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