Inhaled anesthetics Flashcards
Describe Ether
Ether, first “ideal” anesthetic
Easy to make in pure form
Easy to administer
Liquid at room temp, but readily vaporized
Potent anesthetic, few drops needed, can produce anesthesia without diluting oxygen to hypoxic levels
Supports respiration and circulation
Not toxic to vital organs
Flammable!!
Describe Chloroform
Chloroform Pleasant odor Nonflammable Known hepatotoxin Severe cardiovascular depressant High incidence of intra and post-op deaths associated with its use Difficult to administer
Combining carbon with fluorine decreased flammability lead to creation of ?. Withdrawn from market due to ?
Combining carbon with fluorine decreased flammability lead to creation of first halogenated hydrocarbon anesthetic Fluroxene. Withdrawn from market due to organ toxicity
Describe Methoxyflurane
Halogenated methyl ethyl ether Nonexplosive and nonflammable. Most potent of volatile agents. MAC 0.16 Highly soluble B/G 12 70% metabolized (Oxidative metabolites include fluoride (F-) and oxalic acid, both nephrotoxic. Flouridevasopressin-resistant high-output renal failure
. LOWER MAC THE ___ THE POTENCY
. LOWER MAC THE GREATER THE POTENCY
Ideal anesthetic describe
no one agent meets all the requirements
- pharmacokinetics unaltered by patient pathophysiology •high degree of specific action/function •levels easily identified & managed- rapid adjustment of depth of anesthesia •wide margin of safety
- rapid induction and recovery •controllable duration of action •easy to administer •no unwanted effects on organs •no toxic metabolites •predictable elimination •useful in all age groups •Adequate muscle relaxation
Theories of Anesthesia
- GA = “ _____”
- NO ___ THEORY
- CNS (Brain/spinal cord) assumed ___
- Observations of ___ supports the theory that a (mysterious) specific protein receptor interaction “target molecule” is involved
•GA = “ state of unconsciousness of the brain (hypnosis and sedation) plus immobility in response to noxious stimuli” •NO SINGLE UNIFYING THEORY •CNS (Brain/spinal cord) assumed site(s) action •Observations of stereoselectivity supports the theory that a (mysterious) specific protein receptor interaction “target molecule” is involved
Proposed cellular site synapse
- Action secondary to….Neurotransmitter synthesis, transport, release, removal, binding????????
- Theory: GA inhibit excitatory postsynaptic potentials (amino acids- glutamate & asparate) and/or promote inhibitory actions of GABA and glycine
- Unitary theory- all GA act same mechanism •Degenerated theory- different classes = different mechanisms
Various theories explaining anesthetic site of action
- ?- Meyer-Overton Theory absorption of anesthetic molecules expands hydrophobic region– expansion of lipid bilayer beyond critical amount and alters membrane function
- ? – binding modifies membrane structures, alters conductance, conformational change in channels.
- ?- correlation between potency & lipid solubility
- ? - anesthetic displaces lipids necessary for protein function
- ? -anes occupies receptor site –Act on neuronal membrane proteins that permit ionic conductance during membrane excitation
- Critical Volume- Meyer-Overton Theory absorption of anesthetic molecules expands hydrophobic region– expansion of lipid bilayer beyond critical amount and alters membrane function
- Fluidization theory – binding modifies membrane structures, alters conductance, conformational change in channels.
- Lipid theory- correlation between potency & lipid solubility
- Protein/lipid interface - anesthetic displaces lipids necessary for protein function
- Protein receptor theory -anes occupies receptor site –Act on neuronal membrane proteins that permit ionic conductance during membrane excitation
What are the four stages of Guedel?
- Stage I- Amnesia/Analgesia
- Stage II- Delirium/Excitement
- Stage III- Surgical Anesthesia 4 planes
- Stage IV- overdose
If see stage 2 do not do what?
pull OETT
Describe the pupil, resp, pulse, BP with each Guedel stage.
