Exam 2: Lecture 10: Maintenance of Anesthesia Flashcards
What are some commonly used Inhalents
- Isoflurane
- Sevoflurane
- Desoflurane
- N20 (nitric oxide)
- Halothane (not available in the USA)
T/F: The desire for inhalents is to be
- Less reactive
- Less potent
- Nonflammable
- Halogentation (adding Fl, Cl, or Br)
False! everything is true expect you wanr them to be more potent
What properties determine the method of administration for Inhlaents
- Boiling point
- Liquid density (specific gravity)
- vapor pressure
What properties help determine the kinetics in the patient for Inhlaents
Solubility of gas
- Blood/gas partial coefficient
- Oil/gas partition coefficient
Define Gas related to Inhlaents
Agents that exist in gaseous form at room temperature and sea level pressure
EX: N2O
Define Vapor related to Inhlaents
gaseous state of a substance that at ambient temperature and pressure is liquid
EX: Isoflurance, sevoflurance, halothane and desoflurance
What are the 4 gas laws the describe predictable behavior of gases
- Boyle’s law
- Charles’s law
- Gay Lussac’s law
- Daltons law of partial pressure
What is defined as the change in state from a liquid to a gas
vaporization
As equilibrium is reached during vaporization and no further loss of molecules to the gas phase occurs, the gas phase would be called?
Saturated at this point
What is said the be the measure of the ability to evaporate (enter the gas phase)
- saturated vapor pressure = max concentration of molecules in vapor state
- Temperature dependent, unique for each anesthetic agent
Vapor pressure of an anesthestic
Does temperature of liquid need to increase or decrease for more molecules escapes liquid phase and enters the gas phase
increases
- This leads to higher vapor pressure
If the temperature of liquid decreases what happens?
Lower vapor pressure / concentration
Does SVP (Saturated vapor pressure) of most anesthetics mean it is safest for clinical use?
NO!! you have to control the amount delivered to the patient
How do you control the amount of SVP that goes into a patient
Vaporizer
gas diverted into 2 streams
- By pass
- Vaporizing chamber
How are modern vaporizers classified
- Variable bypass
- Concentration calibrated
- Agent specific
- Temperature compenstated
Define blood / gas coefficient
In blood and tissue effects rate of uptake and distribution in body = speed of induction and recovery
Define Oil / gas partition coefficient
Solubility in lipid (oil) correlates with anesthetic potency
- ISO more than SEVO
Does more or less gas dissolve in solvent as temperature increases
less
Which agent will have a longer induction and recovery period based on blood/gas partiion coefficent (PC)?
A: Agent A: blood/gas PC 1.46
B: Agent B: Blood/gas PC 0.68
A
What are the two main ways to increase alveolar delivery
- Increased inspired anesthesic concentration
- Increased alveolar ventilation
What category do the following fit under with Factors that rapidly change alveolar PA?
- Increased vaporization of agent
- Increased vaporizer dial setting
- Increased fresh gas flow (Double the O2 rate)
- Decreased gas vlume of patient breathing circuit
Increased inspired anesthetic concentration for increased alveolar delivery
What category do the following fit under with Factors that rapidly change alveolar PA?
- Increased minute ventilation
- Decreased dead space ventilation
Increased alveolar ventilation in increased alveolar delivery
What are the 3 steps to decrease removal from alevoli
- Decreased blood solubility of anesthesic
- Decreased cardiac output
- Decreased alveolar venous anesthesic gradient
Which anestheic gas has the desired % metabolized
Isoflurance and 0.2%
Define MAC
Minimum alveolar concentration of inhaled anesthetic at 1 atmosphere that produces immobility in 50% of subjects exposed to a supramaximal noxious stimulus
- corresponds to ED50
What is the standard way of measuring potency of a drug?
