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Inhalant Anesthesia Flashcards

(62 cards)

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1
Q

Anesthesia

A

Obtained with the absorption of a drug by the respiratory system, reaching the systemic circulation and the CNS

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2
Q

Clinical effects

A

Amnesia
Unconsciousness (narcosis)
Immobility (muscle relaxation)
Not analgesia (few exceptions)- so we need to include a separate pain drug

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3
Q

Advantages

A 
Rapid adjustment of anesthetic depth
Minimal metabolism
Elimination by respiration
Rapid recovery
Economical
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4
Q

Mechanism of Action

A

Not completely known
Activation of inhibition of different molecular targets- GABA, glycine, glutamate, serotonin, ACh, K+ channels
Amnesia- GABAa- hippocampus
Narcosis- GABAa- cortex
Immobility- dec glutamate receptors and K+ channels/ inc glycine receptor activity- spinal cord

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5
Q

Vapor

A

Gaseous state of a substance that is liquid at ambient temperature and pressure
Halothane, isoflurane, sevoflurane, desflurane

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6
Q

Gas

A

Exists in gaseous state at ambient temperature and pressure

Nitrous oxide, xenon

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7
Q

Nitrous Ocide

A

Laughing gas
low blood gas (0.47)
Mild analgesic
Accumulates in closed gas spaces

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8
Q

Xenon

A

Very expensive
mostly experimental
Minimal cardiovascular depression

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9
Q

Boyle’s law

A

Volume is inverse to pressure

pressure inc = volume dec

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10
Q

Charles’s law

A

Volume and Temperature are proportional

inc volume= inc temp

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11
Q

Gay-Lussac’s law

A

Pressure proportional to temperature

inc pressure = inc temperature

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12
Q

Dawton’s law

A

Total pressure of gas mixture is equal to the sum of the partial pressure of the individual gases

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13
Q

Vapor pressure

A

Pressure exerted by vapor molecules when liquid and vapor phases are in equilibrium
only changes with temperature

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14
Q

Boiling point

A

temperature at which the vapor pressure equal to the atmospheric pressure- inversely related to vapor pressure

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15
Q

Desflurane

A

Boiling point (23.5C) is close to room temperature
Electric heated vaporizer required
-Desflurane maintained in gaseous form (high pressure 2ATM)
-blends with fresh oxygen to achieve vaporizer settings
More used in human medicine
Expensive
Horses

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16
Q

Vapors

A

Maximum administration percentage

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17
Q

Vaporization at ambient

A

Vapor pressure/Barometric pressure

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18
Q

vaporization chamber

A

isoflurane is 32%- this is way higher than the clinical dose so we need a way to reduce this. in a vaporizing chamber the o2 will pass on the surface of the liquid anesthetic and vaporize the anesthetic and they will mix with o2 from the bypass chamber which dilutes it

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19
Q

Solubility

A

Anesthetic vapors dissolve in liquids and solids
Equilibrium is reached when the partial pressure of the anesthetic is the same in each phase
-partial pressures are equal
-number of anesthetic molecules are not equal

expressed as partition coefficient
Concentration ratio of an anesthetic in the solvent and gas phase
Describes the capacity of a given solvent to dissolve the anesthetic gas

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20
Q

Blood-gas partition coefficient

A

Most clinically useful number
Describes the amount of anesthetic in blood vs alveolar gas at equal partial pressures
The alveolar partial pressure represents the brain concentration after equilibrium (although usually measured as %)
anesthetic dissolved in the blood is pharmacologically inactive

Most to least soluble
Halothane, isoflurane, Sevoflurane, Desflurane

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21
Q

Low Blood-gas partition coefficient

A

Less anesthetic dissolved in the blood at equal partial pressures (more in alveoli)
Shorter induction and recovery times (shorter time required to achieve steady state in the brain)
Clinically more useful (iso, sevo, des) (bc faster recovery time)
Hypothermia increases anesthetic solubility
Halothane: high BGPC- longer induction and recovery times

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22
Q

Uptake of inhalants

A

Inhalants move down pressure gradients until equilibrium is achieves
Vaporizer-breathing circuit- alveoli- arterial blood- brain
Partial pressure of the brain is roughly equal to that in alveoli
Pa: gas delivered to alveoli is removed from the lungs by blood

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23
Q

Ways to increase Pa

A

Increase the anesthetic delivery to alveoli
Decrease anesthetic removal from alveoli
Increase speed of induction and change the anesthetic plane

