Nitrous Oxide

Question 1

When was Nitrous discovered and by whom?

Answer 1

1772 by Joseph Priestly

Question 2

When were the analgesic effects of nitrous discovered and by whom?

Answer 2

1800 by Humphrey Davy. coined term laughing gas, primarily used recreationally

Question 3

Who used nitrous clinically and when?

Answer 3

1844 Horace Wells used clinically in dentistry but demo in Boston considered a failure.

Question 4

When was nitrous recognized by the American Dental Association? the American Medical Association?

Answer 4

1864; 1870.

Question 5

Who else persisted with nitrous and when?

Answer 5

1861, Gardner Quincy Colton due to negative effects of chloroform and ether

Question 6

How is nitrous oxide prepared?

Answer 6

ammonium nitrated heated to 250C and breaks down in an exothermic reaction to nitrous oxide and water.

Question 7

What is the MAC of N2O?

Answer 7

104%, HIGH (low potency)

Question 8

What are some characteristics of N2O?

Answer 8

nonflammable but supports combustion, non-irritating, colorless, slightly sweet odor and taste, weak anesthetic with potent analgesic properties: 70% N20=15mg MSO4

Question 9

What is the molecular weight of N2O?

Answer 9

44g, 1.5 times heavier than air, lightest of anesthesia gases.

Question 10

Does N2O trigger MH?

Answer 10

No

Question 11

How is N2O stored?

Answer 11

compressed to liquid and stored in blue cylinders. pressure gauge not reliable as it doesn’t drop until all liquid is vaporized. Weight of the cylinder is what you go by to see how much remains.

Question 12

When do you avoid N2O?

Answer 12

T&A and laser procedures

Question 13

What does N2O decompose to?

Answer 13

nitrogen and oxygen above 450C, no toxic byproducts

Question 14

What is the blood:gas of N2O?

Answer 14

0.47, LOW

Question 15

What is the oil:gas of N2O?

Answer 15

1.4, LOW

Question 16

What are the possible MoA of N2O?

Answer 16

appears to be opiate in nature, may involve neuromodulators in spinal cord, can be reversed with naloxone, triggers release of endogenous opioid peptides, morphine tolerance=N2O tolerance, anxiolytic action mimics benzos with slight action at GABA receptors. NMDA receptors

Question 17

What is the most supported MoA of N2O?

Answer 17

Anesthesia and analgesia appear to be mediated at the NMDA receptors, moderate NMDA antagonism as opposed to other volatiles that potentiate activity of GABA receptors

Question 18

What is required for N2O administration?

Answer 18

anesthesia machine with proper yoke and reducing valve or pipeline inlet connection and flow meter.

Question 19

Does N2O have additive MAC values?

Answer 19

Yes, 0.5 MAC N2O + 0.5 MAC other volatile has same effect at the brain as either drug alone at 1 MAC.

Question 20

What must be used with N2O?

Answer 20

minimum of 0.25 FiO2 in order to AVOID HYPOXIA, machines have safety mechanism to keep max of 70% N2O with 30% O2.

Question 21

What % are analgesia, sedation, induction, and maintenance?

Answer 21

analgesia: 20%; sedation 30-70%, induction 60-70%, maintenance 50-70%

Question 22

What is the vapor pressure of N2O?

Answer 22

38,770 mmHg

Question 23

What is the boiling point of N2O?

Answer 23

-88C

Question 24

What is the concentration effect?

Answer 24

deals with a single gas. When breathing room air nitrogen is primary gas in alveolus, N2O is 34x more soluble in blood than nitrogen so when N2O is introduced to lung the volume of N2O going from alveolus to pulmonary blood is much higher than nitrogen leaving the blood causing alveolus to SHRINK = relative increase in concentration of N2O facilitating gradient into blood

Question 25

What is the second gas effect?

Answer 25

2 gases: if N2O and Iso turned on simultaneously, N2O diffuses into the blood from the alveoli in higher concentrations than N2o diffuses from blood into alveoli, alveoli shrink causing concentration of both N2O and Iso to remain elevated facilitating gradient into blood. If fast anesthetic given with slower second gas, slower gas achieves anesthetic levels more quickly than if it was alone.

