Flashcards in Nitrous Oxide Deck (28)
What is another name for N2O?
What is the drug classification for nitrous oxide?
What is nitrous oxide (describe the gas!)?
it is a low-molecular weight, odorless to sweet-smelling nonflammable gas of low potency and poor blood gas solubility (0.46) that is most commonly administered in combination with opioids or volatile anesthetics to produce general anesthesia
What is the MOA of nitrous oxide?
Current theory is that target proteins (most likely ion channels and/or receptors) are the site of action of the inhaled anesthetics
-separate sites of action for loss of consciousness and immobility have been proposed
How is Nitrous Oxide metabolized?
-an estimated 0.004% of an absorbed dose of nitrous oxide undergoes reductive metabolism to nitrogen in the GI tract
-Anaerobic bacteria, such as Pseudomonas, are responsible for this reductive metabolism
-there is no evidence that nitrous oxide undergoes oxidative metabolism in the liver
What inhibits the metabolism of nitrous oxide by anaerobic bacteria?
-oxygen concentrations of >10% in the GI tract and antibiotics inhibit the metabolism of nitrous oxide by anaerobic bacteria
What is the elimination route for nitrous oxide?
Eliminated almost entirely unchanged via the lungs
How does nitrous oxide produce anesthesia; and how does this involve the volume of distribution?
-When nitrous oxide is added to inspired air at a concentration that will produce anesthesia, the rate at which this equilibrium is approached depends on the blood/gas partition coefficient
-The lower the blood/gas coefficient, the lower the solubility in the blood
-a lower solubility in the blood allows the gas to reach alveolar/arterial equilibrium quickly
Tell me about Nitrous Oxides blood/gas and oil/gas partition coefficient...
Has a LOW blood/gas partition coefficient (0.46), which allows the gas to achieve a given partial pressure in the blood very quickly compared with other available inhaled agents
-In addition, nitrous oxide also has low oil/gas partition coefficient of 1.4, which allows for a fast recovery from anesthesia
Does nitrous oxide reach equilibrium fast or slow? why?
Due to low blood/gas partition coefficient, N2O reaches equilibrium very fast and uses the same principle for elimination or washout; the speed of elimination mirrors that of the rate of equilibrium!!!!
What is diffusional anoxia? What drug is this a side effect of?
(Transient hypoxia) can occur during recovery of nitrous oxide anesthesia due to the transfer of gas from the blood and to the alveoli which can be sufficient to reduce, by dilution, the alveolar partial pressure of oxygen
-side effect of Nitrous Oxide!
What is the typical respiratory pattern with nitrous oxide?
Increased RR, Decreased Tidal Volume, and Reduced hypoxic drive
What are the neurological side effects of nitrous oxide?
Increases in CBF, Cerebral Metabolic Rate (CMR), and ICP
What are the CV side effects of nitrous oxide?
-Myocardial depressant and sympathomimetic
-it may cause increases in pulmonary vascular resistance with the greatest response in patients with pre-existing pulmonary HTN
-may also elicit a compensatory, sympathetically mediated increase in SVR
What can nitrous oxide cause in a gas sense?
-Expansion of gas
-Bowel gas expansion is associated with the use of nitrous oxide in abdominal surgeries and this expansion can interfere with surgical closure
-can accumulate in gaseous cavities and therefore exacerbate such conditions as pneumothorax and pneumocephalus
-75% nitrous oxide can expand a pneumothorax to double or triple its size in 10-30 minutes
-Air-filled cuffs of pulmonary artery catheters and endotracheal tubes also expand with the use of nitrous oxide, possibly causing tissue damage
What are the renal side effects of nitrous oxide?
Decreases RBF, GFR, UO and Hepatic BF
What can occur with prolonged exposure to Nitrous Oxide >6hrs?
Bone marrow depression causing anemia and leucopenia can occur due to prolonged exposure from the inactivation of methionine synthase, an enzyme required for DNA and protein synthesis
With regards to blood disorders, when should nitrous oxide be avoided?
in patients with anemia related to B12 deficiency
What can nitrous oxide do to a fetus? Why?
impaired fetal development may occur when nitrous oxide is used during long cases (over 12 hrs) due to substantial accumulation of metabolic breakdown products
Talk to me about nitrous oxide and pregnancy
linked to increased miscarriage rate
What can nitrous oxide do to hearing?
may be diminished post op
What is a neuromuscular side effect of nitrous oxide?
may increase motor activity with clonus and opisthotonus even in clinically used concentrations
Can nitrous oxide cause malignant hyperthermia?
it can be a weak trigger for malignant hyperthermia
What are the contraindications of nitrous oxide?
-when a patient has a pathologic or iatrogenic closed air space including: pneumothorax, pneumocephalus, ophthalmic procedures involving air injection, vascular air embolism, or if the intestine is obstructed
-GI surgery is a relative contraindication
-Avoided in patients at increased risk for PONV
-Potential toxic effects on cell function via inactivation of Vit. B12 and its adverse effects related to absorption and expansion into air-filled structures and bubbles, and lastly its effect on embryonic development are all potential contraindications for using nitrous oxide
-relative for tympanoplasty because the increased pressure can dislodge a tympanic graft
-Should not be given during a posterior fossa procedure once the intracranial space has been completely sealed from the atmosphere due to the possibility of a tension pneumocephalus
What are the drug interactions with nitrous oxide, specifically the second gas effect?
-Second Gas Effect: a special case of concentration effect applies to administration of a potent anesthetic with nitrous oxide--that is, 2 gases simultaneously. Along with the concentration of the potent agent in the alveoli via its uptake, there is further concentration via the uptake of nitrous oxide
What is the dose of Nitrous Oxide?
What is the vapor pressure of nitrous oxide?
38,770 mmHg at 20C