14 - General Anesthesia

Question 1

Airway management

Answer 1

ABCs
A = airway
B = breathing
C = circulation

Question 2

Purpose of airway management

Answer 2

o Ventilation
o Not necessarily intubation
o It is a continuum (need to maintain an airway despite medication, etc.)

Question 3

3 areas of obstruction

Answer 3

o Nose
o Base of throat
o Base of tongue (shifts back when laying down)

Question 4

Airway adjuncts

Answer 4

o Oral airway or nasal airway

o Keeps tongue off of back of throat

Question 5

Sizing an airway adjunct

Answer 5

o Should go from mouth to angle of mandible (oropharyngeal)

Question 6

Problems with oropharyngeal airway

Answer 6

o Contraindicated in patient with intact gag reflex

o Insertion can cause coughing, vomiting, laryngospasm and loss of airway

Question 7

Nasopharyngeal Airway Considerations

Answer 7

o Can be used in semiconscious patient with intact gag reflex
o Can be used in patient who will not open mouth
o Should be inserted with the bevel down parallel to soft palate and not toward the base of the skull

Question 8

Ventilation options

Answer 8

• Mouth to mouth (Microshield or Barrier Mask)
• Bag-mask Ventilation (with or without airway adjuncts) – usually a prelude to intubation
• Supraglottic airways
• Endotracheal intubation (oral or nasal)
• Surgical airway (tracheostomy or crichothyroidotomy)
• NOTE – there is a video we should watch that you need to watch, so he did not go into them

Question 9

Laryngeal mask airway

Answer 9

• Insert it deflated through the mouth, once in place, insert the cuff (video is in the slide set)
• Prevents gastric aspiration, but not 100%
• Tracheal tube can be used – 96-98% effective, done blind (done when hard to intubate)

Question 10

King airway LMA

Answer 10

• To avoid intubating in the field, growing in popularity
• Once in hospital, you need to follow a specific protocol to remove it and actually intubate
• Prevents gastric regurgitation

Question 11

5 basic steps to intubation

Answer 11

• Optimal positioning of the patient
• Adequate opening of the mouth
• Correct insertion of the blade in the mouth
• Advancement of the blade with exposure and identification of the larynx
• Placement of the endotracheal tube through the glottis into the trachea

Question 12

When to intubate

Answer 12

• Failure of airway protection
• Failure of oxygenation
• Failure of ventilation
• Is there a need for extended mechanical ventilation? If they will likely be ventilated during the post-operative period

Question 13

The 7 Ps

Answer 13

Proper prior preparation prevents piss poor performance

Question 14

Airway exam

Answer 14

• Mallampati Score
• Thyromental distance
• Mouth opening
• Neck Mobility –Normal extension is 45 to 70 degrees
• Ability to protrude lower jaw
• Foreign material in the airway

Question 15

Mallampati score

Answer 15

Class I
- Full visibility of tonsils, uvula and soft palate

Class II
- Visibility of hard and soft palate, upper portion of tonsils and uvula

Class III
- Soft and hard palate and base of uvula are visible

Class IV
- Only hard palate visible

Question 16

Sniffing position

Answer 16

The appropriate position for the patient to be mask ventilated with an oral or nasal airway

Question 17

Laryngoscope blade

Answer 17

o When a patient is coding and the teeth are clenched, you need to use the smallest possible laryngoscope blade or you will break all their teeth

Question 18

Miller 2 blade - RECOMMENDED BLADE

Answer 18

o Universal – can be used for babies to large adults
o Very narrow, easy to use, comes in different lengths
o You can flip it up to get an anterior view of airway to see structures (epiglottis/cords)

Question 19

Macintosh blade

Answer 19

o Larger, harder to use, usually used when you first start out (doesn’t make sense)
o Goes between epiglottis and base of the tongue

Question 20

Endotracheal tube

Answer 20

o Not rigid, just firm enough to hold shape, but becomes more flexible with heat in mouth
o Use with stylet in tube for more control

Question 21

REMEMBER

Answer 21

o When intubating in an emergency situation ALWAYS use a stylet endotracheal tube

Question 22

Cormack-Lehane Classification

Answer 22

• Grade I = visualization of cords
• Grade II = epiglottic overhang over cords
• Grade III = tip of epiglottis, no cords
• Grade IV = can’t even see epiglottis

Question 23

Who in the ER has a full stomach?

