Peripheral Nerve Blocks (PNB)
Peripheral nerve block (PNB) คือการฉีด local
anesthetic (LA) รอบ peripheral nerve หรือ plexus
เพื่อให้เกิด surgical anesthesia หรือ analgesia
โดยลด opioid requirement และหลีกเลี่ยงผลเสียของ
GA/neuraxial anesthesia ได้ในหลายสถานการณ์
1. ข้อบ่งชี้ของ PNB
ใช้แทน General Anesthesia (GA)
เหมาะในผู้ป่วย:
- OSA
- severe
obesity
- pulmonary
disease
- difficult
airway
- high
PONV risk
- ต้องการหลีกเลี่ยง GA
- pregnancy
ใช้แทน Neuraxial anesthesia
เหมาะใน:
- anticoagulation/coagulopathy
(เฉพาะ superficial/compressible block)
- severe
aortic stenosis
- high
urinary retention risk
- BPH
- elderly
- diabetes
Analgesia indications
เหมาะใน:
- opioid
intolerance
- chronic
opioid use
- ambulatory
surgery
- severe
acute pain
- respiratory
compromise risk
2. Contraindications
Absolute contraindications
- patient
refusal
- inability
to cooperate
- LA
allergy
Relative contraindications
- infection
at injection site
- anticoagulation/coagulopathy
- preexisting
neurologic deficit
3. Anticoagulation & Bleeding Risk
Risk สูงใน deep noncompressible blocks:
- lumbar
plexus
- paravertebral
- quadratus
lumborum
- proximal
sciatic
- infraclavicular
หลักการ:
- superficial/compressible
blocks → อาจทำได้
- deep
blocks + anticoagulation →
generally avoid
Complications:
- hematoma
- nerve
compression
- occult
blood loss
4. Types of Blocks
Single-shot block
- single
injection
- duration:
- <1
hr → >24 hr
ขึ้นกับ LA pharmacology
Continuous catheter block
- continuous
infusion ผ่าน catheter
- prolonged
analgesia
- ลด opioid use
- outpatient
use ได้
5. Patient Preparation
ควรประเมิน:
- coagulation
- pulmonary
disease
- neurologic
deficits
- ability
to ambulate after block
ผู้ป่วยควรทราบ:
- limb
protection
- delayed
complications
- fall
precautions
6. Monitoring & Safety
ต้องมี:
- IV
access
- ECG
- BP
monitor
- pulse
oximetry
- lipid
emulsion 20%
- resuscitation
equipment
7. Pre-procedure Checklist
Checklist สำคัญ:
- patient
identity
- allergies
- coagulation
status
- correct
side
- surgical
site marking
- block
site marking
ช่วยลด wrong-sided block
8. Sedation
ควรให้ผู้ป่วย “awake but comfortable”
เป้าหมาย:
- ยังสื่อสารได้
- report
paresthesia/injection pain ได้
Typical sedation:
- midazolam
1–2 mg IV
- fentanyl
25–100 mcg IV
9. Ultrasound Guidance
ปัจจุบันเป็น standard สำหรับหลาย
blocks
ข้อดี:
- visualize
nerve/vessel/needle
- increased
success rate
- faster
onset
- lower
LA volume
- ลด vascular puncture
- ลด LAST
- ลด pneumothorax/phrenic nerve block
Ultrasound Techniques
In-plane
- เห็น entire needle
- safer
- preferred
Out-of-plane
- needle
เห็นเป็น dot
- difficult
tip visualization
- ใช้กับ deep blocks บางชนิด
10. Nerve Stimulator Guidance
หลักการ:
- electrical
current → motor twitch
- current
ต่ำลง = needle closer to nerve
Target:
- twitch
at ≤0.5 mA
- disappear
<0.4 mA
⚠️ diabetic neuropathy:
- stimulation
threshold unreliable
⚠️ absence of twitch ≠
exclude intraneural placement
11. Continuous Catheter Technique
ข้อดี:
- prolonged
analgesia
- ambulatory
catheter possible
Outpatient catheter protocol ควรมี:
- written
instructions
- 24h
contact
- follow-up
- removal
instructions
Catheter usually:
- sterile
placement
- remove
within 48–72 hr (infection risk starts rising)
12. Local Anesthetics (LA)
|
Short acting |
Long acting |
|
Lidocaine |
Bupivacaine |
|
Mepivacaine |
Ropivacaine |
|
Levobupivacaine |
หลักสำคัญ:
- higher
concentration → faster
onset
- long
acting → prolonged
analgesia
- mixing
LA →
unpredictable/intermediate effect
13. Adjuvants
Epinephrine
ช่วย:
- reduce
systemic absorption
- prolong
block
- detect
intravascular injection
Typical:
- 1:200,000–1:400,000
Sodium bicarbonate
- faster
onset
- evidence
mixed
Dexamethasone
Most evidence-supported adjuvant
Benefits:
- prolong
analgesia
- reduce
PONV
- improve
recovery
Dose:
- no
clear benefit >4–5 mg
IV vs perineural:
- both
effective
- perineural
slightly longer in some studies
- perineural
use = off-label
Alpha-2 agonists
Clonidine
ช่วย prolong block
แต่:
- hypotension
- bradycardia
- sedation
Dexmedetomidine
- improves
block quality
- prolongs
motor block
- bradycardia/hypotension
risk
Opioids
- fentanyl/morphine
in PNB → limited
benefit
14. Rebound Pain
Definition:
- severe
pain increase after block resolution
Incidence:
- up
to ~80%
Prevention:
- educate
patient
- start
oral analgesics before block wears off
- avoid
nighttime block resolution
- dexamethasone
- continuous
catheter may help
15. Complications
Nerve Injury
Permanent injury:
- rare
(~0.015–0.09%)
Transient symptoms:
- much
more common
Mechanism:
- intrafascicular
injection
- injection
pressure
- neurotoxicity
- hematoma
compression
Risk factors:
- diabetes
- preexisting
neuropathy
- long-bevel
needles
Warning signs:
- severe
pain during injection
- paresthesia
- high
injection pressure
Management:
- stop
injection immediately
Hematoma
Riskสูงใน:
- anticoagulated
patients
- deep
blocks
LAST (Local Anesthetic Systemic Toxicity)
Presentation:
- tinnitus
- circumoral
numbness
- seizure
- arrhythmia
- cardiac
arrest
ต้องมี:
- lipid
emulsion ready always
Infection
Single-shot:
- infection
rare
Continuous catheter:
- colonization
common
- clinical
infection low (0–3.2%)
Risk factors:
- ICU
- trauma
- immunocompromised
- prolonged
catheter duration
Myotoxicity
Rare:
- prolonged/high
concentration LA
- symptoms
may last months
Secondary Injury
Insensate limb injury
ต้อง:
- protect
extremity
- educate
patient
Falls
โดยเฉพาะ lower extremity blocks
→ assisted ambulation
required
16. High-Yield Clinical Pearls
- Ultrasound
guidance is current preferred standard
- Keep
patient responsive during block placement
- Never
inject against high resistance
- Severe
injection pain = stop immediately
- Deep
blocks + anticoagulation = high bleeding risk
- Always
have lipid emulsion available
- Rebound
pain prevention improves patient satisfaction
- Continuous
catheter provides superior prolonged analgesia
- Motor
block after lower extremity PNB increases fall risk
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