--- Content provided by FirstRanker.com ---GOALS IN NEUROANESTHESIOLOGY
? Haemodynamic stability
? ICP control
? Maintaining Cerebral perfusion
? Providing optimal conditions for surgery
? Smooth emergence
? Rapid awakening
Ideal anaesthetic agent for neuroanesthesia
? Maintains CBF without altering the autoregulation.
? Minimizes or if not doesn't itself causes an increase the ICP.
? Preserves reactivity of cererbral arterioles to PaCO2 changes.
? Decreases the CMRO2 with cerebral protective effects
? Lacks arrythmogenicity
Ideal IV anaesthetic drug- pharmacodynamics
? Minimal cardiorespiratory or motor side effects
? Rapid , predictable amd smooth onset
? Painless and non irritant
? Stable at room temperature
? No adrenal or immunosuppression
? Low potential of anaphylaxis
TIVA IN NEURO- The Introduction
an analgesic agent (typically an opioid) .
? Intravenous (IV) adjuvants such as ketamine, dexmedetomidine, or lidocaine may be used in
some patients to replace or minimize the total propofol or opioid doses
? Hence avoiding their side effects (eg, hypotension due to higher doses of propofol or
? Propofol is most commonly selected as the sedative-hypnotic component of a TIVA technique
? Owing to its rapid onset and recovery; beneficial antiemetic, bronchodilatory, and
? Propofol is infused at 75 to 150 mcg/kg/minute, with titration according to individual
requirements, the degree of noxious surgical stimulation, and coadministration of other
? An opioid is invariably employed as the analgesic component of a TIVA technique.
Advantages of TIVA
? Easily titratable
? Superior recovery profile
? Portable delivery systems( TCI)
? Lowered OT pollution
? Less PONV
? Preserves HPV.
? Improves V/Q mismatch
? Preserves cerebral autoregulation.
? In a 2016 meta-analysis of 4520 patients undergoing noncardiac surgery in
31 trials, intraoperative use of propofol-based TIVA was associated with
generally lower postoperative pain scores at rest and lower requirements for
supplemental opioid analgesia compared with any inhalation-based
Feasibility for neuromonitoring
? Most of the IV agents have less effect on evoked potentials than potent volatile inhalation
agents or N2O.
? In particular, motor-evoked potentials (MEPs) are very sensitive to inhalation agents, while
the effects of inhalation anesthetics.
? TIVA regimes help maintain the level of anesthesia during these critical monitoring periods in
Disadvantages of TIVA
? Blood concentrations of IV agents are not easily obtained ( Vs inhalationals )
? While technology such as target-controlled infusions (TCI) may allow the prediction of propofol
and opioid concentrations in either the plasma or at the effect site (ie, the brain)
However, these methods are not easily available in the developing world.
Edge of TIVA over Inhalational
? Superior recovery profile
? Portable delivery systems( TCI)
? Lowered OT pollution
? Less PONV
? Preserves HPV.
? Improves V/Q mismatch
? Preserves cerebral autoregulation
So , is TIVA superior to the gases?
? TIVA was widely used in neuro anaesthesia on the pretext that all the known
anesthetic gases altered cerebral haemodynamics at therapeutic
concentrations.
? With the advent of various studies suggesting that sevoflurane doesn't alter
cerebral haemodynamics significantly at therapeutic doses for anaesthesia
The resurgence of Sevoflurane
? Kaisiti et al studied via PET study that the cerebral blood flow increase by a Sevoflurane of
MAC 1.5 was comparable to the cerebral blood flow in patients receieving propofol in
healthy volunteers. Anesthesiology. 2002 Jun;96(6):1358-70
? Matta BF et al studied the vasodilatory effects of sevoflurane and Isoflurane.
artery at 0.5 and 1.5 MAC, the increase was significantly less during sevoflurane anesthesia.
Anesthesiology. 1999 Sep;91(3):677-80
intracranial pressure more and sevoflurane less than isoflurane in pigs subjected to intracranial
hypertension J Neurosurg Anesthesiol. 2004 Apr;16(2):136-4
`'Propofol-maintained and volatile-maintained anesthesia were associated with similar
brain relaxation scores, although mean ICP values were lower and CPP values higher with propofol
-maintained anesthesia. There are inadequate data to compare clinically significant outcomes
Can J Anesth/J Can Anesth (2014) 61:347?356
? G. Magni et al studied Emergence Time and Early Cognitive Function
Between Sevoflurane?Fentanyl and Propofol?Remifentanil in Patients
Undergoing Craniotomy for Supratentorial Intracranial Surgery and
concluded " there is no patient benefit of using total intravenous anesthesia with an ultra-
short-acting opioid over the conventional balanced volatile technique in terms of recovery and
cognitive functions."
J Neurosurg Anesthesiol 2005;17:134?138)
? Hence at this level in those patients with normal to mild raise in ICP , CBF
increase by sevoflurane at therapeutic levels may not be as pronounced and
clinically relevant as previously believed to be.
TIVA anaesthesia requirements
? Rapidly achieve an appropriate blood and brain concentration of the drug
? Maintain that concentration.
? Adjust the level as required ( clinically / or if using a neuromonitor )
? Can use manual or automated infusions.
Drug injected into Central compartment V1
? Initial volume of distribution
? Comparable to `plasma
Redistribution into second compartment (V2)
Redistribution into third compartment (V3)
? "vessel-poor" or "slow"
? Governed by rate constant / concentration gradient.
Exponential process
Elimination - Fixed rate
Achieveing a constant plasma level
? initial bolus = concentration desired x vol of distribution
? maintaining however can get tricky
? needs to match the rate of decline of plasma propofol level
? initially high rate de to a rapid redistribution
? ultimately just matches the elimination
Manual infusions
? Inaacurate regimes,
? No control over the exact amount of drug concentration at any level.
? a thorough understanding of the pharmacokinetics of the drugs being used is necessary
? risk of under- or over-dosage
Bristol regime
Target conc : 3mcg/ml
? But:
? Changes to infusion rate will not lead to changes in blood concentration for some time
? Size of bolus has to be `guestimated'
? May result in excessive side effects or awareness
? TCI systems automate the whole process
Target controlled infusions ( TCI)
? Target Controlled Infusions
? Computer driven infusions to achieve a preset plasma concentration
? Multi-compartment pharmacokinetic models used to calculate infusion rate required to
? "open-loop" systems
? Comprised of a user interface, a microprocessor and an infusion device
Alaris Asena? PK (Alaris
Base Primea (Fresenius)
Medical Systems
? Models have sizes and rate constants for the various compartments programmed which allows
the pump to calculate rate of Propofol redistribution and elimination at a given time
? Initial bolus given to achieve rapid rise in plasma level
? 3 superimposed infusion rates are present to match the rate at which drug is being removed
from the central compartment
? When one wants to increase the plasma level then pump will calculate and give a bolus
? When one wants to decrease the level then the pump will stop and allow the level to fall before
restarting
? The lag time between achieving a specific plasma concentration and observing a particular
clinical response.
