1. ) keep pt asleep/ prevent consciousness/awareness 2. ) prevent movement

Inhalational Anesthetics Flashcards by Shalini Raghuraman

Nitrous oxide properties (10)

) clinically considered only inhalational agent w/ analgesic properties
) associated with PONV
) increases pulmonary vascular resistance
) dilates cerebral vasculature
) raises the seizure threshold
) it supports combustion as much as O2
) it can cause postoperative diffusion hypoxia
) expands closed air containing cavities
) increases the cerebral metabolic rate of O2
) prolonged exposure can lead to harmful effects (bone marrow depression, can inhibit enzymes involved in DNA synthesis, and neurologic deficiencies)

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Contraindications for nitrous oxide (8)

) laryngeal/ pharyngeal/facial surgery with a laser or bovie
) ophthalmic sx
) pts w/ severe COPD
) cardiopulmonary bypass sx
) prolonged intestinal procedures and bowel obstruction and laparoscopic sx
) inner ear surgery
) 1st trimester of pregnancy
) neurosurgery situations (intracranial pressure, craniotomy, after dural closure)

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which volatile agent causes coronary steal phenomenon?

isoflurane

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Describe the coronary steal phenomenon

when isoflurane causes coronary vasodilation the stenotic coronary arteries cannot vasodilate as well as the normal coronary arteries

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Advantages of isoflurane (2)

minimal cardiac depression

2. causes coronary vasodilation

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refers to highest blood CO2 level

apneic threshold

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3 anesthetics that can increase apneic threshold

propofol
fentanyl
volatile agent

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pt can hold their breath for longer time before they need to start breathing; have LESS of a drive to breathe

high apneic threshold

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pt cant hold their breath for as long (cant let CO2 get very high) before they need to start breathing; more of a drive to breathe

low apneic threshold

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how do anesthetics affect apneic threshold?

RAISE apneic threshold; suppress the pt’s drive to breathe which means it will take a much higher CO2 than normal in order to stimulate breathing

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how does pain affect apenic threshold?

lowers apneic threshold by stimulating respirations

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Assume pt is on ventilator. how do you get pt to spontaneously ventilate?

) reverse paralysis (if necessary)
) allow the pt’s Co2 to increase (either slow down their RR, or shut the vent off completely)
) pt will begin to breathe when apneic threshold has reached (when CO2 is high enough)

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refers to lowest oxygen level at which pt can no longer remain apneic

hypoxic drive

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hypoxic drive in a normal pt

PaO2 = 60 mm Hg

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what has a greater effect to stimulate breathing in healthy pts?

hypercarbia

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what has a greater effect on stimulating breathing in pts with LUNG disease?

hypoxia

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respond to changes in H+ ion concentration of CSF determined by PaCO2

central chemoreceptors

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in carotid body; affect ventilation by responding to changes in PaO2

peripheral chemoreceptors

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2 goals of MAC

) keep pt asleep/ prevent consciousness/awareness

2. ) prevent movement

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If a pt is exhaling 6% MAC of desflurane.. what does that mean?

they are 50% likely to move when they are cut

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Is it easier to prevent awareness or prevent movement?

prevent awareness

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Why would you want to paralyze pt?

you want to keep pt from moving WITHOUT deeply anesthetizing pt

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MAC refers to ____.

minimum alveolar concentration of an EXHALED gas that will prevent movement in 50% of patients during surgical incision

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end tidal concentration of volatile agent will be (lower or higher) than the concentration on the vaporizer dial

lower

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MAC reflects ____

potency

when are patients less likely to move?

when breathing a higher percentage (MAC value) of agent

MAC value for awake (no stimulation)

0.4 MAC

MAC value for reliable awareness prevention (if narcotics are used)

0.8 MAC

MAC value for reliable awareness prevention (even w/o narcotics)

1.0 MAC

MAC value for 50% chance of movement (w/o paralytics)

1.0 MAC

MAC value for 5% chance of movement (w.o paralytics)

1.3 MAC

Is it possible for a patient to move without awareness?

Yes

Is it possible for a patient to be aware without moving?

yes; only if a paralytics given

How do we know if patients are aware or not when they're paralyzed?

vital signs; if pt is aware: HR & BP >200

2 reasons to give volatile agents?