Answer 23

• Answer: EVERYONE!! – Every ER patient is an aspiration risk
• Use Sellick’s maneuver as a safety precaution

Question 24

Sellick’s maneuver (cricoid pressure)

Answer 24

• Purpose is to compress esophagus to prevent aspiration of stomach contents during intubation
• Press down on cricoid in order to push trachea posteriorly in order to close the esophagus
• Will not help active vomiting, but it can prevent passive regurgitation during intubation
• Not always effective since esophagus can just slip to one side or the other

Question 25

Disheartening news (read on own)

Answer 25

• Mulcaster et al in 2003 found that trainees (medical students, respiratory therapists, paramedics) required a minimum of 47 attempts to assure competence at laryngoscopic tracheal intubation
• Konrad et al in 1998 found an average of 57 attempts were needed by anesthesia residents to achieve a 90% success rate and 18% of the residents needed assistance even after 80 attempts
• Experienced providers in specialties who rarely perform endotracheal intubation also struggle with routine intubations
• No good objective criteria for assessing the quality and efficiency of performing the technique

Question 26

Blind nasotracheal intubation

Answer 26

• Patient must be breathing spontaneously, requires minimal preparation
• An acceptable alternative for patients in CHF who cannot lie flat
• Patients with short fat necks or with clenched teeth awa cervical collars
• High airway velocity will help channel tip of ET tube thru the vocal cords
• Tube cannot be manipulated by the tongue and gives easier access to the oral cavity
• Patient can tolerate better than ET tube placed orally
• If not successful, can transition to fiberoptically assisted intubation if necessary

Question 27

Contraindications to blind nasal intubation

Answer 27

• Should be avoided in severe nasal or midface trauma
• In basal skull fracture, ET tube placed nasally could enter the brain thru the fracture site
• Patients being considered for thrombolytic therapy or patients on anticoagulants or who have a coagulopathy should not be nasally intubated

Question 28

Glidescope

Answer 28

• Allows you to see around the cords (with a light and camera)
• Has a rigid stylet that makes endotracheal tube easier to manipulate
• Can cause soft tissue damage if focus is on screen during insertion of ET tube
• Put tube in first then scope in around it so you don’t cause soft tissue damage - Can penetrate the soft palate

Question 29

Nightmare scenario

Answer 29

can’t intubate, can’t ventilate

Question 30

Introduction to general anesthesia

Answer 30

• At its essence, what we provide in the way of anesthesia is based on the needs of the surgeon and the condition of the patient
• It can be a difficult balance and sometimes requires compromise on the part of both the surgeon and the anesthesia provider
• MAC (Monitored Anesthesia Care) vs Regional vs General or a combination of the above are the usual options
• We will begin with General Anesthesia and what that entails
• Some cases will require basically an immobile patient and loss of consciousness
• Some patients will require neuromuscular blockade and more intense monitoring
• MAC (IV sedation) and Regional Anesthesia will be discussed later

Question 31

Anesthesia continuum

Answer 31

• Awake
• Minimal sedation
• Moderate sedation
• Deep sedation
• Anesthetized

Question 32

History

Answer 32

• How they work is subject of intense debate
• “Anesthetics have been used for 160 years, and how they work is one of the great mysteries of neuroscience. Most injectable anesthetics appear to work on a single molecular target. It looks like inhaled anesthetics work on multiple molecular targets. That makes it more difficult to pick them apart. “

Question 33

Theories of mechanism of action

“I’m not going to spend time on this”

Answer 33

• Lipid bilayer theory
• Modern lipid hypothesis theory
• Modern protein hypothesis
• ***Common in all theories = Disruption of energy flow

Question 34

How vaporizers work

Answer 34

• They are agent specific and are calibrated to specific vapor pressure and temperature of agent
• For some, the O2 flows through the vaporizer and a specific amount agent is added to the flow
• For desflurane, the gas flow bypasses ( flows over )the vaporizer. A set percentage of agent is added to the gas flow

