Local Anaesthesia techniques for surgical procedures and calculation of toxic dose of local anaesthetic agents

1. Local Anaesthesia for
Surgical Procedures
F. Brakatu

2. Lidocaine

3. Bupivacaine

4. What about “Heavy Marcaine”?

5. Practical Considerations
Drug Concentration is expressed as a percentage - 2% = 2g/100ml =
2000mg/100ml = 20mg/ml
Infiltrations and blocks are usually done with 1% Lid and/or 0.25% Bup
To convert 2% Lidocaine to 1% Lid or 0.5% Bup to 0.25% Bup : Dilute with equal
volume of sterile water or saline
To get 20ml of 1% Lid, draw 10ml of 2% Lid and add 10ml of sterile water

6. Maximum Dose of LA
Lidocaine - 3mg/kg
Lidocaine with Adrenaline - 7mg/kg
Bupivacaine - 2mg/kg
Bupivacaine + Adrenaline - 2mg/kg

7. Toxic Dose Calculation

8. Case 1
60kg M scheduled for hydrocelectomy. He came to theater with a 50ml bottle of
2% Lidocaine. What is the maximum volume of 1% Lidocaine that can be given for
his procedure?
Ans: 18ml

9. Case 2
60kg M scheduled for orchidectomy. He came with 0.5% Bupivacaine. What is the
maximum volume of 0.25% Bupivacaine that can be given for his procedure?
Ans: 48ml

10. Case 3
60kg M scheduled for bilateral varicocelectomy. He came with vials of both 2% Plain
lidocaine and 0.5% Bupivacaine. Consultant wants a combination of both 1%
Lidocaine and 0.25% Bupivacaine. What’s the maximum volume to give for both
procedures?
Max Lidocaine - 18ml and Max Bupivacaine - 48ml
Mix by proportions based on desired effect - rapid onset vs
duration of anaesthesia
For equal vols of both- Half of each ie 9ml Lid + 24ml Bup
= 33ml of soln.
For a longer duration (⅓ Lid +⅔ Bup) = 6ml Lid + 32ml Bup = 38ml
of soln; You can use 19ml for left repair and 19ml for right repair

11. Case 4
Patient in Case 3 starts writhing in pain during procedure and surgeon infiltrates some more LA to
complete the procedure.
30s later - Patient starts drowsily slurring his speech, BP- 72/38 HR-52 and SpO2 - 84%.
60s later - Tonic-clonic seizure
90s later - Another seizure, asystole, no pulse and BP on monitor
Diagnosis?
What now?

12. LAST
Ans: Local Anaesthetic Systemic Toxicity (LAST)
ACLS
Intubate
Asystole or PEA- Chest compressions(+ Adrenaline &
Atropine)
Defib for Vtach & Vfib
b) Lipid rescue with IV 20% Lipid Emulsion
1.5ml/kg IV bolus (100ml for a 70kg man) - repeat for CV
collapse
0.25ml/kg/min (18ml/min) - for at least 10min once stable
Upper limit - 10-12ml/kg over 30min
c)Before discharge - 12 lead ECG, Cardiac markers and
Echo

13. Clinical Manifestation of LAST
CNS - Circumoral tingling, tinnitus, slurred speech, muscle twitching, loss of
consciousness, convulsions, coma and respiratory arrest
CVS - Myocardial depression, cardiac arrhythmias, ventricular arrest

14. Take Home Message
~ Always Consider LA as an option
~ Always calculate the toxic dose of LA and stay within safe limits
~ LA can complement other methods to decrease analgesic requirement
~ Prepare to complement with IV Sedation if necessary
~ LA may be an option in morbid patients unfit for surgery