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Pharm II > (1-18-17) Nitrous Oxide (New) > Flashcards

(1-18-17) Nitrous Oxide (New) Flashcards

1
Q

how is nitrous manufactured?

A
  • ammonium nitrate crystals are heated forming water and N2O
  • chemical purification, dehydration, and compression
  • stored as a liquid
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2
Q

how is nitrous distributed?

A
  • blue cylinders

- -30% liquid, 70% gas when full

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3
Q

what are the chemical properties of nitrous?

A
  • stable at room temps
  • cools with vaporization
  • not metabolized
  • nonflammable, non-explosive
  • will support combustion
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4
Q

how pure is nitrous oxide?

A

99%

must be at least 97% for medical use

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5
Q

what are the physical properties of nitrous?

A
  • nonirritating
  • slightly sweet smelling (overwhlemed by rubber smell)
  • colorless
  • INORGANIC, unlike all other anesthetic gases
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6
Q

what is the potency of nitrous?

A
  • LEAST POTENT of all anesthetic gases
  • most used of all anesthetic gases
  • produces LIGHT sedation
  • possible but rare to produce general anesthesia
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7
Q

how is anesthetic gas potency measured?

A

MAC

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8
Q

what is the MAC?

A

the alveolar conc. at which 50% of the population will not respond (with movement) to a standard surgical incision

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9
Q

what is the MAC of N2O?

A

-104%

(most major anesthetic gases have MAC of 1-6%

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10
Q

what are the pharmacodynamic effects of N2O?

A
  • analgesic so it dec perception of pain
  • frequently anxiolytic (reduces anxiety)
  • blunts gagging response
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11
Q

what is blood-gas solubility?

A

a measure of affinity of blood for the gas - the ratio at equilibrium between blood and gas concentrations

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12
Q

what is the blood-gas solubility of N2O?

A

-0.47

  • poorly soluble in blood
  • high gas tension maintained in alveoli
  • rapid entry, rapid removal from blood via lungs
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13
Q

poor solubility of N2O in blood leads to what?

A

rapid high gas tension in highly perfused tissues

  • mostly brain
  • blood-brain saturations in 3-5 minutes
  • fat/skeletal mm not a significant reservoir
  • THIS HELPS BRING ABOUT RAPID RECOVERY
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14
Q

how long does it take for blood-brain saturation for N2O?

A

3-5 minutes

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15
Q

how does diffusion hypoxia occur with discontinuation of N2O?

A
  • nitrous oxide exits blood into alveoli rapidly
  • this DILUTES other alveolar gases, including O2
  • rare in dental conscious sedation setting
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16
Q

how do you avoid diffusion hypoxia?

A

give pt 100% oxygen for 3-5 minutes after using Nitrous

17
Q

which is more soluble: N2O or N2?

A

N2O is 37x more soluble than N2, so N2O enters CLOSED SPACES faster than N2 can be eliminated

*caution with : otitis media, emphysema, gas-filled intestine in bowel obstruction

18
Q

what are the CV effects of nitrous?

A
  • minimal effects at useful conc
  • not change in HR or CO
  • often see DROP in BP and HR from reduced anxiety
19
Q

what are the respiratory effects of nitrous?

A

nonirritating

  • OK to use in pulmonary diseases, INCLUDING ASTHEMA
  • dec anxiety may actually be beneficial
  • may see change in rate, depth of respiration from reduced anxiety
20
Q

what are the CNS effects of Nitrous?

A
  • affects all forms of sedation
  • tingling and hearing changes
  • mild CNS depression, especially in “thinking” centers (concentration, ability to reason, memory)
  • nausea and vomitting
21
Q

what are the GI affects of nitrous?

A
  • no direct effects

- may distend gas-filled intestine

22
Q

what are the renal effects of nitrous?

A

none

23
Q

what are the hepatic effects of nitrous?

A

none

24
Q

what are the hematologic effects of nitrous?

A

chronic exposure may depress bone marrow activity

25
Q

what are the skeletal mm effects of nitorus?

A

relaxation from reduced anxiety

26
Q

what are the effects of nitrous on pregnancy?

A
  • NOT A CONTRAINDICATION
  • used during labor and delivery
  • DOES cross the placenta but without apparent side effects at usual conc
  • is prudent to avoid if possible (like all drugs), especially during FIRST trimester
27
Q

what are the physiologic contraindications of nitrous?

A
  • none
  • should be avoided if:
  • -pt refuses
  • -pt has phychosis (impaired thoughts/emotions) or depression
  • -use with caution with pts with severe COPD
28
Q

what happens if there is chronic exposure to N2O?

A
  • oxidizes colbalt in Vit B12
  • renders inactive methionine synthase (vit B12 dependent)
  • methionine synthase necessary for formation of methionine and conversion of folate to active form
  • inhibition of LHRH from hypothalamus
  • bone marrow depression
  • sensory depression from peripheral neuropathy (tingling fingers)
  • possible inc in spontaneous abortion rate/dec conception rates (w/o scavenging)
29
Q

what is the highest permissible level of N2O?

A

25ppm

30
Q

how many alveoli are there?

A

more than 300 million

31
Q

of the inspired gases in the world (O2, CO2, N2) which one is inspired more, most in the alveoli, and expired more?

A

N2

32
Q

what are blue tanks full of?

A

nitrous oxide

33
Q

what are green tanks full of?

A

O2

34
Q

what are yellow tanks full of?

A

medical air, 30% O2/70% N2

35
Q

what are black tanks full of?

A

nitrogen

36
Q

what is the universal gas law?

A

PV = nRT

  • p = pressure
  • V = volume (constant in cylinder)
  • n = number of moles
  • R = universal gas constant
  • T = temerature (assume constant)

**amount of gas is directly proportional to pressure in tank at fixed volume and temp

37
Q

what is the volume of O2 at 1000psi? 500psi?

A 
1000psi = 330L
500psi = 165L
38
Q

what is the partial pressure of N2O as long as there is gas in the tank?

A

750 psi

  • when pressure starts to drop, all liquid is vaporized
  • approx 400L remains
  • then follows universal gas law

*** see ppt for practice problems with this math

Pharm II (16 decks)

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