? Mathematical or temporal relationship between the conc in the plasma and the clinical
response observed ? time taken to equilibrate is described as a rate constant (Keo)
Plasma vs Effect site
Targeting
? With plasma targeting there is a lag between achieving the plasma level and
the brain level catching up.
? Equilibrium between blood and effect-site depends on several factors:
? Rate of drug delivery to effect-site
? Pharmacological properties of the drug
? Mathematically described by Keo time constant
? Only factor we can control is the concentration gradient
Time to peak effect (TTPE)
the blood and effect-site concentration curves cross.
? Time delay between bolus and this point is known as the "time to peak effect"
TTPE
? Independent of size of bolus
? Propofol TTPE is 1.6 minutes
Just a representational image
? By knowing the Keo and TTPE it is possible to `target' the effect site
concentration
? Nomenclature of TCI:
Ce = Effect site concentration
Which to use ? Manual or TCI
? Cochrane review in 2008
Looked at results of 20 poor quality trials
No significant difference in quality of anaesthesia or adverse outcomes
? Hence,they Couldn't recommend one over the other
? Malgorzata Witkowska et al Compared the target controlled infusion and total intravenous
anaesthesia with propofol and remifentanil for lumbar microdiscectomy and concluded
`'There are no clinically important differences in haemodynamic variables, depth of
controlled and target-controlled infusion of propofol and remifentanil.''
Anaesthesiology Intensive Therapy 2012, vol. 44, no 3, 138?144
Propofol TCI Models : Marsh vs. Schnider
Marsh Model
? First Published in 1991
? Model employed in the original Diprifusor?
? Weight is the only limitation
? Age entered but has no effect on model
? Unless its an age of < 16 in which case pump wont run
? A `modified' Marsh model was published by Struys et al in 2000
? Model used in most of the modern TCI systems.
? Uses total body weight (TBW)
? Ideal Body Weight (IBW) best for induction
? But....
? Maintenance infusion rate is TBW
? Published in 1998 Based on 24 volunteers (11 women, 13 men)
? Uses age, height, weight, age and gender
? V1 fixed - 4.27 L
? V3 fixed - 238 L
? Elimination uses weight, height & LBM
? Uses a TTPE of 1.6 minutes and calculates a Keo for each individual patient
? User enters TBW and pump calculates LBM
? LBM = 1.1 x weight - 128 x (weight/height)2
? Accurate up to BMI of 42 in men and 37 in women - then get paradoxical decrease in LBM
1. Time To Peak Effect
? Schnider model has a faster TTPE (1.6 vs 4.5 min)
? Less `overshoot' and `undershoot' with Schnider effect-site targeting than
with Marsh
? Net effect is less Propofol administered with Schnider vs.Marsh in effect-site
? Probably safer in elderly and compromised patients
2. Size of central compartment
? Marsh is a function of weight (15.9 L for 70kg)
? Striking differences in estimated plasma and effect-site concentrations in
first 10 minutes after the bolus
? Marsh Cp = 4 mcg/ml Ce = 0.9 mcg/ml
? Schnider Cp= 8.2 mcg/ml Ce = 3.6 mcg/ml
? Differences less significant after 10 minutes
? After 30 minutes both estimate the same levels
3. Age
? Volume of central compartment reduces with increasing age
? Marsh model doesn't account for age
? Schnider does
Typical target concentrations in routine practice
drugs administered, and the expected magnitude of surgical stimulus.
? If a relatively rapid induction of anaesthesia is required, initial plasma (Marsh model) or effect
-site (Schnider model) propofol target concentrations of 4-6 g.ml-1 are typically used in
healthy young or middle-aged patients.
? During maintenance of anaesthesia, target concentrations of 3.0-6.0 g.ml-1 (without
opioids) or 2.5-4.0 g.ml-1 (with opioids) are typical
? Other TIVA models used in neurosurgery :
ii. TCI administration of sufentanil infusion in the Gepts model
iii. Older pharmacokinetic models for Dexmeditomidine (Dyck and Talke) were widely
Hannivoort has recently published a new combined PK model for DEX
Practical aspects of the safe TIVA conduct
over-dosing or other complications
? the two commonest causes of accidental awareness during TIVA were failure to
deliver the intended dose of drug and poor understanding of the underlying
pharmacological principles.
? Make sure the concentrations are correct ( 1% vs 2%)
? Syringes used for TIVA should have Luer-lock connectors to reduce the risk of accidental
disconnection.
? Mixing of drugs for infusion in same syringes to be discouraged.
? The infusion set through which TIVA is delivered should have a Luer-lock connector at each
end to reduce the risk of accidental disconnection
catheter lumen) an anti-reflux valve should be present to prevent backward flow of drug up
the infusion tubing.
deadspace in which a drug may accumulate rather than entering the vein
? The infusion line through which TIVA is delivered should have as few potential sites for
leakage as possible.
? A continuous line from syringe to cannula is ideal, without additional connections or three-
? Particular caution should be exercised if a cannula is inserted in a vein in the antecubital
fossa, where inadvertent subcutaneous administration may be difficult to detect
? Previous guidance has recommended that the i.v. cannula through which TIVA is delivered
should be `visible at all times' , although this has been modified in more recent publications
to specify `visible whenever practical'
? Whenever , its not possible to keep an eye at all times , anaesthetists should have a higher
index of suspicion for problems with the infusion and periodically inspect the cannula site, if
possible.
prevent failure due to battery depletion.
? Infusion pumps should only be programmed after a syringe containing the drug to be
infused has been placed in the pump
? Drug labels should be attached to syringes only when the intended drug is drawn-up.
? Propofol must be drawn up using precautions to reduce the risk of contamination.
? All vascular access devices used for TIVA should be flushed with at least twice the
deadspace volume of the device at the end of the procedure
? Use of an EEG monitor is recommended when TIVA is underway especially with manual
infusions.
? Efforts to prevent awareness should, mostly focus on patients who receive a neuromuscular
blocking drug.
who had received a neuromuscular blocking drug ( AAGBI 2017)
? Processed EEG monitoring should commence before administration of the neuromuscular
blocking drug
Dexmeditomidine in TIVA
? Its role during general anesthesia for neurosurgical procedures has been validated as an
adjunct to other agents to decrease the intraoperative opioid dose requirements
? Animal and human studies have shown that DEX causes a reduction in CBF and cerebral
avoid hazardous hypotension and a reduction in the cerebral autoregulation.
? Its role as an intravenous anesthetic agent has been studied as an adjunct to local anesthesia
during awake anesthesia
? Also an adjunct to TIVA techniques including remifentanil during which it decreased analgesic
? A possible disadvantage could be related to its prolonged sedative effect when used as an
adjunct to propofol although this has not been demonstrated in clinical studies.
? Also Look for post op hypertension , shivering , PONV.
Other applications of TIVA in neuroanesthesia
TIVA in Brain trauma
? IV anesthetics can be administered for maintenance of anesthesia as part of a balanced anesthetic that
includes inhalation agents, or as TIVA.