1. ) prevent movement | 2. ) prevent awareness

to reliably prevent movement in a NON-PARALYZED patient, the pt should exhale how much volatile agent?

greater than or equal to 1 MAC; and have narcotics dosed prior to incision

To reliably prevent awareness in a patient w/ no narcotic use should be exhaling ?

greater than or equal to 1 MAC

to reliably prevent awareness in a patient w/ narcotic use the patient should be exhaling?

greater than or equal to 0.8 MAC

Factors that DECREASE MAC (6)

1. ) IV anesthetics 2. ) old age 3. ) ACUTE alcohol intoxication 4. ) pregnancy 5. ) temperature related factors (hypothermia, mild hyperthermia) 6. ) blood related factors (hypoxia, hypercarbia, hypotension, anemia)

Factors that INCREASE MAC (4)

1. ) Young 2. ) Hot (extreme hyperthermia >42 deg. celsius) 3. ) Salty (hypernatremia) 4. ) Alcoholic (chronic alcohol)

pt is hypertensive and tachycardic. they are exhaling 0.7% sevoflurane. what are acceptable tx?

1. ) propofol (pt is breathing 0.35) 2. ) narcotics 3. ) more volatile agent 4. ) NO beta blockers or antihypertensives

what does desflurane's 0.42 B:G coefficient mean?

once equilibrium is reached, the blood is only 42% saturated compared to the lung. Des is not very soluble in blood

True/False: if an agent is not very soluble in the blood, the blood will have less agent and a lower coefficient

TRUE

Isoflurane B:G coefficient is 1.4 what does that mean?

the blood is 40% more saturated than lungs and it's a lot more soluble in the blood than des

If there are 30 volatile agent molecules in the alveoli and 25 in the blood what is the B:G coefficient?

25/30= 0.83; blood is 83% saturated compared to lungs

Neurologic effects of Volatile Agents (4)

1. dilates the cerebral vasculature, increases cerebral blood flow, increases intracranial pressure 2. can cause emergence delirium in kids 3. decrease the possibility of seizures 4. decrease the cerebral metabolic rate of oxygen

Cardiac effects of volatile agents (3)

1. decrease cardiac contractility 2. cause systemic vasodilation 3. cause coronary vasodilation

which volatile agent causes the greatest degree of coronary vasodilation ?

isoflurane

Respiratory effects of volatile agents (4)

1. ) rapid shallow breathing causing CO2 to increase 2. ) increase a patient's apneic threshold 3. ) decrease a patient's hypoxic drive 4. ) cause bronchodilation

higher levels of CO2 is most likely going to drop a patient's ____

minute ventilation

Other effects of Volatile Agents (6)

1. decreases renal blood flow 2. decreases hepatic blood flow 3. prolongs muscle relaxants 4. associated with PONV 5. All volatile agents trigger malignant hyperthermia 6. Inhibit "non shivering thermogenesis" in pediatric pts

how does nitrous oxide expand air bubbles?

when blood comes into contact with air pocket, the NITROUS OXIDE will diffuse into the air pocket faster than nitrogen can diffuse into the blood. this causes pocket expansion

nitrous oxide ___ pt's FiO2 and _____ the risk of pneumothorax

decreases; increases

Which gas causes coronary steal phenomenon?

isoflurane

describe coronary steal phenomenon

when isoflurane causes coronary vasodilation, the stenotic coronary arteries cannot vasodilate as well as the normal coronary arteries. normal arteries receive more blood flow but stenotic arteries receive decreased blood flow

Which agent is ideal for mask induction ?

sevoflurane

disadvantages of Sevo?

1. ) releases nephrotoxic free fluoride ions when metabolized 2. ) can release "compound A" when broken down by a soda lime CO2 absorber

effects of compound A are more significant with ____, _____, and ____.

prolonged exposure to sevoflurane, high concentrations of sevoflurane, low fresh gas flow used

What is the FDA recommendation for using sevoflurane with fresh gas flow rates?

at least 1L/min for exposure up to 1 hr and at least 2 L/min for exposures greater than 1 hour

causes the fastest induction and emergence

desflurane

leads to possible sympathetic response; increase in HR and BP ; most airway irritating pungent agent

desflurane

advantages include: inert, low b:g coefficient (0.115), minimal cardiovascular effects, doesn't trigger MH

xenon

disadvantage of xenon

low potency (MAC 63%)

Inhalational Anesthetics Flashcards

(63 cards)