8. MMeecchhaanniissmm ooff AAccttiioonn ffoorr LLooccaall AAnneesstthheettiiccss
•Block propagation of action potential along neuron
prevent depolarization through blockade of Na Channel
voltage gated K channels also blocked by LA
but the affinity of receptor much less
21. Onset of Action
Onset of Action
· Low pH as found in sites of infection will slow or prevent onset.
· The pKa values of most amides are similar; therefore, onsets are
similar.
· Bupivacaine's higher pKa results in a slightly slower onset.
· The time for diffusion to the nerve is a factor --infiltrations are rapid;
25. CCNNSS TTooxxiicciittyy
Tends to occur first (relative to CVS toxicity)
See excitatory signs and symptoms first
Followed by depressant signs
Circumoral and tongue numbness
Lightheadedness and tinnitus
Visual disturbance
Muscle twitching
Convulsions
COMA
Respiratory arrest
CVS depression
26. CCVVSS TTooxxiicciittyy
Alteration in the excitatory mechanism
slower depolarization
decreased HR
prolonged PR interval
widened QRS
Arrythmias
bradycardia
ectopic beats
ventricular fibrillation
Decreased cardiac output on the basis of
HR
contractility
28. TTrreeaattmmeenntt ooff TTooxxiicciittyy
Identify the problem
signs and symptoms
temporal relationship
IV injection
40-60 min post for peak plasma levels
CNS
treatment with benzodiazepines
29. TTrreeaattmmeenntt ooff TTooxxiicciittyy
CVS signs and symptoms
CNS effects
CVS effects
arrythmia
QRS change
signs of collapse fall in BP
With CVS toxicity
The agent is an important consideration
45. LLiimmiittaattiioonnss ooff LLooccaall AAnneesstthheettiiccss
Amount and complexity of the work to be done
Patient
Area to be anesthetized
Duration of procedure
Immobility