? Propofol infusion ? Propofol infusion causes reduction in CMR, CBF, CBV, and ICP , while CO2
responsiveness and autoregulation are maintained.
clinically irrelevant effects on cerebral physiology
regional cerebral ischemia or compromised flow metabolism coupling (eg, traumatic brain injury
[TBI], subarachnoid hemorrhage, intracranial lesions);
? Drummond JC et al studied Brain tissue oxygenation during dexmedetomidine administration in
surgical patients with neurovascular injuries and found that there was no significant reduction in
Electrophysiological monitorning and TIVA
? Electrophysiological monitoring is applied during cranial and spine surgery for monitoring
and for mapping
? EEGs are usually monitored during craniotomy for cerebral aneurysm clipping, during
procedures, and pharmacological depression of the brain for "cerebral protection.
? The use of TCI allows a constant level of anesthetic effect which can help to avoid
level from true physiologic/pathologic insults to the cortex.
? Inhalational agents and muscle relaxants, are confounders for motor evoked potential
(MEP) monitoring as they have deleterious effects on the amplitude of the waveform signal.
? (TIVA) with no intraoperative muscle relaxants following intubation has been suggested as
the preferred anaesthetic technique for these surgeries.
regimes have been recently established.
(Royan NP, Lu N, Manninen P, Venkatraghavan L. The influence of anaesthesia on intraoperative neuromonitoring changes in
high-risk spinal surgery. J Neuroanaesthesiol Crit Care 2017;4:159-66)
TIVA IN PEDIATRICS
comparison with their body weight.
? This difference gradually reduces from around 12 years of age, reaching adult values at 16
yr.
? Thus, to achieve a given plasma concentration, children require larger propofol bolus
? During prolonged infusions of propofol in children aged < 12 yr, drug accumulation in the
peripheral compartments occurs to a greater extent than in adults.
concentration to decline to a level at which consciousness is regained than in an adult
? Propofol requirements can be reduced, and speed of emergence improved, by remifentanil
(or other opioid) co-administration, and the use of other drugs such as nitrous oxide,
ketamine and 2 agonists.
? Most children regain consciousness at an estimated propofol plasma concentration of
approximately 2g.ml-1, but this can vary considerably from 1-3 g.ml-1 depending on
inter-individual differences and the use of adjunctive drugs
? The two widely available and validated paediatric models which target plasma propofol
concentration are Kataria [11] for ages 3-16 yr and Paedfusor [12] for ages 1-16 yr.
? Effect-site targeting has not been implemented in paediatric TCI systems
? For an average length procedure in a young child, both models administer approximately
50% more propofol than in an adult using the Marsh model, which is why adult models
should not be used in this age group
? Limited use so far due to the due to the original weight restrictions on target controlled infusion
? Modified schnider models have been advocated in children >5years.( ped anaesthesia 2010)
? Propofol use, at induction and as maintenance of anaesthesia, has been seen to reduce the risk of
of sevoflurane versus other general anaesthesia on emergence agitation in children. Cochrane Database Syst Rev 2014: CD007084)
? The incidence of PONV in children over 3 yr is double that of adults. Propofol reduces early PONV
oligodendrocytes in fetal and neonatal rhesus macaque brain. Br J Anaesth 2013; 110(Suppl. 1): i29?38 )
? Remifentanil infusion has been tried in children widely
? A remifentanil infusion commenced at the induction of anaesthesia can readily be titrated
to response and avoids the hypotension and bradycardia associated with boluses of
remifentanil in children.
( Krane EJ, Phillip BM, Yeh KK, Domino KB. Smith RM, Mototyama EK, Davis PJ. Anaesthesia for paediatric neurosurgery, Smith's Anaesthesia for
Infants and Children , 20067th EdnPhiladelphia Mosby(pg. 651-84)
? Remifentanil usually obviates the need for repeated doses of neuromuscular blocking
TIVA IN AWAKE SURGERIES
? Drugs commonly used for conscious sedation include propofol, midazolam, remifentanil,
? Any combination of these drugs may be administered as continuous infusions, bolus
injections, target controlled infusions, or patient controlled boluses
? Dexmedetomidine is increasingly used for awake craniotomy, with or without propofol,
midazolam, and/or opioids,
depression, and does not interfere with electrocorticography.
? The dose of dexmedetomidine infusion must be titrated carefully, since prolonged
administration can cause delayed reversal of sedation after the drug is discontinued
? However, a small study of patients who underwent conscious sedation for AC reported
receive propofol/remifentanil or dexmedetomidine, in addition to fentanyl ( Br J Anaesth.
2016;116(6):811. Epub 2016 Apr 20)
and fewer respiratory adverse events in the dexmedetomidine group.
Strategy of conscious sedation in awake Sxs
1.Administer midazolam 1 to 2 mg intravenous (IV), and fentanyl 25 to 50 mcg IV (no midazolam if
electrocorticography is planned).
by infusion dexmedetomidine 0.3 to 0.7 mcg/kg/hour, titrated to level of sedation. Add propofol infusion as
necessary (start at 25 mcg/kg/min, titrate to level of sedation (25 to 75 mcg/kg/min).
3.For skull pinning, administer propofol boluses until patient is unarousable with tactile stimulation
then places skull pins. Administer fentanyl 25 to 50 mcg IV if necessary to tolerate pinning.
4.When patient awakens, check that head, neck, and shoulders are comfortable, and readjust position if
necessary and as possible. The surgeon infiltrates the scalp with up to 40 mL of 0.25% bupivacaine with
5.Additional boluses of fentanyl 25 to 50 mcg IV, with or without propofol 10 to 20 mg IV may be
administered, or infusions increased, for pain as needed during skull pinning, scalp infiltration, or during
painful portions of surgery (eg, temporalis muscle dissection, dural opening or closure).
6. Stop propofol infusion after bone flap is removed, and wait for the patient to wake up for cortical
mapping. Stop or reduce dexmedetomidine infusion at the same time, depending on the depth of sedation.
For some patients, dexmedetomidine can be continued during mapping.
mapping.
8. During scalp closure, administer ondansetron 4 mg IV, discontinue propofol and dexmedetomidine
infusions, and administer fentanyl 25 mg IV, repeated as necessary for pain.
? For patients who require an asleep-awake-asleep technique, we prefer to use total intravenous
anesthesia (TIVA) with propofol and remifentanil, and to manage the airway with a laryngeal mask
? Asleep portion -
1.After pre-oxygenation, induce general anesthesia with propofol (2 to 2.5 mg/kg IV) and fentanyl
laryngeal mask airway (LMA).
2.Maintain anesthesia with TIVA using propofol (100 to 150 mcg/kg/min) and remifentanil (0.05 to
0.1 mcg/kg/min). Maintain spontaneous ventilation if possible; controlled ventilation may be required
? 3.After skull pinning, position the patient carefully, avoiding extreme neck rotation and/or
flexion, and ensuring access to the face for airway manipulation.
