III. GENERAL PRINCIPLES OF ANESTHESIA

LOCAL / REGIONAL ANESTHETICS

Click the links below to access content on each subject area pertaining to Local / Regional Anesthetics (technique, physiologic alterations, and complications).

QUESTIONS

QUESTIONS

QUESTIONS

QUESTIONS

QUESTIONS

QUESTIONS

Anatomy

Anatomy

  • A-alpha nerve fibers are responsible for proprioception.
  • A-beta fibers are the biggest nerve fibers (along with A alpha) and heavily myelinated.
  • C3, C4, and C5- KEEP THE DIAPHRAGM ALIVE.
  • The brachial plexus is supplied by spinal nerves C5-C8 and T1.
  • The recurrent laryngeal nerve is located directly lateral to the trachea.
  • Trigeminal cranial nerve provides sensation to the nasal septum.
  • The internal oblique is the muscle that can be localized directly from the lumbar triangle of Petit.
  • The most medial structure in the antecubital fossa:
    • From lateral to medial: radial nerve- biceps tendon- brachial artery- median nerve.
  • The radial, musculocutaneous, and median nerves supply sensory innervation to the forearm; ulnarnerve does not.
  • The median nerve of the forearm innervates the pronator teres muscle.
  • The adductor pollicis is affected if the ulnar nerve is damaged.
  • The nerve that lies between the brachioradialis muscle and biceps tendon is the radial.
  • The radial nerve in relation to the axillary artery is posterior and slightly lateral.
  • The most medial structure/vessel in the inguinal crease is the lymphatics in relation to the artery, vein, and nerve.Sensory innervation of the deep peroneal nerve occurs between the great and second toe.
  • The posterior tibial nerve provides sensation to the plantar surface.
  • Nerves are the most caudad structure in the intercostal
  • The musculocutaneous nerve originates from spinal nerves C5-C7.
  • The obturator nerve originates from the lumbar plexus, not the sciatic, common peroneal, or pudendal.
  • The saphenous nerve arises from the anterior branch of the femoral nerve, not the deep peroneal, common peroneal, or posterior tibial.

 

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Infiltration

Infiltration

Topical

Topical

  • The pKa of benzocaine is 3.5, which qualifies it as a weak acid and as such exists uncharged at physiologic pH. All other local anesthetic pKa’s are higher than 7.4, meaning that some fraction of them exists in the protonated form.

Neuraxial Blocks

Neuraxial Blocks

  • The initial cause of bradycardia with a subarachnoid block is from the blockage of cardiac beta-1 receptors.
  • An absolute contraindication to neuraxial anesthesia (specifically spinal and epidural) is severe hypovolemia.

 

ANTICOAGULANT

Heparin 5,000 units 3 times daily SQ

Dalteparin 5,000 units SQ once daily

Enoxaparin 1 mg/kg  2 times daily SQ

WAIT TIME BEFORE BLOCK IS INITIATED

>4-6 hours

≥12 hours

≥24 hours

American Society of Regional Anesthesia and Pain Medicine (ASRA) 4th Consensus Conference in 2018

