(1-18-17) Nitrous Oxide (New) Flashcards
how is nitrous manufactured?
- ammonium nitrate crystals are heated forming water and N2O
- chemical purification, dehydration, and compression
- stored as a liquid
how is nitrous distributed?
- blue cylinders
- -30% liquid, 70% gas when full
what are the chemical properties of nitrous?
- stable at room temps
- cools with vaporization
- not metabolized
- nonflammable, non-explosive
- will support combustion
how pure is nitrous oxide?
99%
must be at least 97% for medical use
what are the physical properties of nitrous?
- nonirritating
- slightly sweet smelling (overwhlemed by rubber smell)
- colorless
- INORGANIC, unlike all other anesthetic gases
what is the potency of nitrous?
- LEAST POTENT of all anesthetic gases
- most used of all anesthetic gases
- produces LIGHT sedation
- possible but rare to produce general anesthesia
how is anesthetic gas potency measured?
MAC
what is the MAC?
the alveolar conc. at which 50% of the population will not respond (with movement) to a standard surgical incision
what is the MAC of N2O?
-104%
(most major anesthetic gases have MAC of 1-6%
what are the pharmacodynamic effects of N2O?
- analgesic so it dec perception of pain
- frequently anxiolytic (reduces anxiety)
- blunts gagging response
what is blood-gas solubility?
a measure of affinity of blood for the gas - the ratio at equilibrium between blood and gas concentrations
what is the blood-gas solubility of N2O?
-0.47
- poorly soluble in blood
- high gas tension maintained in alveoli
- rapid entry, rapid removal from blood via lungs
poor solubility of N2O in blood leads to what?
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
how long does it take for blood-brain saturation for N2O?
3-5 minutes
how does diffusion hypoxia occur with discontinuation of N2O?
- nitrous oxide exits blood into alveoli rapidly
- this DILUTES other alveolar gases, including O2
- rare in dental conscious sedation setting
how do you avoid diffusion hypoxia?
give pt 100% oxygen for 3-5 minutes after using Nitrous
which is more soluble: N2O or N2?
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
what are the CV effects of nitrous?
- minimal effects at useful conc
- not change in HR or CO
- often see DROP in BP and HR from reduced anxiety
what are the respiratory effects of nitrous?
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
what are the CNS effects of Nitrous?
- affects all forms of sedation
- tingling and hearing changes
- mild CNS depression, especially in “thinking” centers (concentration, ability to reason, memory)
- nausea and vomitting
what are the GI affects of nitrous?
- no direct effects
- may distend gas-filled intestine
what are the renal effects of nitrous?
none
what are the hepatic effects of nitrous?
none
what are the hematologic effects of nitrous?
chronic exposure may depress bone marrow activity
what are the skeletal mm effects of nitorus?
relaxation from reduced anxiety
what are the effects of nitrous on pregnancy?
- 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
what are the physiologic contraindications of nitrous?
- none
- should be avoided if:
- -pt refuses
- -pt has phychosis (impaired thoughts/emotions) or depression
- -use with caution with pts with severe COPD
what happens if there is chronic exposure to N2O?
- 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)
what is the highest permissible level of N2O?
25ppm
how many alveoli are there?
more than 300 million
of the inspired gases in the world (O2, CO2, N2) which one is inspired more, most in the alveoli, and expired more?
N2
what are blue tanks full of?
nitrous oxide
what are green tanks full of?
O2
what are yellow tanks full of?
medical air, 30% O2/70% N2
what are black tanks full of?
nitrogen
what is the universal gas law?
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
what is the volume of O2 at 1000psi? 500psi?
1000psi = 330L 500psi = 165L
what is the partial pressure of N2O as long as there is gas in the tank?
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