If there are concerns about the airway after the head fixation, before finalizing positioning,
remove the LMA, verify the ability to ventilate by mask with an oral airway in place, and that
Awake portion -- Call for assistance for awakening.
1. Assure spontaneous ventilation, then turn off propofol, reduce remifentanil to 0.03 to
0.05 mcg/kg/min, and administer 100 percent oxygen.
2.Warn the surgeon that the patient might cough, and gently suction the oropharynx.
3.Extubate or remove the supraglottic airway when awake.
during awake procedure.
Asleep portion -- Induce general anesthesia with propofol and fentanyl as before, and
reinsert the LMA. Maintain anesthesia with TIVA, as before, for the rest of the procedure.
IN CONCLUSION
? Currently, there are no consensus guidelines or recommendations
procedures
? However, its wiser to choose a balanced technique keeping in mind the
technique and above all the acquaintance and knowledge pertaining to the
said technique.-
? Haemodynamic stability
? ICP control
? Maintaining Cerebral perfusion
--- Content provided by FirstRanker.com ---
? Neuroprotection? Providing optimal conditions for surgery
? Smooth emergence
? Rapid awakening
Ideal anaesthetic agent for neuroanesthesia
--- Content provided by FirstRanker.com ---
? Maintains CBF without altering the autoregulation.
? Minimizes or if not doesn't itself causes an increase the ICP.
? Preserves reactivity of cererbral arterioles to PaCO2 changes.
? Decreases the CMRO2 with cerebral protective effects
--- Content provided by FirstRanker.com ---
? Lacks seizure causing potential? Lacks arrythmogenicity
Ideal IV anaesthetic drug- pharmacodynamics
--- Content provided by FirstRanker.com ---
? Wide therapeutic ratio? Minimal cardiorespiratory or motor side effects
? Rapid , predictable amd smooth onset
? Painless and non irritant
? Stable at room temperature
--- Content provided by FirstRanker.com ---
? Rapid recovery ( no rebound or emergence effects)? No adrenal or immunosuppression
? Low potential of anaphylaxis
TIVA IN NEURO- The Introduction
--- Content provided by FirstRanker.com ---
? Total intravenous anesthesia (TIVA) employs a sedative-hypnotic anesthetic combined withan analgesic agent (typically an opioid) .
? Intravenous (IV) adjuvants such as ketamine, dexmedetomidine, or lidocaine may be used in
--- Content provided by FirstRanker.com ---
some patients to replace or minimize the total propofol or opioid doses
? Hence avoiding their side effects (eg, hypotension due to higher doses of propofol or
--- Content provided by FirstRanker.com ---
postoperative nausea and vomiting [PONV] due to opioids).? Propofol is most commonly selected as the sedative-hypnotic component of a TIVA technique
? Owing to its rapid onset and recovery; beneficial antiemetic, bronchodilatory, and
--- Content provided by FirstRanker.com ---
anticonvulsant properties.? Propofol is infused at 75 to 150 mcg/kg/minute, with titration according to individual
requirements, the degree of noxious surgical stimulation, and coadministration of other
--- Content provided by FirstRanker.com ---
anesthetic agents.? An opioid is invariably employed as the analgesic component of a TIVA technique.
Advantages of TIVA
--- Content provided by FirstRanker.com ---
? Easily titratable
? Superior recovery profile
? Portable delivery systems( TCI)
? Lowered OT pollution
--- Content provided by FirstRanker.com ---
? Minimal risk of Malignant hyperthermia? Less PONV
? Preserves HPV.
? Improves V/Q mismatch
? Preserves cerebral autoregulation.
--- Content provided by FirstRanker.com ---
A propofol-based TIVA technique may contribute to postoperative analgesia? In a 2016 meta-analysis of 4520 patients undergoing noncardiac surgery in
31 trials, intraoperative use of propofol-based TIVA was associated with
--- Content provided by FirstRanker.com ---
generally lower postoperative pain scores at rest and lower requirements for
supplemental opioid analgesia compared with any inhalation-based
--- Content provided by FirstRanker.com ---
anesthesia with a potent volatile agentFeasibility for neuromonitoring
? Most of the IV agents have less effect on evoked potentials than potent volatile inhalation
--- Content provided by FirstRanker.com ---
agents or N2O.
? In particular, motor-evoked potentials (MEPs) are very sensitive to inhalation agents, while
--- Content provided by FirstRanker.com ---
somatosensory-evoked potentials (SSEPs) are moderately affected and BAEPs are resistant tothe effects of inhalation anesthetics.
? TIVA regimes help maintain the level of anesthesia during these critical monitoring periods in
--- Content provided by FirstRanker.com ---
order to avoid confounding the interpretation of changesDisadvantages of TIVA
? Blood concentrations of IV agents are not easily obtained ( Vs inhalationals )
? While technology such as target-controlled infusions (TCI) may allow the prediction of propofol
--- Content provided by FirstRanker.com ---
and opioid concentrations in either the plasma or at the effect site (ie, the brain)
However, these methods are not easily available in the developing world.
--- Content provided by FirstRanker.com ---
? Greater risk of intraoperative awareness.Edge of TIVA over Inhalational
? Superior recovery profile
--- Content provided by FirstRanker.com ---
? Portable delivery systems( TCI)
? Lowered OT pollution
--- Content provided by FirstRanker.com ---
? Minimal risk of Malignant hyperthermia? Less PONV
? Preserves HPV.
--- Content provided by FirstRanker.com ---
? Improves V/Q mismatch
? Preserves cerebral autoregulation
So , is TIVA superior to the gases?
--- Content provided by FirstRanker.com ---
? TIVA was widely used in neuro anaesthesia on the pretext that all the known
anesthetic gases altered cerebral haemodynamics at therapeutic
concentrations.
--- Content provided by FirstRanker.com ---
? With the advent of various studies suggesting that sevoflurane doesn't alter
cerebral haemodynamics significantly at therapeutic doses for anaesthesia
--- Content provided by FirstRanker.com ---
? Led to a role reversalThe resurgence of Sevoflurane
? Kaisiti et al studied via PET study that the cerebral blood flow increase by a Sevoflurane of
--- Content provided by FirstRanker.com ---
MAC 1.5 was comparable to the cerebral blood flow in patients receieving propofol in
healthy volunteers. Anesthesiology. 2002 Jun;96(6):1358-70
? Matta BF et al studied the vasodilatory effects of sevoflurane and Isoflurane.
--- Content provided by FirstRanker.com ---
? They found that although both agents increased blood flow velocity in the middle cerebralartery at 0.5 and 1.5 MAC, the increase was significantly less during sevoflurane anesthesia.