Question 35

Inhalation agent potency

Answer 35

• Determined experimentally by a response to a surgical stimulation
• Looking for the percentage of agent that prevents movement in 50% of the stimuli
• This value is called the minimum alveolar concentration ( MAC ) of the agent
• 1.3 MAC will prevent movement in 95% of patients

Question 36

MAC of commonly used agents

Answer 36

Desflurane MAC = 6.0

Enfulrane MAC = 1.7

Halothane MAC = 0.77

Isoflurane MAC = 1.15

Sevoflurane MAC = 1.71

Question 37

Factors which INCREASE anesthetic requirements

Answer 37

• Chronic alcohol abuse
• Infant (highest MAC at 6 months old)
• Red hair
• Hypernatremia
• Hyperthermia

Question 38

Factors which DECREASE anesthetic requirements

Answer 38

• Acute alcohol intoxication
• Elderly
• Hyponatremia
• Hypothermia
• Anemia (

Question 39

General anesthesia

Answer 39

• Drug induced loss of consciousness (LOC)
• Pt’s do not respond to painful stimuli
• Ventilation function often impaired
  o Airway assistance & positive pressure ventilation may be required
• Cardiovascular function may be impaired

Question 40

General Anesthesia Induction Options

Answer 40

• Mask induction – Mask is placed on the patient’s face and the inhalation agent concentration is gradually increased until patient is unconscious
• Usually used in infants and small children who do not tolerate an IV start
• Can be technically difficult if patient is crying or struggling
• In adults and cooperative children, an IV is started and an IV induction agent is used so induce loss of consciousness.
• These agents have a rapid distribution and are eventually excreted. Blood levels fall quickly causing their apparent duration of action to be short (known as context-sensitive t1/2)
• Immediately followed by simultaneous administration of other agents to deepen anesthetic level

Question 41

Effects of inhalaion anesthetic agenst

Answer 41

• They cause loss of consciousness, immobility, amnesia and muscle relaxation ( except Nitrous Oxide which increases skeletal muscle tone )
• They do not necessarily provide analgesia
• Because they administered by a calibrated vaporizer, their effects can be easily titrated
• They affect multiple organ systems
• They lower BP by decreasing SVR and to a lesser extent through myocardial depression
• They decrease alveolar ventilation but not total ventilation except at higher doses resulting in gradual rise of PCO2
• Cerebral vasodilators and can inhibit cerebral autoregulation and cause ICP to increase
• Interferes with hypoxic pulmonary vasoconstriction (HPV) which causes increased shunting of blood in the lungs to poorly ventilated areas - ↓ PO2

Question 42

Induction agents

Answer 42

• Barbiturates – Sodium thiopentol the “gold standard” but now of less importance – not used
• **Propofol – most commonly used induction agent
• Benzodiazepenes– primarily Midazolam. It enhances the effect of GABA at the receptor
• Ketamine – causes dissociation and can be used as sole anesthetic for certain procedures

Question 43

Basics on induction agents

Answer 43

o Cause dose dependent sedation and hypnosis – reach the brain
o The assumption is that the concentration in the blood will equal the effect sit
 [effect site]=[brain]
o The dose of the drug is determined by it’s therapeutic window
o Induction dose for Propofol is 2 – 2.5mg/kg
o NOT analgesics, just induction

Question 44

After induction

Answer 44

After induction of anesthesia, other drugs will be administered to provide the best outcome for the surgical procedure being performed
o Neuromuscular blocking drugs may be given to facilitate airway management and provide surgical relaxation
o Opioids will be given to provide analgesia during the procedure and to provide analgesia after emergence
o An anticholinergic may be given to dry the airway and to maintain the heartrate
o Benzodiazepines may be given to decrease risk of recall
o Antinausea medications are usually given to reduce the risk of nausea and vomiting in the postoperative period
o Nonopioid IV analgesics can also be given to reduce the postoperative analgesic requirements ( ie – IV ketorolac , acetominophen )

NOTE - The surgeon may inject local anesthetics into or near the operative site to provide additional longer term pain relief

Question 45

How are all these drugs administered?

