Tiva Pumps

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    TOTAL INTRAVENOUSANESTHESIA (TIVA) & PUMPS

    Juan E Gonzalez, CRNA, MSClinical Assistant Professor

    Florida International University

    Anesthesiology Nursing Program

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    TIVA

    Total Intravenous Anesthesia

    General Anesthesia Anesthesia via IV drugs (usually Propofol,

    Narcotics, Versed) drips and/or boluses

    No Volatile Agents

    N2O sometimes used (not really a TIVA!)

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    Receptors

    Propofol, barbiturates, etomidate, benzos Enhance the inhibitory effects of GABA (gamma-

    aminobutyric acid) GABA activation increases Chloride conductance

    hyperpolarizes membrane inhibition of synapse

    Ketamine

    Blocks excitatory effects of glutamic acid Four types of receptors

    Ketamine inhibits one of these receptors (N-methyl-D-aspartate) decrease in Sodium flux and decrease inintracellular Calcium levels

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    Receptors (Cont)

    Opioids: receptor activation of mu, kappa,

    delta receptors Decrease excitability by increasing influx of K+1

    and decreasing outflow of Na+1 via a G-proteinmechanism linking the receptors to the ionchannels

    Muscle Relaxants: act as the n-typeacetylcholine receptors at the NMJ

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    Selection of Cases

    Any case can be done as TIVA (preference

    vs. cost) Malignant Hyperthermia (triggered by VAA, Sux)

    Spine surgery. If monitoring of:Somatosensory Evoked Potentials (SSEP),

    Motor Evoked Potentials (MEP),Electromyography (EMG).

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    Indications for SSEP monitoring

    Any surgery with the potential for mechanical orvascular compromise of the sensory pathways along

    the peripheral nerve, within the spinal canal, orwithin the brain stem or cerebral cortex. Neuro: resection of tumor or vascular lesion in spinal cord,

    tethered cord release, resection of a sensory cortex lesion(aneurysm, thalamic tumor), repair of AAA or TAA, carotid

    endarterectomy. Ortho: scoliosis (Harrington rods), spinal cord

    decompression/stabilization after acute injury, spinal fusion

    Brachial plexus exploration

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    SSEPs

    SSEP: electrophysiologic responses of the

    nervous system to the application of adiscrete stimulus at a peripheral nerveanywhere in the body.

    SSEPs reflect the ability of a specific neural

    pathway to conduct an electrical signal fromthe periphery to the cerebral cortex

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    How are SSEPs generated

    A skin surface disc electrode or a SQ fine-needleelectrode is placed near a major peripheral sensory

    nerve (median/ulnar nerve at the wrist, commonperoneal nerve at the popliteal fossa, posterior tibialnerve at the ankle, etc)

    An electrical stimulus is applied with an intensity toproduce minimal muscle contraction

    The resulting electrical potential is recorded atvarious points along the neural pathway from theperipheral nerve to the cerebral cortex

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    Some SSEPs Recording Sites

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    SSEP waveform

    Amplitude: measured from baseline topeak. Any decrease in amplitude (50%OR greater) may indicate disruption ofthe sensory nerve pathways.

    Latency: time from onset of stimulus to

    occurrence of a peak. Any increase inlatency (10% or greater) may indicatedisruption of the sensory nervepathways.

    * The spinal cord can tolerate ischemia

    for 20 minutes before SSEPs are lost

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    Anesthetic Implications on SSEPs

    All VAA cause dose-dependent decreases inamplitude and increases in latency

    The above can be worsened with theaddition of N2O

    If possible, bolus injections of drugs should

    be avoided, especially during critical stagesof surgery

    Continuous infusions are preferable

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    Neuro Monitoringhttp://analgesic.anest.ufl.edu/anest2/mahla/snacc/eps/index.htm

    Always check with Neuro Technician what isgoing to be monitored (SSEP, MEP, EMG)and what is their preference in terms of theanesthetic (no VAA, half MAC on VAA, N2Oat 50%, keep 1 to 2 twitches in TOF or 4/4 atcertain point of Surgery, etc)

    For long procedures, can start with VAA andswitch over to Propofol, narcotic drips ASAP(few minutes after induction)

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    Other factors can affect SSEPs

    Temperature

    Hypothermia increases latency

    Hyperthermia decreases amplitude Hypoxia

    Decreases amplitude

    Hypotension

    Decreases amplitude

    Hypocarbia Increased latency with ETCO2

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    Corrective Measures

    if SSEPs change significantly

    Anesthesia Provider can: Increase MAP (especially if induced hypotension is used) Correct anemia, if present Correct hypovolemia, if present Improve O2 tension Goal: find the proper anesthetic combination that does not affect

    SSEPs and keep it constant (avoid drastic changes since it willconfuse the cause of a negative change noticed in the neuromonitor: is it the anesthetic or the surgery?)