Anesthesiology. 1999 Sep;91(3):677-80
--- Content provided by FirstRanker.com ---
? Holmstorm A et al studied in animal models and concluded that Desflurane increasesintracranial pressure more and sevoflurane less than isoflurane in pigs subjected to intracranial
hypertension J Neurosurg Anesthesiol. 2004 Apr;16(2):136-4
--- Content provided by FirstRanker.com ---
? JASON CHUI et al in 2014 after metaanalysing 14 studies comprising 1819 patients concluded`'Propofol-maintained and volatile-maintained anesthesia were associated with similar
brain relaxation scores, although mean ICP values were lower and CPP values higher with propofol
-maintained anesthesia. There are inadequate data to compare clinically significant outcomes
--- Content provided by FirstRanker.com ---
such as neurological morbidity or mortality.''Can J Anesth/J Can Anesth (2014) 61:347?356
? G. Magni et al studied Emergence Time and Early Cognitive Function
--- Content provided by FirstRanker.com ---
Between Sevoflurane?Fentanyl and Propofol?Remifentanil in Patients
Undergoing Craniotomy for Supratentorial Intracranial Surgery and
concluded " there is no patient benefit of using total intravenous anesthesia with an ultra-
short-acting opioid over the conventional balanced volatile technique in terms of recovery and
--- Content provided by FirstRanker.com ---
cognitive functions."
J Neurosurg Anesthesiol 2005;17:134?138)
? Hence at this level in those patients with normal to mild raise in ICP , CBF
--- Content provided by FirstRanker.com ---
increase by sevoflurane at therapeutic levels may not be as pronounced and
clinically relevant as previously believed to be.
TIVA anaesthesia requirements
--- Content provided by FirstRanker.com ---
? Rapidly achieve an appropriate blood and brain concentration of the drug
? Maintain that concentration.
? Adjust the level as required ( clinically / or if using a neuromonitor )
? Can use manual or automated infusions.
--- Content provided by FirstRanker.com ---
Pharmacokinetic principlesDrug injected into Central compartment V1
? Initial volume of distribution
? Comparable to `plasma
Redistribution into second compartment (V2)
--- Content provided by FirstRanker.com ---
? "vessel-rich" or "fastRedistribution into third compartment (V3)
? "vessel-poor" or "slow"
? Governed by rate constant / concentration gradient.
--- Content provided by FirstRanker.com ---
Exponential process
Elimination - Fixed rate
Achieveing a constant plasma level
--- Content provided by FirstRanker.com ---
? initial bolus = concentration desired x vol of distribution
? maintaining however can get tricky
? needs to match the rate of decline of plasma propofol level
? initially high rate de to a rapid redistribution
--- Content provided by FirstRanker.com ---
? reduces overtime as V2 and V3 fill up? ultimately just matches the elimination
Manual infusions
? Inaacurate regimes,
--- Content provided by FirstRanker.com ---
? `shooting in the dark'? No control over the exact amount of drug concentration at any level.
? a thorough understanding of the pharmacokinetics of the drugs being used is necessary
? risk of under- or over-dosage
Bristol regime
--- Content provided by FirstRanker.com ---
Target conc : 3mcg/ml
? But:
? Changes to infusion rate will not lead to changes in blood concentration for some time
--- Content provided by FirstRanker.com ---
? Manual boluses have to be given to rapidly change depth? Size of bolus has to be `guestimated'
? May result in excessive side effects or awareness
? TCI systems automate the whole process
Target controlled infusions ( TCI)
--- Content provided by FirstRanker.com ---
? Target Controlled Infusions
? Computer driven infusions to achieve a preset plasma concentration
? Multi-compartment pharmacokinetic models used to calculate infusion rate required to
--- Content provided by FirstRanker.com ---
achieve the target concentration.? "open-loop" systems
? Comprised of a user interface, a microprocessor and an infusion device
Alaris Asena? PK (Alaris
--- Content provided by FirstRanker.com ---
Base Primea (Fresenius)
Medical Systems
--- Content provided by FirstRanker.com ---
How it works? Models have sizes and rate constants for the various compartments programmed which allows
the pump to calculate rate of Propofol redistribution and elimination at a given time
--- Content provided by FirstRanker.com ---
? Initial bolus given to achieve rapid rise in plasma level
? 3 superimposed infusion rates are present to match the rate at which drug is being removed
from the central compartment
--- Content provided by FirstRanker.com ---
? When one wants to increase the plasma level then pump will calculate and give a bolus
? When one wants to decrease the level then the pump will stop and allow the level to fall before
restarting
--- Content provided by FirstRanker.com ---
Effect site equilibration? The lag time between achieving a specific plasma concentration and observing a particular
clinical response.
--- Content provided by FirstRanker.com ---
? Mathematical or temporal relationship between the conc in the plasma and the clinical
response observed ? time taken to equilibrate is described as a rate constant (Keo)
--- Content provided by FirstRanker.com ---
? This Is different for each drug.Plasma vs Effect site
Targeting
--- Content provided by FirstRanker.com ---
? The clinical effect of Propofol is related to brain concentration = effect site? With plasma targeting there is a lag between achieving the plasma level and
the brain level catching up.
--- Content provided by FirstRanker.com ---
? Therefore the lag in induction and lag in changing depth of anaesthesia? Equilibrium between blood and effect-site depends on several factors:
? Rate of drug delivery to effect-site
--- Content provided by FirstRanker.com ---
? Pharmacological properties of the drug
? Mathematically described by Keo time constant
--- Content provided by FirstRanker.com ---
? Concentration gradient? Only factor we can control is the concentration gradient
Time to peak effect (TTPE)
--- Content provided by FirstRanker.com ---
? After a bolus, maximum effect-site concentration occurs at the point wherethe blood and effect-site concentration curves cross.
? Time delay between bolus and this point is known as the "time to peak effect"
--- Content provided by FirstRanker.com ---
TTPE
? Independent of size of bolus
? Propofol TTPE is 1.6 minutes
--- Content provided by FirstRanker.com ---
Just a representational image
? By knowing the Keo and TTPE it is possible to `target' the effect site
concentration
--- Content provided by FirstRanker.com ---
? Nomenclature of TCI:
Ce = Effect site concentration
--- Content provided by FirstRanker.com ---
Cp = Plasma concentrationWhich to use ? Manual or TCI
--- Content provided by FirstRanker.com ---
? Use TCI if its available !!!!!? Cochrane review in 2008
Looked at results of 20 poor quality trials
--- Content provided by FirstRanker.com ---
1759 patients patient pool were studiedNo significant difference in quality of anaesthesia or adverse outcomes
? Hence,they Couldn't recommend one over the other
--- Content provided by FirstRanker.com ---
? Malgorzata Witkowska et al Compared the target controlled infusion and total intravenous
anaesthesia with propofol and remifentanil for lumbar microdiscectomy and concluded
`'There are no clinically important differences in haemodynamic variables, depth of
--- Content provided by FirstRanker.com ---
anaesthesia, time to recovery and doses of propofol/remifentanil between manuallycontrolled and target-controlled infusion of propofol and remifentanil.''
Anaesthesiology Intensive Therapy 2012, vol. 44, no 3, 138?144
Propofol TCI Models : Marsh vs. Schnider
--- Content provided by FirstRanker.com ---
Marsh Model
? First Published in 1991
? Model employed in the original Diprifusor?
