II. Indications
-
Procedural Sedation (esp. pediatrics)
- Low intensity procedures (e.g. Lumbar Puncture, Laceration Repair, minor Fracture reduction)
- Moderate analgesia
- Best used in combination with Local Anesthesia (e.g. local infiltration, Hematoma Block)
III. Contraindications (related to gas expansion risks)
- Pneumothorax
- Pulmonary Blebs
- Bowel Obstruction
- Air Embolism
- Pneumocephalus
- Recent eye surgery
IV. History
- First used for Anesthesia in U.S. in 1845
- Used in a majority of pediatric dental offices
V. Mechanism
- Nitrous Oxide is a colorless, tasteless gas
- Effects Opioid spinal modulators, GABA Receptors, NMDA receptors
- Also releases endorphins
VI. Pharmacokinetics
- Rapidly absorbed in lung and cleared from lung
- Excreted unchanged (not metabolized) primarily from lung within one minute of inhalation
- Poorly soluble in blood
- Onset: 2-3 minutes
- Duration: 3-5 minutes
- Rapidly off-loads with oxygen (often given for 5 minutes after procedure)
- Effects
- Mild anxiolysis: <50% Nitrous Oxide
- Analgesia: 50-70% Nitrous Oxide
- Amnesia
- Minimum Alveolar Concentration (MAC): 105.0%
- Nitrous Oxide MAC is much higher than other inhalation Anesthetics (e.g. Isoflurane)
- With a high MAC, Nitrous Oxide is a poor general Anesthetics alone, but offers good lower level sedation
VII. Adverse Effects
- Light Headedness
- Somnolence
- Confusion
- Paresthesias
- Nausea or Vomiting (1-2% of cases)
- Inadequate sedation (1.2% of cases)
- Airway obstruction or Hypoxia (0.25% of cases)
- More common with concurrent Opioids or Benzodiazepines
VIII. Safety
- Among the safest sedation agents with proper use and monitoring (ACEP, 1984)
- Airway obstruction or Hypoxia is rare (0.25% of cases)
- Has not been associated with apnea
- Hemodynamically stable without effects on Heart Rate or Blood Pressure
- Very rare mortality (case reports)
- No Allergic Reactions reported
- No pregnancy data, and not recommended in first or second trimester
- Considered likely safe in third trimester
- No delay in Lactation
- Not considered Procedural Sedation unless combined with other agents (e.g. Fentanyl, Midazolam)
- Does not require cardiac monitoring, End-Tidal CO2 or Intravenous Access
- Pulse Oximetry is typically adequate monitoring for Nitrous Oxide
IX. Preparation
-
General equipment
- Oxygen supply
- Wall suction
- Airway equipment
- Educate patient on use of mask
- Patient instructed to take deeper breaths if feels more pain
- Nitrous Oxide delivery device
- Full Face Mask or Nasal mask (may be scented)
- Delivery mix: 50:50 to 70:30 mix of Nitrous Oxide and oxygen
- Preferred mix appears to be 70:30
- Typically portable unit with Nitrous Oxide tanks, and attached to wall oxygen
- Device should have audible alarms, flow control and scavenger functionality (suction)
- Scavenger functionality prevents bystander exposure to Nitrous Oxide
- Does not require a medical gas vacuum system
X. Dosing
- Goal Nitrous Oxide effects (expect onset within 2-3 min of starting Nitrous Oxide)
- Apathy
- Somnolence
- Still responds to verbal stimuli
- Start with total liter flow estimation
- Child: 4-5 L/min
- Adult: 6-7 L/min
- Watch reservoir bag while on oxygen only, and goal inflation is 2/3 full (not collapsed and not full)
- Initiate Nitrous Oxide
- Start 10-15% Nitrous Oxide and increase every couple of minutes to effect (see above)
- Patient asked to breath normally through their nose and to relax
- Prepare patient that they may have arms and legs
- Titrate Nitrous Oxide
- Self-titration method
- Patient holds mask to their own face
- As sedation increases, the mask drops away
- When they awaken again, they replace the mask to once again increase sedation
XI. References
- Acker, Koval and Leeper (2017) Crit Dec Emerg Med 31(4): 3-13
- Cordle (2016) Nitrous Oxide Lecture, ACEP PEM Conference, attended 3/9/2016
- Lapietra and Swaminathan in Swadron (2022) EM:Rap 22(3): 6-8