Lecture Notes - HIGHLIGHTS Flashcards
what are the 4 desirable attributes of an anesthetic?
· lack of toxicity
· non-flammable
· non-addictive
· minimal allergenicity
what does “balanced anesthesia” mean?
This a concept in which combinations of drugs are used to produce general anesthesia, with each drug chosen for a specific effect.
In this context, the following drugs might be selected: nitrous oxide for its analgesic and anesthetic actions, a benzodiazepine for amnesia, a neuromuscular blocking drug for muscle relaxation, and an opioid for additional analgesia and hemodynamic stability.
Lecture: piecing together the desirable attributes of different drugs
what are the 4 components of “balanced anesthesia”?
· analgesia - no pain
· amnesia - no memory
· relaxation and immobility
· loss of consciousness (hypnosis)
what are the 7 desirable attributes of N2O
· analgesic · anxiolytic · relative amnestic · rapid onset · titration possible · rapid cognitive recovery · minimal side effects
define moderate sedation
minimally depressed level of consciousness that retains the patient’s ability to maintain an airway independently and continuously and respond appropriately to physical stimulation or verbal command
define deep sedation
depressed consciousness accompanied by partial loss of protective reflexes, including the inability to maintain an airway contiuously and independently and or respond purposefully to physical stimulation and verbal command
define general anesthesia
unconsciousness accompanied by partial or complete loss of protective reflexes, including the inability to maintain an airway continuously and independently and respond purposefully to physical stimulation or verbal command
what are the 4 stages of anesthesia as classified by Guedel?
· stage I - analgesia
· stage II - delerium/excitment
· stage III - surgical anesthesia
· stage IV - respiratory paralysis
MUST KNOW THESE!
what characterizes stage I as classified by Guedel?
· ANALGESIA
· this stage starts with the administration of anesthesia and ends with the loss of consciousness
· the patient unresponsive to mild pain provoking stimuli and is able to respond to verbal commands
· this is where moderate sedation occurs in this stage (i.e. N2O)
what characterizes stage II as classified by Guedel?
· DELIRIUM/EXCITEMENT
· patients are hyperresponsive
· uncontrolled movements
· retching (sound/movements of vomiting, heaving, almost vomiting)
· laryngospasm can occur
· it is desirable to bypass this stage rapidly
what characterizes stage III as classified by Guedel?
· SURGICAL ANESTHESIA
· this is the stage where you can actually preform surgical procedures
· pupil diameter
· loss of reflexes
· muscle relaxation
· depth/regularity of respirations
· separation of the thoracic and abdominal (diaphragmatic) phases of respiration
what characterizes stage IV as classified by Guedel?
· RESPIRATORY PARALYSIS
· this stage begins with the disappearance of the purely diaphragmatic respiration and ends with complete respiratory collapse
· use of ventilator and monitoring of positive pressure is required
average minute ventilation
6-7 L/min
why is minute ventilation important?
· Lecture: If you think about N2O, it affects the amount you will give the patient, if you cranked the flow rate up to say 20 L/min you are giving the patient more gas then they can actually take in.
· Text: Minute ventilation is significant in terms of N2O administration, because it considers the amount of gas mixture (N2O/O2) that should be given to a patient. Inadequate amounts are likely to produce a suffocating feeling and make the act of breathing laborious. Conversely, too much gas forced into the nasal hood of the delivery system will cause some to be wasted. The gas will escape, because it is not being consumed by the patient. This excess airflow not only blows into the patient’s eyes, causing dryness, but also exposes personnel to unnecessary amounts of trace gas.
how is alveolar ventilation different then minute ventilation?
Text: Alveolar ventilation is the amount of air per minute entering the alveolar units capable of gas-blood exchange. This volume is less than the minute volume, because not all of the inspired air reaches the alveoli during inspiration. A portion of the inhaled air occupies the conducting airways and does not enter the lungs and, therefore, is not utilized by the exhaust system. Hence, this air is not able to participate in the gas-blood exchange. This is known as anatomic dead space. Therefore, alveolar ventilation is calculated by subtracting the dead space volume (approximately 150ml) from the tidal volume and then multiplying by the respiration rate.
gas exchange of nitrous oxide
- N2O is NOT dissolved in the blood
- this allows for quick equilibrium in the blood and brain
diffusion hypoxia
- likely cause of post operative headache, nausea, and lethargy
- treated with post operative 100% O2 for 3-5 minutes
is the oxygen tank gauge an accurate?
yes, the oxygen tank gauge is rarely accurate
is the N2O tank gauge accurate?
- NO
- Text: Because the liquid is vaporized as the gas is used, this reading is not proportional to the actual amount of gas available in the cylinder. Therefore, the gauge will show a pressure decrease when the tank contains approximately 20% N2O. The drop in the dial on the N2O tank is not proportional to the contents of the tank as with O2. Figure 6-7 illustrates pressure gauge readings for full and empty N2O and O2 cylinders.
second gas effect
· with high concentrations N2O causing rapid uptake there is a simultaneous effect of increasing uptake of a second gas
· this second gas uptake occurs FASTER than it normally would
· web resource: The “second gas effect” says that large volume intake of one gas enhances the intake of a second gas
IMPORTANT CONCEPT TO UNDERSRAND
minimum alveolar concentration (MAC)
· amount of drug necessary to prevent movement in 50% of individuals with surgical stimulation
· text: the alveolar concentration of anesthetic at which 50% of patients do not respond to a standard surgical stimulus. MAC is used for quantifying the relative potencies of inhalation anesthetics.
what is the MAC value for N2O and what does it mean?
· 104%
· it takes a higher concentration then we even provide (70% is the highest dose to which we titrate) for 50% of patient to not respond to a surgical stimulus
· it is the LEAST POTENT of all anesthetic gasses
what receptor does N2O act on?
the opioid receptor
t/f N2O is metabolized in the liver
- false (0.004% is metabolized in the GI tract)
