Anesthesia

What are the four goals of anesthesia?

1. amnesia (decreased memory)

2. Induction (Hypnosis)

3. Analgesia (block pain)

4. Paralysis (muscle relaxation)

Anxiolytic

Reduce anxiety

What is a bolus of anesthetic agent called?

A loading dose

NSAIDs

Non-steroidal anti-inflammatory drugs

- over the counter drugs

Narcotics (opiods)

- non-synthetic opiate narcotics such as morphine

- synthetic opiate narcotics such as Fentanyl, Sufentanil and Alfentanil

Common narcotics in the OR

- Morphine: Post op

- Fentanyl: Sublimaze

- Alfentanil: Alfenta

- Sufentanil: Sufenta

- Remifentanil: Ultiva

- Demerol: Meperidine

Fentanyl

Sublimaze

Alfentanil

Alfenta

Sufentanyl

Sufenta

Demerol

Meperidine

Remifentanyl (remi)

Ultiva

How do narcotics affect EPs?

They have no to minimal affect on them

What are the inhalant induction agents?

Isoflurane (Forane)

Desflurane (Suprane)

Sevoflurane (Altane)

Nitrous Oxide

What are the injectable induction agents?

Propofol (non barb sedative)

Thiopental (barbiturate)

Pentathal (barbituate)

Barbituates are what?

Injectable Induction agents

What are common barbituates used?

Thiopental

Brevatol Methohexital

Phenobarbital

Pentobarbital

* end in -al *

What are common non-barbituate induction agents?

- Propofol (Diprivan)

- Ketamine

- Etomidate (Amidate)

Ketamine

Ketalar

How does Etomidate (Amidate) affect IOM?

Increases amplitude in SSEP, MEP and enhances EEG

Which induction agent has analgesic properties?

Ketamine

What affect do barbituates have on EPs?

No affect

What affect do barbituates and benzo's have on EEG?

Barbs and Benzo's cause BETA.

What affect do non-barbituates have on EPs?

- Ketamine and Etominate cause an increase in cortical amplitudes in SSEPs

- Bolus of Propofol causes a decrease in amplitude and increase in latency

What are common benzodiazepines?

- Midazolam: Versed

- Diazepam: Valium

- Lorazepam: Ativan

- Midazolam

* end in -am *

What do benzodiazepines do?

drugs that lower anxiety and reduce stress

What are other names for inhalation gases?

- Halogenated Gases

- Volatile Agents

What are amnesia inducing drugs

- Inhalants agents: N2O, SEVO, DES, ISO

- IV anesthesia: Ketamine and Etomindate

MAC

Minimal Alveolar Concentration

1.0 MAC

Relative value of gas related to ability to keep 50% of patients asleep when given painful stimulus: spinal cord reflex

-Despite different chemical properties, 1 MAC of gas is physiologically equivalent in each agent

-Increase MAC: youth, hyperthermia, ETOH/drug abuse - Decrease MAC: age, hypothermia, pregnancy, anemia, drunk/high

pungency

Irritation of lungs

What does inhalation gases effect?

synapses

Gases effect on SSEP responses:

- Peripheral nerve/spinal cord: 0 synapses= no effects from anesthesia

- Subcortical: 2-3 synapses= minimal effects from anesthesia

- Cortical: Million of Synapses= profound effects from anesthetics

Gases effect on brainstem responses:

- Early subcortical waves I-III= minimal effects from anesthesia

- Later cortical waves III-V= more than minimal effects from anesthesia

Gases effect on MEPs:

- Direct D-wave: 0 synapses= no effects from anesthesia - Indirect I-wave: Multiple cortical synapses= profound effects from anesthetics

- Spinal Cord Gray Matter: Multiple synapses= profound effects from anesthetics

- More proximal muscles have more synapses

- Anterior horn of spinal cord out to peripheral muscle: relies on I waves and other secondary tracts to produce muscle response, all of which inhibited by anesthesia= profound effects from anesthetics

End Tidal (ET)

The amount of anesthetic agent exhaled, thus present in the patient's circulation

Inhaled Tidal (IT)

The % of gas going into the lungs

What factors decrease the sensitivity or effectiveness of a MAC of agent, thus requiring a higher concentration of % ET to achieve the same sedative effects?

- Extremely young population

- Extremely old population

- Hypothermia

- Pregnacy

What factors increase the sensitivity or effectiveness of a MAC of agent, thus requiring a lower concentration of % ET to achieve the same sedative effects?

Hyperthermia

1 MAC Isoflurane (flurane)

1.2%

1 MAC Sevoflurane (altane)

2.2%

1 MAC Desflurane (suprane)

6.0%

1 MAC N2O

106%

Which inhalation agent has thee fastest onset and recovery?

Isoflurane

Which inhalation agent has the slowest onset and recovery?

Desflurane

What percentage is Nitrous typically given?

Less than 70%

What wave is most sensitive to inhalation agents?

P100 of VEPs

When do cortical SSEPs disappear?

- 1 MAC w/o Nitrous

- 1/2 MAC w/ Nitrous

When do inhilation agens (-anes) have muscle relaxant properties?

At high MAC

At what MAC of DES will there be a marked decrease in CMAP to spinal stimulation?

1.5 Mac

How does Nitrous affect SSEPs?

decreased waveform amplitude and increases latency of cortical responses

How do depolarizing muscle relaxants work?

