Egar Video #15 : Clinical Application of Inhaled Anesthetics

Question 1

What are the 3 C’s that make inhaled anesthetics the mainstay in the practice of anesthesia?

Answer 1

-They supply “CONTROL”
-Supply a “COMPLETE package”
-and are relatively “low COST”

Question 2

What are the 3 primary anesthetics that we deal with?

Answer 2

Sevoflurane
Isoflurane
Desflurane

Question 3

What does CONTROL in the 3 C’s of inhaled anesthetics refer to?

Answer 3

It refers to the better control of inhaled anesthetics during maintenance of anesthesia
-Ex: Study comparing Propofol vs Desflurane
Only 5% of anesthetized by Des moved, 40% anesthetized by Prop moved

Question 4

What does the “COMPLETE package” in the 3 C’s of inhaled anesthetics refer to?

Answer 4

It provides immobility, amnesia, relaxation, suppression of autonomic reflexes, and (“although imperfect) supplies an element of analgesia

Question 5

What does COST in the 3 C’s of inhaled anesthetics refer to?

Answer 5

Inhaled anesthetics are “relatively LOW cost” 🤑

Question 6

What are the advantages of Sevo?

Answer 6

~Non-pungent
~Low solubility
~Minimal cardiovascular stimulation (No arrhythmogenic effects)
~Minimal effects on ozone layer (No chlorine)

Question 7

What are the disadvantages of Sevo?

Answer 7

~Not the least soluble
~Agitation during recovery
~High acquisition cost
~Greatest degradation

Question 8

Advantages of Isoflurane?

Answer 8

~Low cost (the CHEAPEST gas)
~Limited cardiovascular stimulation
~Intermediate resistance to degradation
(Both resistant to degradation by metabolism and absorbent)

Question 9

Disadvantages of Isoflurane?

Answer 9

~Highest solubility
~Intermediate pungency
~Degradation by dry absorbents (turns to carbon monoxide)
~Minor effect on ozone layer (d/t Cl atom)

Question 10

Advantages of Des?

Answer 10

~Least soluble
~Fastest recovery of all functions
~Greatest resistance to degradation (least degraded)
~Used @ low inflow rates
~Minimal effect on ozone layer (No Cl)

Question 11

Disadvantages of Des?

Answer 11

~Pungent at concentrations >MAC
~Produces CV stimulation at >MAC
~High acquisition cost
~Degradation to dry absorbent (turns to carbon monoxide)
~Agitation during recovery (particularly in young patients)

Question 12

General considerations when anesthetizing a 3 yo pt?

Answer 12

~MAC is higher (concentration must be higher)
~Neonates metabolism may be altered d/t reduced hepatic enzymes and hepatic shunts that increase DUA with drugs *not an issue w/ 3yo)
~Apprehension/separation anxiety (pre medicate w/ anxiolytic)

Question 13

What was the proposed anesthetic plan for a 3 yo?

Answer 13

“Inhalation technique”:
-premedicate with 0.5 mg/kg of midazolam
-8% Sevo w/ 6L of nitrous and 3L oxygen
-once child is asleep THEN place IV and intubate (no IV placed prior d/t child resistance and having to hold child down for IV considered “barbaric”
-NO halothane d/t bradycardia in children

Question 14

Why use Sevoflurane rather than halothane? What are the disadvantages of Sevo?

Answer 14

~ Quicker induction-recovery
~Smoother
~Less PONV
~Safer (better for bp, hr, and decreased hepatotoxicity)

BUT it is more expensive, and can have post-op agitation

Question 15

How to avoid post-op agitation in a 3 yo?

Answer 15

~Administer opioid (Morphine d/t longer effects, but slower peak OR Fentanyl prior to emergence)

Question 16

What are the concerns administering inhaled anesthetics to the elderly?

Answer 16

~They have more comorbidities so more of their drugs affect our anesthetic technique
~ they’re sensitive to depressants/anesthesia: opioids, benzos – need to decrease dose
~they awaken confused (use anesthetics that don’t linger AKA use the poorly soluble anesthetics)

Question 17

Does minutes to PACU increase or decrease when administering a standard 2mg of Midazolam to an elderly pt?

Answer 17

INCREASES *w/ elderly pts

Question 18

How does administering a standard 2mg in elderly pts affect their saturations post-operatively?

Answer 18

Based on the research: desaturations less than 94% increases significantly from 50% to close to 85%

Question 19

How will the duration of the anesthesia influence the choice of anesthetic?

Answer 19

If the case is longer, the choose a less soluble agent so they patient will awaken faster (a poorly soluble agent)

Question 20

Recovery is ___ rapid with less soluble anesthetic and __ influenced by the duration of anesthesia

Answer 20

-more rapid;
-less influenced

Question 21

Desflurane takes __ time to recover than from Sevo

Answer 21

Less time

Question 22

Obese Patient Disadvantages:

Answer 22

-Large fat stores (both depo fat and fat adjacent to highly perfused tissue).
-Enzyme induction (caution w/ highly metabolized anesthetics; can lead to toxicitiy)
-Decreased respiratory reserve (↓ FRC & chest wall compliance)
-limited mobility (difficult transfers)

Question 23

What did the study on Post op movement to gurney of 130Kg patients show?