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  • One way to assess motor blockade during neuraxial anesthesia is plantar flexion of the foot.
    • Increased skin temperature is the first sign that an epidural or spinal block is working. Local anesthetics block nerve impulses according to the degree of myelination, diameter of nerve fibers, and conduction velocity.
    • C nerve fibers are those that are responsible for pain and temperature. They have no myelination, are the smallest in diameter, and are the slowest in conduction velocity.
  • The patient’s level of alertness or arousal is determined by the reticular excitatory area in the brainstem, primarily the amount of sensory input received from the body. Therefore, because neuraxial anesthesia blocks these impulses, patients normally experience a decreased level of arousal or alertness. 
  • The most common cause of back pain following an epidural or spinal is paraspinous muscle relaxation.
  • The ventilatory change seen after a SAB/epidural block is decreased tidal volume.
  • SUBARACHNOID
    • The primary site of action for local anesthetics within the spinal cord is the nerve roots.
    • Density and dose are the two most important factors that determine the spread and duration of subarachnoid anesthesia.
    • The usual mechanism given for bradycardia with spinal anesthesia is blockade of the sympathetic efferents from T1-T4 (cardioaccelerator fibers) with subsequent unopposed parasympathetic stimulation (bradycardia). The primary deficiency in the development of spinal hypotension is a decrease in venous return.
    • Dextrose is added to spinal bupivacaine to make the solution hyperbaric. Dextrose makes the specific gravity of the solution to be injected greater than the specific gravity of the spinal fluid.
    • Isobaric solution has a baricity of 1.
    • Adding epinephrine increases the duration of action the most in tetracaine when compared to lidocaine, bupivacaine, and ropivacaine.
    • Cesarean section requires a T4 sensory level. Because of the associated high sympathetic blockade, all parturients should receive a 1-2 L bolus of Lactated Ringer’s prior to spinal.
    • The most common side effect of intrathecal opioids is pruritus.
    • The local anesthetic administered during spinal anesthesia is between the pia and arachnoid layers.
    • The motor blockade is two levels below the sensory level.
    • Clonidine has no effect on PONV. Epinephrine increases the incidence of PONV and morphine increases PONV in a dose-dependent fashion. Fentanyl and sufentanil have been shown to decrease PONV intraoperatively below placebo.

 

  • EPIDURAL
    • Ropivacaine is a long-acting local anesthetic like bupivacaine in pKa, protein binding, potency, and clinical uses. Ropivacaine is less cardiotoxic and produces less motor blockade (an advantage for obstetric patients).
    • Narcotics delivered via epidural produce the least amount of respiratory depression when compared to spinal and intravenous.
      • Morphine is responsible for late depression of ventilation.
    • A “test dose” is often used to rule out inadvertent intravascular or intrathecal catheter placement. Addition of epinephrine (15 mcg) with careful hemodynamic monitoring may signal intravascular injection when followed by a transient increase in heart rate and blood pressure.
      • The “classic” test dose combines 3 mL of 1.5% lidocaine with 15 mcg of epinephrine.
      • A test dose is designed to detect both subarachnoid and intravascular injection.
    • Adding epinephrine to epidural bupivacaine will only lengthen the sensory blockade.
    • The Tuohy stylet should be removed when the epidural needle is within the interspinous ligament.
    • During the advancement of the epidural catheter, patients may experience a paresthesia. If the feeling is persistent, the catheter should be withdrawn and epidural attempted at a new level.
    • The paramedian approach is more difficult for the beginner because advancement into the interspinous ligament does not occur. The needle advances primarily through paraspinous muscle mass, and resistance is only felt when entering the ligamentum flavum.
      • It bypasses the interspinous and supraspinous ligament.
    • Entry into the epidural space is confirmed by a loss of resistance (LOR) technique or hanging drop:
      • Air
      • Saline-
      • Hanging drop. Saline droplet is drawn inward when the needle enters the epidural space.
    • To speed the onset and increase the duration of action of an epidurally-administered local anesthetic, increasing the dose is the most effective.
    • The sensory and sympathetic epidural level are the same.
    • The best method to detect an epidural abscess is by MRI.
    • When a moderate dose is accidentally injected into an epidural vein, systemic toxicity can occur. The CNS is the first system affected. Symptoms include:
      • lightheadedness, tinnitus, circumoral numbness and tingling, numbness of the tongue, and blurred vision

 

  • PARAVERTEBRAL
    • Referred to as a unilateral epidural.
    • It blocks somatic and sympathetic fibers but sympathectomy is less significant. For a targeted dermatome, three segments are needed to be blocked because of nerve overlapping.

 

  • ERECTOR SPINAE
    • Significant craniocaudal spread occurs and generally provides sufficient coverage to multiple dermatomes with only one injection.
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Peripheral Blocks

Peripheral Blocks

  • CERVICAL PLEXUS
    • The nerves that must be blocked for a carotid endarterectomy are C2-4.
    • The transverse process of C6 is referred to as Chassaignac’s tubercle.

