidural/spinal anesthesia in patients who are at high risk for urinary retention or other side effects of these procedures.
- Local anesthetics with or without opioids and alpha-adrenergic agonists are injected into the epidural space and act on the spinal nerve roots.
- Used for a variety of surgeries of the lower body (e.g., cesarean section, hernia repair, appendectomy, prostate and bladder surgeries, knee surgery)
- During labor
- Chronic pain management (e.g., spinal stenosis, disc herniation)
- The puncture site determines which area the epidural anesthesia affects.
|Puncture site||Surgery/area of surgery|
- Uncorrected hypovolemia
- Obstetric emergencies
- Increased intracranial pressure
- Infection at the puncture site
- Spinal deformities
- Heart valve diseases in combination with a right-to-left shunt, pulmonary hypertonia, and high-grade aortic or mitral stenosis
- Sepsis, systemic bacteremia, amniotic infection syndrome
- Neurological deficits caused by, e.g., disc prolapse, paraplegic syndrome, and multiple sclerosis
- Injection site
- Approaches to inject the local anesthetic:
- Catheter placement, which has the advantage of repeated/continuous administration of anesthetic drugs (most commonly performed)
- Single-shot technique: A single dose of the local anesthetic drug is injected (e.g., bupivacaine), if necessary in combination with sufentanil.
- Needle: traumatic needle (e.g., Tuohy needle), atraumatic needle (e.g., Sprotte needle)
- Preparation: The patient is seated with the back being curved/hunched over at the level of the puncture site.
- Selection of the injection site/spinal level as required
- Hygiene: face mask, hand disinfection, sterile gown, sterile gloves, disinfectants for the puncture site following injection, application of a sterile fenestrated drape
- Local anesthetic drug containing lidocaine
- Accessing the epidural space:
- The spinal needle punctures the skin at the median or paramedian line of the spine.
- The needle is gently inserted into the interspinal ligament (2–3 cm).
- Remove the mandrin.
- Attach a special, smooth-running syringe filled with physiological saline solution to the needle adapter.
- Move the needle slowly forward by pushing the plunger of the syringe with constant, gentle pressure.
- When the needle breaches the ligamentum flavum the resistance usually first increases before suddenly decreasing again, allowing saline solution to be more easily injected (Loss of resistance technique).
- An alternative approach to detect the epidural space based on the lower pressure within the epidural space is the Hanging drop technique.
- Negative aspiration test: neither CSF nor blood may be aspirated!
- If CSF is aspirated: The needle must be retracted! Repeat puncture if necessary.
- If blood is aspirated: repeat puncture
- At this point one of two alternatives may be chosen:
- Single shot: A single dose of the local anesthetic drug is injected (e.g., bupivacaine), if necessary in combination with sufentanil.
- Catheter insertion (advantage: repeated/continuous drug administration possible)
- A catheter may be inserted into the needle (without major resistance) and advanced not more than 3 cm into the epidural space.
- Epidural test dose: A test dose of 2–3 mL local anesthetic drug in combination with 10–20 μg epinephrine is injected to exclude intravascular or intrathecal (= spinal) catheter placement.
