Regional Anesthesia Flashcards
Regional anesthetic techniques
■ epidural and spinal anesthesia (neuraxial anesthesia)
■ peripheral nerve blocks
■ IV regional anesthesia (e.g. Bier block)
What is regional anesthesia
local anesthetic agent (LA) applied around a peripheral nerve at any point along the length of the nerve (from spinal cord up to, but not including, the nerve endings) for the purpose of reducing or preventing impulse transmission
regional anesthesia monitoring required
monitoring should be as extensive as for general anesthesia
benefits of regional anesthesia
- Reduced perioperative pulmonary complications
- Reduced perioperative analgesia requirements
- Decreased PONV
- Reduced perioperative blood loss
- Ability to monitor CNS status during procedure
- Improved perfusion
- Lower incidence of VTE
- Shorter recovery and improved rehabilitation
- Pain blockade with preserved motor function
epidural and spinal anesthesia indication
most useful for sx performed below level of umbilicus
anatomy of spinal/epidural area
- spinal cord extends to L2, dural sac to S2 in adults
- nerve roots (cauda equina) from L2 to S2
- needle inserted below L2 should not encounter cord, thus L3-L4, L4-L5 interspace commonly used
structures penetrated from outside to inside in epidural and spinal anesthesia
■ skin ■ subcutaneous fat ■ supraspinous ligament ■ interspinous ligament ■ ligamentum flavum (last layer before epidural space) ■ dura + arachnoid for spinal anesthesia
landmarking epidural/spinal anesthesia
• Spinous processes should be maximally flexed • L4 spinous processes found between iliac crests • T7 landmark at the tip of the scapula
classic presentation of dural puncture headache
- Onset 6 h-3 d after dural puncture
- Postural component (worse when sitting)
- Occipital or frontal localization
- ± tinnitus, diplopia
Epidural deposition site
LA injected in epidural space (space between ligamentum flavum and dura) Initial blockade is at the spinal roots followed by some degree of spinal cord anesthesia as LA diffuses into the subarachnoid space through he dura
Spinal deposition site
LA injected into subarachnoid space in the dural sac surrounding the spinal cord and nerve roots
Epidural onset
Significant blockade requires 10-15 min
Slower onset of side effects
Spinal onset
rapid blockade onset in 2-5 minutes
Epidural effectiveness
variable
spinal effectiveness
very effective
epidural difficulty
technically more difficult greater failure rate
spinal difficulty
easier to perform due to visual confirmation of csf flow
epidural patient positioning
Position of patient not as important; specific gravity not an issue
spinal patient positioning
hyperbaric LA solution - position of patient important
specific gravity/spread epidural
Epidural injections spread throughout the potential space; specific gravity of solution does not affect spread
dosage epidural
larger volume/dose of LA (usually > toxic IV dose)
spinal dosage
smaller dose of LA required (usually < toxic IV dose)
epidural continuous infusion
use of catheter allows for continuous infusion or repeat injections
continuous infusion epidural
use of catheter allows for continuous infusion or repeat injections
continuous infusion spinal
none
complications epidural
Failure of technique
Hypotension
Bradycardia if cardiac sympathetics blocked (only if ~T2-4 block), e.g. “high spinal”
Epidural or subarachnoid hematoma
Accidental subarachnoid injection can produce spinal anesthesia (and any of the above complications)
Systemic toxicity of LA (accidental intravenous)
Catheter complications (shearing, kinking, vascular or subarachnoid placement) Infection
Dural puncture
complications spinal
Failure of technique
Hypotension
Bradycardia if cardiac sympathetics blocked (only if ~T2-4 block), eg. “high spinal”
Epidural or subarachnoid hematoma
Post-spinal headache (CSF leak)
Transient paresthesias
Spinal cord trauma, infection
combined spinal - epidural
Combines the benefits of rapid, reliabe, intense blockade of spinal anesthesia together with the flexibility of an epidural catheter
Absolute contraindications to spinal/epidural anesthesia
■ lack of resuscitative drugs/equipment
■ patient refusal
■ allergy to local anesthetic
■ infection at puncture site or underlying tissues
■ coagulopathies/bleeding diathesis
■ raised ICP
■ sepsis/bacteremia
■ severe hypovolemia
■ cardi c lesion with fixed output states (severe mitral/aortic stenosis)
■ lack of IV access
Relative contraindications to spinal/epidural anesthesia
■ pre-existing neurological disease (demyelinating lesions)
■ previous spinal surgery, severe spinal deformity
■ prolonged surgery
■ major blood loss or maneuvers that can compromise reaction
Peripheral nerve block procedure
- deposition of LA around the target nerve or plexus
- ultrasound guidance and peripheral nerve stimulation (needle will stimulate target nerve/plexus) may be used to guide needle to target nerve while avoding neural trauma or intraneural injection most major nerves or nerve plexi can be targeted (brachial plexus block, femoral nerve block, sciatic nerve block, etc.)