 

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BRACHIAL PLEXUS

Interscalene

Supraclavicular

Infraclavicular

Axillary

The ulnar nerve is often spared.

Pneumothorax is the greatest risk.

Most painful block.

The musculocutaneous nerve is often spared.

Interscalene

Supraclavicular

Infraclavicular

Axillary

Roots

Trunks/divisions

Cords

Branches

SUPRACLAVICULAR

  • Pearls:
    • Targets the trunks/divisions
    • Good block for the arm, not shoulder
    • Greatest risk is pneumothorax- pleura is immediately inferior to 1st rib
    • The most serious complication of supraclavicular block is pneumothorax.

INFRACLAVICULAR

  • Pearls:
    • Targets the cords
    • Cords are named according to their anatomic relationship with the axillary artery (lateral, posterior, and medial)
    • With nerve stimulation of the cords, the fifth digit will move in these directions: lateral- laterally; medial- flex; posterior- extend
    • The goal is to place the needle posterior to the axillary artery.
    • Phrenic and stellate blockade is greatly reduced
    • The most painful of the brachial plexus blocks is the infraclavicular because the needle must pass through the pectoralis major and minor muscles.

AXILLARY

  • Pearls:
    • Targets four terminal branches
    • Provides anesthesia to the arm distal to the elbow
    • Primary nerves are radial, median, and ulnar (located around the axillary artery); musculocutaneous is outside the axillary sheath.
    • Coracobrachialis is the muscle which the musculocutaneous nerve exits.
    • Complications are uncommon
    • While performing an axillary block, the musculocutaneous nerve is unlikely to be blocked.
    • The musculocutaneous nerve lies within the coracobrachialis muscle.
    • The trans-arterial approach to an axillary block most blocks the radial nerve.
    • The axillary artery is intentionally penetrated and confirmed by aspiration of blood. Then the needle is inserted past the artery until blood is no longer aspirated. Posterior to the axillary artery is the radial nerve (and slightly lateral).
    • The axillary block is typically chosen for anesthesia distal to the elbow.

INTERSCALENE BLOCK

  • Pearls:
    • Targets the roots
    • Hypoechoic roots stacked between the ASM and MSM are called the snowman or stoplight sign ULTRASOUND.
    • Complications: unilateral phrenic nerve blockade; stellate ganglion blockade leading to Horner’s syndrome; inadvertent arterial injection
    • The ulnar nerve is often missed with interscalene block.
    • The highest risk of unilateral phrenic nerve blockade of the brachial plexus blocks is the interscalene.

HORNER’S SYNDROME

  • Horner’s syndrome results in ipsilateral ptosis and miosis.
  • Horner’s syndrome is not common with the cervical plexus block.

LUMBAR PLEXUS (COMPARTMENT)

  • Pearls:
    • L2-L4 nerve roots form the lumbar plexus within the psoas muscle.
    • AKA 3-in-1 block (femoral, obturator, and lateral femoral cutaneous nerves).

FASCIA ILIACA

  • Pearls:
    • The anterior approach to the lumbar plexus block; aims to block the femoral, obturator, and lateral femoral cutaneous nerves.

PERICAPSULAR NERVE GROUP BLOCK (PENG)

  • Pearls:
    • Single injection for hip fracture/arthroplasty
    • Targets the articular branches of the femoral nerve, accessory obturator, and obturator nerves while sparing the femoral nerve’s quadriceps innervation.
        •  

SCIATIC

  • Pearls:
    • Does not block the femoral or saphenous.

ADDUCTOR CANAL

  • Pearls:
    • This block spares the quadriceps strength (as compared to the femoral nerve block).
    • An adductor canal block is performed for postoperative pain control following an ACL repair.
    • This block is used for surgeries involving the anteromedial knee and spares the quadriceps muscle.
    • The midpoint of the adductor canal is just distal from the midpoint of the anterior superior iliac spine and patellar base.
          •  

FEMORAL

  • Pearls:
    • When combined with the sciatic nerve block, the femoral nerve block provides complete coverage of the lower extremity.
    • NAVL (nerve, artery, vein, lymphatics) from lateral to medial
    • The femoral nerve block (along with the sciatic nerve block) provides complete anesthesia to the lower extremity.
          •  

ILIOHYPOGASTRIC

  • The iliohypogastric nerve is blocked for an inguinal hernia repair.