- Fixation of the catheter at the insertion site using transparent tape , proper fixation of the connecting tube to the patient's back with tape, injection of the full drug dose and attachment of a PCEA pump (patient-controlled epidural analgesia)
- Pain at the injection site
- Dural puncture
- Spinal-epidural hematoma
- Epidural abscess
- Pathophysiology: sympathetic blockade causes vasodilation and decreases venous return → reduced cardiac output
- Clinical features: hypotension, dizziness, lightheadedness, and nausea shortly after administering anesthetic
- Diagnosis: clinical diagnosis
- Treatment: IV fluid resuscitation + small doses of epinephrine
- Local anesthetics with or without opioids and alpha-adrenergic agonists are injected into the cerebrospinal fluid (CSF) in the lumbar spine and act directly on the spinal cord
- Combined spinal and epidural anesthesia (CSE)
- C-section: Th4–6 (mamillary line)
- Pelvic, urethral, and renal pelvic surgery: Th6–8 (xiphoid)
- Transurethral surgery including stretching of the bladder, vaginal birth, hip surgery: Th10 (navel)
- Transurethral surgery without stretching of the bladder: L1 (inguinal ligament)
- Knee and foot surgery: L2/3
- Perineal surgery: S2–5
Duration and site of action of spinal anesthesia
- Local anesthetic drugs are selected based on the expected duration of surgery (e.g., mepivacaine in a concentration of 4% for interventions taking up to 1 h; bupivacaine 0.5% for interventions longer than 1 h (duration of anesthesia ∼ 2.5 h))
- The specific spinal levels that are affected by the anesthesia depends on the dose of the local anesthetic drug.
- See “Contraindications of epidural anesthesia” above.
- Injection site
- Needle: atraumatic (e.g., Sprotte needle)
- Preparation: The patient is seated (pregnant women may lie on one side, if necessary) with the back being curved at lumbar level.
- Identification of the puncture site by palpation of the iliac crests: The puncture site (L3–4 or L4–5) may be found at the intervertebral space on an imaginary line between the two iliac crests.
- Hygiene: hand disinfection, sterile gown, sterile gloves, face mask, utensils for wipe disinfection of the puncture site afterward, application of a sterile fenestrated drape if necessary (e.g., patient in a lateral position)
- Local anesthetic drug, combined with lidocaine (optional)
- Insertion of a wider but shorter needle (introducer needle) to guide the thin spinal needle.
- Puncture of the skin in the cranial direction (∼ 10–30°) up to the dural sac
- Bone contact: retract needle, repeat needle insertion in an even more cranial direction
- Paresthesia: retract needle and repeat needle insertion in a more median direction
- Blood: wait for the CSF to clear up again; if CSF does not clear up, retract needle and repeat insertion at a different lumbar level.
- After removal of the mandrin, CSF drops out of the spinal needle if the needle tip is in the correct position (in the subarachnoid space, so far same procedure as )
- Gentle attachment and fixation of the syringe filled with the local anesthetic drug to the needle, followed by quick injection
- Approach: almost always single-shot technique
- Identification of the puncture site and needle insertion as describe above, followed by one of two options differing in the sequence of spinal and epidural anesthesia. The choice depends on the CSE equipment:
- First spinal anesthesia, then insertion of the epidural catheter (needle with one working channel)
- First insertion of the epidural catheter, then spinal anesthesia (needle with two working channels)
- Two separate working channels run parallel in a single needle. This enables the practitioner to insert the epidural catheter first, including an to check the correct placement.
- Spinal anesthesia
- Bleeding complications (e.g., hematoma) → nerve compression → neurological symptoms depending on the localization and degree of the hematoma
- Infections: local inflammation/abscess formation
- Allergic reactions
- Toxic reactions
- Local tissue toxicity
- Systemic toxicity (see “Side effects” in )
- Septic/aseptic meningitis
- Sympathetic block → peripheral vasodilation, bradycardia, and hypotension (Bezold-Jarisch reflex) → relative hypovolemia
- Urinary retention and overflow incontinence : treat with indwelling catheter for 24 hours if postvoid residual volume > 50 ml and/or the patient is unable to empty the bladder voluntarily
- Back pain
Total spinal anesthesia: complete spinal space affected by local anesthetic drug
- Drug overdose during spinal block or accidental spinal anesthesia during epidural block (intrathecal injection) → excessive cranial spread of the local anesthetic drug → inhibition of the intercostal respiratory muscles and sympathetic block → bradycardia and hypotension → reduced perfusion of the brainstem → total spinal anesthesia → circulatory and respiratory arrest
- Clinical features
- Prophylaxis: correct catheter placement
We list the most important complications. The selection is not exhaustive.