Describe the four Guedel stages
- · Stage 1 is called the stage of analgesia or induction. During this period, the patient experiences dizziness, a sense of unreality, and a lessening sensitivity to touch and pain. At this stage, the patient’s sense of hearing is increased, and responses to noises are intensified.
- · Stage 2 is the stage of excitement. During this period, there is a variety of reactions involving muscular activity and delirium. At this stage, the vital signs show evidence of physiological stimulation. It is important to remember that during this stage the patient may respond violently to very little stimulation. Pupils are dilated.
- · Stage 3 is called the surgical or operative stage. There are four levels of consciousness (also called planes) to this stage. It is the responsibility of the anesthetist or anesthesiologist to determine which plane is optimal for the procedure. The determination is made according to specific tissue sensitivity of •the individual and the surgical site. Each successive plane is achieved by increasing the concentration of the anesthetic agent in the tissue.
- · Stage 4 is called the toxic or danger stage. Obviously, this is never a desired stage of anesthesia. At this point, cardiopulmonary failure and death can occur. Once surgical anesthesia has been obtained, the healthcare provider must exercise care to control the level of anesthesia. The fourth level of consciousness of stage 3 is demonstrated by cardiovascular impairment that results from diaphragmatic paralysis. If this plane is not corrected immediately, stage 4 quickly ensues.
Nitrous Oxide descibe
- Only inorganic anesthetic gas
- 34 times more soluble than nitrogen in blood.
- Colorless
- sweet smell-odorless
- Nonexplosive and nonflammable
- Supports combustion
- Gas at room temperature
- MAC = 105% low potency
- Blood/Gas partition coefficient – 0.47
N20
Low potency
Stored as _ in cyclinder. _ PSI. we not go down until the very last drop is gone. Still some in there as vapor. It is used as balance technique. Very rare used n20 ONLY.
Low potency
Stored as liquid in cyclinder. 745 PSI. we not go down until the very last drop is gone. Still some in there as vapor. It is used as balance technique. Very rare used n20 ONLY.
N20
•Most commonly administered in combination with ___ aka -Balanced Technique
With a MAC value of __, not suitable or safe as a sole anesthetic agent
· Effective ___
· 70% nitrous oxide + oxygen significantly reduces MAC for _____
•Most commonly administered in combination with induction agent, skeletal muscle relaxant, opioids and/or volatile agents-Balanced Technique
With a MAC value of 105%, not suitable or safe as a sole anesthetic agent
· Effective analgesic
· 70% nitrous oxide + oxygen significantly reduces MAC for Halothane, Enflurane, Isoflurane, Desflurane, and Sevoflurane
High inhaled concentration used-low ___
•Concentration effect speeds ___ as fresh gas is literally drawn into the lung from the breathing circuit.
· Since nitrous oxide is often administered with a second gas, the second gas effect __ the rate of induction
· Rapid transfer from blood and tissues to the alveoli ___ arterial tension of oxygen aka ____
Administer O2 in PACU
High inhaled concentration used-low MAC
•Concentration effect speeds induction as fresh gas is literally drawn into the lung from the breathing circuit.
· Since nitrous oxide is often administered with a second gas, the second gas effect enhances the rate of induction
· Rapid transfer from blood and tissues to the alveoli decreases arterial tension of oxygen- diffusion hypoxia. Administer O2 in PACU
N20
Describe cardiovascular effects
- Stimulates sympathetic nervous system.
- Direct myocardial contractility depressant.
- Arterial BP, SVR, CO, & HR unchanged or elevated secondary to stimulation of catecholamines (sympathomimetic effect)
- May unmask undiagnosed myocardial depression in CAD, severe hypovolemia, and opioids
- Constricts pulmonary vascular smooth muscle and increases PVR, increases RA pressure.
- Associated with higher incidence of epinephrine induced dysrhythmias
Describe pulm effects of nitrous oxide
- Increases respiratory rate.
- Decreases VT.
- Minimal change in VE and resting CO2 levels. •Hypoxic drive markedly depressed.
