Local anesthetics can have systemic effects at high levels. They primarily act by depressing the central nervous system and lowering seizure thresholds. Preconvulsive signs may include numbness, shivering, or twitching. Convulsions last less than a minute and increase blood flow and metabolism. Local anesthetics have direct effects on the cardiovascular and respiratory systems by relaxing muscles and decreasing heart rate and blood pressure. Toxicity is caused by rapid intravenous injection, absorption from vascular sites, or overdose. Factors reducing toxicity include using the minimum effective dose and concentration and slowly injecting while aspirating.

1. SYSTEMIC EFFECTS
OF
LOCAL
ANAESTHETICS
DR. SWATI SAHU
MDS FELLOW
ORAL & MAXILLOFACIAL SURGERY

2. CNS
• In one word : DEPRESSION
• At high levels, LA will produce tonic-clonic convulsions
• Procaine, Lidocaine etc produce ANTICONVULSANT properties.

3. • This drugs are used for management of grand mal & petit mal seizures
• The depressant action of LA raise the seizure threshold by decreasing the
excitability of cortical neurons in epileptic patients

4. PRECONVULSIVE SIGNS &
SYMPTOMS
• Numbness of the tongue & circumoral regions
• If excitation or sedation occurs in the first 5 or 10 minutes after administration of
LA, it should consider as a warning that convulsive activity could be possible.
• Shivering, slurred speech, muscular twitching, visual/auditory disturbances,
dizziness, drowsiness, disorientation & tremor.

5. CONVULSIVE PHASE
• Duration of seizures is related to blood level of LA & inversely related to
arterial pCO2 levels.
• Seizures last less than or equal to one minute.
• In seizure,
1) cerebral blood flow &
2) cerebral metabolism increase

6. 1 ) CEREBRAL BLOOD FLOW

7. 2 ) CEREBRAL METABOLISM

8. RESPIRATORY SYSTEM
• DUAL EFFECTS :
1. Non-overdose levels : Direct relaxant action on bronchial smooth muscle
2. Overdose levels :

9. CVS
• Direct action on myocardium & peripheral vasculature.
• Increased LA blood levels result in decreased myocardial depolarization
• Decrease in myocardial excitation, decrease in conduction rate & decrease in
the force of contraction
• Produces hypotension ( direct relaxation effect on vascular smooth muscle )

10. LOCAL TISSUE TOXICITY
• Skeletal muscle will heal within 2 weeks of being injected with local
anaesthetic.
• Longer acting LA produces more damage to skeletal muscle than shorter
acting LA.

11. TOXICITY OF LOCAL ANAESTHESIA
1- Causes
2- Factors reducing toxicity.

12. CAUSES
• Accidental rapid intravenous injection.
• Rapid absorption, such as from a very vascular site i.e mucous membranes.
• Overdose

13. FACTORS REDUCING TOXICITY
• Decide on the concentration of the local anaesthetic that is required for the block to
be performed. Calculation of the total volume of drug should be done.
• Use the least toxic drug available.
• Use lower doses in frail patients or at the extremes of ages.
• Always inject the drug slowly (around 1ml /minute) and aspirate regularly looking
for blood to indicate an accidental intravenous injection

14. • If Injection of a test dose of 2-3ml of local anaesthetic containing adrenaline is accidentally
given intravenously it will often (but not always) cause significant tachycardia.
• Add adrenaline (epinephrine) to reduce the speed of absorption. The addition of adrenaline
will reduce the maximum blood concentration by about 50%. Usually adrenaline is added in
a concentration of 1:200,000, with a maximum dose of 200 micrograms.
• Make sure that the patient is monitored closely by the anaesthetist or a trained nurse during
the administration of the local anaesthetic and following the surgery.

15. ADVANTAGES OF LOCAL
ANAESTHESIA
• During local anesthesia the patient remains conscious
• Maintains his own airway.
• Excellent muscle relaxant effect.
• Requires less skilled nursing care as compared to other anesthesia like general
anesthesia.
• Non inflammable.

16. • Less pulmonary complications
• Aspiration of gastric contents unlikely.
• Less nausea and vomiting.
• Contracted bowel so helpful in abdominal and pelvic surgery.
• Postoperative analgesia.
• There is reduction surgical stress.
• Earlier discharge for outpatients.

17. • Suitable for patients who recently ingested food or fluids.
• Local anesthesia is useful for ambulatory patients having minor procedures.
• Ideal for procedures in which it is desirable to have the patient awake and
cooperative.
• Less bleeding.
• Expenses are less.

18. DISADVANTAGES OF LOCAL
ANAESTHESIA
• There are individual variations in response to local anesthetic drugs.
• Rapid absorption of the drug into the bloodstream can cause severe,
potentially fatal reactions.
• Apprehension may be increased by the patient's ability to see and hear.
• Some patients prefer to be unconscious and unaware.

19. • Direct damage of nerve.
• Post-dural headache from CSF leak.
• Hypotension and bradycardia through blockade of the sympathetic nervous
system.
• Not suitable for extremes of ages.
• Multiple needle pricks may be needed.