Ch. 8: Inhalational Anesthetics Flashcards
Methoxyflurane: Is metabolized to ___________ which can cause this adverse effect: ___________.
Solubility:
Vapour pressure:
Type of compound:
Methoxyflurane: Is metabolized to fluoride which can cause this adverse effect: renal failure.
Solubility: High
Vapour pressure: Low
Type of compound: Halogenated
Induction and emergence with methoxyfluorane is ________ (fast or slow?)
Why? (2 reasons)
Induction and emergence with methoxyfluorane is slow.
Why?
- Low vapour pressure
- High solubility
Discuss the solubility of Nitrous Oxide.
- Relatively insoluble compared with other agents
- But, compared to Nitrogen, nitrous oxide is 35x more soluble in blood. Therefore, it tends to diffuse into air-containing cavities such as bowel obstruction, pneumothorax, air emboli, tympanic membranes, and ETT cuffs.
Nitrous Oxide:
- Blood/gas coefficient:
- Fat/blood coefficient:
- Mechanism of action:
- Flammable?
- CV effects (including effect on PVR):
- Changes to RR, Vt and MV:
- Changes in respiratory drive:
- Effects on ICP and CMRO2:
- Effect on renal and hepatic blood flow:
- Effect on muscle tone:
- Is it an MH trigger?
- Is it safe in pregnancy?
- One common side effect:
- Two adverse effects of prolonged exposure:
Nitrous Oxide:
- Blood/gas coefficient: 0.47
- Fat/blood coefficient: 2.3 (low)
- Mechanism of action: Inhibits NMDA receptors
- Flammable? : Nonflammable, but supports combustion like O2
- CV effects (including effect on PVR): Direct myocardial depressant + increases sympathetic tone = Fairly unchanged HR, BP and CO, but may increase slightly. Unless pt has CAD or is hypovolemic. Increases PVR.
- Changes to RR, Vt and MV: RR increases, Vt decreases (rapid, shallow breathing) - result is minimal change in MV
- Changes in respiratory drive: Hypoxic drive is markedly reduced
- Effects on ICP and CMRO2: Mild increase in ICP and increases CMRO2
- Effect on renal and hepatic blood flow: Decreases both
- Effect on muscle tone: No muscle relaxation per se, but potentiates. At high concentrations in hyperbaric chambers, can cause rigidity.
- Is it an MH trigger? Nope.
- Is it safe in pregnancy? It is possibly teratogenic so should be avoided before the 3rd trimester.
- One common side effect: N/V
- Two adverse effects of prolonged exposure: Inhibits Vitamin B12-dependent enzymes, so prolonged exposure can cause bone marrow depression (megaloblastic anemia) and peripheral neuropathies.
Enflurane:
Type of compound:
Flammable?
Pungent?
CV effect:
Two unique things:
Enflurane:
Type of compound: Halogenated ether
Flammable? No
Pungent? No
CV effect: Myocardial depressant
Two unique things:
- Risk of seizures
- Decreases CSF production
Xenon:
Mechanism of action:
Metabolism:
Toxicity level:
Blood solubility:
MH trigger?
2 other advantages:
2 disadvantages:
Xenon:
Mechanism of action: Inhibits NMDA receptors
Metabolism: Likely none (inert)
Toxicity level: Likely none (inert)
Blood solubility: Low
MH trigger? No.
2 other advantages: Environmentally friendly and has little effect on CV, hepatic or renal systems.
2 disadvantages: Expensive and low potency (MAC = 70%)
In terms of MAC, what equals the ED50 and the ED95?
How much MAC equals MAC awake?
(What is the MAC awake?)
ED50 = 1 MAC
ED95 = 1.3 MAC
MAC awake = 0.3-0.4 MAC*
*when the only anesthetic agent onboard is the inhaled anesthetic
MAC awake = the MAC at which the pt awakens from anesthetic.
MAC of common agents:
Nitrous Oxide:
Halothane:
Isoflurane:
Sevoflurane:
Desflurane:
MAC of common agents organized by potency going up:
Nitrous Oxide: 105%
Desflurane: 6.0%
Sevoflurane: 2.0%
Isoflurane: 1.2%
Halothane: 0.75%
For each decade of age, MAC decreases by how much?
For each 1oC drop in temperature below 37oC, how much does MAC increase or decrease by?
6% decrease per decade of age
15% decrease per 1oC drop below 37oC
What effect does hyperthermia have on MAC?
It decreases it, just like hypothermia.
Exception: if the temperature is over 42oC, then the MAC actually increases.
- What is the site of inhibition of motor responses by volatile anesthetics?
- Is MAC affected by the duration of anesthesia and how?
- The spinal cord
- No it is not.
Effects of the following on MAC:
Hypoxemia:
Hypercarbia:
Thyroid disease:
Pregancy (And by how much? When does it return to normal?):
Hypercalcemia:
Hyponatremia:
Hypernatremia:
Effects of the following on MAC:
Hypoxemia: decreases
Hypercarbia: decreases
Thyroid disease: has no effect on MAC
Pregancy (and by how much?): Decreases. By 1/3 at 8 wk’s gestation. Back to normal by 72h postpartum.
Hypercalcemia: decreases
Hyponatremia: decreases
Hypernatremia: increases
Halothane:
- Hemodynamic effects:
- Effect on coronary blood flow specifically?
- Effect on oxygen demand:
- Effect on renal and hepatic blood flow:
Halothane:
- Hemodynamic effects:
- Direct myocardial depressant
- No effect on SVR
- Dose-dependent decrease in BP
- Increases right atrial pressure
- Blunts the baroreceptor reflex so the HR drops too
- Effect on coronary blood flow specifically? Decreases coronary blood flow because of the overall drop in BP, even though it is a coronary vasodilator
- Effect on oxygen demand: Oxygen demand decreases
- Effect on renal and hepatic blood flow: Decreases both.
Halothane:
Effect on RR, Vt and MV:
Effect on drive to breath:
Effect on resting PaCO2:
2 other effects on the pulmonary system:
Halothane:
Effect on RR, Vt and MV: Increases RR, decreases Vt and overall effect on MV: decreases it.
Effect on drive to breath: Decreases the hypoxic drive to breath severely, even at low doses. Increases the apneic threshold.
Effect on resting PaCO2: Increases it
2 other effects on the pulmonary system: Potent bronchodilator; not through B-agonism but through Ca++ inhibition. Secondly, depresses mucous clearance.
Discuss using halothane for a pheochromocytoma.
Bad idea to use halothane for a pheo.
Reason: Halothane sensitises the myocardium to the arrythmogenic effects of epinephrine.