BIER BLOCK

  • Lidocaine 0.5% 50 mL is the local anesthetic is used for upper extremity intravenous regional anesthesia.
  • Toradol is the only additive agent that has been shown to offer any significant clinical benefit in a bier block.
  • The tourniquet needs to stay inflated for 20 minutes for an intravenous regional anesthetic.
  • Patients with history of seizures, history of strokes, and malignant hyperthermia may still have a Bier block. These are NOT contraindications.
  • The intercostobrachial nerve is blocked for tourniquet pain.

DIGITAL

  • Epinephrine should NOT be used in digit blocks because it can cause ischemia and necrosis.

ULNAR

  • Pearls:
    • Blocks at the elbow and wrist are primarily sensory (meaning can still move their arm) and are often used as a rescue to a failed upper extremity block.
    • Intercostobrachial and brachial cutaneous nerves can be blocked for tourniquet pain. Musculocutaneous/coracobrachialis is also beneficial.
    • Ulnar nerve block at the ulnar sulcus should be limited to ≤ 3mL
    • Elbow blocks are:
      • Primarily sensory only
      • Used as an adjunct to a failed brachial plexus block
      • The maximum amount of local anesthesia that can be injected for an ulnar nerve block at the ulnar sulcus is 3 mL.

FOOT

  • For complete coverage of the foot, the saphenous nerve must be blocked along with the sciatic via popliteal approach.
  • The terminal branch of the femoral nerve in the foot is the saphenous nerve.

TRANSVERSUS ABDOMINUS PLANE (TAP)

  • A TAP block:
    • Does NOT provide sensory coverage to the abdominal viscera.
    • Requires two injections bilaterally to provide complete coverage.
    • Local anesthesia is injected between the internal oblique and transversus abdominus muscles.
    • Transversus abdominus plane block is a fascial plane block between the internal oblique and transversus abdominus muscles. It does not cover sensory to the viscera.
  • The provider has the advantage of using ultrasound, perform fascial plane blocks on patients on anticoagulation, and lack of sympathectomy when compared to paravertebral and thoracic epidural.

PECS 1 BLOCK

  •  local anesthesia is injected between the pectoralis major and pectoralis minor muscles and targets the medial and lateral pectoral branches of the brachial plexus.

FASCIAL PLANE BLOCKS

  • Pearls:
    • Pecs I- inject between the pectoralis major and pectoralis minor muscles; targets the medial and lateral pectoral branches of the brachial plexus.
    • Pecs II- modification to the Pecs I; adds a second injection between the pectoralis minor and serratus anterior muscles at the 3rd-4th ribs; targets the long thoracic nerve and lateral cutaneous branches of the thoracic intercostal nerves.

Other Blocks

Airway

TRANSTRACHEAL

  • When performing a transtracheal block, the aspiration of air indicates proper placement of needle.

 

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RETROBULBAR

  • The medial rectus muscle can trigger the oculocardiac reflex during ocular surgery.
  • Retrobulbar block can stimulate and block oculocardiac reflex.
  • Important considerations for ocular blocks include the position of the eye, needle depth, and needle angle.

 

Ultrasound and / or Nerve Stimulator Guided Concepts and Techniques

Ultrasound and / or Nerve Stimulator Guided Concepts and Techniques

 

Longitudinal

Mechanical

Compression

Rarefaction

Cycle

Hertz

Waves that propagate in their direction of movement.

Waves that require a medium.

A generated sound wave that creates an area of high pressure.

Area of low pressure from a sound wave.

A single compression and rarefaction.

The number of cycles that occur in 1 second.