- Diffusion hypoxia
f we do not give supp oxygen at the end of case after everything is turned off… n20 is quickly being washed out and will dilute …
dilutional hypoxia
N20 - CEREBRAL EFFECTS
•Increases CBF, produces mild elevation of ICP. •Increases CMRO2.
N20 neuromuscular effects
- Does not provide significant muscle relaxation.
- May cause skeletal muscle rigidity at >1 MAC. •Probably not a triggering agent for MH. (may be weak trigger).
No muscle relax. Unless you are in a hyperbaric chamber.
N20 RENAL EFFECTS
- Decreases renal blood flow by increasing renal vascular resistance.
- Decreases GFR and urine output.
n20 hepatic effects
hepatic BF mildly decreased
N20 GI effects
- May cause postoperative nausea and vomiting (activation of chemoreceptor trigger zone and vomiting centers in medulla and/or middle ear volume changes).
- Causes distention of the bowel- NOT indicated when pt. has bowel obstruction
n20 is absolutely contraindicated with what surgical procedure?
bowel obstruction
N20 biotransformation and toxicity
- Almost exclusively eliminated by __. •Biotransformation limited to __
- Irreversibly oxidizes cobalt atom in vitamin B12 and inhibits __.
- Includes methionine synthetase, necessary for myelin formation and thymidylate synthetase, necessary for __.
•Almost exclusively eliminated by exhalation. •Biotransformation limited to < 0.01% •Irreversibly oxidizes cobalt atom in vitamin B12 and inhibits vitamin B12 dependent enzymes. •Includes methionine synthetase, necessary for myelin formation and thymidylate synthetase, necessary for DNA synthesis.
N20 biotransformation and toxicity
•Prolonged exposure (>24 hrs) and abuse can result in ___ (megaloblastic anemia), peripheral neuropathies, and pernicious anemia •Avoid use in pregnant patients •May alter immune response to infection (dont give if a patient has ___)
•Prolonged exposure (>24 hrs) and abuse can result in bone marrow depression (megaloblastic anemia), peripheral neuropathies, and pernicious anemia •Avoid use in pregnant patients •May alter immune response to infection
dont give if a patient has septiciemia
Contraindications of N20
Diffuses rapidly into air-containing cavities
•Air embolism •Pneumothorax •Acute intestinal obstruction •Intracranial air •Pulmonary air cysts •Intraoccular air bubbles •Tympanic membrane grafting
n20 CONSIDERATIONS
•Diffuses into __ •Avoid in patients with ___ •Limited value in patients requiring ___
•Diffuses into ETT cuff •Avoid in patients with pulmonary HTN •Limited value in patients requiring high FIO2
Drug interactions with N20
•Cannot be used as complete anesthetic (high MAC) •Decreases MAC requirements of other agents •Potentiates neuromuscular blockade
Volatile agents
are _ compounds
_ substitutions increase anesthetic potency
=Lower weight halogens (___) decreased potency more than those of higher atomic weight (__)
=__ substitution leads to most stable cpd. However it leads to ___
=Fluorination reduces __ and may produce potential for ___ (flouride ions inhibit sodium reabsorption in ascending loop)
•Volatile liquids- breathed in while in __ state •Physical properties –MAC, BP, VP, B/G
•Carbon compounds •Halogen substitutions increases anesthetic potency –Lower weight halogens (fluorine a.w.19) decreased potency more than those of higher atomic weight (chlorine a.w.35.5) –Chloride substitution leads to most stable cpd. However it leads to myocardial depression –Fluorination reduces flammability, and may produce potential for renal damage (fluride ions inhibit sodium reabsorption in ascending loop) •Volatile liquids- breathed in while in gaseous state •Physical properties –MAC, BP, VP, B/G
know what is a methane, ether, etc.
chemical name, compound, etc
•Vapor Pressures (mmhg, 20 C) Bld-Gas (37 C) MAC (% with O2)
what is the vapor pressure?
