23. Ax principles Flashcards
two methods used to initiate and maintain a state state concentration of drug at the level of the brain
- loading dose (usually higher than target dose), followed by a CRI (lower dose maintenance dose)2. start maintenance dose CRI allowing it to accumulate over time (~ 5 half lives)
administration of any drug in the the body is balanced by what two factors
- redistribution2. metabolism/excretion
T/Fdrugs that are more lipid soluble take longer to achieve stead state
TRUEDrugs that are more lipid soluble take longer to achieve stead state because they readily redistribute to many areas of the body
Can diazepam be given as a CRI
NO it is unable to be diluted bc it is water insoluble
what are anesthetic drug delivery and redistribution dependent on
- cardiac output (CO = SV x HR)
the time necessary to to achieve steady state of an anesthetic depends on what
- minute ventilation2. cardiac output3. speed of redistribution4. amount of drug that is eliminated5. with inhalants, speed on inhalant action depends on gas solubility
low flow (closed circuit) anesthesia
at equilibrium, only enough inhalant must be supplied to make up for that lost from the system during redistribution/metabolism only enough oxygen must be supplied to meet metabolic needs (5 ml/kg/m)
methods of vaporization
vaporizers are designed and calibrated to deliver a constant concentration of anesthetic vapor1. flow over ** most common**2. bubble through3. direct injection
most common vaporizer output
variable bypass vaporizersthe incoming gas is split to direction some into the vaporizing chamber to pick up inhalant and other part through the bypass champed straight to the outlet
T/FIN circuit vaporizers have highly variable output
TRUEIN circuit vaporizers have variable output based on ambient temp, patient ventilation, and volatility of agentvet med uses OUT of circuit vaporizers; not part of patients breathing circuit; deliver a constant dose regardless of the patient’s minute volume
what happens if an incorrect inhalant agent is placed in an agent specific vaporizer
higher or lower concentrations will be usedout of circuit vaporizes are designed and calibrated for use with a single agent only
two types of anesthesia patient circuits
- rebreathing/circle circuit (uses CO2 absorbent to remove CO2; one way valves)2. nonrebreathing (use high gas flow rates to decr CO2–Bain)
CO2 absorbent in rebreathing systems
SODA LIME–strong base–granular–changes color upon saturation and interaction with acid(ethyl violet)
T/FDilution of inhalant gas occurs with rebreathing circle circuits
TRUEDilution of inhalant gas occurs with rebreathing circle circuits. Thus, inspired concentration may be less than vaporizer setting initially.nonrebreathing circuits, no dilution occurs, thus the inhalant concentration on the vaporizer indicates the inspired concentration by the patient
How to adjust for dilution gas entering the circuit at the beginning of anesthesia in a rebreathing circuit
increase vaporizer settingor increase the carrier gas flow
minimum oxygen flow for rebreathing circuit
Rebreathing/circle circuitmin O2 flow = patient’s metabolic O2 demand = 10 x kg
why do you want to minimize dead space in a circuit
to minimize rebreathing of CO2
recommended fresh gas flow rate for a nonrebreathing circuit
min flow = 3 x MV = 3 x (RR x TV)TV= tidal volume = 15 ml/kg~ 200-500 ml/kg
rebreathing circuits are reserved for patients larger than _____kg
5 kgbc nonrebreathing systems cannot eliminate CO2 readily enough for large patients
4 benefits of an endotracheal tube
- maintains patent airway2. ensures delivery of gas to lungs3. protects against aspiration4. minimizes personal exposure to inhalants
2 disadvantages of endotracheal tube
- increases airway resistance2. increases dead space
what is the advantage to Murphy’s eye at the end of an endotracheal tube
allows air passage should the end of the tube get occluded
In a patient breathing room air, hypoxemia will develop within _____________sec of apnea
30 s
a patient breathing 100% oxygen may not become hyperemic for _______ minutes after onset of apnea
