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TOTAL INTRAVENOUS ANESTHESIA TIVA PUMPS

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Slide 1 :

TOTAL INTRAVENOUS ANESTHESIA (TIVA) & PUMPS Juan E Gonzalez, CRNA, MS Clinical Assistant Professor Florida International University Anesthesiology Nursing Program

Slide 2 :

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!)

Slide 3 :

Receptors Propofol, barbiturates, etomidate, benzo’s 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 in intracellular Calcium levels

Slide 4 :

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-protein mechanism linking the receptors to the ion channels Muscle Relaxants: act as the “n-type” acetylcholine receptors at the NMJ

Slide 5 :

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).

Slide 6 :

Indications for SSEP monitoring Any surgery with the potential for mechanical or vascular compromise of the sensory pathways along the peripheral nerve, within the spinal canal, or within 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

Slide 7 :

SSEP’s SSEP: electrophysiologic responses of the nervous system to the application of a discrete stimulus at a peripheral nerve anywhere in the body. SSEP’s reflect the ability of a specific neural pathway to conduct an electrical signal from the periphery to the cerebral cortex

Slide 8 :

How are SSEP’s generated A skin surface disc electrode or a SQ fine-needle electrode is placed near a major peripheral sensory nerve (median/ulnar nerve at the wrist, common peroneal nerve at the popliteal fossa, posterior tibial nerve at the ankle, etc) An electrical stimulus is applied with an intensity to produce minimal muscle contraction The resulting electrical potential is recorded at various points along the neural pathway from the peripheral nerve to the cerebral cortex

Slide 9 :

Some SSEP’s Recording Sites

Slide 10 :

SSEP waveform Amplitude: measured from baseline to peak. Any decrease in amplitude (50% OR greater) may indicate disruption of the sensory nerve pathways. Latency: time from onset of stimulus to occurrence of a peak. Any increase in latency (10% or greater) may indicate disruption of the sensory nerve pathways. * The spinal cord can tolerate ischemia for 20 minutes before SSEP’s are lost

Slide 11 :

Anesthetic Implications on SSEP’s All VAA cause dose-dependent decreases in amplitude and increases in latency The above can be worsened with the addition of N2O If possible, bolus injections of drugs should be avoided, especially during critical stages of surgery Continuous infusions are preferable

Slide 12 :

Neuro Monitoring http://analgesic.anest.ufl.edu/anest2/mahla/snacc/eps/index.htm Always check with Neuro Technician what is going to be monitored (SSEP, MEP, EMG) and what is their preference in terms of the anesthetic (no VAA, half MAC on VAA, N2O at 50%, keep 1 to 2 twitches in TOF or 4/4 at certain point of Surgery, etc) For long procedures, can start with VAA and switch over to Propofol, narcotic drips ASAP (few minutes after induction)

Slide 13 :

Other factors can affect SSEP’s Temperature Hypothermia increases latency Hyperthermia decreases amplitude Hypoxia Decreases amplitude Hypotension Decreases amplitude Hypocarbia Increased latency with ETCO2 <25 mmHg Anemia (baboon studies) If Hct <15% ? increased latency If Hct < 10% ? decreased amplitude (probably R/T tissue hypoxia

Slide 14 :

Corrective Measures if SSEP’s 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 SSEP’s and keep it constant (avoid drastic changes since it will confuse the cause of a negative change noticed in the neuro monitor: 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

Slide 15 :

Motor Evoked Potentials (MEP’s) SSEP monitoring is useful in preventing neurologic damage but it is no foolproof Because motor tracts are not monitored, the patient may wake up 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 (MEP’s) along with SSEP’s 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) MEP’s are more sensitive to VAA (may choose TIVA).

Slide 16 :

TIVA and Awareness TIVA recipe: Propofol/opioid +/- ketamine Ketamine is controversial since Ketamine (as well as Etomidate) enhance both SSEP’s and MEP’s Wake up test (rarely done anymore!) BIS monitoring Small bolus (eg, 1-2mg) of Midazolam intraop (too much will affect monitoring!!)