- •Halothane 2.3 .74 •
- Enflurane 1.8 1.68 •
- Isoflurane 1.4 1.15 •
- Desflurane 0.42 6.0 •
- Sevoflurane 0.69 2.05 •
- N2O 0.47 104
- Vapor Pressures (mmhg, 20 C) Bld-Gas (37 C) MAC (% with O2)
- •Halothane 243 2.3 .74 •
- Enflurane 175 1.8 1.68 •
- Isoflurane 239 1.4 1.15 •
- Desflurane 664 0.42 6.0 •
- Sevoflurane 157 0.69 2.05 •
- N2O 38, 770 0.47 104
•Vapor Pressures (mmhg, 20 C) Bld-Gas (37 C) MAC (% with O2)
what is the blood gas?
- •Halothane 243 .74 •
- Enflurane 175 1.68 •
- Isoflurane 239 1.15 •
- Desflurane 664 6.0 •
- Sevoflurane 157 2.05 •
- N2O 38, 770 104
- Vapor Pressures (mmhg, 20 C) Bld-Gas (37 C) MAC (% with O2)
- •Halothane 243 2.3 .74 •
- Enflurane 175 1.8 1.68 •
- Isoflurane 239 1.4 1.15 •
- Desflurane 664 0.42 6.0 •
- Sevoflurane 157 0.69 2.05 •
- N2O 38, 770 0.47 104
- Vapor Pressures (mmhg, 20 C) Bld-Gas (37 C) MAC (% with O2)
- •Halothane 243 2.3
- Enflurane 175 1.8 •
- Isoflurane 239 1.4 •
- Desflurane 664 0.42 •
- Sevoflurane 157 0.69 •
- N2O 38, 770 0.47
- Vapor Pressures (mmhg, 20 C) Bld-Gas (37 C) MAC (% with O2)
- •Halothane 243 2.3 .74 •
- Enflurane 175 1.8 1.68 •
- Isoflurane 239 1.4 1.15 •
- Desflurane 664 0.42 6.0 •
- Sevoflurane 157 0.69 2.05 •
- N2O 38, 770 0.47 104
What does blood gas mean?
MAC mean?
vapor pressure?
MAC % determines the potency.
BG = uptake adn distribution in emergence
Vapor pressure: these are liquids that constantly create a pressure. That is the vapor pressure at equilibrium at room temp. the vapor pressure of the gas relative to atompsheric pressure will deptermine how much is in the bottle. Know barimetric pressures. Higher atomp. Pressure the concentration is much higher… so use at a lower concentration.
Physical properties
Vapor pressure
boiling point
Molecules of a volatile agent in a closed container are distributed between teh ____ phases.
•Vapor pressure – the pressure created when gas molecules bombard the surface of a liquid and the walls in a closed container. • •Boiling Point – Vapor pressure equals Barometric pressure
•Molecules of a volatile agent in a closed container are distributed between the liquid and gas phases
Temp, Alt, and Vapor pressure •Temperature Direct Relationship
Altitude:
- Increase Altitude, _ Barometric Pressure
- Decrease Altitude, _ Barometric Pressure
- Boiling Point occurs when
Vapor Pressure = Barometric Pressure
•So what happens when we change the barometric pressure??
•Temperature Direct Relationship
Altitude:
- Increase Altitude, decrease Barometric Pressure
- Decrease Altitude, increase Barometric Pressure
- Boiling Point occurs when
Vapor Pressure = Barometric Pressure
•So what happens when we change the barometric pressure??
VP/ BP 240/760 = 1/3 = 33%
Air = 67%
Forance Vapor = 33%
Forane Vapor Pressure = 240, 50cc
VP/BP 240/500 =1/2=50%
Partial pressures:
Air 50%
Forane Vapor 50%
Forane vp = 240
50ml
Minimum alveolar concentration
describe
•Minimum Alveolar Concentration (MAC) –The minimum alveolar concentration @ 1 ATM that produces immobility in 50% of patients exposed to noxious stimuli –Measures the anesthetic potency of IA –Inhalation equivalent of ED50 –Immobility appears to be a result of action at the spinal cord (note: it appears the hypnotic effect is mediated through a different action and site in the CNS)
What are the factors not affecting MAC?
