11. Outpatient Anesthesia

Question 1

Accepted Definitions of Sedation and Anesthesia

Answer 1

Minimal sedation (anxiolysis): patients respond normally to verbal commands. Cognitive function and physical coordination may be impaired.

Moderate Sedation: patients respond purposefully to verbal commands. No airway intervention.

Deep Sedation: patients cannot be easily aroused but respond purposefully following repeated or painful stimulation. May require airway assistance.

General Anesthesia: Patients not arousable even by painful stimulation. Often require airway assistance.

Question 2

What is the Mallampati Score?

Answer 2

A clinical sign to predict difficult intubation.

Class I: soft palate, uvula, tonsillar pillars, and fauces are visible.
Class II: superior 2/3 of uvula and soft palate visible.
Class III: <1/3 of uvula and soft palate visible.
Class IV: soft palate not visible.

Question 3

What are some elements of airway assessment?

Answer 3

Dental exam
Mallampati score
Maximum incisal opening
Thyromental distance (>6.5cm)
Mandibular protrusion/upper lip bite test
Body mass index and obesity
Neck circumference (>17in)

Question 4

What is a MET?

Answer 4

Metabolic equivalent tasks (METs) is a measure of exercise tolerance.

Physiological measure that expresses energy cost of performing various physical activities expressed as the ratio of a pateient’s metabolic rate during a specific physical activity over reference metabolic rate, which is resting or basal oxygen consumption of a 40-year-old, 70kg man.

Question 5

Describe how you would perform a cricothyrotomy

Answer 5

1. Extend head and neck, identify cricothyroid membrane (make an initial vertical incision if identification is not possible).
2. Make a horizontal stab incision through the skin and cricothyroid membrane and keep the blade in place.
3. Use a tracheal hook to apply caudal and outward traction on the cricoid cartilage; remove the scalpel
4. Insert the ETT tube (6.0 cuffed) or tracheostomy tube (No.4 cuffed) and inflate the cuff.
5. Ventilate with low-pressure source
6. Confirm pulmonary ventilation.

Notes: Contraindicated childrent <6 (cricoid cartilage is narrowest portion of the airway). Needle cricothyrotomy indicated in this population. Conversion to tracheostomy within 72 hours to prevent subglottic stenosis.

Question 6

How would you perform transtracheal needle ventilation?

Answer 6

1. Extend head and neck, immobilize cricothyroid membrane. 2cm in width and 2-3cm below laryngeal prominence.
2. Puncture cricothyroid membrane at 90* angle with saline filled syringe (14g peds, 18g adult) and draw back until air enters.
3. Advance catheter caudally at a 30-45* angle.
4. Attach syringe to 100% wall O2 at 50psi for adults, 10-25psi for children 5-8 yrs. Bag valve mask using connector from 7 ET tube inserted into the back of a plunger-less 3mL Luer lock syringe can also be used.

Question 7

Pediatric airway and anatomy considerations

Answer 7

1. Pediatric airway is smaller (greater risk of obstruction from small foreign bodies).
2. Large tongue relative to small mouth.
3. Infants have a larger occiput.
4. Infants are obligatory nose breathers.
5. Trachea is softer, more collapsible.
6. Tonsils may be enlarged.
7. Larynx is higher and more anterior.
8. Epiglottis is floppy and projects posteriorly.
9. Cricoid ring is narrowest point in the airway.
10. Length of trachea is smaller (risk of dislodgement of ETT).

Question 8

What is the modified Aldrete Score?

Answer 8

Assigns a score of 0-2 to the following categories: activity, breathing, circulation, consciousness, and oxygen saturation. Score of 9/10 is required for discharge.

Question 9

What is capnography?

Answer 9

Change in concentration of CO2 (mmHg) gas over a function of time (normally seconds).

Phase I: inspiratory baseline
Phase II: expiratory upstroke
Phase III: expiratory plateau
Phase IV: expiratory downstroke

Slow uptake in phase II may represent upper airway obstruction, obstruction of ETT, or bronchospasm. Shark fin pattern without an expiratory plateau may be suggestive of obstructive lung disease such as asthma or COPD.

Question 10

Define pharmacokinetics

Answer 10

Absorption, distribution, metabolism, and excretion of drugs.

