Introduction to Nitrous Oxide Practice Flashcards

Historical Development and Regulatory Standards

• Training and Certification Requirements: Practitioners using nitrous oxide must be trained to a stage at least one or two stages beyond the level at which they intend to work. This ensures they can manage patients who may inadvertently drift into deeper levels of sedation.

• Historical Timeline of Nitrous Oxide:

  • The drug was discovered approximately $255$ years ago.
  • Initially, it was used primarily for recreation for several decades.
  • In the early days of its discovery, there was no concept of "analgesic" medicine (pain relief).
  • In $1844$, a dentist named Horace Wells identified it as what was then termed a "general anesthetic."

• Key Figures in Early Use:

  • Horace Wells: The dentist credited with discovering its medical application.
  • Dr. Riggs: He performed a molar extraction on Horace Wells using only nitrous oxide as the anesthetic agent. This occurred prior to the discovery of Lidocaine's lesion.

• Evolution of Administration:

  • For many decades, it was used without supplemental oxygen. This resulted in a combination of nitrous oxide effects and hypoxia, which was dangerous and often led to patients losing consciousness simply from lack of oxygen.
  • Modern usage mandates the use of oxygen to prevent hypoxia.

Physical and Chemical Properties

• Storage and Pressure Standards:

  • Nitrous oxide is stored in steel cylinders.
  • Color coding: Nitrous oxide cylinders are blue; oxygen cylinders are green.
  • At room temperature, nitrous oxide in a steel cylinder creates a pressure of $750\,PSI$ (pounds per square inch).

• Sensory Characteristics:

  • Taste: Tasteless.
  • Odor: Odorless (though some describe it as having a slight sweet smell).
  • Color: Colorless.

• Preparation and Environmental Factors:

  • Synthesis: It is prepared by heating ammonium nitrate; the resulting nitrous oxide is then collected.
  • Density: It is heavier than air. If released in a room, it will sink to the floor rather than rising.

• Interaction with Mucosa:

  • It is non-irritating to the nasal, pharyngeal, or bronchial mucosa.
  • It does not trigger coughing or asthma attacks.

• Combustion and Flammability:

  • Nitrous oxide is not a flammable gas on its own; it will not burn if a match is struck in a room full of the gas.
  • However, it supports combustion because it contains an oxygen atom.
  • Application: Used in high-performance nitrous injection systems for cars/dragsters to remarkably increase horsepower.

Pharmacokinetics and Physiological Mechanisms

• Analgesic Potency:

  • $20\%$ nitrous oxide combined with $80\%$ oxygen is equivalent in analgesic effect to a $10\,mg$ dose of morphine delivered intravenously.

• Interaction with Opioid Receptors:

  • The analgesic effects of nitrous oxide can be blocked by Naloxone ($Narcan$), a competitive narcotic antagonist.
  • This demonstrates that nitrous oxide bonds to the same opioid receptors in the Central Nervous System (CNS) that morphine utilizes.

• Neurological Mechanism:

  • Nitrous oxide works indirectly by interacting with inhibitory neurons to increase the level of endorphins.
  • These endorphins interact in the presynaptic area to turn down neurotransmitters, similar to the action of morphine.

• Solubility and Onset:

  • Nitrous oxide is relatively insoluble in blood. It does not dissolve or ionize in the bloodstream; it is simply carried by it.
  • Low solubility results in a rapid onset and rapid recovery ("quick on, quick off").
  • Primary saturation of the blood occurs within $3$ to $5$ minutes.

• Metabolism:

  • Nitrous oxide is not metabolized in the body. It passes through the liver completely unchanged and is eliminated through the lungs.

Physiological Effects and Vital Signs

• Respiratory System:

  • Strictly speaking, it causes insignificant respiratory depression.
  • A patient's breathing rate may drop (e.g., from $15-18$ breaths per minute down to $12$), but this is due to relaxation and reduced anxiety, not a pharmacological depression of the respiratory drive.
  • Tidal volume (the amount of gas inhaled per breath) may decrease, but frequency changes ensure the minute volume (total gas per minute) remains stable.

• Cardiovascular System:

  • Causes extremely mild cardiac depression that is usually clinically insignificant.
  • Causes sympathetic nervous system stimulation.
  • Causes cutaneous vasodilation, which may lead to facial flushing and sweating (perspiration).

• Other Systems:

  • No effect on the gastrointestinal system, kidneys, or skeletal muscles.

• Monitoring Statistics:

  • Typical oxygen saturation ($SAO_2$) while breathing room air ($20\%$ oxygen) is $95\%$ to $98\%$.
  • On nitrous oxide/oxygen mixtures (which often contain $40\%$ to $50\%$ oxygen), patients often reach $100\%$ saturation.

Clinical Indications and Contraindications

• Indications:

  • Anxious patients.
  • Long or unpleasant procedures (provides a sense of time distortion, making ceremonies feel shorter).
  • Hyperactive gag reflexes: It turns down the physical and psychological gag reflex.
  • Medically compromised patients who benefit from reduced stress.

• General Contraindications:

  • Acute respiratory infection or nasal obstruction (colds, swollen mucosa, septal deviations) as the patient cannot breathe through the nose.
  • Severe personality disorders or psychotic disorders: Nitrous can unhook inhibitions and make these patients difficult to manage.
  • Patient refusal: Some patients find the feeling of being sedated uncomfortable.
  • Previous overdose trauma: Patients who have had bad experiences (nausea/vomiting) from excessive concentrations in the past.