•Factors NOT affecting MAC
–Variable stimulus
–Species
–Sex (gender)
–Duration of anesthesia
–Acid-base disturbances
PaO2 (40-500 torr) (nothing affects MAC between 40-500)
Factors decreasing MAC
- Increasing age •Hypothermia •Hyponatremia •Hypotension –< 40mmhg •Pregnancy •Hypoxemia –< 38 mmHg •Anemia –4.3 ml/dl
- Opioids •Ketamine •Benzodiazepines •Clonidine •A2 agonists •Local Anesthetics •ETOH (acute)
Factors increasing MAC
hyperthermia
cns stimulants
youth under one year of age
Clinical application of MAC
- MAC values of different agents are additive
- 50% move at _ MAC
- To avoid movement when no muscle relaxant is on board in 95% of patients requires _ above 1 MAC or 1.3 MAC
- MAC __- the concentration that permits voluntary response- Not a constant relationship to 1 MAC: At 1/3 MAC for Des, Sevo, Iso; ½ for Halothane; 60% for N2O
•MAC values of different agents are additive •50% move at 1 MAC •To avoid movement when no muscle relaxant is on board in 95% of patients requires 10-30% above 1 MAC or 1.3 MAC •MAC Awake- the concentration that permits voluntary response- Not a constant relationship to 1 MAC: At 1/3 MAC for Des, Sevo, Iso; ½ for Halothane; 60% for N2O
Halothane
describe
•Halogenated alkane derivative •Vapor Pressure 243 •BG Partition Coefficient 2.3 (intermediate solubility) •MAC 0.76 (high potency) •Nonflammable •Sweet, Non-pungent •Contains Thymol
halothane cardio effects
•Direct myocardial depressant = BP decrease •Dose dependent decreases in CO •Does not decrease SVR (iso, des, sevo do) •Coronary artery vasodilator, coronary blood flow decreased from drop in systemic BP, can cause ischemia. •Protection from decreased myocardial oxygen demands. •Blunts baroreceptor response to hypotension, no increase in HR. •Increase cutaneous blood flow
halothane arrhythimas
decreased?
prone to ?
decreased conduction ?
caution when __ is injected
•Decreased SA node depolarization- prone junctional •Decreased conduction AV node/His-Purkinje •Caution when epinephrine is injected! –EPI Concentration no > 1:100,000 or 1:200,000 –Adult dose EPI no more than 10 ml of 1:100K or 20 ml of 1:200K within 10 minutes –Total EPI dose within 1 Hour should not exceed 30 ml 1:10000k or 60 ml of 1:200K –Lidocaine does have a somewhat protective effect
halothane respiratory effects
•Increased rate •Decreased VT –Decreased VE, increased resting PACO2 •Apneic threshold rises •Hypoxic drive severely depressed (even at low doses 0.1 MAC) •Potent bronchodilator can reverse asthma-induced bronchospasm
Halothane cerebral effects
•Increases CBF, increases ICP, increases IOP •Autoregulation blunted. •Can prevent rise in ICP by hyperventilation prior to halothane administration •Cerebral activity decreased •Modest decrease in CMRO2
KNOW
What is the only common agent that does not increase CVP?
CORONARY STEAL?
SNS ACTIVATION WITH INCREASES IN CONCENTRATION?
IDEAL FOR __ INDUCTIONS
WHAT COMPD IS PRODUCED BY SEVO
recommend use at least __ l/min total FGF when administering sevo
contraindications
MAC/BG
SEVO
NO
NO
PEDS
COMPD A
2
impaired kidney disease and MH
2.0/0.65
DESFLURANE
contraindications
transient increase in __ and __ and __ cardiac wise
MH
hr, bp, catecholamine release