How the BODY affects the DRUG.

Question 11

Define pharmacodynamics

Answer 11

The therapeutic and toxic organ system effects of drugs.

How the DRUG affects the BODY.

Question 12

What is MAC

Answer 12

Minimum Alveolar Concentration or partial pressure at one ATM which will prevent “gross purposeful movement” in response to a surgical stimulus in 50% of patients.

1.25-1.3 MAC rquired to include 90+% of patients

Higher MAC, less potency of inhalational anesthetic.

Nitrous oxide 104
Sevofluorane 2.3
Isofluorane 1.15
Halothane 0.75
Desflurane 6.00

Question 13

Propofol MOA, metabolism, excretion, onset, clearance

Answer 13

Sedative hypnotic. Potentiation of GABA receptor causing depression of the reticular activating system.

Metabolized in liver, excreted by kidneys. Metabolites are inactive.

Fast onset (40s) and short duration due to rapid clearance.

Question 14

Propofol dose for induction, maintenance of GA

Answer 14

Induction of GA adults: 1-2.5 mg/kg
Induction of GA children: 2.5-3.5 mg/kg

Maintenance of GA 100-200 mcg/kg/min

Sedation 25-100 mcg/kg/min; intermittent bolus 20-50 mg

Question 15

Ketamine MOA, metabolism, excretion

Answer 15

Derivative of phencyclidine providing dissociative anesthesia which causes disassociation between thalamus and limbic system. NMDA receptor antagonist. Potent analgesic. High lipid solubility and low protein binding = rapid onset. Metabolized in liver, excreted by kidneys.

Question 16

Side effects ketamine

Answer 16

psychomimetic effects
increase in salivation attenuated by premedication with anticholinergic such as glycopyrrolate. Can increase risk of laryngospasm in children.

Question 17

Dose ketamine for induction (IV/IM) or sedation (IV/PO)

Answer 17

IV induction: 1-2mg/kg
IM induction: 3-5 mg/kg
IV sedation: 0.2-0.5mg/kg intermittent boluses
PO sedation: 1mg/kg

Question 18

Midazolam MOA

Answer 18

sedative hypnotic
GABA potentiation
High lipid soluble, rapid onset
Anterograde amnesia

Question 19

Reversal of benzodiazepines

Answer 19

Flumazenil (Romazicon): competitive antagonist at BZD receptor site.

0.2mg IV once over 15 seconds

Repeat doses 0.2mg every minute until desired level of conciousness is achieved (max dose 1mg).

Question 20

Fentanyl MOA, metabolism, elimination

Answer 20

Narcotic agonist-analgesics of opiate receptors (primarily u) that inhibit ascending pain pathways.

Fast onset, short duration. Metabolized by liver (CYP3A4), end products mostly eliminated by kidneys.

Question 21

Opioid reversal

Answer 21

Naloxone (narcan) - competitive opioid receptor antagonist.

0.4mg to 2mg IV

If desired response is not obtained, doses should be repeated at 2-3 minute intervals, generally up to total dose of 10mg.

Peds: 0.01mg/kg IV. If desired response not obtained, may give 0.1mg/kg IV.

Question 22

Succinylcholine (Anectine)

Answer 22

Depolarizing non-competitive agent that works at the cholinergic receptor, which has a rapid onset (30-60 seconds) and short duration (2-3 minutes).

Associated with muscular pain and anaphylactic reactions. Known trigger for MH. Repeated doses associated with bradycardia and possible asystole. Pretreatment with atropine lessens this. Rarely (1/4000), a deficiency in enzyme pseudocholinesterase occurs, which would prolong its metabolism and duration of action substantially).

Question 23

Succinylcholine doses

Answer 23

Facilitation of endotracheal intubation and rescue from laryngospasm.

Intubation dose: 0.3-1.1mg/kg IV bolus

Rescue from laryngospasm: 20% of intubating dose, 20mg IV or consider intubating dose if RSI is planned.

Question 24

Serious pediatric risks with Succinylcholine

Answer 24

Rare reports of acute rhabdomyolysis with hyperkalemia followed by ventricular dysrhythmias, cardiac arrest, and death after administration of succinylcholine to healthy children who have subsequently been found to have undiagnosed skeletal muscle myopathy (Duchenne’s muscular dystrophy).