--- Content provided by FirstRanker.com ---
? Based on study of 3 groups of 6 patients? Weight is the only limitation
? Age entered but has no effect on model
? Unless its an age of < 16 in which case pump wont run
? A `modified' Marsh model was published by Struys et al in 2000
--- Content provided by FirstRanker.com ---
? Results in less overshoot and undershoot when using Marsh effect-site targeting? Model used in most of the modern TCI systems.
? Uses total body weight (TBW)
--- Content provided by FirstRanker.com ---
? Will tend to overdose in obesity? Ideal Body Weight (IBW) best for induction
? But....
? Maintenance infusion rate is TBW
--- Content provided by FirstRanker.com ---
Schnider Model? Published in 1998 Based on 24 volunteers (11 women, 13 men)
? Uses age, height, weight, age and gender
--- Content provided by FirstRanker.com ---
? V1 fixed - 4.27 L
? V3 fixed - 238 L
--- Content provided by FirstRanker.com ---
? V2 variable of age? Elimination uses weight, height & LBM
? Uses a TTPE of 1.6 minutes and calculates a Keo for each individual patient
--- Content provided by FirstRanker.com ---
? Uses lean body mass (LBM)? User enters TBW and pump calculates LBM
? LBM = 1.1 x weight - 128 x (weight/height)2
? Accurate up to BMI of 42 in men and 37 in women - then get paradoxical decrease in LBM
--- Content provided by FirstRanker.com ---
Marsh Vs Schnider1. Time To Peak Effect
? Schnider model has a faster TTPE (1.6 vs 4.5 min)
? Less `overshoot' and `undershoot' with Schnider effect-site targeting than
--- Content provided by FirstRanker.com ---
with Marsh
? Net effect is less Propofol administered with Schnider vs.Marsh in effect-site
--- Content provided by FirstRanker.com ---
targeting? Probably safer in elderly and compromised patients
2. Size of central compartment
--- Content provided by FirstRanker.com ---
? Schnider has fixed V1 (4.27 L)? Marsh is a function of weight (15.9 L for 70kg)
? Striking differences in estimated plasma and effect-site concentrations in
first 10 minutes after the bolus
--- Content provided by FirstRanker.com ---
? One minute after bolus:? Marsh Cp = 4 mcg/ml Ce = 0.9 mcg/ml
? Schnider Cp= 8.2 mcg/ml Ce = 3.6 mcg/ml
? Differences less significant after 10 minutes
? After 30 minutes both estimate the same levels
--- Content provided by FirstRanker.com ---
? Net effect is Schnider administers less Propofol3. Age
? Volume of central compartment reduces with increasing age
--- Content provided by FirstRanker.com ---
? It decreases by 50% from 25 to 75 years? Marsh model doesn't account for age
? Schnider does
Typical target concentrations in routine practice
--- Content provided by FirstRanker.com ---
? Target concentrations are individually determined based on patient characteristics, otherdrugs administered, and the expected magnitude of surgical stimulus.
? If a relatively rapid induction of anaesthesia is required, initial plasma (Marsh model) or effect
--- Content provided by FirstRanker.com ---
-site (Schnider model) propofol target concentrations of 4-6 g.ml-1 are typically used in
healthy young or middle-aged patients.
? During maintenance of anaesthesia, target concentrations of 3.0-6.0 g.ml-1 (without
--- Content provided by FirstRanker.com ---
opioids) or 2.5-4.0 g.ml-1 (with opioids) are typical
? Other TIVA models used in neurosurgery :
--- Content provided by FirstRanker.com ---
i. Remifentanil in neuroanesthesia with the Minto model,ii. TCI administration of sufentanil infusion in the Gepts model
iii. Older pharmacokinetic models for Dexmeditomidine (Dyck and Talke) were widely
--- Content provided by FirstRanker.com ---
used which tended to under predict the plasma concentration at higher concentrations.Hannivoort has recently published a new combined PK model for DEX
Practical aspects of the safe TIVA conduct
--- Content provided by FirstRanker.com ---
? Errors during TIVA can lead to failure to deliver the intended drug, under-dosing,over-dosing or other complications
? the two commonest causes of accidental awareness during TIVA were failure to
--- Content provided by FirstRanker.com ---
deliver the intended dose of drug and poor understanding of the underlying
pharmacological principles.
? Make sure the concentrations are correct ( 1% vs 2%)
--- Content provided by FirstRanker.com ---
? Familiarity with the equipment? Syringes used for TIVA should have Luer-lock connectors to reduce the risk of accidental
disconnection.
--- Content provided by FirstRanker.com ---
? Alarms to be enabled? Mixing of drugs for infusion in same syringes to be discouraged.
? The infusion set through which TIVA is delivered should have a Luer-lock connector at each
end to reduce the risk of accidental disconnection
--- Content provided by FirstRanker.com ---
? Where more than one infusion is given through a single i.v. cannula (or central venouscatheter lumen) an anti-reflux valve should be present to prevent backward flow of drug up
the infusion tubing.
--- Content provided by FirstRanker.com ---
? Drug and fluid lines should join together as close to the patient as possible to minimisedeadspace in which a drug may accumulate rather than entering the vein
? The infusion line through which TIVA is delivered should have as few potential sites for
--- Content provided by FirstRanker.com ---
leakage as possible.
? A continuous line from syringe to cannula is ideal, without additional connections or three-
--- Content provided by FirstRanker.com ---
way taps? Particular caution should be exercised if a cannula is inserted in a vein in the antecubital
fossa, where inadvertent subcutaneous administration may be difficult to detect
--- Content provided by FirstRanker.com ---
? Previous guidance has recommended that the i.v. cannula through which TIVA is delivered
should be `visible at all times' , although this has been modified in more recent publications
to specify `visible whenever practical'
--- Content provided by FirstRanker.com ---
? Whenever , its not possible to keep an eye at all times , anaesthetists should have a higher
index of suspicion for problems with the infusion and periodically inspect the cannula site, if
possible.
--- Content provided by FirstRanker.com ---
? Pumps must be charged before use and, where practical, mains-powered during use toprevent failure due to battery depletion.
? Infusion pumps should only be programmed after a syringe containing the drug to be
--- Content provided by FirstRanker.com ---
infused has been placed in the pump
? Drug labels should be attached to syringes only when the intended drug is drawn-up.
? Propofol must be drawn up using precautions to reduce the risk of contamination.
--- Content provided by FirstRanker.com ---
? Syringes should be prepared just shortly before use? All vascular access devices used for TIVA should be flushed with at least twice the
deadspace volume of the device at the end of the procedure
--- Content provided by FirstRanker.com ---
Monitoring in TIVA? Use of an EEG monitor is recommended when TIVA is underway especially with manual
infusions.
--- Content provided by FirstRanker.com ---
? Efforts to prevent awareness should, mostly focus on patients who receive a neuromuscular
blocking drug.
