Local anaesthetics overview
△ membrane permeability
→ ✖ nerve impulse
Topical Direct infiltration Blocks including IV RA Spinal Epidural
Stored as acidic salts, activated when put into alkalinity of tissue
i.e. ineffective in infected wounds
1% = 10mg/ml
LA & Doses
Lidocaine: 3mg/kg
+ Epi : 7mg/kg
Bupivacaine : 2mg/kg
Prilocaine : 6mg/kg
Epi doesn’t affect max dose in last 2.
Last 2 also cardiotoxic in spinals & Bier’s blocks respectively
Avoid LA near end-arteries
LA & Toxicity
Local: Inflam & Nerve Dmg
Systemic: Perioral tingling & parathesia Anxiety, Tinnitus Drowsy, ↓ GCS Paralysis, apnoea CVS collapse (-ve inotropic & a vasodilator)
Mx:
Stop LA → ABC (IVT +/- inotropes)
Regional Anaesthesia using LA
Field block: affects entire surgical field
e.g. Hernia repair uses infiltration of LA + Injection of LA into Ilioinguinal nerve
Ring block: area usu. digit / penis
- do not use with Epi
Plexus block:
- Brachial, Femoral, Sciatic
- Bier’s , Intercostal
Brachial plexus (C5-T1)
Interscalene (trunk)
Supra/Infra-clav (divisions)
Axillary (cords)
Femoral (L2-L4)
- 1cm lateral to femoral artery as it exits the inguinal ligt
Sciatic (L4-S3)
- 2cm lateral to ischial tuberosity at level of GT
Regional anaesthesia & IV LA
IV regional anaesthesia
Bier’s block
- exsanguinate, ↑ upper cuff then LA, ↑ lower & ↓ upper
Intercostal: chest drains etc
- nerve under overhanding edge of rib
- Posterior ⦞ of rib at Post. axillary line, needle below rib edge
Regional Anaesthesia : Spinal
Contraindications;
- anticoagulation
- septic
- previous back Sx
- Aortic stenosis
Subarachnoid space @L1-2.
Complications: toxicity, ↓ BP,h-ache, urinary retention
Regional Anaesthesia: Epidural
Extra-dural space
- △ in resistance as needle passes through ligament flavum signifying placement
Complications:
Dural tap, backache, infection, haematoma
↓ haematoma by leaving catheter until 12h post-heparin
↑ Inf if catheter left >72h
Important dermatomes & RA
T5 : Nipples
T10: Umbilicus
T12: Inguinal ligt
Block @ C4 → Respiratory arrest
Sedation Overview
Premedication anxiolytic Amnesic For invasive inv e.g. OGD RA adjunct ICCU e.g. tolerate tube
Caution in
Elderly
Obese
Cardio-resp disease
GA Overview
Pre-op assessment & prep Induction & muscle relax Maintenance & monitoring Recovery Post-op monitoring & transfer
ASA
1 healthy 2 mild systemic 3 sev systemic, limits ADLs 4 incapacitating dis, constant threat 5 Moribund
Pre-op medications considerations
Anxiolytic (benzo) Antiemetic Anticholinergic Abx Anticoagulation Antirejection Addison's (Steroid)
GA induction agents
IV quicker, hydrophobic
- Na Thiopentone (barbiturate)
- Narrow TI → CVS/RS dep
- Propofol (phenol)
- better antiemetic
- but -ve inotrope
- Etomidate
- better CVS profile
Complications
- ↓ BP
- RS Dep
- Laryngospasm
- Allergy
Avoid in allergy & porphyria
GA muscle relaxants
Depolarising
- Sux (2Ach):
- hydrolysed by cholinesterase
- rapid onset, 2-6 min duration
Complications: ↑ K+ → ∴ avoid in burns ↓HR ↑/↓ BP Myoglobinaemia Malig hyperpyrexia
Non-depolarising
- Atri, Cis-Atri,
- non-enzymatic metabolism
- slower than Sux
- Reverse with neostigmine
↑ NM Blockade in
- ↓ Temp
- ↓ pH
- ↑ K+
- ↑ Age
- Concurrent Sux use
MG : ↓ post-syn receptors 2° to auto- Ab
- ↑ Sensitivity to Atric
- ↑ resistance to Sux
GA Maintenance agents
Isoflurane (halogenated ether)
- CVS & RS Depression
Sevoflurane (halogenated ether)
- rapid recovery ∴ need to plan post-op pain relief
NO2
- allow dose ↓ of other agents.
- can lead to bowel distention.. avoid in pneumothorax, recent diving or high p(Atm) exposure
- Prolonged expo → myelosuppression & anaemia
Containdications
- pyrexia after halothane admission
- Hx of jaundice
GA & Complications
Intubation
- difficult intubation
- post-op sore throat
- trauma in OP
Anaesthetic Rx
- Anaphylaxis
- Malign Hyperpyrexia
- PONV
- Drowsy
CVS:
- Myocardial ischaemia
- ↓/↑ BP
- Arrhythmia
RS:
- Obstr
- ↓ Ventilation, ↓ O2
- Residual NM block
- Aspiration
Malignant Hyperpyrexia
Usu. inhalation agents & Sux
- except NO2
- AD inheritance
Rapid Ca2+ influx into muscle
- M. Rigidity
- ↑ Temp, HR & RR
- DIC
- ↑ CO2 prod & O2 demand → acidosis & ↑ K+
Mx:
Dantrolene 1mg/kg & rpt
Cooling
↑ Ventilation to ↓ CO2