4. Nitrous I Flashcards
What are the conducting airways
larynx, trachea, bronchi, bronchioles
What are the respiratory airways
respiratory bronchioles
alveolar ducts
alveoli
Blood supply to lungs
- To the alveolar= bronchial circulation
- Participating in gas exchange= pulmonary arteries
Muscles that partake in inspiration and expiration
Inspiration- diaphragm and intercostals (accessory mm= SCM, scalenes and abdominal mm.)
Exhalation= passive elastic recoil
Autonomic and Voluntary control centers of the brain for respiration
- Autonomic- medullary reticular formation in pons
- Voluntary= cerebral cortex
Central and peropheral chemoreceptors that stimulate breathing
Central= H+ conc. and Partial pressure CO2 Peripheral= Carotid and aortic bodies (Partial pressure O2)
Me chanoreceptors that modulate the rate and depth of respiraiton
- J receptors
- In lung periphery
- Simulate ventilation in response to pulmonary vascular engorgement
Rate of gas diffusion is directly proportional to
the partial pressure created by the gas
How does gas exchange between alveoli and capillaries occur
simple diffusion down a partial pressure gradient (rate of gas exchange primarily depends on the difference in partial pressures)
Factors that increase the alveolar partial pressure (tension)
- Increased delivery (increase ventilation)
- Decreased removal (decreased solubility or CO)
Gasses with (high/low) solubility have a faster rate of equilibrization
low
The lower the solubility of a gas the (faster/slower) the onset and the (faster/slower) the recovery
faster… faster
Solubility of a gas in blood is expressed how
- Blood: gas or tissue: blood coefficient
- Oil:gas partition coefficient
Define MAC
Minimal alveoalr concentration- concentration of anesthetic needed to produce immobility in 50% pateints
What is the MAC of Nitrous
105
Nitrous has a (high/low) blood: gas partition coefficient
low (lowest of all the gases
General anesthesia is defined how
drug-induced state by absence of perception to all sensations
MAC is a measure of the drugs (what property?)
potency
Factors that lead to a decrease in MAC
- Hypoxia
- Increased hypercarbia (increased CO2)
- Anemia (less O2 carrying ability)
- Old age
- Hypotension
- Hypothermia
- CNS depressants
- LAs
- Pregnancy
Factors that increase the MAC s
- Hyperthermia
- Infants and adolescents
- Microsomal inducing agent (chronic EtOH and Drug use)
What is the most commonly used inhalation anesthetic in dentistry
nitrous oxide
Four properties of N2O that can be beneficial or harmful
- Expands the colume of gas filled spaces- not beneficial
- Concentration effect- beneficial
- Second gas effect- beneficial
- Diffusion hypoxia- not beneficial
Describe why N2O has the tendency to fill gas spaces
-N2O is more soluble in blood than N2 –> spaces fill more rapidly than the gas can diffuse out
Areas where gas accumulation can lead to issues
- Middle ear
- Eye (post- retinal surgery)
- Pneumothorax
- GI in case of bowel obstruction
- Air emboli enlargement
- Emphysema blebs
Describe diffusion hypoxia
Rapid outflow of N2O from the alveoli –> dilution of O2 (hypoxic conditions)
Describe the concentration effect of n2O
the higher the conc. of anesthetic gas the greater the uptake and augmentation of inspired volume of that gase
Describe the second gas effect
The use of one gas potentiates the sedative effects of a second gas
N2O gas is mainly eliminated how? Minorly eliminated how?
Majorly= through lungs unchanged
-Minorly via gut flora ( pseudomonas dentrificans –< free radical formaiton)
MOA of N2O causing analgesia
Direct interaction with opiod receptors and indirect increase in bodies endogenous opioids
MOA of N2O in producing anxiolysis
-Bind GABA A receptors at the benzo site
Chronic exposure to N2O can lead to
MS like symptoms (Irreversible inhibition of the cobalt atom on VitB12). Reduces the activity of VitB12 enzymes (methionine and thymidylate synthetase) vital in the synthesis of myelin and nucleic acids
N2O exposure leads to (sympathetic/parasynpathetic) stimulation
sympathetic (offsets the myocardia depressive effects)
Main side effect of N2O .
nausea (depression of the reflexes and GE sphincter muscles)
Effect of N2O on airway resistance
increased airway resistance and decreased mucociliary activity (issue for asthmatics)
What percent N2O is needed for Amnesia, Anxiolysis and analgesia
Amnesia= 70% (not recommended) Anxiolysis= 20-30% Analgesia= 10-40%
Absolute contraindications of nitrous
- Pregnant
- Bowel obstruction
- Cranial injury with pneumocephalus
- Neurosurgical procedure (craniotomy)
- Open chest surgery
- Pneumothorax
- Bullous emphysema
- Ocular surgery (recent)
- Recent tympanic surgery
- Air embolus
Acute toxicity of N2O
bone marrow suppression
Chronic toxicity of N2O
- Inhibition of the cobalt atom of VitB12 (neurologic changes- ataxia and paresthesia)
- Mutagenicity (changes in DNA)
- Carcinogenicity (increased cervical cancer)
- Teratogenic (spontaneous abortions)