Block at post synaptic junction membrane

- Succ

Most common depolarizing paralytic?

Succinylcholine (Anectine)

How do non-depolarizing muscle relaxants work?

Block depolarizing action of acetylcholine at the neuromuscular junction

Common non-depolarizing Paralytics

- Vecuronium (Norcuron)

- Rocuronium (Zemuron)

- Atracuronium (Cisatracurium)

- Pancuronium (Pavulon)

* end in -ium* -iums make me screa-um when i'm doing EMG-um and MEPs and CN too

Short acting paralytics

- Succinylcholine (Anectine) 10 minutes

- Mivacurium (Mivacron)

Intermediate paralytics

- Atracurium (Tracrium)

- Cisatracurium (Nimbex) 45 minutes

- Vecuronium (Norcuron) 33 minutes

- Rocuronium (Zemuron) 33 minutes

Long lasting paralytics

- Turbocurarine (Curare)

- Pancuronium (Pavulon) 60 minutes

- Pipercuronium (Arduran)

What percentage of muscle is still paralyzed if you have 0/4 twitches?

98 - 99%

What percentage of muscle is still paralyzed if you have 1/4 twitches?

95%

What percentage of muscle is still paralyzed if you have 2/4 twitches?

85%

What percentage of muscle is still paralyzed if you have 3/4 twitches?

75%

What percentage of muscle is still paralyzed if you have 4/4 twitches?

0%

Where should TOF stimulation be performed for complex spine surgeries?

Leg or arm

What is the minimum requirement of twitches for EMG and MEPs?

3/4 twitches

Vasodialator

Decreases bleeding in the operative field by decreasing the blood pressure

Neostigmine (Prostigmin)

Used together with atropine to end the effects of neuromuscular blocking medication of the non-depolarizing type

What are the four stages of anesthesia?

1. Depression - Cerebral cortex is inhibited and onset of analgesia / lack of consciousness

2. Excitement - increased BP, HR and respiratio. Cardiac arrhythmia is possible

3. Surgical - CNS depression, cardiovascular and respiratory functions return to normal, no muscle contractions

4. The overdose of anesthesia leading to medullary paralysis. The cardiovascular and respiratory centers are inhibited leading to death

What is the Stagnara test?

Wake up test - Anesthesia wakes patient just enough to follow directions and then put them back to sleep

What type of physiological changes would affect data?

- Blood pressure - significant MEP changes when MAP is below 60mmHg

- Temperature - significant SSEP changes below 25C, BAERs disappear below 30C, EEG isoelectric at or below 25C

- CO2 - changes in cortical SSEPs when low

- Intracranial Pressure (IP) - increased IP lead to regional ischemia, increased latency and decreased amplitude in EPs

Propofol is also called what?

Diprivan or milk of amnesia

How can propofol affect data?

Attenuates cortical SSEPs and MEPs, but to a lesser degree than N2O

- Propofol is preferred to gas for IOM

How can a paralytic (NMB) help facilitate SSEP monitoring?

It decreases muscle artifact

How do you differentiate between systemic and local manipulation effects during surgery?

record IONM data from surgically unaffected structures as a control such as during a thoracic surgery systemic effects would affect UE & LE whereas local manipulation would alter only LE

TIVA

total intravenous anesthesia

What agents are used when running TIVA?

- Propofol (Dipravan)

- Ketamine

- Etomidate (Amidate)

What affects does TIVA (Ketamine & Etomidate) have on SEP cortical waveforms?

improves the amplitude 5-10 fold

How do anesthetic agents affect the brain stem?

The brain stem is NOT affected by medication

How do narcotics/opiods affect SSEP data?

Causes a slight increase in cortical latency

How do narcotics/opiods affect EEG data?

May cause burst suppression when given at a high dose

Intraoperative neurophysiologic monitoring replaced which test in the OR?

The wake up test

Succinylcholine inhibits the transfer of what?

acetylcholine

Which tract is not affected by Succinylcholine?

Spinal Thalamic Tract

Which obligate peak is most affected by Ketamine or Etomidate?

P37

Which anesthetic agents may precipitate electrical seizure activity?

- Breuatal

- Etomidate

- Enflurane

- Ketamine

What is the longest acting muscle relaxant?

Panatronium

What is a normal adult heart rate?

60-100 BPM

What is a normal childrens heart rate?

70 - 100 BPM

At what systolic pressure with your responses become attenuated?

120

What is a normal blood pressure?

Systolic 90-120 mm/Hg

Diastolic 60-80 mm/Hg

What is a normal core temperature?

36.5 to 27.2 C

At what temperatue is N20 lost?

about 15-26 C

At what temperature is P14 lost?

12-20 C

Hypothermia

Anything under 36.5C

What anesthetic agents effect IOM from greatest to least?

○ Gas

■ Propofol

● Barbiturate

○ Benzodiazepine

■ Narcotic

Antimuscarinics (Anticholinergics):

Control Vagal Refluxes

What anesthetic can cause generalized seizure activity?

Enflurane

What is the effect on SSEP's of 50ug/kg Fentanyl?

Decreased latency and increased amplitude

A significant reduction in amplitude of ABR wave V can result from what?

Intravenous lidocaine

What is the best anesthetic protocol to use for median nerve SSEP monitoring?

Midazolam infusion

What anesthetics affect facial nerve EMG monitoring the most?

muscle relaxants