5 minutesPREOXYGENATE 4-5 L min w 100% O2 for 5 minsaturates alveoli with oxygen, providing a reservoir of oxygen
most common carrier gas for inhalant anesthesia
oxygen!100% oxygen causes more alveolar collapse than 40% O2 bc of the nitrogen in mixed gas is not absorbed and keep alveoli open longerabsorption atelectasis
T/FNitrogen causes structural support of alveoli
TRUE
how to prevent surgical fire (high OXYGEN + laser sx)
protect endo tracheal tube (tape, moist gauze) orHe : O2 ratio 70 : 30
T/F the oxygen flowmeter should not be used with rebreathing circuits
FALSEthe oxygen flow meter should not be used with NONrebreathing circuits because of the significant risk of barotrauma
when is a leak more noticeable under positive pressure mechanical ventilation
leaks are more noticeable during expiration when bellows are ascended
initial pressure settings for dogs v cats on mechanical pressure cycled ventilation
Peak inspiratory pressurescats 12 mm Hgdogs 15 mm Hg
T/Foxygen content of the blood is largely dictated by [Hb]
TRUECaO2 = 1.34 x Hb x SaO2 + PaO2 x 0.003as Hb decr, CaCo2 decreases in a linear fashion (changes more radically with Hb than with PaO2)
The heart spends more of its time in what phase
DIASTOLEthus, it has more impact on MAPMAP = DAP + [(SAP-DAP)/3]
Doppler MOA
recognition of a sound change that is produced when blood passes under the doppler crystalonly detect SAP
cats and doppler measurements
in catsdoppler UNDERestimates SAP up to 25 mm Hg
dogs and doppler measurements
in dogsdoppler correlates well with direct ABP in anesthetized patients
cats and oscillometric BP monitoring
in catsoscillometric UNDERestimates SAP but precise for MAP, DAP
dogs and oscillometric BP monitoring
in dogsoscillometric UNDERestimates SAP, DAP, MAP
Oscillometric vs doppler BP readingswhich one is affected by irregular heart rates and rhythms?
Oscillometric
what does hypercarbia lead to
hypoventilation –> hypercarbia (PCO2 > 45 mm Hg)1. resp acidosis2. vasodilation3. incr intracranial P4. SNS stimulation5. anxiety, arrthymias
what does hypocarbia lead to
hyperventilation –> hypocarbia (PCO2 < 25 mm Hg)1. resp alkalosis2. vasoconstriction
T/Falveolar CO2 closely approximates arterial CO2
TRUEbc COs efficiently passes out of the blood stream and is exhaledmonitored by end tidal CO2 monitors as an accurate and reliable way to monitor PaCO2
end tidal CO2 readings and nonrebreathing circuit
bc high gas flow rates, end tidal CO2 will be diluted and read artificially lowcan be overcome with a side stream CO2 monitor that samples close to endotracheal tube
normal capnograph reading and phases
begins with inspiration of fresh gas = 0 (phase 0on expiration, CO2 should rapidly elevate (phase 1)due to mixing with dead space and gas it will plateau (phase 2)peaks at the end of expiration (phase 3)next inspiration = 0 (phase 4)
abN CO2 readings indicate
–confirms intubation–dx of impending cardiac arrest/cardiac arrest–rebreathing–malignant hyperthermia–disconnection of the circuit–dislodgment of endotracheal tube
Pulse oximetry MOA
Estimates the % of Hb that is saturated with O2; ARTERIAL; relies on pulsatile nature–emits 2 light frequencies (specific for oxyHb & deoxyHb) through the tissue and into the sensor–calculates the amt of OxyHb and deoxyHb based on the amount of light arriving at the sensor% = amount of oxyHb
T/Fcarboxyhemoglobin and methemoglobin can affect pulse oximetry readings
TRUE
two types of pulse oximetry probes
transmittance—light emits from one side and sensed on the other side; MOST COMMONreflectance–light is sent and reflected back to a sensor adjacent to the light source
60 mm Hg defines hypoxia and corresponds to what pulse oximetry reading
90%
what are inaccuracies in pulse oximetry due to
- vasoconstriction,decr CO, poor perfusion2. movement3. pigment4. profound anemia < 10% HCT5. profound hypoxemia
end tidal inhalant monitoring closely parallels what?
brain concentrations of inhalantbasis for determination of minimum alveolar concentration values
normal CVP values
0-5 mm Hg0-8 cm H20