Answer 45

• The undesirable side-effects of any one drug is seen at their higher doses. Inhalation agents can cause hypotension from vasodilatation, bradycardia from decreased autonomic activity, decreased cardiac output from decreased myocardial contractility
• The expression of side effects is also true for all other drugs given
• To minimize the undesirable side effects of any one class of drug, they are given as a combination of inhalation anesthetic drugs and intravenous agents – a concept known as “balanced anesthesia” ***
• Ideally this will provide a smoother anesthetic and more rapid emergence with fewer intraoperative and postoperative complications

Question 46

Neuromuscular blocking drugs

*These are important”

Answer 46

DEPOLARIZING = Depolarizing muscle relaxants. Only one used clinically is succinylcholine***

NONDEPOLARIZING = Nondepolarizing muscle relaxants. Curare-like actions. Contain an aminosteroid nucleus.
o Rocuronium
o Vecuronium
o Pancuronium (not as common anymore)

Question 47

Depolarizing muscle relaxants - SUCCINYLCHOLINE

Answer 47

• Is the only depolarizing muscle relaxant used clinically
• Causes persistent depolarization of the NMJ
• Binds to ACH receptor and prevents repolarization, so muscle stays relaxed
• Hydrolyzed by pseudocholinesterase
• After the drug is metabolized, the NMJ can repolarize
• Initial response is muscle contraction followed by relaxation
• Fasciculations are seen and repolarization is inhibited

Question 48

Succinylcholine pharmacology

Answer 48

• Hydrolyzed by plasma pseudocholinesterase

- Plasma half-life

Question 49

Succinylcholine side effects

Answer 49

• Sinus Bradycardia and possibly cardiac arrest with a second dose
• Anaphalaxis (rare)
• Fasciculations (can be painful)
• Myalgias
• Hyperkalemia- do not use on burns cases, cases with major tissue damage or in patients with neuromuscular diseases ( ie: muscular dystrophy ) – can cause cardiac arrest

Question 50

Nondepolarizaing muscle relaxants

Answer 50

Work both presynaptically and postsynaptically
o Presynaptically – bind to alpha3 beta2 receptors to inhibit mobilization of ACh and inhibit it’s release
o Postsynaptically- competes with Ach for binding sites on the alpha subunit of the nicotinic receptor and prevents depolarization of the neuromuscular end plate…no muscle contraction

Agent only has to block one of the alpha subunits to be effective

Metabolism by ester hydrolysis and Hofmann elimination (if you have a warm body and normal pH, you can easily eliminate the drug) - EASY METABOLISM

Question 51

Nondepolarizing muscle relaxants with no steroid nucleus

Answer 51

Cisatracurium and Atracurium
o They are tetrohydroisoquinilone derivatives
o Cisatracurium is one of twelve isomers of atracurium and associated with less histamine release than the parent drug - The benefit of cisatracurium is that you can use it over a long period of time
o Does not rely on hepatic or renal metabolism - EASY METABOLISM in the blood

Question 52

Dosing of neuromuscular blocking drugs

Answer 52

These are polar molecules so the Vd of these molecules is only to the extracellular fluid compartment

They do not distribute to lipid compartment

Dosing of these drugs is NOT based on total body weight but lean body weight
o Dosing on total body weight leads to drug overdose and difficult reversal
o If you have an obese patient, you will overdose them

Question 53

Reversal of neuromuscular blockers

Answer 53

• Administration of pseudocholinesterase inhibitors slow breakdown of Ach to allow it to compete for alpha unit binding sites
• Most commonly used drugs are Neostigmine and Edrophonium. Neostigmine 12 times more potent than Edrophonium
• In addition to the nicotinic receptors in muscle cells, Ach also binds at muscarinic receptors
• When NM blockers are reversed, the increased Ach acting at these muscarinic receptors cause undersirable side effect
  o These would include bradycardia, bronchospasm, increased intestinal motility and increased salivation
• For this reason an anticholinergic drug is given at the same time neostigmine or edrophonium is given ( atropine or glycopyrralate )
• These drugs act at the muscarinic receptors to prevent these side effects
• Newest drug to being reverse neuromuscular blockade by primarily Rocuronium is Suggamadex
  o Directly binds Rocuronium and to a lesser extent Vecuronium and Pancuronium
  o Binds drugs with an aminosteroid nucleus only
  o Available for release in U.S. in January 2016