--- Content provided by FirstRanker.com ---
? large majority of cases of self-reported awareness that were identified occurred in patientswho had received a neuromuscular blocking drug ( AAGBI 2017)
? Processed EEG monitoring should commence before administration of the neuromuscular
--- Content provided by FirstRanker.com ---
blocking drug
Dexmeditomidine in TIVA
? Its role during general anesthesia for neurosurgical procedures has been validated as an
--- Content provided by FirstRanker.com ---
adjunct to other agents to decrease the intraoperative opioid dose requirements
? Animal and human studies have shown that DEX causes a reduction in CBF and cerebral
--- Content provided by FirstRanker.com ---
metabolism rate of oxygen (CMRO2) and suggest a careful control during its administration toavoid hazardous hypotension and a reduction in the cerebral autoregulation.
? Its role as an intravenous anesthetic agent has been studied as an adjunct to local anesthesia
--- Content provided by FirstRanker.com ---
during awake anesthesia
? Also an adjunct to TIVA techniques including remifentanil during which it decreased analgesic
--- Content provided by FirstRanker.com ---
requirements and improved hemodynamic stability.? A possible disadvantage could be related to its prolonged sedative effect when used as an
adjunct to propofol although this has not been demonstrated in clinical studies.
--- Content provided by FirstRanker.com ---
? Also Look for post op hypertension , shivering , PONV.
Other applications of TIVA in neuroanesthesia
TIVA in Brain trauma
--- Content provided by FirstRanker.com ---
? IV anesthetics can be administered for maintenance of anesthesia as part of a balanced anesthetic that
includes inhalation agents, or as TIVA.
--- Content provided by FirstRanker.com ---
? Most commonly, TIVA includes an infusion of propofol along with infusion of a short-acting opioid? Propofol infusion ? Propofol infusion causes reduction in CMR, CBF, CBV, and ICP , while CO2
responsiveness and autoregulation are maintained.
--- Content provided by FirstRanker.com ---
? Opioids ? When administered as part of IV anesthesia with controlled ventilation, opioids have minimal,clinically irrelevant effects on cerebral physiology
--- Content provided by FirstRanker.com ---
? The vasoconstrictive property of dexmedetomidine may be of concern in patients at risk forregional cerebral ischemia or compromised flow metabolism coupling (eg, traumatic brain injury
[TBI], subarachnoid hemorrhage, intracranial lesions);
--- Content provided by FirstRanker.com ---
? Data regarding Dexmed in TBI is very limited barring few animal studies? Drummond JC et al studied Brain tissue oxygenation during dexmedetomidine administration in
surgical patients with neurovascular injuries and found that there was no significant reduction in
--- Content provided by FirstRanker.com ---
CBF as postulated popularly. ( J Neurosurg Anesthesiol. 2010 Oct;22(4):336-41. )Electrophysiological monitorning and TIVA
? Electrophysiological monitoring is applied during cranial and spine surgery for monitoring
--- Content provided by FirstRanker.com ---
and for mapping
? EEGs are usually monitored during craniotomy for cerebral aneurysm clipping, during
--- Content provided by FirstRanker.com ---
carotid endarterectomy, cardiopulmonary bypass, extracranial?intracranial bypassprocedures, and pharmacological depression of the brain for "cerebral protection.
? The use of TCI allows a constant level of anesthetic effect which can help to avoid
--- Content provided by FirstRanker.com ---
misinterpretation of EEG depression caused by boluses or rapid changes in anestheticlevel from true physiologic/pathologic insults to the cortex.
? Inhalational agents and muscle relaxants, are confounders for motor evoked potential
(MEP) monitoring as they have deleterious effects on the amplitude of the waveform signal.
--- Content provided by FirstRanker.com ---
? (TIVA) with no intraoperative muscle relaxants following intubation has been suggested as
the preferred anaesthetic technique for these surgeries.
--- Content provided by FirstRanker.com ---
? However balanced anaesthetic technique with a low dose inhalational and an adjunct IVregimes have been recently established.
(Royan NP, Lu N, Manninen P, Venkatraghavan L. The influence of anaesthesia on intraoperative neuromonitoring changes in
--- Content provided by FirstRanker.com ---
high-risk spinal surgery. J Neuroanaesthesiol Crit Care 2017;4:159-66)
TIVA IN PEDIATRICS
--- Content provided by FirstRanker.com ---
? Compartment volumes in children are about twice the size of those in adults incomparison with their body weight.
? This difference gradually reduces from around 12 years of age, reaching adult values at 16
--- Content provided by FirstRanker.com ---
yr.
? Thus, to achieve a given plasma concentration, children require larger propofol bolus
--- Content provided by FirstRanker.com ---
doses and initial infusion rates relative to body weight than adults? During prolonged infusions of propofol in children aged < 12 yr, drug accumulation in the
peripheral compartments occurs to a greater extent than in adults.
--- Content provided by FirstRanker.com ---
? Therefore, when the infusion is stopped it typically takes longer in a child for the propofolconcentration to decline to a level at which consciousness is regained than in an adult
? Propofol requirements can be reduced, and speed of emergence improved, by remifentanil
--- Content provided by FirstRanker.com ---
(or other opioid) co-administration, and the use of other drugs such as nitrous oxide,
ketamine and 2 agonists.
? Most children regain consciousness at an estimated propofol plasma concentration of
--- Content provided by FirstRanker.com ---
approximately 2g.ml-1, but this can vary considerably from 1-3 g.ml-1 depending on
inter-individual differences and the use of adjunctive drugs
? The two widely available and validated paediatric models which target plasma propofol
--- Content provided by FirstRanker.com ---
concentration are Kataria [11] for ages 3-16 yr and Paedfusor [12] for ages 1-16 yr.
? Effect-site targeting has not been implemented in paediatric TCI systems
? For an average length procedure in a young child, both models administer approximately
--- Content provided by FirstRanker.com ---
50% more propofol than in an adult using the Marsh model, which is why adult models
should not be used in this age group
? Limited use so far due to the due to the original weight restrictions on target controlled infusion
--- Content provided by FirstRanker.com ---
devices? Modified schnider models have been advocated in children >5years.( ped anaesthesia 2010)
? Propofol use, at induction and as maintenance of anaesthesia, has been seen to reduce the risk of
--- Content provided by FirstRanker.com ---
Emergence Delirium in comparison with sevoflurane anaesthesia. Costi D , Cyna AM, Ahmed Set al. . Effectsof sevoflurane versus other general anaesthesia on emergence agitation in children. Cochrane Database Syst Rev 2014: CD007084)
? The incidence of PONV in children over 3 yr is double that of adults. Propofol reduces early PONV
--- Content provided by FirstRanker.com ---
significantly. (Creeley C , Dikranian K, Dissen G, Martin L, Olney J, Brambrink A. Propofol-induced apoptosis of neurones andoligodendrocytes in fetal and neonatal rhesus macaque brain. Br J Anaesth 2013; 110(Suppl. 1): i29?38 )
? Remifentanil infusion has been tried in children widely
? A remifentanil infusion commenced at the induction of anaesthesia can readily be titrated
--- Content provided by FirstRanker.com ---
to response and avoids the hypotension and bradycardia associated with boluses of
remifentanil in children.
