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08.05.07 (11 months ago)
#11
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NITROUS OXIDE
Indications¾ Anesthetic potency relatively weak; usually must be supplemented with other agents.
Often given concurrently with one of the more potent inhalation anesthetics to reduce the requirement for the other anesthetic.
Also indicated in low doses to provide analgesia in obstetrics and for procedures not requiring loss of consciousness.
Pharmacology/pharmacokinetics¾ Minimum alveolar concentration (MAC) in oxygen:
> 100%.
Blood-to-gas partition coefficient (37 °C):
0.47
Oil-to-gas partition coefficient (37 °C):
1.4
Biotransformation:
None of dose metabolized.
Elimination:
Primary: 100% excreted unchanged by exhalation.
Other actions/effects:
Blood pressure generally unchanged.
Heart/pulse rate increases.
Constriction of peripheral vasculature.
No dose-related muscle relaxation.
Precautions¾ Pregnancy:
Studies in animals have shown that nitrous oxide causes fetal death, growth retardation, and skeletal anomalies.
Drug interactions and/or related problems:
In addition to the increased CNS depressant, respiratory depressant, and hypotensive effects that may occur when an anesthetic is used concurrently with any CNS depressant, concurrent use of high doses of fentanyl or its derivatives with nitrous oxide may decrease the heart rate and cardiac output. These effects may be more pronounced in patients with poor left ventricular function.
Medical considerations/contraindications:
Caution needed in the presence of air-enclosing cavities (such as pulmonary, renal, or occluded middle ear air cysts or air embolism), acute intestinal obstruction, or pneumothorax, or during or recently following the procedure of pneumoencephalography, as nitrous oxide may increase pressure within rigid-walled cavities or volume within nonrigid-walled cavities.
Additional Dosing Information
Nitrous oxide must be administered with at least 30% of oxygen to reduce the risk of hypoxia.
For anesthesia
Premedication of the patient with an opioid analgesic or a barbiturate may be necessary in order to achieve induction of anesthesia.
Nitrous oxide may diffuse into the cuff of an endotracheal tube; periodic deflation of the endotracheal tube is recommended during administration.
The concentration administered during maintenance of anesthesia must be individualized, depending upon the condition of the patient and the type and quantity of supplemental medications administered.
When prolonged administration of nitrous oxide is discontinued, 100% oxygen should be administered briefly to reduce the risk of diffusion hypoxia
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