Pharmacology of Nitrous Oxide Flashcards
How is Nitrous distributed?
blue cylinders that have 30% liquid, 70% gas when full
what are the chemical properties of Nitrous?
- stable at room temp
- cools with vaporization
- hardly metabolized
- non-flammable
- will support combustion if heated high enough
who pure must nitrous be for medical use?
99%
what are the physical properties of Nitrous?
- nonirritating
- slightly-sweet smelling (odor overwhelmed by rubber)
- colorless
- inorganic (UNLIKE ALL OTHER ANESTHETIC GASES)
how is the dose of nitrous quantified?
by the concentration (percentage) delivered
how is the potency of nitrous measured?
minimum alveolar concentration (MAC)
when do the effects of nitrous wear off?
usually minutes following end of delivery
the alveolar conc. at which 50% of the population will not respond (with movement) to a standard surgical incision
minimum alveolar concentration (MAC)
what is the MAC of nitrous?
104%
*most major anesthetic gases have a MAC of 1-6%
is nitrous the most/least potent of all anesthetic gases used?
least
is GA possible with nitrous?
yes but rare
a measure of affinity of blood for the gas - the ratio at equilibrium btw blood and gas concentrations
blood-gas solubility
what is the solubility coefficient for N2O?
0.47
- poorly soluble in blood
- high gas tension maintained in alveoli
- rapid entry, rapid removal from blood via lungs
poos solubility in blood leads to what?
high conc in highly perfused tissues
- mostly brain
- fat, skeletal mm NOT sig reservoir
- reason for rapid recovery
what is the conc effect of nitrous?
- high levels are taken up rapidly into blood
- this sucks more gas into lungs
- effect is as if higher conc was given
how long does it take for blood-brain saturation
3-5 minutes
what is diffusion hypoxia?
- when nitrous oxide enters lungs form blood rapidly
- this pushes other gases out, including O2
- to avoid give pts 100% O2 for 3-5 minutes after use
dec perception of pain
analgesic
what are the effects on the cardiovascular system?
- minimal effects at useful conc
- no change in HR, cardiac output
- often see drop in BP from reduced anxiety
- may see slight peripheral vasodilation, causes flushing
what are the effects on the central nervous system?
- affects all forms of sensation
- tingling, hearing changes
- mild CNS depression, especially of thinking centers (memory concentration, ability to reason)
what are the effects on the respiratory system?
- nonirritating (OK with pulmonary disease)
- may see change in rate, depth of respiration from reduced anxiety
what are the effects on the GI system?
- no direct effects
- may distend gas-filled intestine in bowel obstruction pt
what are the effects for the renal system?
none
what are the effects for the hepatic system?
none
what are the effects for the hematologic system?
chronic exposure may depress bone marrow activity
what are the effects for the skeletal m?
relaxation from reduced anxiety
what are the effects for pregnancy?
- NOT a contraindication
- used during labor and delivery
- DOES cross the placenta but without apparent effect at usual concentrations
- is prudent to avoid if possible (like all drugs) esp during first trimester
when should N2O be avoided?
- if pt refuses
- if pt has psychosis, uncontrolled depression
*use with caution in pts with severe COPD and emphysema
what does chronic exposure lead to?
- bone marrow depression secondary to abusive exposure
- sensory depression from peripheral neuropathy (tingling fingers)
- possible inc in spontaneous abortion rate
