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