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Pharmacology Exam I > Nitrous Oxide > Flashcards

Nitrous Oxide Flashcards

1
Q

When was Nitrous discovered and by whom?

A

1772 by Joseph Priestly

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2
Q

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

A

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

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3
Q

Who used nitrous clinically and when?

A

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

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4
Q

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

A

1864; 1870.

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5
Q

Who else persisted with nitrous and when?

A

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

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6
Q

How is nitrous oxide prepared?

A

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

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7
Q

What is the MAC of N2O?

A

104%, HIGH (low potency)

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8
Q

What are some characteristics of N2O?

A

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

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9
Q

What is the molecular weight of N2O?

A

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

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10
Q

Does N2O trigger MH?

A

No

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11
Q

How is N2O stored?

A

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.

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12
Q

When do you avoid N2O?

A

T&A and laser procedures

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13
Q

What does N2O decompose to?

A

nitrogen and oxygen above 450C, no toxic byproducts

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14
Q

What is the blood:gas of N2O?

A

0.47, LOW

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15
Q

What is the oil:gas of N2O?

A

1.4, LOW

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16
Q

What are the possible MoA of N2O?

A

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

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17
Q

What is the most supported MoA of N2O?

A

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

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18
Q

What is required for N2O administration?

A

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

19
Q

Does N2O have additive MAC values?

A

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

20
Q

What must be used with N2O?

A

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

21
Q

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

A

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

22
Q

What is the vapor pressure of N2O?

A

38,770 mmHg

23
Q

What is the boiling point of N2O?

A

-88C

24
Q

What is the concentration effect?

A

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

25
Q

What is the second gas effect?

A

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.

26
Q

How is N2O eliminated?

A

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

27
Q

What is diffusion hypoxia?

A

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

28
Q

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

A

Volume; pressure

29
Q

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

A

Pressure; volume

30
Q

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

A

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

31
Q

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

A

bowel, pneumoperitoneum.

32
Q

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

A

middle ear, brain during intracranial procedures.

33
Q

What are some contraindications to N2O use?

A

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

34
Q

What are the cardiovascular effects of N2O?

A

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

35
Q

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

A

ENIGMA II study

36
Q

What are the respiratory effects of N2O?

A

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.

37
Q

What are the GI effects of N2O?

A

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

38
Q

What are the renal effects of N2O?

A

decreased renal blood flow, GFR, and UOP.

39
Q

What are the hepatic effects of N2O?

A

decreased hepatic blood flow but less than other gases

40
Q

What are the nervous system effects of N2O?

A

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

41
Q

What are the musculoskeletal effects of N2O?

A

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

42
Q

What are the hematologic effects of N2O?

A

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

43
Q

What is subacute combined degeneration of the spinal cord?

A

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

44
Q

How long can N2O last in the atmosphere?

A

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

Pharmacology Exam I (11 decks)

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