  • 4 in MHz is the sound frequency when scanning deeper abdominal structures.
  • Impedance is the term that describes a tissue’s stiffness, or resistance against the sound propagation.
  • Scattering is when the ultrasound wavelength is greater than the structure it contacts.
  • When a wave strikes the border of two tissues at an oblique angle, the reflection of sound is refraction.
  • Bone is an example of a hyperechoic structure on ultrasound.
  • Muscle is an example of a hypoechoic structure on ultrasound.
  • The ultrasound transducer movement in which the probe is manipulated clockwise or counterclockwise to view structures in both cross-sectional and longitudinal views is rotating.
  • The ultrasound probe used for epidural guidance should be curvilinear.
  • Advantages of ultrasound-guided regional techniques versus nerve stimulation:
    • Faster onset time
    • Improved block quality
    • Improved patient satisfaction
  • When using a nerve stimulator for an infraclavicular block, the medial cord is stimulated if the 5th finger flexes.

Management of Complications

  • The blood flow at the injection site will help determine the rate of absorption (IV>tracheal>intercostal> caudal> paracervical > lumbar epidural > brachial plexus > sciatic/subarachnoid/femoral> subcutaneous).
  • The rate of absorption depends on blood flow to the tissue at the injection site.
  • Epinephrine is a vasoconstrictor that decreases absorption of the local anesthetic and prolongs the effect of the local anesthetic.
  • Absorption of a local anesthetic is determined by:
    • Total dose of drug
    • Blood flow to tissue
    • Vasoconstrictor: epinephrine/phenylephrine
    • Lipid solubility of the local anesthetic; inverse relationship (as lipid solubility increases, absorption rate decreases)
    • Protein binding of the local anesthetic (greater the protein binding, slower the absorption)
    • pH (higher the pH, greater the amount of drug in nonionized form and the greater the amount of drug diffusing into the blood stream).
  • The use of ultrasound, aspiration, test doses, and incremental dosing along with vigilance can help decrease the chance of LAST.
  • The rate and extent of systemic absorption depends on the site of injection, the dose, the drug’s intrinsic pharmacokinetic properties, and the addition of a vasoactive agent.
  • The maximum safe dose of lidocaine without epinephrine is 5 mg/kg.
  • The maximum safe dose of bupivacaine is 3 mg/kg.
  • Para-aminobenzoic acid is a metabolite of procaine and other ester local anesthetics.
  • The addition of bicarbonate to local anesthetics results in a quicker onset of action.
  • Most LAs will not produce cardiovascular (CV) toxicity until the blood concentration exceeds three times that necessary to produce seizures.

NERVE BLOCK

COMPLICATION

Celiac plexus

Backache; diarrhea

Lumbar plexus

Genitourinary

Stellate ganglion

Horner’s syndrome

Interscalene

Phrenic nerve paralysis

Supra- and infraclavicular

Pneumothorax

Paracervical

Fetal bradycardia

LOCAL ANESTHETIC SYSTEMIC TOXICITY

    • With the explosion of ultrasound in peripheral nerve blocks, advent of incremental dosing, epidural test dosing, etc., local anesthetic systemic toxicity has decreased tremendously since the 1980s. However, these early signs should be appreciated to monitor for a more severe reaction.
    • Spinal anesthesia is less likely to cause systemic toxicity than epidural.
    • The first sign of lidocaine toxicity is tinnitus.
    • The first thing to do during local anesthetic toxicity is intubate and ventilate.
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POSTDURAL PUNCTURE HEADACHE

    • The hallmark of PDPH is its association with body position. The pain is aggravated by sitting or standing and relieved or decreased by lying down flat.
    • Postdural puncture headache occurs more frequently in younger people, in females, with larger needle, pregnancy, and multiple attempts/punctures.
    • Quincke is an example of a cutting spinal needle. Cutting spinal needles have a higher incidence of PDPH when compared to pencil point spinal needles (e.g. Whitacre and sprotte).

CAUDA EQUINA

    • Spinal Lidocaine 5% is associated with this complication.