- performed with standard monitors
risk of late neurologic injury
approximately 2-4 per 10,000 risk of late neurologic injury
what must be available during peripheral nerve blocks
resuscitation equipment
Absolute contraindications to peripheral nerve blockade
■ allergy to LA
■ patient refusal
Relative contraindications to peripheral nerve blockade
■ certain types of pre-existing neurological dysfunction (e.g ALS, MS, diabetic neuropathy)
■ local infection at block site
■ bleeding disorder
Definition and mode of action of local anesthetics
- LA are drugs that block the generation and propagation of impulses in excitable tissues: nerves, skeletal muscle, cardiac muscle, brain
- LA bind to receptor on the cytosolic side of the Na+ channel, inhibiting Na+ flux and thus blocking impulse conduction
- different types of nerve fibres undergo blockade at differen rates
Absorption, distribution, metabolism of local anesthetics
- LA readily crosses the blood-brain barrier (BBB) once absorbed into the bloodstream
- ester-type LA (procaine, tetracaine) are broken down by plasma and hepatic esterases; metabolites excreted via kidneys
- amide-type LA (lidocaine, bupivicaine) are broken down by hepatic mixed-function oxidases (P450 system); metabolites excreted via kidney
Selection of local anesthetic is based on
■ onset of action: influenced by pKa (the lower the pKa, the higher the concentration of the base form of the LA, and the faster the onset of action)
■ duration of desired effects: influenced by protein binding (longer duration of action when protein binding of LA is strong)
■ potency: influenced by lipid solubility (agents with high lipid solubility penetrate the nerve membrane more easily)
■ unique needs (e.g. sensory blockade with relative preservation of motor function by bupivicaine at low doses)
■ potential for toxicity
Local anesthetic systemic toxicity CNS effects
• CNS effects first appear to be excitatory due to initial block of inhibitory fibres, then subsequent block of excitatory fibres
• effects in order of appearance ■ numbness of tongue, perioral tingling, metallic taste ■ disorientation, drowsiness ■ tinnitus ■ visual disturbances ■ muscle twitching, tremors ■ unconsciousness ■ convulsions, seizures ■ generalized CNS depression, coma, respiratory arrest
CVS effects local anesthetic toxicity
- vasodilaton, hypotension
- decreased myocardial contractility
• dose-dependent delay in cardiac impulse transmission
■ prolonged PR, QRS intervals
■ sinus bradycardia
• CVS collapse
occurs after CNS effects
Treatment of local anesthetic systemic toxicity
- early recognition of signs, get help
- 100% O2, manage ABCs
- diazepam
- manage arrhythmias
- Intralipid® 20% to bind local anesthetic in circulation
Where not to use local anesthetic with epinephrine
ears, fingers, toes, penis nose
local infiltration procedure and use
- injection of tissue with LA, producing a lack of sensation in the infiltrated area due to LA acting on nerves
- suitable for small incisions, suturing, excising small lesions
- can use fairly large volumes of dilute LA to infiltrate a large area
- low concentrations of epinephrine (1:100,000-1:200,000) cause vasoconstriction, thus reducing bleeding and prolonging the effects of LA by reducing systemic absorption
Fracture hematoma block description, procedure
- special type of local infiltration for pain control during manipulation of certain fractures
- hematoma created by fracture is infiltrated with LA to anesthetize surrounding tissues
- sensory blockade may only be partial
- no muscle relaxation
topical anesthetics
- various preparations of local anesthetics available for topical use, may be a mixture of agents (EMLA cream is a combination of 2.5% lidocaine and prilocaine)
- must be able to penetrate the skin or mucous membrane
Common post-op anesthetic complications
Uncontrolled/Poorly Controlled Pain
Nausea and Vomiting
• hypotension and bradycardia must be ruled out
• pain and surgical manipulation also cause nausea
• often treated with dimenhydrinate (Gravol®), metoclopramide (Maxeran®; not with bowel obstruction) prochlorperazine (Stemetil®), ondansetron (Zofran®) granisetron (Kytril®)
Confusion and Agitation
• ABCs first confusion or agitation can be caused by airway obstruction, hypercapnea, hypoxemia
• neurologic status (Glasgow Coma Scale, pupils), residual paralysis from anesthetic
• pain, distended bowel/bladder
• fear/anxiety/separation from caregivers, language barriers
• metabolic disturbance (hypoglycemia, hypercalcemia, hyponatremia – especially post-TURP)
• intracranial cause (stroke, raised intracranial pressure) drug effect (ketamine, anticholinergics, serotonin)
• elderly patients are more susceptible to post-operative delirium
Respiratory Complications
• susceptible to aspiration of gastric contents due to PONV and unreliable airway reflexes
• airway obstruction (secondary to reduced muscle tone from residual anesthetic, soft tissue trauma and edema, or pooled secretions) may lead to inadequate ventilation, hypoxemia, and hypercapnia
• airway obstruction can often be relieved with head tilt, jaw elevation, and anterior displacement of the mandible. If the obstruction is not reversible, a nasal or oral airway may be used
Hypotension
• must be identified and treated quickly to prevent inadequate perfusion and ischemic damage
• reduced cardiac output (hypovolemia, most common cause) and/or peripheral vasodilation (residual anesthetic agent)
• first step in treatment is usually the administration of fluids ± inotropic agents
Hypertension
• pain, hypercapnia, hypoxemia, increased intravascular fluid volume, and sympathomimetic drugs can cause hypertension
• sodium nitroprusside or β-blocking drugs (e.g. esmolol and metoprolol) can be used to treat hypertension
Risk factors for post-operative nausea and vomiting (PONV)
- Young age
- Female
- History of PONV
- Non-smoker
- Type of surgery: ophtho, ENT, abdo/pelvic, plastics
- Type of anesthetic: N2O, opioids, volatile agents
Pain and nociception definitions
- pain: perception of nociception, which occurs in the brain
- nociception: detection, transduction, and transmission of noxious stimuli
Pain classifications
- temporal: acute vs. chronic
* mechanism: nociceptive vs. neuropathic
Acute pain
- pain of short duration (<6 wk) usually associated with surgery, trauma, or acute illness; often associated with inflammation
- usually limited to the area of damage/trauma and resolves with healing
