Chapter 15- Inhalation Anesthetics and Gases Flashcards
How is inhaled anesthesia produced?
By controlled administration of gaseous volatile drugs
How can the magnitude of depression of the CNS be controlled when using inhaled anesthetics?
By altering the partial pressure or concentration of anesthetic
Why is it important to be able to supplement a horse with oxygen during anesthesia?
Because GA and recumbency reduce the horse’s ability to oxygenate arterial blood
The degradation process of the sevoflurane produces ____
Compound A
The degradation of sevoflurane and isoflurane produces ____
Carbon monoxide
What is the partition coefficient?
It is the ratio of the anesthetic between two phases after equilibration
Solubility of an inhaled anesthetic is expressed as the ____
Partition coefficient
What happens at equilibrium with:
1. Partial pressure of the anesthetic
2. The concentration of the anesthetic
- The partial pressure in the two phases is the same
- The concentration can differ greatily
What does a PC of 2.5 mean for an anesthetic X in equilibrium?
The concentration of the anesthetic in blood is 2.5 times greater than in gas, whereas partial pressure is equal in both phases
If anesthetic X has a PC of 2.5 and anesthetic Y has a PC of 0.5, which one can induce the patient faster?
Anesthetic Y
How is solubility (PC) related to the speed of induction?
Higher solubility (PC) is related to slower induction
The blood:Gas PC correlates inversely with ____
Anesthetic potency
Relationship between the administered dose and the magnitude if the effect is an expression of ____
Potency of the anesthetic
What is the ED50
The dose at which 50% of the horses get anesthetized
True/False: MAC is represented by the vaporizer setting
False, MAC is ALVEOLAR concentration and not the inspired concentration
At equilibrium of gas and arterial blood, and the arterial and brain anesthetic partial pressure, MAC should be an indication of ____
Partial pressure of the anesthetic in the CNS
MAC of most common anesthetics
- Halothane 0.9-1.05%
- Isoflurane 1.31-1.64%
- Sevoflurane 2.31-2.84%
- Desflurane 7.02-8.06%
- Nitrus oxide 205%
Most patients require ____ to ____ MAC or less for an adequate anesthesia
1.2 to 1.4 MAC
True/False: Sites of action for the inhaled anesthetics are located in the brain and the spinal cord
True
Anesthetic moves through phases by
Down the partial pressure gradients
Measuring alveolar anesthetic pressure is a reliable method to monitor ____
Anesthetic dose (MAC)
What happens after reducing the anesthetic to zero?
Reversal on gradients occur
Moving down from CNS to blood to alveoli to athmosphere
Delivery of the anesthetic to alveoli depends on
Inspired concentration and alveolar ventilation
What can increase delivery of anesthetic to the alveoli?
Increasing the vaporized dial setting or supplementing alveolar ventilation
How can an elevated PC make the induction slower?
It enhances the removal of the anesthetic from the alveoli retarding equilibration of partial pressure between alveoli:blood:brain
How can a high cardiac output affect the induction?
It increases the amount of blood match with alveoli per unit time decreasing the rise of alveolar partial pressure and slowing down the induction
Venous partial pressure is dictated by
Solubility in tissues (tissue:blood PC), blood flow, PC arterial blood:tissue
Solubility of the common inhaled anesthetics
- Halothane 2.4
- Isoflurane 1.4
- Sevoflurane 0.7
- Desflurane 0.5
- Nitrous oxide 0.5
Organize the most common anesthetics from higher to lower solubility
Halothane > Isoflurane > Sevoflurane > Desflurane/Nitric oxide
Alveolar partial pressure decreases ____ with more soluble anesthetics
More slowly
If large quantities of the anesthetic are dissolved in tissues, they serve as reservouir that maintains alveolar partial pressure, this leads to
Slower recovery
Halothane effect on CO
It decreases stroke volume decreasing CO
True/False: With halothane, there is usually no change in vascular resistance
True
What effect do inhaled anesthetics have in EEG?
Brain waves become larger and slower in frequency
The risk of developing elevations of hepatic enzymes in serum can happen after ____ of surgery
After 3 hours of surgery
Halothane depresses these in the kidney (2)
- Renal blood flow
- GFR
About ____ of the administered halothane undergoes biotransformation
20-25%
The major metabolite from halothane biotransformation is
Trifluoroacetic acid
Eliminated by the kidney
Isoflurane undergoes a ____ of biotransformation
0.17%
What effect do variations in temperature have on desflurane delivery?
Unacceptable variations in delivery
True/False: Desflurane has the lowest solubility providing the fastest induction and recovery
True
What happens with desflurane after 1.5 MAC?
Looses hemodynamic advantage and becomes a similar or greater cardiovascular depressant
Desflurane undergoes a ____ of biotransformation
0.02%
Sevoflurane undergoes a ____ of biotransformation
3%
What byproduct of sevoflurane biotransformation is potentially nephrotoxic?
Fluoride
What are the methods of control for occupational exposure with inhaled anesthetics? (3)
- Clean up sources of gas spillage
- Adequate ventilation
- Use waste anesthetic scavenging
Anesthesia machines
(Table)