    Surgeon can: Reduce excessive retractor pressure Reduce surgical dissection in affected area

    Decrease Harrington rod traction if indicated

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    Motor Evoked Potentials (MEPs)

    SSEP monitoring is useful in preventing neurologic damage butit is no foolproof

    Because motor tracts are not monitored, the patient may wakeup with preserved sensation but lost motor function

    Motor pathways: blood supply from anterior spinal artery

    Sensory pathways: blood supply from posterior spinal artery

    The use of Motor Evoked Potentials (MEPs) along withSSEPs provides a more complete assessment of neural

    pathway integrity Electrical stimulation done by Neuro Tech b/w key surgical

    periods (when twitching does not affect operative field)

    MEPs are more sensitive to VAA (may choose TIVA).

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    TIVA and Awareness

    TIVA recipe: Propofol/opioid +/- ketamine

    Ketamine is controversial since Ketamine (as wellas Etomidate) enhance both SSEPs and MEPs

    Wake up test (rarely done anymore!)

    BIS monitoring

    Small bolus (eg, 1-2mg) of Midazolamintraop (too much will affect monitoring!!)

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    Drugs commonly used in TIVA

    (titrate to effect)

    Propofol (Diprivan) Induction: 2-2.5 mg/kg Maintenance: 50-200 mcg/kg/min

    Remifentanil (Ultiva) Induction: 0.5-1 mcg/kg (over 30-60 sec) Maintenance:

    0.1-2 mcg/kg/min with 50% N2O 0.05-2 mcg/kg/min with Propofol at 100-200 mcg/kg/min 0.05-2 mcg/kg/min with Isoflurane at 0.4-1.5 MAC

    After turning off drip, make sure IV tubing is free of Remifentanil

    Dexmedetomidine (Precedex) (alpha-2 agonist) Maintenance:

    Loading infusion: 1mcg/kg over 10 minutes Maintenance infusion: 0.2-0.7 mcg/kg/hr

    Can keep infusion going after extubation

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    Drugs commonly used in TIVA

    (titrate to effect)

    Fentanyl Induction 5.75mcg/kg

    Maintenance 0.01-0.05mcg/kg/min Sufentanyl

    Induction 1-10mcg/kg

    Maintenance 0.0025-0.15mcg/kg/min

    Ketamine

    Induction 0.5-2mg/kg Maintenance 20-90mcg/kg/min Can combine w/propofol 4:1 e.g.200mgpropfol+50mg

    ketamine

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    Mixing and Diluting

    Remifentanil (Ultiva) Usually comes as powder in vial (5mg vial)

    Dilute to 50 mcg/cc (by adding 5mg to 100 N.S.)

    Dexmedetomidine (Precedex)

    Usually come as 100mcg/ml in 2ml vial Dilute to 4 mcg/cc (by adding 2 vials of 200mcg

    each to 96cc of N.S.) Total solution will be400mcg in 100 cc = 4 mcg/cc

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    Drugs commonly used in TIVA

    (titrate to effect)

    Equations

    Loading dose (mcg/kg) Vd (ml/kg) x Cp (mcg/ml)

    Maintenance infusion (mcg/kg/min)

    Cl ml/kg/min x Cp mcg/ml

    Source NZ 3rd Ed. P. 154

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    Drugs commonly used in TIVAContext sensitive half times

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    Pumps

    The safe and continuous administration of IVanesthetics depends upon a reliable deliverysystem and a vigilant anesthetist

    A simple gravity intravenous infusion can bepiggy-backed to a carrier line

    A pump offers the advantages of moreprecise dose selection, lower risk ofoverdose and minimal flow variation fromchanges in venous pressure or bag height

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    Types of Pumps

    Syringe Pumps:

    Use a driver that pushes fluid out of a syringe by advancing

    its plunger while the barrel is kept stationary.

    Small units, light weight, cordless, accurate at very low flowrates. May have program library

    Volumetric Pumps:

    Use a disposable cassette within IV system that controlsrate by a variety of methods

    Larger size, added cost of cassette tubing, more susceptibleto air bubbles

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    Infusion Pumps

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    Infusion Pumps

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    General Recommendations

    Vigilant anesthetist will continuously monitor: Connection of pump tubing to IV

    Possible occlusion and retrograde flow up thecarrier line