Question 26

How is N2O eliminated?

Answer 26

almost all by exhalation through lungs, quick, 3-5 min after discontinuation. small amount diffuses through skin, <0.1% undergoes reductive metabolism in GI tract by anaerobic bacteria

Question 27

What is diffusion hypoxia?

Answer 27

When N2O turned off it diffuses from blood into alveoli so rapidly that alveolar size INCREASES and PaO2/PaCO2 are diluted. Admin 100% O2 for 3-5 min after N2O stopped to mitigate

Question 28

When N2O diffuses into air containing cavities _______ increases and _______ remains unchanged in a COMPLIANT compartment.

Answer 28

Volume; pressure

Question 29

When N2O diffuses into air-containing cavities ________ increases and _________ remains unchanged in a NON-COMPLIANT compartment.

Answer 29

Pressure; volume

Question 30

What are some compliant airspaces with fast equilibrium between space and blood?

Answer 30

pulmonary blebs, air bubbles in blood, sulfa hexafluoride bubble in eye.

Question 31

What are some compliant airspaces with slow equilibrium between space and blood?

Answer 31

bowel, pneumoperitoneum.

Question 32

What are some fixed airspaces with fast equilibrium between space and blood?

Answer 32

middle ear, brain during intracranial procedures.

Question 33

What are some contraindications to N2O use?

Answer 33

PONV, pulm HTN due to increased PVR, gas bubbles used in retinal detachment surgeries, pneumothorax, bowel obstruction, emphysematous blebs, pneumopericardium, etc. Vit B12 deficiency

Question 34

What are the cardiovascular effects of N2O?

Answer 34

stimulatory SNS, increased catecholamines, mild depression of contractility, unchanged BP/CO/HR/SVR, constriction of pulm vascular smooth muscle--increased PVR/modest elevation in RVEDP, peripheral vascular resistance not altered

Question 35

What study showed no increased risk of death or CV complications with use of N2O?

Answer 35

ENIGMA II study

Question 36

What are the respiratory effects of N2O?

Answer 36

doesn't depress resp drive, non-irritating, increased RR and decreased tidal volume, minimal change in minute ventilation and CO2 levels, hypoxic drive markedly depressed--3-5 min of 100% O2, slight increase in airway resistance, not a bronchodilator, cough reflex supressed.

Question 37

What are the GI effects of N2O?

Answer 37

GI motility unaffected, pancreatic functions unaffected, increased risk of PONV (controversial: proposed activation of CTZ, stim of vomiting center in medulla, middle ear changes) increased risk nearly eliminated with prophylactic antiemetics

Question 38

What are the renal effects of N2O?

Answer 38

decreased renal blood flow, GFR, and UOP.

Question 39

What are the hepatic effects of N2O?

Answer 39

decreased hepatic blood flow but less than other gases

Question 40

What are the nervous system effects of N2O?

Answer 40

increased CMRO2, increased CBF and ICP, less than other gases

Question 41

What are the musculoskeletal effects of N2O?

Answer 41

no sig muscle relaxation, can increase muscle tone at high concentrations, not a MH trigger, slightly potentiate NDMB

Question 42

What are the hematologic effects of N2O?

Answer 42

interacts with vitamin B12 in intestinal bacteria and inactivates things necessary for DNA synthesis resulting in decreased RBCS (pernicious anemia), bone marrow depression (megaloblastic anemia), and peripheral neuropathy (signs of B12 deficiency)--neurotoxic effects (numbness paresthesia progressing to weakness/poor gait/impotence. Possible teratogenic effects, avoid in pregnancy before 3rd trimester, may alter immune response to infection, prolonged exposure=bone marrow depression

Question 43

What is subacute combined degeneration of the spinal cord?

Answer 43

type of myelopathy related to vit B12 deficiency, exposure to N2O leads to inhibited myelin sheath production progressing to degeneration of spinal cord--numbness/tingling/inability to walk

Question 44

How long can N2O last in the atmosphere?

Answer 44

up to 150 years, GWP 298 (12x higher than methane)