• Specific Clinical Risks:

  • Eustachian Tube Dysfunction: Nitrous oxide accumulates in the middle ear. If the Eustachian tube is blocked (due to infection), the pressure can increase to the point of rupturing the eardrum.
  • Pregnancy: There is a historical reputation for nitrous oxide causing spontaneous abortions, though research is inconclusive. Current recommendations suggest consulting with an obstetrician and offering staff/students the option to avoid exposure.
  • Emphysema (specifically Bullous Emphysema): In emphysema, the lung structure breaks down into large cavities called blebs. Nitrous oxide can diffuse into these blebs.
  • Expansion Formula: For a patient breathing a fractional concentration of nitrous oxide ($f$), the volume of the bleb increases by a factor of $\frac{f}{1-f}$.
  • Example: At $60\%$ nitrous ($f = 0.6$), the bleb volume increases by $1.5$ ($150\%$ larger), which can cause the bleb to pop, leading to a pneumothorax (medical emergency).

Complications and Side Effects

• Diffusion Hypoxia:

  • When nitrous oxide is turned off, it rushes out of the blood into the lungs so quickly that it can displace oxygen in the alveoli.
  • To prevent this, patients should be given $100\%$ oxygen for approximately $10$ minutes at the end of the procedure.

• Hyperventilation:

  • Fearful patients may breathe too deeply and rapidly, blowing off their $CO_2$.
  • This raises the blood pH above the normal $7.4$, leading to respiratory alkalosis.
  • Treatment involves using a brown paper bag to increase inspired $CO_2$ levels and return the pH to $7.4$.
  • Clinicians must instruct patients to breathe once every $5$ seconds ($12$ breaths per minute).

• Overdose Signs:

  • Nausea and vomiting.
  • Excessive perspiration (soaking through clothes).
  • Uncomfortable disorientation or panicky feelings.
  • Shivering: Caused by vasodilation and inactivity in the dental chair; the body's temperature falls because muscles are not contracting to generate heat.

Recreational Abuse and Safety

• Health Risks of Chronic Abuse:

  • Neurological damage consistent with Vitamin $B_{12}$ deficiency.
  • Permanent neuropathies.
  • Symptoms: Paresthesia (tingling), dysesthesia, ataxia (stumbling), spastic paralysis of the bladder and bowel, impotence, and impairment of memory/intellect.

• Occupational Safety:

  • The goal is to limit personnel exposure to less than $50\,ppm$ (parts per million).
  • Scavenging Systems: Modern masks use a double-lumen system (inflow and outflow) to suck exhaled gas into the "sewer" (vacuum system).
  • Clinicians must prevent "mouth breathing" or "talking," as this releases nitrous oxide directly into the operator's face.

• Security:

  • Oxygen and nitrous oxide cylinders must be stored securely and vertically.
  • Cylinders must be tested every $5$ years.
  • Valves should never be lubricated.
  • If a cylinder falls and its top breaks off, it can become a "rocket" propelled by high pressure.

Administration and Titration Techniques

• Safety Features of Delivery Units:

  • Pin Index Safety System: Prevents an oxygen cylinder from being mistakenly attached to a nitrous inlet.
  • Diameter Index Safety System: Hose sizes differ so oxygen lines cannot be screwed into nitrous ports.
  • Oxygen Fail-Safe: If the oxygen cylinder becomes empty, the machine automatically shuts off the flow of nitrous oxide.

• The Titration Process:

  • Start by pre-oxygenating the patient with $100\%$ oxygen.
  • Introduce nitrous at $20\%$.
  • Increase in increments (e.g., $25\%$, $30\%$, $35\%$) until the titration endpoint is reached.

• Titration Endpoints (Desired Effects):

  • Patient feels relaxed and calm.
  • A sense of floating or heaviness in the limbs.
  • Warmth and tingling in the fingers, toes, and lips.
  • Vital signs show decreased pulse and blood pressure due to reduced anxiety.

Questions & Discussion

• Q: What is a normal oxygen saturation level?

  • A: Approximately $95\%$ to $98\%$ while breathing room air ($20\%$ oxygen). On nitrous systems, it usually reaches $100\%$.

• Q: Can patients go to sleep on nitrous oxide?

  • A: Patients must understand they will remain conscious. True "sleep" is general anesthesia, which is universes apart from the level of sedation provided by nitrous oxide. If a patient hyperventilates to try to "go under," the clinician must stop them.

• Q: Is it okay to use nitrous oxide on children?

  • A: Yes, healthy children without a history of ear infections do very well. It settles restless or nervous children, allowing them to remain "cool" during the procedure.

• Q: What happened in the case of the dental assistant who abused nitrous?

  • A: He used a key to enter a neurosurgeon’s office over the weekend, used the gas solo, and was found unconscious Monday morning. He had been breathing nitrous and oxygen for two days and was lucky to survive, though he was hypotensive/hypoxic due to immobility and lack of monitoring.

• Dialogue Note: The session concluded with informal discussion regarding individual plans to visit Costco in Redmond and the challenges of the final quarters of the curriculum." , "title": "Comprehensive Study Guide on Nitrous Oxide Administration and Pharmacology"}