( Krane EJ, Phillip BM, Yeh KK, Domino KB. Smith RM, Mototyama EK, Davis PJ. Anaesthesia for paediatric neurosurgery, Smith's Anaesthesia for
--- Content provided by FirstRanker.com ---
Infants and Children , 20067th EdnPhiladelphia Mosby(pg. 651-84)
? Remifentanil usually obviates the need for repeated doses of neuromuscular blocking
--- Content provided by FirstRanker.com ---
agents significantly in childrenTIVA IN AWAKE SURGERIES
? Drugs commonly used for conscious sedation include propofol, midazolam, remifentanil,
--- Content provided by FirstRanker.com ---
fentanyl, and dexmedetomidine .? Any combination of these drugs may be administered as continuous infusions, bolus
injections, target controlled infusions, or patient controlled boluses
--- Content provided by FirstRanker.com ---
? Dexmedetomidine is increasingly used for awake craniotomy, with or without propofol,
midazolam, and/or opioids,
--- Content provided by FirstRanker.com ---
? the primary benefits of dexmedetomidine for AC are that it does not cause respiratorydepression, and does not interfere with electrocorticography.
? The dose of dexmedetomidine infusion must be titrated carefully, since prolonged
--- Content provided by FirstRanker.com ---
administration can cause delayed reversal of sedation after the drug is discontinued
? However, a small study of patients who underwent conscious sedation for AC reported
--- Content provided by FirstRanker.com ---
similar efficacy of sedation and quality of brain mapping in patients randomly assigned toreceive propofol/remifentanil or dexmedetomidine, in addition to fentanyl ( Br J Anaesth.
2016;116(6):811. Epub 2016 Apr 20)
--- Content provided by FirstRanker.com ---
? Arousal time after discontinuation of the study drug was also similar (five to eight minutes)and fewer respiratory adverse events in the dexmedetomidine group.
Strategy of conscious sedation in awake Sxs
--- Content provided by FirstRanker.com ---
? Administer sedation with a combination of dexmedetomidine with propofol, as follows1.Administer midazolam 1 to 2 mg intravenous (IV), and fentanyl 25 to 50 mcg IV (no midazolam if
electrocorticography is planned).
--- Content provided by FirstRanker.com ---
2.Administer loading dose of dexmedetomidine 1 mcg/kg IV, dose adjusted for patient factors, followedby infusion dexmedetomidine 0.3 to 0.7 mcg/kg/hour, titrated to level of sedation. Add propofol infusion as
necessary (start at 25 mcg/kg/min, titrate to level of sedation (25 to 75 mcg/kg/min).
3.For skull pinning, administer propofol boluses until patient is unarousable with tactile stimulation
--- Content provided by FirstRanker.com ---
(propofol 10 mg IV boluses, total usually 30 to 40 mg IV). Surgeon infiltrates pin sites with 1 or 2% lidocaine,then places skull pins. Administer fentanyl 25 to 50 mcg IV if necessary to tolerate pinning.
4.When patient awakens, check that head, neck, and shoulders are comfortable, and readjust position if
necessary and as possible. The surgeon infiltrates the scalp with up to 40 mL of 0.25% bupivacaine with
--- Content provided by FirstRanker.com ---
epinephrine 1:200,0005.Additional boluses of fentanyl 25 to 50 mcg IV, with or without propofol 10 to 20 mg IV may be
administered, or infusions increased, for pain as needed during skull pinning, scalp infiltration, or during
painful portions of surgery (eg, temporalis muscle dissection, dural opening or closure).
--- Content provided by FirstRanker.com ---
6. Stop propofol infusion after bone flap is removed, and wait for the patient to wake up for cortical
mapping. Stop or reduce dexmedetomidine infusion at the same time, depending on the depth of sedation.
For some patients, dexmedetomidine can be continued during mapping.
--- Content provided by FirstRanker.com ---
7. Restart sedation after mapping, with propofol bolus 10 to 20 mg IV, followed by infusion as beforemapping.
8. During scalp closure, administer ondansetron 4 mg IV, discontinue propofol and dexmedetomidine
infusions, and administer fentanyl 25 mg IV, repeated as necessary for pain.
--- Content provided by FirstRanker.com ---
Strategy for asleep-awake-asleep technique? For patients who require an asleep-awake-asleep technique, we prefer to use total intravenous
anesthesia (TIVA) with propofol and remifentanil, and to manage the airway with a laryngeal mask
--- Content provided by FirstRanker.com ---
airway, as follows:? Asleep portion -
1.After pre-oxygenation, induce general anesthesia with propofol (2 to 2.5 mg/kg IV) and fentanyl
--- Content provided by FirstRanker.com ---
(0.5 to 1 mcg/kg IV). Test and note the degree of difficulty with mask ventilation before inserting alaryngeal mask airway (LMA).
2.Maintain anesthesia with TIVA using propofol (100 to 150 mcg/kg/min) and remifentanil (0.05 to
0.1 mcg/kg/min). Maintain spontaneous ventilation if possible; controlled ventilation may be required
--- Content provided by FirstRanker.com ---
to reduce PaCO2 for brain relaxation.? 3.After skull pinning, position the patient carefully, avoiding extreme neck rotation and/or
--- Content provided by FirstRanker.com ---
flexion, and ensuring access to the face for airway manipulation.
If there are concerns about the airway after the head fixation, before finalizing positioning,
remove the LMA, verify the ability to ventilate by mask with an oral airway in place, and that
--- Content provided by FirstRanker.com ---
the LMA can be reinserted easily. If necessary, adjust the head position.Awake portion -- Call for assistance for awakening.
1. Assure spontaneous ventilation, then turn off propofol, reduce remifentanil to 0.03 to
0.05 mcg/kg/min, and administer 100 percent oxygen.
--- Content provided by FirstRanker.com ---
2.Warn the surgeon that the patient might cough, and gently suction the oropharynx.
3.Extubate or remove the supraglottic airway when awake.
--- Content provided by FirstRanker.com ---
4.If necessary, continue remifentanil infusion (0.03 to 0.05 mcg/kg/min) for analgesiaduring awake procedure.
Asleep portion -- Induce general anesthesia with propofol and fentanyl as before, and
reinsert the LMA. Maintain anesthesia with TIVA, as before, for the rest of the procedure.
--- Content provided by FirstRanker.com ---
IN CONCLUSION
? Currently, there are no consensus guidelines or recommendations
--- Content provided by FirstRanker.com ---
suggesting any one as the best anesthesia technique for neurosurgicalprocedures
? However, its wiser to choose a balanced technique keeping in mind the
--- Content provided by FirstRanker.com ---
nature of surgery , condition of the patient , risks and benefit for choosing atechnique and above all the acquaintance and knowledge pertaining to the
said technique.-
--- Content provided by FirstRanker.com ---