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)
where is N2O eliminated?
the lungs (recovery in 3-5 minutes)
why is N2O so used so frequently?
- it relieves anxiety
- it reduces intra-operative awareness
- it provides a SYNERGISTIC effect with sedative and hypnotic agents, thereby REDUCING the DOSE the primary anesthetic agents required (second gas effect)
- has ANALGESIC effects which seem to be related to activation of OPIOID receptors in the PERIAQUEDUCTAL gray matter and NORADRENERGIC neurons in the LOCUS CERULEUS
what agencies regulate N2O?
DOT - hazardous transport
FDA - drug status
what color are the N2O tanks?
blue
what color are the O2 tanks?
green
what prevents the inadvertent attachment of N2O cylinder to O2 yoke site?
pin index safety system
what prevents the inadvertent attachment of N2O hose to O2 outlet?
diameter index safety system
what provides automatic termination of N2O flow if O2 supply is inadequate or depleted?
O2 failsafe mechanism
what provides rapid delivery of 100% O2 when needed?
O2 flush valve
t/f N2O will suppress the respiratory rate?
false
what is the primary organ system affected by N2O?
CNS (however its affect is less than other inhaled anesthetics)
chronic exposure of N2O leads to what type of changes to the hematopoietic system?
megaloblastic bone marrow changes
patients with what vitamin deficiency should use N2O with caution?
vitamin B12 deficiency
t/f patients with malignant hyperthermia can use N2O safely
true
N2O use is contraindicated for patients on what cancer drug because it can increase pulmonary fibrosis?
bleomycin sulfate
what trimester of pregnancy should N2O be avoided?
first trimester
N2O absolute contraindications
- pneumothorax
- cystic fibrosis
- chronic obstructive pulmonary disease
- recent pneumoencephalography
- pernicious anemia or vitamin B12 deficiency
- significant bowel obstruction
- first trimester of pregnancy
- cancer therapy using bleomycin sulfate
- psychological impairment
- current psychotropic drug use
- current or recovering drug use/addiction
- patient in shock, semi-conscious or with serious head/facial injuries
- inability to understand procedure or unwilling to consent to procedure
N2O relative contraindications
- current upper respiratory tract infection
- middle ear disturbance/surgery (e.g., grafting)
- recent eye surgery using perfluoropropane or sulfur hexafluoride
N2O appropriate sedation symptoms
- light headedness
- tingling hands/feet
- wave of warmth
- numbness hands/feet
- euphoria
- feeling of lightness/heaviness of extremities
- analgesia
N2O appropriate sedations signs
- BP / heart rate – initial rise from baseline
- respirations – normal / smooth
- peripheral vasodilation
- flushing
- decreased muscle tone
N2O mild oversedation symptoms
- Hearing more acute
- Confused visual images
- Sleepiness
- Laughing / Crying
- Dreaming
- Nausea
N2O mild oversedation signs
- Movement
- Heart rate
- Blood pressure
- Sweating
- Lacrimation
N2O profound oversedation symptoms
· Spontaneous mouth breathing · Persistent closing of mouth · Complaints of: - Nausea - Uneasiness - Too intense an experience
N2O profound oversedation signs
- Failure to respond rationally
- Sleepiness / dreaminess
- Incoherent speech
- Uncooperative
- Laughing / crying / giddy
- Uncoordinated movements
diffusion hypoxia
- Capillarly tension quickly rises to that above alveolar pressure
- N2O is quickly forced into the alveoli & exhaled through the lungs
- N2O exits faster than the N2 that replaces it, diluting the supply of O2
- O2 blood saturation (SaO2) is reduced
