SIVA audio

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SIVA/Balanced Anesthesia:

SIVA /Balanced Anesthesia Dr. Luiz Santos DVM MSc Dip. ACVAA Anaesthesia Lecturer

Definition of SIVA:

Definition of SIVA ‘Maintaining GA by administration of any inhalation agent , with simultaneous administration of an intraveous drug ( s ).’

Slide3:

0.9 % for non-colic surgical cases 7 . 9 % in surgical colics Johnston 2002 Cardiac arrest 33% Fractures 26% Myopathy 7% last two normally manifesting during anaesthetic recovery.

CEPEF study TIVA vs. Inhalants:

CEPEF study TIVA vs. Inhalants TIVA cases vs. volatile anaesthesia significantly reduced mortality following TIVA Anaesthetic -related M&M due to marked CP depression with inhalants Reduced CO, with resultant hypotension, considered major risk for myopathy Myopathies manifest in recovery M ay contribute to limb fracture TIVA may cause less CV depression than inhalants, with better CO and BP M uscle perfusion may be superior In addition , lower PaCO2 and higher PaO2

Ideal anaesthetic agent:

Ideal anaesthetic agent Wide therapeutic index Rapid onset of action Short duration Analgesic effect Muscle relaxation Metabolites non- toxic and inactive Rapid recovery with no hangover effect

Potential advantages SIVA over inhalational anaesthetics alone:

Potential advantages SIVA over inhalational anaesthetics alone Superior analgesia Less cardiorespiratory depression Less likelihood of movement in response to surgical stimuli??? Improved recoveries Less pollution of surgical suite Save inhalant $$

Potential disadvantages of TIVA alone:

Potential disadvantages of TIVA alone Potential for drug accumulation Build- up of active metabolites with prolonged infusions . Managed by decreasing the infusion rate/time. A fluid or syringe pump for accurate drug delivery. Immature liver and kidney  newborn foals

Methods of drug delivery:

Methods of drug delivery Bolus technique Single Intermittent Continuous infusion technique CRI: constant rate infusion TCI: target controlled infusion

Single bolus technique:

Single bolus technique Minutes - 10 0 5 10 15 20 25 Plasma drug concentration

Relationship plasma drug concentrations & drug effects:

Relationship plasma drug concentrations & drug effects Studies in horses Minutes -10 0 5 10 15 20 25 Pharmacodynamics (PD) Pharmacokinetics (PK)

Intermittent bolus:

Intermittent bolus CV depression Anesthetized Awake

Continuous infusion:

Continuous infusion Delayed induction Awake Anestheti z ed CV depression

Continuous infusion:

Continuous infusion CV depression Anestheti z ed Awake Loading dose

Context Sensitive Half-Time:

Context Sensitive Half -Time Time to 50% drop (min) 100 75 50 25 0 0 100 200 300 400 500 600 Infusion duration (min) Propofol Thiopental/Norketamine Ketamine Etomidate

MAC:

MAC

Examples of drug protocols:

Examples of drug protocols A . Ketamine Reduces MAC by ~ 30% Analgesia (NMDA antagonist ) Norketamine B. Alpha-2 agonists Dexmedetomidine (CRI 1.75ug/kg/ h ) Dose- dependet MAC reduction ~25% C. Ketamine and alpha-2 agonists Expected MAC reduction ~ 50–60%

SIVA:

S IVA D. Lignocaine Dose- dependent MAC reduction MAC reduction @ 50-100ug/kg/min by ~ 25% - 50% E. Lignocaine + ketamine Combination reduces MAC by 60–80% F. Lignocaine + ketamine + alpha2 MAC reduction of 80–90%

Lignocaine CRI:

Lignocaine CRI

What about opioids?:

What about opioids? Studies reported variable effect on MAC Administration during GA in fact increased the requirement for inhalant agents Steffey 2003

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