Slide 17 :

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

Slide 18 :

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

Slide 19 :

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 be 400mcg in 100 cc = 4 mcg/cc

Slide 20 :

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

Slide 21 :

Drugs commonly used in TIVA Context sensitive half times

Slide 22 :

Pumps The safe and continuous administration of IV anesthetics depends upon a reliable delivery system and a vigilant anesthetist A simple gravity intravenous infusion can be “piggy-backed” to a carrier line A pump offers the advantages of more precise dose selection, lower risk of overdose and minimal flow variation from changes in venous pressure or bag height

Slide 23 :

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 flow rates. May have program library Volumetric Pumps: Use a disposable cassette within IV system that controls rate by a variety of methods Larger size, added cost of cassette tubing, more susceptible to air bubbles

Slide 24 :

Infusion Pumps

Slide 25 :

Infusion Pumps

Slide 26 :

General Recommendations Vigilant anesthetist will continuously monitor: Connection of pump tubing to IV Possible occlusion and retrograde flow up the carrier line Misassembly of pump It is recommended that: Anesthetic infusions have a dedicated IV line Infusion line is placed as close to the patient as possible

Slide 27 :

Manual Calculations Can’t blame the pump!!! Use whatever method let’s you double check mannually the desired dosed given by the pump Just a review from Nursing 101!!

Slide 28 :

Manual Calculations Dose/concentration If you only have a basic pump that gives you cc/hr only, can you deliver the desired dose? My SIMPLE method of manual calculations: Dose = ml/hr Example: dose 80mcg/kg/min (propofol) Concentration concentration 10mg/cc weight: 75kg (80mcg)(75kg)(60min) = 36cc/hr 10,000mcg/cc

Slide 29 :

Manual Calculations (Examples) Remi Dose: 0.1mcg/kg/min Concentration: 50mcg/cc Weight: 60kg (0.1mcg)(60kg)(60min) = 7.2 cc/hr 50mcg/cc

Slide 30 :

More Calculations Dopamine Renal dose: 3mcg/kg/min Concentration: 400mg/250cc = 1.6mg/cc = 1600mcg/cc Weight: 90kg (3mcg)(90kg)(60min) = 10.1cc/hr 1600mcg/cc

Slide 31 :

More Examples Precedex Dose: 0.5mcg/kg/hr Concentration: 4mcg/cc Weight: 65kg (0.5mcg)(65kg)(1hr) = 8.1 cc/hr (4mcg/1cc)

Slide 32 :

Shortcut Only works with 250cc bag Does not take into consideration pt’s weight Dose is “eye-balled” to an initial rate of 15cc/hr Rule Any “X” amount of mg added to a 250cc bag will give that “X” amount in mcg/min if you set the pump at 15cc/hr

Slide 33 :

Example of shortcut (Any “X” amount of mg added to a 250cc bag will give that “X” amount in mcg/min if you set the pump at 15cc/hr) Example: Neosynephrine comes in a 10mg/cc vial If you add 10mg of Neosynephrine to a 250cc bag and run it at 15cc/hr, you will be delivering 10mcg/min

Slide 34 :

PATIENT SAFETY ISSUES Warm air devices (Bair Hugger) DO NOT USE HOSE BY ITSELF Can cause 3rd degree burns C/I in AAA surgery Fires Pacers/ICDs and Magnets an attractive overview

Slide 35 :

References http://analgesic.anest.ufl.edu/anest2/mahla/snacc/eps/index.htm Clinical Anesthesia Procedures of the Massachusetts General Hospital Anesthesia Secrets Physician’s Drug Handbook Morgan and Mikhail

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Neuro: resection of tumor or vascular lesion in spinal cord, tethered cord release, resection of a more 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 less