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24
Q

Increase alveolar delivery

A 
Increase inspired anesthetic concentration
-increase vaporizer setting
-increase fresh gas flow 
-decrease breathing circuit volume
Increase alveolar ventilation
-increase minute ventilation
-decrease dead space ventilation
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25
Decrease removal from alveoli
decrease blood solubility of anesthetic -different agents decrease cardiac output -low CO - lower extraction of anesthetics from the lungs- faster rise of Pa Decrease alveolar-venous anesthetic gradient -tissue uptake from anesthetic
26
Concentration effect
The higher the Pi the more rapid Pa approached Pi A high Pi is required at the beginning of gas anesthesia to quickly increase Pa Offsets impact of uptake (removal of anesthetic by pulmonary circulation) As uptake into blood decreases, Pi should be decreased
27
Anesthetic elimination
requires decrease in Pa Same variable that affect rise in Pa Especially agent solubility and alveolar ventilation Anesthetic time and decreased body temperature
28
How would you quickly decrease Pa
turn off vaporizer disconnect patient and flush the breathing system with O2 Turn up O2 flow (dilute the anesthetic in the circuit) Increase ventilation (increase fresh gas to alveoli)
29
Minimum Alveolar Concentration (MAC)
MAC of an anesthetic necessary to prevent movement in 50% of patients exposed to a noxious stimulus at sea level MAC between species is consistent Dose of the inhalant anesthetic- allow comparison between agents -high mac- low potency ``` Alveolar concentration (%)-way to measure the dose given Measures in % and not partial pressure MAC colorado= MAC sea level/Barr col/barsealevel ```
30
Gas analyzer
gold standard to measure anesthetic dose | end tidal gas concentration
31
Factors that change MAC- increase
``` Hyperthermia Hypernatremia Drugs causing stimulation of CNS decreased age Red hair in people ```
32
Factors that change MAC- decrease
``` Hypothermia hyponatremia drugs causing depression of CNS increased age severe hypotension hypoxemia metabolioc acidosis/hypercapnia pregnancy anemia ```
33
MAC multiples
Used to describe dose 1 MAC- immobility in 50% of the patients 1.3 MAC- immobility in 95% of the patients MAC is additive: 0.5MACa+ 0.5 MACb= 1MACab changing the anesthetic agents during the procedure, using N2O, using partial intravenous anesthesia (PIVA)
34
Systemic effects of volatile anesthetic
``` Cardiovascular Respiratory Neurologic Renal Hepatic Other ```
35
Cardiovascular effects
``` dec CO dec BP dec Systemic vascular resistance dec contractility (inotropy) no change to inc HR (chronotropy) ```
36
Respiratory system
Dec ventilation -inhibit central CO2 and peripheral O2 chemoreceptors Apnea at 1.5-3 MAC bronchodilation Desflurane and isoflurane: irritating odor Sevoflurane: less irritating- used for mask inductions (usually bird)
37
Ventilation
arterial partial pressure of CO2 monitor ventilatory status Normal PaCO2: 35-45 mmHg Hypoventilation PaCO2 > 45mmHg
38
Neurology system
Inc intracranial pressure (ICP) at > 1 MAC -due to cerebral vasodilation -sevoflurane increases less the ICP-so use for MRI for neuro patient Decrease cerebral metabolic rate immobility, hypnosis, amnesia-spinal cord and brain Suppress seizure activity (except for enflurane)
39
Renal system
Decrease glomerular filtration rate and renal blood flow Due to decrease in CO (dec blood flow to like every organ) Renal failure (methoxyflurane)- dont have anymore
40
Compound A
``` Produced by secoflurane breakdown in CO2 absorbent -Baralyme > soda lime Higher concentrations formed during -prolonged anesthesia -desiccated absorbent -low fresh gas flow Nephrotoxic in rats ```
41
Hepatic system
Reduced liver blood flow and O2 delivery -decrease CO Halothane hepatotoxicity -increased liver enzymes- mild, self limiting -halothan hepatitis- immune-mediated, often fatal Minimal hepatic metabolism (modrn agents)
42
Malignant hyperthemia
Myopathy occurring in genetically predisposed animals and humans Exposure ot inhalant anesthetics (esp halothane, but also others) Increase in intracellular calcium-uncontrolled muscle contractions Severe hyperthermia- death Extremely rare First sign can be rapid increase in ET CO2 Tx: administer dantrolene- calcium channel antagonist- muscle relaxation -discontinue volatile anesthetic, change the machine and flush with O2 -Provide 100% O2 -fluids, active cooling Death is likely despite treatment
43
Nitrous oxide
used more in people and some universities maximum administration is 74% (need >25% O2) low solubility (BGPC: 0.47) Minimal cardiorespiratory depression Analgesic effect (NMDA antagonist) Transfer to closed spaces -some organs contain air (stomach, intestines, middle ear) -other (GDV, colic horse, pneumothorax, cuff of ET tube) N2O is more soluble in blood than Nitrogen N2O accumulate rapid while Nitrogen leaves slowly Avoid in disease states causing increased closed gas space
44
Diffusion hypoxia
when N2O is stopped- diffuses quickly out of the blood to alveoli Displaces O2 and other gases from alveoli If breathing room air- hypoxemia Provide 100% O2 when discontinuing for at least 10 min
