Tiva

TOTAL INTRAVENOUS ANESTHESIA (TIVA) & PUMPS

Juan E Gonzalez, CRNA, MS

Clinical Assistant Professor

Florida International University

Anesthesiology Nursing Program

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!)

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

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

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).

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

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

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

Some SSEP’s Recording Sites

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

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

Neuro Monitoringhttp://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)

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

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

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).

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!!)

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

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

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

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

Drugs commonly used in TIVAContext sensitive half times

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

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

Infusion Pumps

Infusion Pumps

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

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!!

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

Manual Calculations (Examples)

RemiDose: 0.1mcg/kg/min

Concentration: 50mcg/cc

Weight: 60kg

(0.1mcg)(60kg)(60min) = 7.2 cc/hr

50mcg/cc

More Calculations

DopamineRenal dose: 3mcg/kg/min

Concentration: 400mg/250cc = 1.6mg/cc = 1600mcg/cc

Weight: 90kg

(3mcg)(90kg)(60min) = 10.1cc/hr

1600mcg/cc

More Examples

PrecedexDose: 0.5mcg/kg/hr

Concentration: 4mcg/cc

Weight: 65kg

(0.5mcg)(65kg)(1hr) = 8.1 cc/hr

(4mcg/1cc)

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

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

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

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