Answer 23

Those given the less soluble anesthetic had a greater ability to move from the operating table to the gurney (Des)

Question 24

In an obese patient, referring to their decreased FRC -> ensure what two things to prevent desaturation

Answer 24

-At induction, make sure the lungs are full of 02 and that
-you have the capability of applying Positive pressure

Question 25

Renal and Hepatic Failure concerns?

Answer 25

-prolongation of effects using fixed drugs (so opioids +/- in addition to inhalation) *choose inhaled agents instead
-Choose poorly soluble anesthetics which esp important with muscle relaxants (a poorly soluble agent will help better w/ muscle relaxation and be safer)
-Decreased capacity to metabolize/eliminate drugs

Question 26

What are difficult airway concerns w/ fixed cervical spine and inability to open mouth widely?

Answer 26

-examine pt ROM/Mallampati
-Possible awake fiberoptic intubation or laryngoscopy
-Use a poorly soluble agent to allow the patient to return back to spontaneous ventilation in case its difficult and you cannot get an airway

Question 27

What are steps to induce a difficult airway w/ decreased ROM? (video reference 26:45)

Answer 27

-Induce w/ nitrous and Sevo
-When pt sleeps; turn Sevo down, bolus Remi (Remi allows us to decrease Sevo)
*Benefit: if a problem occurs then can turn Remi off or stop bolus, and the pt wakes up
-Gradually take over hand ventilating pt (Maintain pts spontaneous RR’s and transition to trial ventilating for the pt)
-Administer paralytic (if pt is ventilating easily)
*Benefit: By administering paralytic, Sevo can be reduced
-Intubate w/ fiber optic

Overall: This method allows us to avoid having to do an awake intubation

Question 28

If proceeding with inhaled difficult airway technique and pt has laryngospasm?

Answer 28

-Use Positive pressure ventilation and Administer paralytic earlier

Question 29

What are the downsides to awake fiberoptic intubation? What can you do to make it more tolerable?

Answer 29

It is uncomfortable, and distressing - can administer Benzos and Opioids

Question 30

What are the issues r/t airway and Thoracic Surgery Problems:

Answer 30

-Have a compromised airway
-Competing with the surgeon for airway access
-Thoracic surgery may deflate the lungs, so concerned with ventilation/perfusion abnormalities.
-Need to sustain the airway until patient is awake -> use poorly soluble agents (des or sevo)

Question 31

What are the issues r/t Ear, Nose, and Throat Surgery Problems:

Answer 31

-Competition for the airway
-Need to awaken the patient quickly bc the ETT is in place to ensure airway is patent until end of anesthesia
-Less soluble agents are favored (des and sevo)

Question 32

What are the issues r/t to Eye surgery?

Answer 32

-Older pts esp can have bradycardia from oculocardiac reflex
*Oculocardiac reflex:
-can treat w/ atropine (0.4 mg of can lead to paradoxical reflex leading to worsening bradycardia
-give longer acting antimuscarinics
-ask surgeon to stop for a bit
-can do a block but risk also precipitating the reflex more
-If pt bucks on tube, can⬆IOP (extubate deeper to reduce this)
-“Bubble in the Eye”: Do not use Nitrous in the EYE cases -> increases pressure in air filled cavities and decreases blood flow to the eye

Question 33

What are the issues r/t Heart Surgery problems?

Answer 33

-Compromised blood flow to the heart.
-Effects of potent inhaled agents on the heart as protective agents (iso, des, and sevo)
-W/ open heart surgery (coronary heart surgery) where we rely heavy on opioids is the need to provide amnesia -> chose an anesthetic other than N2O that will give us good amnesia

Question 34

Concerns r/t Neurosurgery?

Answer 34

Expansion of the brain:
-give mannitol
-Use Iso since it produces less change in CBF
-Hyperventilate the pt to decrease CO2 which decrease BF
-Keep anesthetic lower at 1 MAC or 3/4 MAC (give w/ opioids instead of Nitrous to help decrease MAC)

Question 35

For neuro, once procedure is over the surgeon usually wants to assess LOC - because of this it is important to use which kind of agent?

Answer 35

-Less soluble agents

Question 36

Seizure activity is another concern post neuro surgery - what anesthetics would be concerning to use?

Answer 36

Enflurane and Sevoflurane (avoid these agents)

Question 37

Orthopedic surgery concerns:

Answer 37

Blood loss and ways to manage:
-Can do Induced hypotension esp in spine, or hip surgery
-Can give regional anesthesia with inhaled anesthetic (choose poorly soluble agent)