Rescue from laryngospasm and facilitation of emergent intubation is still performed with Succinylcholine, but increasing depth of anesthesia with propofol or volatile agent may be considered. (Or use rocuronium).

Question 25

Rocuronium (Zemuron)

Answer 25

Non-depolarizing muscle relaxant that works at the cholinergic receptor. Much faster onset than other non-depolarizing agents, especially when used in higher doses (comparable with succinylcholine).

Question 26

Rocuronium dose

Answer 26

Intubation: 0.45-0.6mg/kg IV
RSI: 0.6-1.2mg/kg IV

Question 27

Reversal of rocuronium

Answer 27

Sugammadex (a cyclodextrin) is a selective relaxant-binding agent. Exerts reversal effect by forming tight complexes in 1:1 ratio with steroidal non-depolarizing agents.

Question 28

Prothrombin time measures what?

Answer 28

PT: measures adequacy of extrinsic and common pathway of the clotting cascade.

Measures clotting ability of factors I (fibrinogen), II (prothrombin), V, VII, IX, X.

Deficiencies in these clotting factors prolong prothrombin time (Normal 11-13 seconds).

Usually expressed as International Normalized Ratio (INR)

Question 29

Coumadin therapy affects function of factors:

Answer 29

II, VII, IX, X

VII has shortest half life and is most important factor in initially determining the function of the extrinsic pathway.

Question 30

Bleeding secondary to therapeutic Coumadin can be treated with _____

Answer 30

Vitamin K (although it takes 12-24 hours for any significant reversal of the anticoagulation to occur).

Question 31

Bleeding secondary to unfractionated heparin can be treated with _____

Answer 31

Protamine sulfate (with immediate reversal of the anticoagulation).

Question 32

Bleeding associated with low-molecular weight heparins (e.g. Lovenox) reversal

Answer 32

Can not be directly reversed due to a different mode of action (indirect inhibitor factor Xa). Treatment with fresh frozen plasma is required.

(Unfractionated heparin, in contrast, can be reversed with protamine sulfate).

Question 33

Bleeding secondary to dabigatran (Pradaxa) reversal

Answer 33

Bleeding secondary to dabigatran (Pradaxa) - a direct thrombin inhibitor - cannot be directly reversed. Requires administration of FFP, recombinant factor VIIa, or prothrombin complex concentrate. Dialysis can be used for life-threatening bleeding because it can reduce plasma levels up to 60% in 2-3 hours.

Question 34

Bleeding secondary to use of Xarelto (rivaroxaban) reversal

Answer 34

Bleeding secondary to use of Xarelto (rivaroxaban) - a direct factor Xa inhibitor - cannot be directly reversed and requires FFP.

Question 35

How does Coumadin work?

Answer 35

Inhibition of enzyme vitamin K epoxide reductase, which is required to maintain vitamin K in the reduced state needed for functional coagulation protein synthesis. Factors II, VII, IX, X are reduced.

Question 36

Max dose lidocaine

Answer 36

7mg/kg (with epi)
4mg/kg (no epi)

Question 37

Max dose bupivacaine

Answer 37

2mg/kg (w/ or w/o epi)

Question 38

Max dose mepivacaine

Answer 38

5mg/kg (w/ or w/o epi)

Question 39

Max dose articaine

Answer 39

7mg/kg (w/ or w/o epi)

Question 40

Treatment of Clostridium Difficile colitis

Answer 40

• Discontinue antibiotics
• Supportive therapy
• Prophylactic antibiotic therapy should not be given routinely
• Once diagnosis confirmed, metronidazole PO is preferred (can be given empirically before diagnosis if patient is seriously ill)
• Vancomycin PO is reserved for the following: failed therapy with metronidazole, organism resistant to metronidazole, patient allergic or cannot tolerate metronidazole or being treated with ethanol-containing solutions, patient pregnant, a child under 10, or critically ill.

Question 41

Metronidazole dose for C. Diff

Answer 41

500mg PO TID x 10-14 days

Question 42

Treatment of acetaminophen toxicity

Answer 42

Induced emesis (if diagnosed early)
Gastric lavage
GI decontamination with activated charcoal
Administration of N-acetylcysteine (NAC)