MAC level
- highly potent inhlant such as halothane has a low MAC value
What values are determined in the lab setting with healthy patients and the absence of other drugs or common clinical circumstances
MAC
The Ed95 is 1.2 to 1.4 which means what % patients
95%
What is the MAC % for isoflurane
around 1.3%
What is the MAC % of Sevoflurance
around 2.3%
Do the following conditions cause an increase, decrease or no chane in MAC?
- Drugs that cause CNS depression
- Smaller body weight or size
- Age of animal
Decrease
Do the following conditions cause an increase, decrease or no chane in MAC?
- Hyponatremia
- PaO2 less than 40 mmHg
- PaCO2 greater than 95 mmHg
- Pregnancy
- Disease state
Decrease
Do the following conditions cause an increase, decrease or no chane in MAC?
- Blood pressure greater than 50 mmHg
- Anticholinergics
- Duration of anesthesics
- Gender
- Abornal K+ ions
- Metabolic alkalosis or acidosis
No change
Which anesthetic is described by the following?
- Stable in storage (no preservatives needed)
- Low blood gas solubility
- More potent than sevoflurane
- Fairly rapid induction and recovery (Good muscle relaxation)
Isoflurane
Which anesthetic is described by the following?
- Less cardiac depression than halothane, but more respiratory despression
(Hypotensions due to vasodilation and decreased myocardial contraciltility)
(Hypoventilation is common (decreased breathing))
Isoflurance
Which anesthetic is described by the following?
- Less than 1% metabolized in body, mostly elimated by lungs
- Reasonable cost
- Mask induction = noxious odor may lead to breath holding and bronchoconstriction
- Produces carbon monoxide when exposed to desiccated CO2 absorbent
Isoflurane
Which anesthetic is described by the following?
- Lower blood gas partiton coefficient than isoflurane
- More rapidly induction and recovery
- Lower potency than iso (need higher vaporizer setting)
- Similar cardio-respiratory depression to isoflurane
Sevoflurance
Which anesthetic is described by the following?
- Good muscle relaxation
(could trigger malignant hyperthermia) - Mask induction = less odor so smoother induction
- around 3% metabolized in the body and the rest eliminated via the lung
Sevoflurane
Which anesthetic is described by the following?
- Can be degraded by CO2 absorbents to produce Compound A (no clinical sig.)
Sevoflurane
Describe the Pharmocodynamics of the CNS when using anesthetics
decreases cerebral metabolic rate (oxygen consumption)
- either no chnage or an increase in cerebral blood flow
- decrease in cerebral perfusion pressure
- Increase ICP
Describe the Pharmocodynamics of the respiratory when using anesthetics
Drug and species specific depression of ventilation = increased CO2
- bronchodilation
- Desflurane irritates airway
Describe the Pharmocodynamics of the cardiovascular system when using anesthetics
Can decrease cardiac output and BP; arrythmias associated with certain drugs may be exaggerated
What does TIVA stand for
Total intravenous anesthesia
What does PIVA stand for
Partial intravenous anesthesia
Should TIVA OR PIVA be limited to 1 hour
- due to prolonged recovery time associated with longer time?
TIVA
Does the following describe TIVA OR PIVA?
- “triple dip” infusion of ketamine, xylazine, and guaifenesin to produce general anesthesia in a horse having a casteration
TIVA
Does the following describe TIVA OR PIVA?
“MLK” + reduced isoflurane concentration for a dog having a TPLO
PIVA
What medication is a centrally acting muscle relaxant with sedative properties
- co-admisitered with other anesthesic agents for the IV induction and/or maintance of anesthesia
Guaifenesin (GG)
T/F: Guaifenesin (GG) is never used in horses, only ruminants?
FALSE!!
they are used in both
What drug is described as?
- MOA unknown but works on the brain and spinal cord
- No analgesic properties
- wide theraputic margin, but overdose can result in cardio-respiratory depression
Guaifenesin (GG)
What medication does the following describe?
- Hepatic metabolism and renal excretion (more rapidly eleminated in female ponies)
Guaifenesin (GG)