45
Environmental safety
Trace levels of inhalant anesthetics can cause adverse health effects Fetal development and health Reduce occupational exposure Greenhouse effect/ozone layer
46
Reducing Occupational exposure
Use scavenging system check and minimize leaks avoid mask and chamber induction keep patients attaches to the circuit after anesthetics are turned off Minimize exposure to exhaled gas from patient (specially horses) monitor waste gas concentration Ventilate operation rooms
47
Common complications of inhalant anesthesia-anesthesia related
hypotension hypoventilation hypothermia
48
Common complications of inhalant anesthesia-machine related
Closed pop-off stuck inspiratory expiratory valves exhausted soda lime inadequate O2 flow in non-rebreathing circuits
49
Common complications of inhalant anesthesia- human error
``` Anesthetic overdose Intubation mishaps -laryngeal damage -stuck tube -aspirated tube -tracheal tears -obstructed ET tubes ```
50
Hypotension
MAP <60 mmHg (SA) and <70 LA- doppler below 80-90 mmHg Maintain cerebral, renal, and striated muscle blood flow 50% of cases can be treated turning the vaporizer down -patient is deep- achieve adequate anesthetic depth -patient is light- consider administering a MAC sparing drug before turning vaporizer down- benzo, opioid, ketamine If still hypo, evaluate underlying cause dec vascular tone (dehydration, hypovolemia)- crystalloids and or colloids Vasodilation- vasopressor Dec contractility- inotrope
51
Hypoventilation
ETCO2 >45 mmHg -mild hypercapnia can be tolerated in certain patients IPPV- manual, mechanical Check patient depth- turn vaporizer down if possible
52
Hypothermia
``` Inhalant anesthesia abolish normal thermoregulation -vasoconstriction, shivering impaired -vasodilation occurs as an effect of the drug Prevention more effective than tx: warm patient before induction keep covered minimize scrub time inc room temp forced air heating warm water blankets radiation lamps/devices ```
53
Closed pop off valve
should be open increase in the breathing system pressure transmitted to pts lungs and thoracic cavity dec CO -decreases venous return (preload) -compress great vessels (afterload) CS: apnea, bradycardia, fading doppler signal, cardiopulmonary arrest pneumothorax in some cases safety checklist use quick release valve to ventilate dont take hand off closes pop off until open again
54
Closes pop off valve- tx
pull rebreathing bad off/unscrewing pop-off start CPR if patient arrested Evaluate pulmonary injury (auscultation, chest radiographs)
55
Stuck inspiratory/expiratory valves
Rebreathing system becomes bidirectional -causes rebreathing of expired gases- hyper capnia Signs: capnograph- rebreathing wave form -no capnograph: observe movements of valves -respiratory acidosis Tx: dry and clean valves frequently replace valves
56
Exhausted soda lime
CO2 is no longer removed from the expiratory gas Patient rebreaths CO2 Signs: capnograph: same as stuck inspiratory/expiratory valves -waves never return to baseline during inspiration Differentials for rebreathing wave: inadequate O2 flow in non rebreathing systmes damage of inner tube of bain circuits
57
Intubation mishaps-Laryngeal damage
from laryngoscope or stylet usually- be gental swelling can lead to post operatory airway obstruction Stylet should not protrude past the end of the tube bougie place laryngoscope at base of tongue-dont touch epiglottis
58
Intubation mishaps-stuck tube
dont force large ET tubes on your patient it may go in and not come out re anesthetize the patient and cut the tube to decompress
59
Intubation mishaps-obstructed ET tubes
plugs (secretions), blood, FB loss of capnograph waves/high EtCO2 aspirate the lumen of tube replace the tube
60
Intubation mishaps-aspirated tube
Usually if patient bites reanesthetize patient quickly- provide O2 Retrieve tube- long forceps, reintubate with smaller tube, inflate cuff, then pull both tubes out together traceoscopy Provide proper patient monitoring- aggressive dogs, parrots
61
tracheal tears
not uncommon in cats overfilling of the ET tube fill until there is no leak at 20 cmH20 do not add more air unless there is a leak Movement of the patient connected to breathing systme always disconnect patient before moving CS: subq emphysems; pneumothorax and pneumoperitoneum Tx: supportive care- provide time for trachea to form a fibrin seal; surgical repair Birds- complete tracheal rings- uncuffed tubes
62
Anesthetic overdose
Inhalant anesthetics- low therapeutic index- fatal dose/therapeutic dose Overdose can happen fast- esp at high flow rates and vaporizer settings If in doubt about status of pt, turn inhalants off while you evaluate situation- movement doesnt mean you pt is conscious; its preferable that your patient is light than deep in anesthesia Severe hypotension )MAP< 40-50 mmHG) -MAC sparing, if tx of hypotension not effective, turn inhalants off Sick pts: MAC sparing-metabolic acidosis; need very little inhalant; use MAC sparing drugs/TIVA

Anesthesia (12 decks)

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